Module 5
Introduction to
Electricity
o
Table of Contents
Module 5 - Basic Electricity
Section
5.1
5.2
5.3
5.4
5.5
5.6
5.7
5.8
Page
The Energy of the Atom
2
5.1.1 Repulsion, Attraction, and Conduction
5.1.2 Electrical Induction
5.1.3 Electromagnetism
6
9
10
The Electrical Pathway
15
5.2.1 Conductors and Insulators
19
Electrical Terms and Relationships
23
5.3.1 Electrical Pressure or Voltage
5.3.2 Current or Amperage
5.3.3 Resistance or Ohms
23
26
29
Tools of Electrical Measurement
33
5.4.1
5.4.2
5.4.3
5.4.4
33
38
42
46
General Requirements for Meter Use
Voltmeter
Ammeter
Ohmmeter
Components of a Simple Circuit
49
5.5.1
5.5.2
5.5.3
5.5.4
5.5.5
50
58
66
70
77
Electrical Supply
Conductors
Fuses and Circuit Breakers
Switches
Loads
Ohm’s Law and Watt’s Law
79
5.6.1 Ohm’s Law
5.6.2 Watt’s Law
5.6.3 Other Measurements of Work and Power
79
82
84
Types of Circuits
85
5.7.1 Series Circuit
5.7.2 Parallel Circuit
5.7.3 Series-Parallel Circuit
85
88
93
Alternating Current
97
5.8.1 Phases
5.8.2 Factors Effecting Alternating Current in a Circuit
5.8.3 AC Power Distribution
97
99
107
Section Page
5.9
Electromagnetic Action
111
5.9.1 Solenoid Valves
5.9.2 Relays
5.9.3 Motors
111
115
118
5.10 Transformers
5.10.1 Ignition Transformers
5.10.2 ControlTransformers
5.11 Code Requirements Related toElectrical Work
5.11.1 Certification Requirements
5.11.2 B149 Codes
5.11.3 Standards
5.11.4 Electrical Code
5.12 Safety First
5.12.1 Lockout / Tag-out Procedures
5.12.2 Responding to Electrical Emergencies
5.12.3 Electrical Fire Hazards
125
129
133
135
135
136
137
137
143
149
150
151
Summary
152
Review Questions
153
Gas Technician 3
Module 5
Basic Electricity
Module
Basic Electricity
Electrical energy is integrated with all facets of appliance operation from fuel and air
delivery to safe ignition to circulation of the heated medium and even to venting in many
cases. Approximately 80% of all appliance service calls are related to electrical issues.
A person with a strong foundation in electrical theory who can apply that theory to any
situation enjoys greater personal safety, greater job satisfaction and greater value in the
marketplace.
Unfortunately, fear of abstract theories, unfamiliar terms and math equations often
impedes learning about electricity. This basic introduction to electricity recognizes that the
lights of learning go out when a person’s own 'circuits’ are overloaded with abstract
theories and terms.
This Module along with your participation in the practical exercises related to the appliance
wiring systems will hopefully integrate theory and practice. The focus is on practical
electrical knowledge and skills that are applicable to work conducted by a Gas Technician.
It does not attempt to make you into an electrician or electrical designer. This Module can
provide a sound basis for safe and productive work experience.
The Module, as outlined below, emphasizes safety and a logical progression through the
‘how, why and what if building blocks of understanding. Question every step, make the
theories your own, and most importantly, have fun with this fascinating subject.
•
The Energy of the Atom
•
The Electrical Pathway
•
Electrical Terms and Relationships
•
Tools of Electrical Measurement
•
Components of a Simple Circuit
•
Ohm's Law and Watt's Law
•
Types of Circuits (Series Circuits, Parallel Circuits, Series-Parallel Circuits)
•
Alternating Current
•
Electromagnetic Action (Solenoids, Relays, Motors)
•
Transformers
•
Code Requirements Related to Electrical Work
•
Electrical Safety
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Basic Electricity Module 5 Gas Technician 3
5.1 The Energy in the Atom
We live in the “atomic age". The symbol and basic concept of
the atom as the smallest building block of all matter are
common place in our lives.
We commonly refer to the simpler substances by their
molecular formula or atomic components such as H2O. CO2,
02, etc. Water or H2O, as shown below, is constructed of two
hydrogen atoms and one oxygen atom.
Water like all matter can be subdivided to its smallest component - the molecule.
Just as a molecule is the smallest division of a
substance, the atom is the smallest division of an
element. Whereas there are an unlimited number of
different molecules, there are only 103 elements or
different atoms known to exist.
The difference between the 103
elements lies in their different atomic
structure. Atoms are made up of
electrons, protons, and neutrons.
The hydrogen and oxygen atoms,
shown below, have different quantities
of the three sub-atomic building blocks,
which accounts for their different
properties and characteristics.
Sub-atomic structure of hydrogen and oxygen atoms.
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Generally, there are an equal number of electrons
and protons but the number of neutrons varies - e.g.
copper has 29 protons and 35 neutrons.
The number of protons in an atom is employed to
classify the elements by atomic number in the
Periodic Table of Elements e,g. hydrogen’s atomic
number is 1 while oxygen is 8 and copper is 29.
Electrons in all atoms are exactly the same just as all
protons or neutrons are the same. It is only their
unique combination in an element that makes the 103
elements different from one another.
Copper atom
Although the electron is three times as large as the
proton, the proton weighs approximately 1800 times
more than the electron. Electrons are incredible small
particles of energy - one electron measures
approximately .07 trillionth of an inch in diameter. It
would take 28 billion, billion, billion electrons to weigh
one ounce. The protons and neutrons form the
nucleus in the center of the atom similar to the sun in
our solar system while the electrons orbit around the
nucleus like the planets around the sun.
Electrons orbit the nucleus just as the planets orbit the sun.
The energy evident in the movement of electrons around the nucleus has been named
electrical energy. Its exact nature is unknown although a great deal is known about what
it can do. Protons and electrons have equal but opposite electrical charges or force fields
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that act to hold them in physical relationship to each other.
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Protons have a positive electrical charge while electrons have a negative electrical
charge. Neutrons have no charge and, as their name indicates, are considered neutral.
All electrons have precisely the same negative charge and all protons have precisely the
same positive charge. The force emitted by each of the opposing charges is, in turn,
precisely equal.
Electrical charges of electrons and protons
As the imaginary lines of force in the above diagram indicate, the energy of the opposite
electrical charges can affect each other and other charged particles. The effects are
succinctly stated in the law of electrical charges - opposite electrical charges
attract and like electrical charges repel.
Like - charges repel Like + charges repel Unlike charges attract
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Energy is the ability to do work. The work normally performed by the electrical energy
of the charged particles is to hold the atom together. The energy of "opposites attract"
holds the nucleus and electrons together while the energy of “likes repel” evenly spaces
the electrons in orbit around the nucleus and causes electrons and protons from different
atoms to repel each other. The energy of the atom is consumed in the structure of the
atom.
The law of electrical charges acts to keep an atom in electrical balance with an equal
number of electrons and protons with equal, counterbalancing electrical charges. If not
disturbed by an outside force an atom is in balance with a neutral electrical charge.
Valence Electron
Each level or plane of electron orbit - called a “shell” - can
only contain a set number of electrons.
The outer orbit - known as the valence shell - can only
contain a maximum of 8 electrons - called valence electrons.
Compared to the inner-shell electrons, valence electrons
are weakly held by the positive attraction of the nucleus.
Electron orbits or shells
Some elements like copper, silver, and gold only have one
valence electron. This electron is commonly traded back and forth between atoms. Other
elements like carbon, oxygen, and nitrogen have 4 to 6 valence electrons indicating that
there is a strong attraction force at the valence shell level of these elements. These valence
electrons are tightly held in the atom and hard to displace.
If electrons are added to or removed from an atom or substance (i.e. body of atoms), an
electrically unbalanced atom or substance is created - called an ion or ionized substance.
If an atom has an excess of electrons it is negatively charged or a negative ion. An atom
with electrons removed is positively charged or a positive ion.
An ionized atom or ionized body of atoms is no longer neutral. It will act the same as an
electron or a proton depending on its electrical charge. An electrical charge will:
•
repel its like charge
•
attract its opposite charge
•
conduct its charge to a body with a different charge
•
induce (or cause without contact) the opposite charge in another body
•
create a magnetic field when in motion.
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These five characteristics of electrical charges will be employed in a variety of ways to turn
electrical charges into electricity for transmission and use in our appliances. They should
be clearly understood before proceeding in our study of electricity.
•
.1.1 Repulsion, Attraction, and Conduction
The first three characteristics of electrical charges are employed to transmit electrical
energy from one place to another and to convert that energy into the energy of particles in
motion. The latter conversion results in friction and heat as the electrons move.
A force from an external energy source (such as a battery or generator as will be discussed
later in this Module) can be applied to start the movement of valence electrons from atom
to atom. Once the force is applied to one part of a material (e.g. one end of a wire) the
electrical charge of the displaced electrons causes an almost instantaneous movement of
electrons through the wire in a domino effect. The displaced or free electrons repel other
electrons out of orbit, which in turn repel other electrons out of orbit, which in turn repel
other electrons etc. in a chain reaction.
ZE?
Domino movement
However, just like a domino movement, the application of force will not create movement
unless the electrons have a place to move to. The force will simply create a potential for
movement once the dominos or electrons can move.
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Mechanical
Force
Exerted but no
Domino movement
Electromotive force applied to wire creates potential for movement but no actual
movement unless electrons have a place to move to.
With continued application of force, electrons will continuously flow only if they have a
return path back to the source of electron movement. This path home to the source of
the imbalance is necessary for continuous flow to occur. Without a path home the
electrons cannot move - the force or pressure simply builds up in the material (as shown
above) until a path home is allowed.
The flow of electrons in a wire is similar to the movement of marbles in a tube - applying
force to one causes them all to move instantaneously.
Electrons flow from atom to atom is like instantaneous movement of marbles in a tube.
The distance traveled by one electron is incredibly small but the overall effect when
focused in a wire is an almost instantaneous transfer of energy at the speed of light 297,600 kilometers per second (186,000 miles per second).
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Only electrons flow. Therefore, electrical flow - or current — is from negative to positive - from
a material with an excess of free electrons to one with a deficiency of electrons.
The electron theory of flow from negative to positive was not always the accepted theory. In
the early days of electrical research, it was assumed that the flow was from positive to negative.
This latter theory is known as the conventional theory of electricity and will be discussed later
in reference to automotive circuits.
The direction of electron flow in a wire may be in one direction only or it may alternate back and
forth many times a second due to an attraction and repulsion force. Electron flow in one direction
is called direct current (DC) as commonly produced by batteries. The electrical current in house
wiring alternates 120 times per second and is called alternating current (AC).
As long as free electrons are moving, their energy is available for use so the direction of flow
only affects the transmission and use of that energy. Issues related to the two types of current
will be discussed later in this Module.
If movement is allowed but the force is removed, the electrons will immediately return to their
balanced relationship with the nucleus and no longer emit electrical charge. It is like a game of
musical chairs except that no chairs are added or removed. The external force of music causes
the players (energy emitters) to get up and move from chair to chair until the music stops. They
return to their seats and energy is no longer expended.
The external force from a battery, generator etc. causes electrons to move not by adding or
subtracting electrons to a wire but rather by starting the chain reaction of attraction and repulsion
by displacing or freeing electrons in one part of a loop of joined atoms. An imbalance is created
in the loop and the only way of correcting the imbalance is for the electrical energy to travel full
length around the loop. When the force from the electrical source stops or the loop of joined
atoms is broken, the electrons immediately return to a balanced condition in neutral atoms.
The ability or characteristic of electrical charges to attract and repel electrons is employed to
conduct the charge from one atom to another resulting in electron movement. Electricity is the
movement of electrons.
The movement of any particle results in friction as particles hit each other or encounter
resistance to flow. Friction causes heat so the energy of motion results in a conversion or transfer
of motion energy to heat energy. This is essentially what is happening in a heater or light bulb.
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The bulb’s filament, made of tungsten metal, is more resistant
to electron flow than the copper wire, which delivers the
electron particles. This resistance to motion causes the filament
to heat up and glow. The energy of particles-in-motion is
converted to heat and light energy.
The same thing is happening in the copper wire but to a lesser
degree because copper atoms offer less resistance to electron
flow than the tungsten atoms in the bulb’s filament. However,
with excessive electron flow, the copper wire delivering the
electrons may also heat up significantly.
Electron flow causes filament to glow
The fourth characteristic of electrical charges - the ability to
5.1.2 Electrical Induction
induce (or cause without contact) the opposite electrical charge in another body - is also
employed in a variety of ways to turn electrical charges into electricity for transmission to
and use in appliances.
When an electrically neutral object is brought close to either a positive or negative charged
body, the neutral object and charged body are attracted to each other. This occurs because
the electrical forces induce the opposite charge in the surface of the neutral object.
Wail
For example, a balloon that has been negatively or positively charged by the application of
the force of friction to displace electrons (i.e. create a static electrical charge), will adhere to
a wall as a result of this induced charge. In the case
+ —b — + — -+-+-+ 4- - + -4--+-+-+ +-+-+- —+—+—+
of a negatively charged balloon it repels the electrons
4- +4- -----------in the surface of the wall leaving a positive charge on
5- + + -----------+ 4 + ------------the wall surface.
4-4-4- -----------6- 4-4- ----------------
Opposites attract so the balloon adheres to the wall.
That this happens without them actually touching
indicates that electrons have not been transferred
but rather that the electrical charge has induced the
opposite charge in another body without contact.
Electrical charges induce opposite
charge in neutral body
+ + + ------------+ ++ ------------- r
-+- + -+ \ +-+7+" Electrons —
4— 4- — 4,
+ - + -4-_ repelled + tit' + by
n
®9atively - + ~ + t+ charged
balloon
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Over a long period of contact, the imbalance in electrons will cause a flow of electrons
from the balloon to the wall (or surrounding air) resulting in a loss of attraction. The balloon
then falls off the wall.
This characteristic of electrical charges to induce electron movement in another body is
easily demonstrated with static electrical charges but is more useful under the dynamic
condition of electrical charges in motion. For example, electrical induction is employed in
capacitors to increase the starting torque and efficiency of electric motors. An alternating
electrical flow is induced from one thin aluminum plate into another separate aluminum
plate. Direct current cannot be used for this purpose.
Induction is the process of causing something to happen without physical contact.
Electricity can cause things to happen in a number of ways. The most common use of the
term relates to electric motors, which are called induction motors. Electrical charges are
not inducing the action but rather another property of electricity - electromagnetism.
5.1.3 Electromagnetism
To this point you may be thinking that the above four characteristics of electrical charges
exhibit all the characteristics of magnetic forces. North and south poles of a magnet attract
but similar poles repel; a piece of metal (such as a compass) bought close to either of the
magnetic poles will cause an induced attraction.
Magnetic poles attract and repel.
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The fifth characteristic of electrical charges is the ability to create a magnetic field.
Electrons flowing through a wire will create a magnetic field around the wire as illustrated
below. The direction of flow determines the polarity of the magnetic field and the amount
of electron flow determines the strength of the magnetic field,
Direction of current
Intensity of current
Small Large
Electricity flowing in a conductor creates a magnetic field.
Direction of current determines polarity of magnetic field.
Amount of electron flow determines the strength of the magnetic field.
At first glance, the only difference between electrical energy and magnetic energy appears to
be in the names of their opposing forces - North/South vs. positive/ negative.
On closer examination, the similarities between magnetic charges and electrical charges are
strong because the principles underlying both are based in the structure of the atom but they
are also significantly different. Let's take a brief look at magnets to explain that difference.
A magnet is a material that has the property of attracting metals such as iron and steel. All
magnets have two poles - called North and South. Between the two poles a magnetic field
exists consisting of many lines of magnetic force - often called magnetic lines of flux. The laws
governing magnetic charges are like the law of electrical charges - opposite poles attract and
like poles repel.
Permanent or natural magnets are usually one or a combination of three substances - iron,
nickel, or cobalt. Their atomic structure is different from other atoms. All electrons spin on their
axis creating a magnetic charge. In effect, the spinning causes each electron to become a tiny
permanent magnet.
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In most substances, electrons pair together such that they spin in opposite directions thus
canceling out the magnetic force. These substances are non-magnetic. Iron, cobalt, and
nickel atoms have some electrons that pair together such that they spin in the same
direction. This increases the magnetic effect.
Joined together in alloys, these elements form concentrated fields of magnetic flux that
direct the magnetic energy of electrons in a common direction. This allows the energy of the
atom to act upon other substances without having to free electrons from their orbit.
|N
sj
|N , 8|
|N
a!
|N
s|
Magnetized
ns N s| IN s| |N s| (Ñ
s
|N
S]
|N
S
|N
s|
'
|N
|N
S|
|N
S]
|N
S|
S|
Magnetic energy results from electrons
spinning but is cancelled out if electron is paired with an electron spinning in the
opposite direction as indicated on the left or intensified if paired with an electron
spinning in the same direction.
A magnetic field can be thought of as a stationary electrical charge and an electrical charge
can be thought of as a moving magnetic field. The force of these actions is only apparent
on some metals although there are indications that magnetic and electrical forces influence
all substances to a greater or lesser degree. For example, magnets are being used to treat
physical ailments in muscles and joints and there is a growing fear of the effect of “electronic
radiation” from electrical devices like smart phones.
The major difference between electrical energy and magnetic energy is that electrons do
not flow in a magnet. If contact is allowed between two bodies with opposite electrical
charge, electrons will flow from the body with an excess of electrons to the body with a
deficiency of electrons.
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Body A
Negatively Charged
Relative to B
Gas Technician 3
Body B
Positively Charged
Relative to A
Bodies Connected, Free Electrons Flow from A to B
Both Bodies Contain Same Number of Electrons
Electron Flow Stops, Balanced Energy Condition
Electrons flow from negatively charged body to positively charged body to become balanced.
This flow of electrons does not occur with magnetic energy - north and south poles of a magnetic
can touch, be separated, and still attract or repel as before. Magnetic energy is fixed or trapped
in the magnet; electrical energy is transportable.
The ability of electrical charges to create a magnetic field is employed extensively in electrical
devices such as solenoid valves, relays, and motors. A magnet's ability to attract electrons to its
north pole and repel electrons from its south pole is employed to free electrons in conductors
thus producing electricity in electrical generators.
The similarities and differences of magnetic energy and electrical energy are worth considering
early in this session since magnetism is employed to produce electricity and electromagnetism
is a major use of electricity in motors, electric valves, and relays.
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This section has introduced the source and characteristics of electrical energy in the atom. This
energy exists in all atoms and simply must be unlocked by the freeing of electrons. The force
necessary to free electrons varies from element to element as will be discussed in the next section.
Electrical energy just has to be freed by creating a difference in electrical charges between two
points in the same body. As long as a difference is maintained there will be a flow of electrons from
the point where there is an excess of electrons to the point where there is a deficiency of electrons.
While free electrons are flowing, the energy forces of the atom and the energy of particles in motion
can be used in an almost unlimited variety of ways.
Energy is the ability to do work. Electrical energy can easily be transformed into other forms of
energy - heat, light, magnetism, and mechanical energy to name a few. The atom’s abilities to repel,
attract, conduct, or induce electrical charges and to create magnetic fields are the basis of electricity.
The principles underlying the flow of electrons will occupy most of our attention in the rest of this
Module. We will study ways to confine, control, create, and use electricity in our gas-fired appliances.
We will employ some similarities between water flow and electron flow to explain the characteristics
of electrical flow. However, we must never lose sight that electricity - the flow of electrons - begins
and ends with the energy in the atom.
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5.2 The Electrical Pathway
Electricity is the flow of electrons. For electrons to flow there must be a difference of
electromotive force or pressure* between two points in a continuous pathway that allows electron
flow from the source of the imbalance back to that source. This pathway is called a circuit.
An analogy with a water system will be helpful to explain these two requirements for flow to exist
- a difference in pressure and a continuous pathway.
Open Valve I Closed Switch
tight
Bulb
Water
Wheel
Pool of energy
Water / Electron
Power Source Motor
driven / Chemical driven Water
pump I Battery
Electrical circuit is similar to a water piping system.
Both of the above systems employ an outside energy source to create a difference in
pressure. That pressure causes a current or flow of electrons through the closed loop
system to the working device (water wheel and light bulb). The energy of the current is
used to overcome the device's resistance to flow thereby converting the current’s energy
to another form of energy (mechanical energy and light/heat energy respectively) to
produce work. The spent energy of the current returns back “home" to a fixed pool of
energy (water or electrons) under zero pressure.
Nothing is added; the difference in pressure creates the current that overcomes the
resistance of an energy-converting device to produce work. The four factors - pressure,
current, resistance and work - are interrelated.
Before examining each factor individually and how they affect each other, let’s confirm the
requirements for a complete path back home.
* Although the proper term to use when speaking of the force supplied to an electrical circuit is
electromotive force (EMF) or voltage, this introduction to electricity will use the term electrical
pressure to help explain the basic principles of electricity.
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For proper operation of electrical systems and for your own safety, it is crucial to
understand that electricity will take the easiest path home through a material that
provides the least resistance to flow.
As shown above, the water pressure difference created by the pump causes the water to
flow through the system as long as the valve is open and the water returns to the pool.
Under these conditions the water wheel will operate. The electrical pressure difference
created by the battery causes the electrons to flow through the system as long as the
switch is closed and the electrons return to the pool. Under these conditions the light will
glow.
Pressure
Closed Valve / Open Switch
An electrical switch is like a valve in controlling current through the circuit
If the valve is closed or the switch is open (as shown above) or the pathway does not
return to the source (as shown below) then flow will stop. There is still pressure in both
lines but no current. Without current, no energy is available and no work is done.
Pressur
e
A continuous pathway is required from source back to source for flow to exist.
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In some electrical circuits, the complete path home is not made through wiring. If the
applied pressure and electron flow output are sufficient, a path home may be provided if
the source is connected to a neutral body of atoms capable of conducting electricity.
The battery powered electrical systems in older vehicles employ the metal parts of the
vehicle as a pathway. Building wiring systems employ a neutral wire as the normal,
preferred path for electrons to flow back to source. However, a ground wire is provided
as an alternate path home for safety reasons.
Alternate paths home are provided in some electrical circuits.
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In building wiring systems (as shown above in Figure B) the alternate paths home are
required to protect the higher pressure and higher current electrical system against a fault
situation. A source line accidentally coming into contact with the appliance, motor casing or
other object capable of conducting electricity could create such a fault. The circuit is
commonly called a ground fault protection system. The ground or ground wire only
function as parts of the circuit in cases of a fault. If the electrical system is operating
properly, the path back to the source is the neutral (white) wire.
Alternate paths home are provided if source line touches motor casing or
appliance.
Due to this necessary safety precaution to protect the electrical system, the ground may
become an easier pathway for the electrical current if a grounded object or person touches
the exposed source wire.
Alternate path home provided through person in contact with source and ground.
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As previously mentioned, a dry human body has a relatively high resistance to electrical
flow but a wet one will allow an almost unrestricted current flow between an electrical
source and ground. Never allow your body to be a path home for an electrical system.
Electrical current will always take the easiest path home. But what makes one path easier
than another? If all matter is composed of atoms, why don’t the atoms in the air allow for
a balancing of electrical charges in two oppositely charged bodies? Why doesn’t electricity
flow out of the end of a wire like water out of a hose? To answer these questions, we must
return to the structure of the atom to determine why some materials allow electron flow
more easily than others do.
5.2.1 Conductors and Insulators
The force or pressure necessary to displace valence electrons depends largely on the
number of valence electrons in the atom and the strength of their bond to the nucleus.
Some elements, particularly the metallic elements, give up their outer electron(s) easily
like silver, copper, and gold. Each of these elements has one valence electron. Other
substances like air, glass/porcelain, and rubber do not easily give up electrons. They are
composed of atoms with 4 or more valence electrons (nitrogen - 5; oxygen - 6; silicon - 4;
carbon - 4).
Copper atoms with one valence electron make excellent conductors of electricity.
Oxygen atoms with 6 valence electrons make air a poor conductor of electricity.
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An element or substance that easily gives up electrons is called a conductor of electricity. Silver
is the best conductor followed by copper, gold, and aluminum. A very small force will cause
these elements to give up electrons. Their valence electrons are loosely held and easily
displaced. In fact, most good conductors regularly trade free electrons without any force
supplied. The force or pressure applied by an electrical source simply increases and gives
direction to this easy flow of electrons.
An element or substance that does not easily give up electrons is called an insulator. Insulators
can be used to contain and control the flow of electrons along a conductor such as a copper
wire. The plastic, rubber or lacquer coatings over copper wires contain and direct the electron
flow along the easier path of the conductor. The rubber handle on electrical-grade pliers can
insulate your hand from a flow of electrons if a live electrical wire is unfortunately cut.
There are no perfect conductors or insulators. All materials will offer some opposition or
resistance to flow that requires a force to overcome. The lower that resistance the lower the
force necessary to overcome it and the better the conductance of the material. Conductance
is the opposite of resistance.
An insulator has a high resistance to flow requiring a greater force to cause electron flow.
However, with enough force any substance will conduct electricity. Air, for example, is a good
insulator but with the massive forces created by positively or negatively ionized clouds, electron
flow in the form of lightning will travel miles through air to balance the charge of the atoms in
the clouds.
Even air becomes a conductor of electricity given a sufficient difference in electrical pressure.
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On the other hand, even conductors offer some resistance to flow. Resistance to flow in a
copper wire is increased by its length, diameter, and temperature. The less the resistance
the greater the flow given a steady electrical pressure. Thus, a short wire can conduct
more electricity than a long one, a thick wire more than a thin one, and a cool wire more
than a hot one.
More Flow Less Flow
More Flow Less Flow
More Flow Less Flow
The resistance in a conductor is increased by its length, diameter, and temperature.
Some materials allow the easy flow of electrons in one direction but resist flow in the
opposite direction - like a check valve in a water system. A component called a diode located
in some controls is made of such material.
Other materials resist electron flow until a certain electrical pressure is applied and then
allow easy flow after that force is reached, A component called a bi-lateral switch located in
some controls is made of such material.
Still other materials - called semi-conductors - are neither good conductors nor good
insulators. They usually contain four valence electrons (e.g. silicon and germanium) and
have the advantage that their resistance decreases as they are heated. Heat has the
opposite effect on conductors, whose resistance increases with an increase in temperature.
Semi-conductors are used extensively in solid-state components such as transistors,
diodes, and integrated circuits - all found in gas-fired appliances.
To return to our original questions: Electrons cannot flow out of the end of a wire like water
out of a hose because the resistance of the atoms in the air stops the electrical flow just as
the resistance of the insulation around the wire confines the flow. The air atoms act like a
plug would on the end of a water hose.
With enough pressure the resistance of the “plug” will be overcome and a spark or arc will
issue from the wire and travel along the easiest, most direct path through the closest
conductive material back to the source. The ignition electrodes in a gas burner are an
example of this condition.
With a sound appreciation of the basic requirements and concerns related to a complete
circuit, we can now explore some terms and relationships in electrical circuits.
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NOTES:
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5.3 Electrical Terms and Relationships
The end purpose of an electrical circuit is to safely and efficiently deliver energy to a device
that can convert that electrical energy into another, more useful form of energy. To achieve
that end purpose of delivering power to carry out work, three interdependent factors must
be considered:
• Electrical Potential
• Current
• Resistance
Again, a comparison with a water piping system will serve to explain the terms and
relationships of these three factors. The end purpose of the piping system, shown on the
next page, is to deliver waterpower to the flywheel to convert the energy of water flow into
mechanical energy. The purpose of the electrical circuit, illustrated below it, is to deliver
electrical power to the light bulb to convert electrical energy into light energy.
5.3.1 Electrical Potential (or Pressure)
In a water piping system, the force or pressure may be measured in pounds per square inch
(psi) or in kilopascals (kPa). Electrical pressure is measured in VOLTS and commonly
referred to by the following terms:
•
•
•
•
Electromotive force or emf
Potential difference
Voltage
The symbol E
A water pressure gauge is used to measure the difference in water pressure between two
points in the system or to measure the difference in pressure between any point in the pipe
and the pressure at the return point, which is at atmospheric pressure.
A voltmeter is employed to measure the difference in electrical pressure between two
points in a circuit or between any point in the circuit and the path home or ground (if the
electrical system is grounded).
Just as water pressure is a measurement of pressure difference between two points so too
is electrical pressure or voltage a pressure difference. One point in either system cannot
have a pressure except in relation to a second point.
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NOTE: A water pressure gauge does not appear to be measuring a difference between the
pipe pressure and source when only one sensing point is connected but its other port is in
communication with atmospheric pressure which is the pressure applied at the water source.
A voltmeter must be connected between two points in the circuit.
Electrical pressure measured in volts is similar to a water pressure measured in psi.
An electrical switch is like a valve in controlling the application of pressure.
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If the valve is closed or the switch is open (as shown immediately above) or the pathway is
not complete (as shown below) the applied pressure will not result in flow.
Without flow or current, no energy is delivered and no work is done.
Applied pressure requires a complete pathway back to source for flow to exist.
Just as there would be no water pressure drop across an open full flow valve, there is no
electrical pressure drop measured in volts across a closed switch, as shown above.
However, the pressure drop will be the applied pressure across:
•
an open switch (bottom illustration on the previous page)
•
from an energized line back to the return point of the source (above diagram)
•
across an energized single load† (water wheel or bulb in the top illustration on
the previous page)
Pressure applied is pressure consumed; voltage applied is voltage consumed. This
fundamental principle of electrical circuits - that whatever voltage is applied to a circuit will
be consumed by that circuit - means that the measurement of voltage is the most important
and informative measurement for determining whether a circuit is operating safely and
properly.
The multiple uses of voltage measurement will be discussed and practiced after we explore
some other necessary terms and relationships and after we learn the basics of voltmeter
use.
† A load is anything that consumes energy by converting it to another (usually more useful) form of energy.
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5.3.2 Current or Amperage
At this point it is common to confuse pressure with flow -■ to think of voltage flowing
instead of electrons. But a volt is like a psi. Just as it is not a psi of water pressure that
flows through piping neither is it a volt of electrical pressure that flows through a circuit.
Flow or current is measured as a specific quantity of something passing a specific point
over a specific time. Gas flow may be measured in cubic metres per hour or cubic feet per
minute (cfm). Liquid flow may be measured in litres per second or gallons per hour (gph)
or any other agreed upon and useful quantity and time period.
Electron flow or electrical current is also measured in quantity over time. Given the
incredibly small size of an electron (-.07 trillionths of an inch), the speed at which they
move (light speed), and the almost imperceptible energy available from the movement of
one free electron, it would be impractical to measure the quantity of that current in any
normal units.
The agreed upon unit of measurement for the quantity of electrons is called a Coulomb‡
and the time period is one second. When one Coulomb of electrons passes a point over
a period of one second the flow rate is one ampere (commonly abbreviated to amp).
Current measured in amperage (amps) is the flow of a set number of electrons
past a point over the time period of one second.
‡ Some of you may be interested in knowing that one Coulomb equals 6,280,000,000,000,000,000 (or 6.28
X 10ts) electrons - a number first determined by mathematical calculation by French scientist, Charles
Coulomb, in the 1700's. Unless you also think it's important to know how many H2O molecules there are in a
litre or gallon of water, the actual number is meaningless for our purposes beyond its use as a standardized
unit of measurement.
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Just as we spoke of draft intensity, we often refer to electrical current intensity so the symbol
employed to denote current is the letter I. The tool employed for measuring current flow is called
an ammeter. It measures the rate (quantity over time) of electron flow in units of amperes. As
such, it is similar to a water flow meter in our piping system.
Electron Flow Meter or Ammeter in
amperes
(amps)
Electrical current measured in amperage (amps) is similar to water current measured in gph.
Amperes or amps are a measure of electron flow that can be used for the same purpose that
we use any measurement of flow - cfm, gph etc. For example, we require a certain gas flow
(measured in cfh) to allow the burner and appliance to function as designed and we require a
certain electron flow (measured in amps) to allow electrical components to operate as designed.
Gas lines are sized to exceed the required flow rate of the burner just as electrical wires are
sized to exceed the amp rating of the burner motor. If the gas supply is restricted, the burner
operation and flame suffer just as the electrical components would if the electrical flow is
restricted.
Current is proportional to voltage in a given circuit. Whatever happens to one will happen to
the other in a predicable proportion. In some circuits, such as DC circuits and some AC circuits,
that proportion is a direct relationship - if voltage doubles, current doubles; if current decreases
by one half, voltage decreases by one half. In other types of AC circuits found in motors,
transformers and control relays, the proportion is not direct but it is still proportional and
predictable.
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Water Flow Meter Electron Flow Meter or Ammeter
Increasing current by increasing pressure
Doubling the pressure increases the current, increases the power delivered to the load and
increases the work done by the load. If the components are not designed for this workload they may
fail!
Current is energy in motion. The greater the current the greater the energy delivered (power) and
the greater the energy conversion (work). As indicated in the above diagram, current is proportional
to power and work. Power is the rate of energy delivery while work is the rate of energy conversion.
Essentially, power and work are the same thing. Increasing current increases power and work.
You have probably heard the phrase “voltage won’t hurt you, current wilF. This is based on the fact
that no matter how high the pressure, electrical energy will not be released or pose a hazard until
electrical current flows. It takes very little current flowing through a human body to cause damage.
Less than 50/1000 (0.05) of an amp can cause severe pain. One tenth of an amp can kill.
The greater the flow, the greater the energy release. The higher the amperage the greater the
hazard. Of course, in most circuits, the higher the potential difference (voltage), the greater the
potential for flow.
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5.3.3 Resistance or Ohms
Flow of any material causes resistance. Electron flow is no different. Electrical resistance is
anything that opposes the flow of electrons. Resistance or the opposition to flow is caused
by:
•
the conducting material - its ability to conduct, its size and temperature
•
flowing particles hitting each other or hitting stationary particles
•
opposing energy forces such as magnetic fields or induced currents.
Resistance is both necessary and useful in an electrical circuit. Without the resistance of the
load there would simply be a free flow of electrons from the source back to the source. Only the
small resistance of the wire conductor would impede current.
This condition is called a short circuit.
In our low voltage battery circuit (1.5 volts) this
would result in a rapid draining of the battery’s
charge and the production of heat in the battery
and the conductor.
In higher voltage circuits, such as building wiring
circuits at 120 volts, the unrestricted current flow
would result in dangerous overheating of the
wires as electrons rapidly flow from source back
to source creating friction heat.
Live short circuit and Dead circuit
The primary resistance to flow in a properly
operating circuit will be the load(s), which converts electrical energy into another (usually more
useful) form of energy - heat, light, mechanical motion, etc. However, as previously discussed,
the conductor may also oppose flow especially if it is undersized, excessively long, or hot.
Resistance opposes flow created by force. Voltage overcomes resistance to create flow.
Voltage, current and resistance are directly proportional. Any change to resistance will cause
the opposite change in current. Given a constant voltage (as is usually the case in our circuits):
• An increase in resistance causes a decrease in current.
• A decrease in resistance causes an increase in current.
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The scientist that first noticed this relationship was Georg Ohm in 1826 and it is in his honour that
the unit of measurement for resistance is called the Ohm. An ohm is defined by its relationship to
voltage (force) and amperage (current):
It takes 1 volt to push 1 amp through 1 ohm.
The symbols employed to represent resistance are either the letter R or the Greek symbol Q for
Omega. An ohmmeter is used to measure the resistance between two points by introducing a
steady voltage from the meter’s internal battery through a deenergized line or component and
measuring the resulting current in ohms (volts : amps)
To continue our analogy with the water system: the ohmmeter would be like a flow resistance
meter that takes the place of the water pump and exerts 1 psi of pressure to push water through
the system to determine its resistance in "psi per gallons per hour". The ohmmeter also takes the
place of the electrical source to exert a steady voltage on the system and measure the return rate
of flow as expressed in ohms.
Measures & reads out
rate of return in psi/gph
An ohmmeter is similar to a water flow resistance meter.
If no current returns to the meter because the pathway between the two measuring points
is broken, the resistance is volts : 0 which results in a reading of infinite resistance commonly shown as the symbol oo for infinity. The ohmmeter is a valuable tool for
determining the continuity or “connectedness" of a circuit or component.
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Any reading between 0 and infinity (co) indicates the level of opposition to flow posed by
the material - its capacity to conduct due to atomic structure, size, length, and condition.
However, an ohmmeter cannot measure other forms of resistance to flow such as
opposing energy forces (magnetic fields, induced currents etc.) or changes in component’s
resistance caused by increased flow (e.g. change in temperature).
If the resistance of the material is the only opposition to flow in the circuit (i.e. a purely
resistive circuit), the relationships between resistance, voltage, current and power are
simple and straightforward. The following diagrams give the basic relationship between
the four factors.
Decreasing the resistance by half doubles the current, doubles the power
delivered to the load and doubles the work done by the load. If the components
are not designed for this workload they may fail!
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The resistance of electrical components determines their voltage rating and amperage
rating (ampacity). If those ratings are exceeded the components may overheat, melt, and
possibly cause a fire. This is especially dangerous with concealed wires inside hollow
walls where the overheating may progress unnoticed until the fire is well established.
On the other hand, if the voltage and amperage ratings of a load are not met the load will
not operate as designed. A load, such as a light bulb, presents a resistance that requires
a certain voltage to cause a current to pass through it at a rate that will allow it to work. In
the case of the light bulb, current through the resistance of the tungsten filaments causes
those filaments to glow and emit light and heat. Electrical energy - the energy of electron
movement - is converted to light and heat energy due to the applied voltage causing the
flow of electrons to overcome the resistance of the bulb.
120 volts
Lamp operates
as designed.
Normal current
220 volts
Lamp burns out.
Design ratings
exceeded.
50 volts
Lamp not lit or
glows dimly.
Design ratings
not met.
Excessive voltage causes increased current resulting in overheating while
insufficient voltage resulting in insufficient current may not overcome resistance
of the load.
The size of the filaments in a bulb or the amount of resistance in any load is designed for
a certain voltage since voltage against a fixed resistance will determine current flow
through that resistance. If insufficient voltage is applied the bulb will not glow properly. If
too much voltage is applied the filaments will overheat and melt.
The electrical terms and relationships, discussed above, will become more meaningful to
you after some hands-on experience in the lab sessions. However, to get to that point of
practical application we must first learn the basics of instrument use.
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5.4 Tools of Electrical Measurement
Electrical test instruments are employed on a daily basis to ensure personal safety and
to quickly and effectively troubleshoot problems with electrical circuits and components.
The most common measurements are taken for voltage, amperage, and resistance. A
meter that can perform all three functions by selecting the appropriate function and scale
on one portable instrument is usually employed.
Such an instrument is called a multimeter or VOM meter (VOM stands for Volt, Ohm,
Milliammeter) or DMM (digital multimeter). The first term - multimeter - is more appropriate
since many of these instruments can also measure temperature, frequency, and
capacitance (the latter is discussed later in this Module).
The purpose of this text is to introduce some basic principles for the safe and effective
use of these instruments. The discussion is general in nature and will have to be applied
to your specific test instrument. Issues that relate to all functions of the meter(s) will be
discussed first and followed by a focused discussion about measuring voltage, amperage,
and resistance.
5.4.1 General Requirements for Meter Use
There are two types of meters: analog and digital. Analog meters indicate measurements
by the position of a needle on a dial while digital meters provide LED read-outs of the
measurement. Digital meters are more popular due to their accuracy, versatility, and ease
of reading the instruments. A technician should be able to use both types with confidence.
Analog (left) and digital (right) s.
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In both cases, the meter should not be turned on until you decide what value is being
measured and what the expected reading is. Those decisions will determine the type of
instrument or function selection on the multimeter and the scale setting within that
function. Using or selecting the ohmmeter function to measure a live (i.e. energized) circuit
could destroy the meter as could selecting a scale setting that is exceeded by the actual
measurement (e.g. measuring 120 V on the 50V scale).
Switching the function selection dial while attached to a live circuit will also expose the
various meters to potential damage. Always disconnect the test jacks or de-activate
the circuit when changing the selection dial.
Each instrument has a maximum and minimum range of measurement. The maximum
limit is important for personal safety and protection of the instrument. The minimum range
determines the accuracy of the reading. Make yourself aware of the range limits of your
particular instrument. It is unfortunately all too common for a novice to destroy his first
meter by trying to test the voltage of an ignition transformer with an instrument that was
not designed for the high voltage produced by those transformers. Injury, damage to
meters, and inaccurate measurements are usually the result of choosing the wrong
function or scale.
The symbols employed on test equipment are standardized. The test leads are black and
red with the black lead always connected to the COM or common plug jack. The position
of the red lead varies from function to function based on the following symbols.
V ~or DC : voltage as used in battery circuits and electronic controls
V~ or AC : voltage as used in building wiring circuits
A
: amperage or current
mA : milliamperage or 1 .OOOths of an ampere for smaller currents
Q
: ohms or resistance
ne
: capacitance, used to measure a capacitor (discussed later)
Various combinations of these symbols (e.g. VQA) will direct you to the correct position
for the red plug jack depending on the desired measurement.
Various ranges are available for each function on the multi-position rotary switch to permit
precise reading of large to small values. The units of volts, amps and ohms are sometimes
too small or too large to be useful in some circuits. Larger and smaller units of each term
are designated by a pre-fix system that you will need to know for proper and safe use of
the testing instruments.
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The common ones encountered are:
•
Megaohm (MQ): 1,000,000 ohms or 106 or ‘R X 1000K'
•
Kilo ohm (KO): 1000 ohms or 103 or ‘R X 1000’ or ‘R X 1K’
•
Millivolt (mV): 1/1000ths of a volt or 0.001 volts or 10-3
•
Milliamp (mA): 1/1000ths of an amp or 0.001 amps or 103
•
Microamp (pA): 1/1,000,000ths of an amp or 0.000001 amp or 10‘6
SPERRY DM-4100A
Once the proper function is chosen the range
selection should be the next highest above the
known value to be measured. For example, we
want to measure the voltage across the open
disconnect switch to a furnace so an AC voltmeter
or V~ function is selected.
If you are unsure of the expected reading but are
confident that it is within the maximum range of your
meter, then the maximum range should be selected
(750V in this case). Once the reading is known
(120V in this case), the setting just above it should
be selected for accuracy (200 V in this case).
Highest range is initially chosen
and then reduced to range that is
lust higher than actual reading.
Whereas digital meters give an easy LED read-out, the needle-dial reading given by
analog meters requires special attention for proper use and interpretation. The force of
gravity may affect the operation of the analog meter so the position(s) specified by the
manufacturer must be followed - usually horizontal on a flat level surface. The needle must
be zero-adjusted before each use and all readings must be taken with the eyes level with
the needle and perpendicular to the dial. A special mirror or glass is often employed on
the dial face to ensure that the needle is read from the proper position.
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An analog meter dial, as shown below, requires further interpretation in reading the correct
line and/or multiplying the reading by the appropriate value. Usually the value is read
directly from the correct line but if the selector switch setting does not have a designated
scale then a multiplier must be employed.
Using the above diagram, let’s say we are measuring voltage at a wall outlet. Since we
Ohms Scale
Read right to left
ihms Zero position
DC & AC Scales
Read left to right
Amperage
Scale
Zero Position _ For
AC /DC ! Amps
. AC / DC / Amps
Zero Adjustment
know that it will be approximately 120 V AC we insert the black lead into COM and the red
lead into V - Q - A. Before turning on the meter ensure that the needle is at zero or adjust
Zero Adjustment
for Ohms
Red test probe jacks
For Ohms, Amps and.
ACV or DCV to 750V
Analog meter and scale ranges.
Function / Range
Black test probe jack
Selector Switch
for all measurements
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it using the adjustment screw at the top center of the dial.
The switch is turned to 250 V AC (approximately the 1 o’clock position) since the next
smallest value is 50, which would exceed our expected reading and thus could damage
the meter. The test probes are inserted into the wall plug and the reading on the 0 to 250
line is approximately 158 volts (obviously a problem!). Each increment between the
numbered values (on this scale only) is 5 volts.
The relative positions of the test probes do not matter when measuring AC voltage
because the voltage alternates. However, DC voltage is applied and measured from
negative to positive - from the black test probe to the red probe. Most analog meters are
polarity sensitive when measuring V DC so the probes’ relative position is important.
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Using the same diagram but measuring an unknown DC voltage of less than 750 we would
use the following procedure. The test probe positions remain in the COM and V - (1 ■ A
jack and the meter is again zero adjusted while the meter is off. The switch is moved to
750 V DC scale (approximately the 11:30 o’clock position) since we are only sure that the
reading will be less than 750 V.
The black (-) probe is firmly attached or held at one point in the circuit and the red (+)
probe is momentarily touched to the other test point in the circuit. If the needle deflects
below zero, reverse the position of the probes since the DC voltage measurement function
is polarity sensitive (unlike AC voltage).
Again, touching the leads momentarily to the circuit finds that the needle deflects only
slightly to the right. Keep moving the selector switch downward on the scale until the
needle is past the middle of the scale. The most accurate readings are closer to full scale.
In this case, we find the best needle position is when the selector is on the 2.5 scale.
However, there is no corresponding 0 to 2.5 line on the dial; the lowest scale is 0 to 10.
Since 2.5 divides evenly into 250 one hundred times, the reading on the 250 scale can be
used as long as we divide that reading (-160 in our example) by 100 resulting in a correct
reading of 1.6V DC.
This procedure is applicable to all measurements taken on an analog meter. Digital meters
do not normally require zero adjustment or interpretation of the reading and often have an
automatic polarity switch for reading V DC. A negative sign will appear if the test probes
are reversed indicating that the flow is from red to black.
Proper care and storage of sensitive electrical measuring devices requires:
•
Protection from damp or high temperature conditions
•
Replacement of worn or cracked test leads
•
Storage in a case even between jobsites to prevent excessive jostling
•
Inspection of the battery compartment for corrosion
•
Removal of the batteries during long periods of storage
•
Calibration checks against a known voltage, amperage, and resistance on a
regular and recorded basis.
Get to know your meter. Read the instructions carefully and follow the procedures
recommended in those instructions.
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5.4.2 Voltmeter
A voltmeter measures the difference in electrical pressure or the potential difference in
EMF between the two points in contact with the test leads. It can be as simple as a light
bulb or as complicated as an oscilloscope. We will focus on the test light and multimeter
illustrated below.
Examples of instruments for testing voltage.
No matter which voltage tester is employed the two most important points to remember
when testing for voltage on an energized circuit are:
1.
There must be a resistance between the two points being measured to make a
zero reading meaningful.
2.
There must be a complete circuit or “path home" to make a zero reading
meaningful.
In the wiring diagrams on the following page, two AC energized circuits are shown. Two
voltage testers - a voltmeter and a test light - have their test probes across a:
• switch used to connect or disconnect the electrical source. The symbols for an
open switch or “OFF” switch and a closed switch or “ON" switch are:
Symbols for open switch (left) and closed switch (right).
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• load or electric device that consumes electricity to do useful work - such as
motors, heaters, lights etc. There are various symbols for the different types of
loads. The one shown here is for a motor:
0 VAC
L1
Source line
Hot
120 Volts AC
N
Neutral line
Voltage measurements taken on a live circuit.
The test light with its probes on either side of the resistive load of the motor is glowing but
the voltmeter connected to the terminals on the closed switch is reading zero. There is no
pressure difference or voltage drop across the switch so there is no voltage reading but
the test light glows because the motor is consuming all the applied voltage and there is a
voltage drop. Voltage applied is voltage consumed.
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Open the switch, as shown above, and the readings reverse. The potential difference or
difference in electrical pressure between the two poles of the switch is the applied voltage
and the test light does not glow because there is no applied voltage getting to that part of
the circuit.
You may be thinking "That’s simple. I'll just remember that:
1/ A closed switch gives a zero reading while an open switch gives a voltage reading
2/ An energized load gives a voltage reading while a de-energized load does not.”
Think again while you consider the following diagram:
N
Neutral line
120 Volts AC
L1
Source line
Voltage measurements taken on a disconnected circuit that has been improperly wired.
Looks the same as the figure on the bottom of the previous page and you may assume that
since the switch Is open it is safe to work on the motor. BUT notice that the voltage is applied
through the motor first - not through the switch first. Working on the motor may result in the
circuit being completed through your body to ground.
NEVER ASSUME that there is a resistance between the two points being tested or that the
circuit is complete. ALWAYS CHECK by using the resistance of the tester between all
potential sources and ground.
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Voltage measurements taken on a disconnected circuit to prove if circuit is properly wired.
The readings are taken to confirm that the motor is de-energized. Reading #1 between the
assumed electrical source terminal on the switch and ground (i.e. grounded junction box or
ground wire) indicates zero voltage where there should be an electrical pressure difference or
voltage drop. We immediately know that the source and neutral lines are reversed but to
confirm this we take readings #2 to #4 and find a voltage drop to ground where there should
not be one. Our assumption that the motor is deenergized has quickly been proven wrong.
Determining whether a circuit is energized is only one of many uses of a voltmeter. Once the
relationship between voltage, current, resistance and power is clearly understood, you will see
that the measurement of voltage can be an indication of what is occurring with the other three
factors. Other uses of measuring voltage will be explored later in this Module.
Proper use and interpretation of a voltmeter requires knowledge of the source or applied
voltage. In most cases, it is best to measure the applied voltage at the source to the circuit the disconnect switch to the furnace or point of voltage change in the circuit. The common
supply voltages encountered are:
• 240V AC to appliance motors, pumps, etc.
• 120V AC to the appliance, motors, transformers, valves
• 24V AC to the control wiring, thermostats, humidifier (in most appliances)
• 6,000V AC from the ignition transformer in older appliances
• 8,000 - 17,000V DC for ignition transformers in newer appliances
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5.4.3 Ammeter
An ammeter is used for measuring current or the rate of electron flow in a circuit. For a load to
function properly it must be supplied current within its design rating - minimum and maximum.
Current causes friction and friction causes heat so the current must also be limited to the maximum
design rating of all components in the circuit to prevent overheating and fires.
There are two types of ammeters - the in-line ammeter and the clamp-on ammeter. The in-line
type is included as a function of most multimeters. The clamp-on type may also be a function of
some special multimeters but usually requires a separate attachment to the multimeter or is a
separate instrument. They employ two very different principles to determine current and must be
used differently as a result.
Clamp-on attachment to a multimeter, combination clamp-on/multimeter, and a
dedicated clamp-on ammeter.
The in-line ammeter function on a multimeter usually requires the user to insert the red test lead
into either the 10A or mA jack. Good quality meters will indicate on the meter if these jacks are
protected by a fuse that will prevent damage to the meter if the designed amp reading is exceeded.
Do not rely on the fuse to determine if the maximum range will be exceeded. Check the amp rating
in the manufacturer’s instructions for the component you are testing and start at the highest range
setting.
The selector dial is then turned to either A~ (Amps AC) or A ~ (Amps DC) and the appropriate
scale of amps or milliamps. Zero adjust the analog meter if necessary.
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In-line ammeters offer a very low resistance to flow (often less than 1 ohm) unlike voltmeters
that employ a very high resistance (megaohms). This lower resistance of an in-line ammeter
makes it act like a very thin conductor wire. It must be used as the only conductor of electricity
to the load by breaking the circuit and connecting the ammeter in series with the load, as shown
below.
L1
Circuit A
In-line ammeter function on a multimeter. Meter must be in the circuit.
The resistance of the load acts as an impediment to flow and prevents a short circuit or
unrestricted electrical flow from source back to the source resulting in instantaneous
overheating of the sensing conductor in the ammeter. Given the low resistance of the ammeter,
connecting it as a separate or parallel circuit (as a voltmeter is connected) across the load
creates the short circuit. Unrestricted flow through an ammeter results in immediate
overheating and meter damage. Some meters may even explode!
Extreme care must be taken when using the in-line ammeter or when moving the multimeter
selector switch past the ammeter function. Ensure that the circuit is dead or de-energized
before connecting the ammeter in-line. Zero the meter prior to activating the circuit.
The clamp-on ammeter is much easier to use and is the more popular instrument for
measuring current. It employs the principle of electromagnetic induction. Briefly stated, a
current passing through a wire creates a magnetic field around that wire and the strength of
that magnetic field will increase or decrease with the amount of current.
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High Current
Low Current
Clamp-on ammeter senses the magnetic field created by current flow through conductor.
The clamp-on ammeter converts the strength of the magnetic field into a current reading. After
choosing the appropriate scale, simply open the jaws of the meter, insert one line, close the
jaws, and take the reading. This type of meter can be used safely on a live circuit without
disconnecting the power since the magnetic field is not affected by the wire’s insulation.
The direction of the magnetic lines of force depends on the direction of the current flow through
the wire so clamping the source and neutral lines in the meter results in a cancellation of the
magnetic effect and therefore no reading even though there is current. Either the source or
neutral line can be tested but not both. Due to the differences between magnetic induction
caused by direct current and alternating current the meter must be designed or set for DC or
AC current measurement.
If the current is very low, looping the wire around the jaws several times can increase the
sensitivity of the clamp-on ammeter. However, the number of turns must be divided into the
meter reading to record the final current reading. For ease of division, 10 loops are usually
employed.
------------------- Live circuit
wire
Clamp-on ammeters sense the electromagnetic field created by current flowing
10 wraps of one wire
through a wire. Increasing the number of
turns increases the electromagnetic field.
Divide reading by 10
Wrapping loops of one wire through the jaws can increase small current readings.
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As previously discussed in relation to voltage, once the relationship between voltage,
current, resistance and power is clearly understood, you will see that the measurement of
current can be an indication of what is occurring with the other three factors.
Proper use and interpretation of an ammeter requires knowledge of:
•
the type of circuit
•
the design ampacity (or current carrying capacity) of the components
•
the design current draw of the load(s).
The type of circuit, as explained later in this Module, determines if the current will be
consistent throughout the circuit or vary at different points or branches in the circuit.
The design ampacity is usually marked on each component and must be higher than the
amp rating of the fuse protecting that component. Components exposed to 120 VAC should
be protected by a 15-amp fuse. Lower voltage control components are limited to 2 amps
but commonly operate in the milliamps range (i.e. 1000ths of an amp).
The common design current draw of a load is usually
listed on its rating plate. Be aware that the listed amp
draw is for steady-state normal operation. At start up
and under reduced stress (e.g. free-wheeling motor
or dirty fan blades on a blower motor), the amp draw
will be higher than the listed value due to reduced
resistance.
The surge current draw on initial start up of a motor
may be double or more of its normal current draw. In some cases, the surge current rating
is also listed on motors.
Inversely, if the load is under abnormal stress the current draw may be significantly less
than the listed rating. This reduction in current is accompanied by a reduction in work.
Abnormal stress is caused by making the load work harder than it is designed for (e.g. a %
horsepower motor doing work requiring a 1 horsepower motor) or by fault in the load or
installation (e.g. seized bearings on a motor or a misaligned pulley or coupling).
Abnormal current draws indicate a problem in the circuit. Given the proper constant voltage,
increased current draw indicates a decrease in resistance. A decrease in current indicates
increased resistance. Current and resistance are inversely proportional. Measurement of
current can determine whether a circuit is operating safely and properly.
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5.4.4 Ohmmeter
An ohmmeter is used to measure resistance between two points. In some cases, the
technician is simply interested in whether there is a connection between the two points so the
ohmmeter is used as a continuity tester. The actual ohm reading may not even be displayed
but rather replaced by a beep indicating continuity. In either case the same principles and rules
of operation are employed.
Ohmmeter function on multimeter and a continuity tester
Unlike the voltmeter or ammeter, the ohmmeter must never be connected to a live circuit.
It has its own internal electrical source - a battery - that will be damaged along with the
measuring device if an outside current passes through it.
To use the ohmmeter or continuity tester, disconnect the power supply and isolate the line or
component being tested from any other paths back to source. This latter precaution is to
prevent reading the resistance along any other pathway in the circuit. It does not adversely
affect the meter if an alternate path exists unless you are measuring across a device called a
capacitor (commonly employed on burner motors) which stores an electrical charge.
The ohmmeter must be zero adjusted before every test. Simply touch the two test probes
together (thus creating a short circuit or zero resistance) and use the zero adjustment dial.
Most digital meters automatically zero adjust. If either type cannot be made to read zero at one
of the range settings the battery is too weak and must be replaced.
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Ohms scale on an analog meter
As shown in the above diagram, the dial scale on an analog meter is read from right to left
and is non-linear. Non-lineal means that the divisions or increments between the
measurement values are not equal. Close attention must be given to the increments and
range setting when reading an actual ohms value on an analog meter.
The range setting determines the accuracy of the measurement. The “R X 1" setting on
an analogy meter is the most accurate and the only setting that you can use without
multiplying the scale reading. “R X 10” requires the scale reading to be multiplied by 10
and “R X 1K” requires multiplying by 1000. Digital meter scale ranges give the maximum
reading but are read directly without multiplication.
With the power off, connect the two probes on either side of the line or component to be
tested. If there is no resistance the reading will be zero. If there is no connection between
the two points the reading will be infinity ( oo ); the analog meter dial will deflect to the
opposite side of the scale or the digital meter will read OL for overload. A reading between
zero and the maximum scale setting indicates the resistance between the connected
points.
Ohmmeter readings taken on analog and digital meters.
No Resistance (Short)
Measurable Resistance Infinite Resistance (Open)
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A continuity tester or continuity function on a multimeter will usually just
beep or light up if there is any connection between the two points.
Continuity Test ( "UI )
The resistance reading
required to produce the
beep indicating continuity
will vary from meter to
meter. In some cases, it
may be hundreds of ohms.
It is important that the
technician using the meter
is aware of the level of
resistance that causes this
beep. Connect the meter
to a variable resistor and
decrease the resistance
until the continuity meter beeps and then select the appropriate ohm meter
scale and read the actual ohms of resistance that caused the beep.
Continuity test taken on a
digital meter.
As previously mentioned, the component under test must not only be
isolated from the electrical source but also from the rest of the circuit.
Failure to do so, as shown below, may result in a resistance reading of
another load or a false indication of continuity through another
component.
Component under test must be isolated from electrical source and rest of circuit.
An ohmmeter is primarily used for troubleshooting electrical problems. Properly used, it
can quickly locate a fault in the circuit - a broken path in the circuit, a short circuit, or a
component with an abnormal resistance.
This brief introduction to the safe use and operation of electrical test instruments will allow
for further development of your understanding of both electricity and the instruments. The
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pursuit of further information on test instruments as found in the manufacturer's
instructions or more advanced texts and courses are highly recommended.
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5.5 Components in the Simple
Circuit
The basic circuit has an electrical supply, one load
and a conductor connecting the two and
completing the path to source. It will function but it
is neither practical nor safe since it operates
continuously, has no safety limits, and requires
direct human intervention on a live circuit to correct
any faults.
The simple circuit is safer and more useful. The added switch allows for operational
control without touching live wires and the fuse can limit the current to the designed
capabilities of the components if the source could exceed those limits.
The five components of the simple circuit form the base upon which to build the series
circuit, parallel circuit, and series-parallel circuit. Various types of those five
components along with some important issues will be presented to ensure that it is a
strong base upon which to build. The above circuit may appear simple yet mysterious at
first glance. Given the long explanation of each component, it may at times appear
complex. By the end, the complexity will again give way to simplicity but without the
mystery.
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5.5.1 Electrical Supply
There are six methods of producing a potential difference or voltage as listed below with
common examples:
1.
2.
3.
4.
5.
6.
Chemical action
Magnetism
Friction
Heat
Light
Pressure
battery
generator
static
thermocouple
photocell
piezo ignitor
Although they are often taken for granted, all six are encountered by trained personnel
who should be familiar with the principles underlying each method. The first two are the
most commonly employed so more attention is given to batteries and generators In the
following brief discussion of each method.
It is worth noting and considering that anything that can create electricity can itself be
created by electricity. This conversion of one energy form to another will be highlighted in
our discussion of electrical sources and will help us understand the last component of the
simple circuit - the load.
1. Chemical actions between two dissimilar metals immersed in an acidic solution were
first found to produce electricity in the 1700’s by Alessandro Volta.
The voltaic cell, as illustrated to the right, functions on the principle that copper atoms
easily give up electrons to certain chemicals while zinc
atoms easily accept electrons from the same chemicals.
The zinc plate becomes negatively ionized and
the copper positively ionized as long as the
chemical bath - known as the electrolyte maintains its chemical structure.
Copper
(+)
A circuit connecting the two electrodes results
in 1.1V DC supply. Unfortunately, the
electrolyte and zinc break down over a short
time and the charges are then neutralized.
CI“ H+ Zn++
” zn++ cr
H+ cr zn++
n- 7n++ u+ H+
Voltaic cell
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One Piece Metal Cover (+)
Top Washer
Anode—Zinc Can
Wax Ring Seal
Asphalt Seal
Support Washer
Cathode Mix—
Manganese
Dioxide Carbon
Electrolyte Air
Space
Kraft
Carbon Electrode
Paste-Separator
Flour. Starch.
Electrolyte
Labet
Zinc Can Plastic Film
Jacket—
Labeled Polyethylene
Bonded Tube
Metal Bottom Cover
Cup and Star Bottom
CUTAWAY OF A CYLINDRICAL GENERAL PURPOSE LECLANCHE CELL
Dry cell
The storage battery as used in automobiles
employs the same principles as used in the
primary cells discussed above but since it can
be recharged it is called a secondary cell.
Gas Technician 3
The now common dry cell improved upon
Volta’s design but still may use a zinc
casing with a carbon rod in the center
and a moist paste forming the electrolyte
separating the two. This cell will produce
1.5 V DC.
Further improvements using other
metals and chemicals allow for longer life
and higher voltages. Nevertheless, they
still function on essentially the same
principle.
Although commonly called a battery, the
term actually applies to a device with
more than one cell. Of the common
portable “batteries" only the rectangular
9V battery deserves the name. It
consists of six 1.5V cells.
VENT
PLUG
FILLER OPENING IN
CELL COVER
With thin, large surface areas of alternating PLATE
positive and negative electrode plates STRAP
immersed in an electrolyte solution or paste,
the battery stores a chemical action that CONTAINER
produces electricity. It is a reversible NEGATIVE
PLATE
chemical action allowing the battery to last for
years while supplying significantly more SEPARATOR
voltage at higher current levels.
CASE
TERMINAL
POST
CONNECTOR
LINK
CONNECTOR
POSITIVE
PLATE
SEDIMENT
SPACE
Secondary cell battery or car battery
As previously noted, anything that can create electricity can be created by electricity. The
reversal of the chemical action in the storage battery by the electrical generator in a car is
one example. Another use of this principle is electroplating whereby an electrical circuit is
created between dissimilar materials through a chemical solution resulting in transfer and
bonding of one metal onto the surface of the other. Electricity creates the chemical action
in electroplating.
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—
+
All batteries produce direct current.
On wiring diagrams, these symbols
are used for a cell and a battery.
+
Cell
Battery
Wiring symbols for cell and battery
Automobile electrical wiring diagrams and installation methods are probably the best
example of the use of the conventional theory of electron flow. The negative terminal of
the car battery is attached to the engine, which is usually in contact with all metal parts.
The wires are run from the positive terminal to the electrical devices so electricity would
appear to travel from positive to negative.
CONNECTION
^/GROUND^^ / ..............................
'I™ "nfn^——y
Automotive electrical wiring is based on the conventional theory of electricity.
In reality, the continuous metal surface (at least in older vehicles) is an extension of the
negative terminal of the battery so electrons flow through those metal parts and return to
the battery through the wires. Given the low levels of electrical current, no danger is
posed. Newer vehicles with fewer metal parts usually employ a two-wire system to
complete the electrical path or circuit.
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2. Magnetism is the major source of electricity produced and used in the world.
Alternators and generators produce electricity by magnetic induction. The principle is
quite simple although the variety of production methods and uses of the principle is
almost unlimited.
When a conductor such as a copper wire is
passed through a concentrated magnetic field
cutting across the force field between the north
and south poles, a current is induced in the
copper wire (i.e. caused to occur by influence
rather than direct contact). If the conductor is
passed through the magnetic field in the
opposite direction, the current will be reversed.
If the conductor is stationary in the field, there
is no current.
The negative charge of the electrons in the
conductor atoms are attracted to the north pole
of a magnet and repulsed by the south pole
with sufficient force to free the valence
electrons of the conductor atom.
Mechanical motion of either the magnet or
conductor is necessary to prevent the
electrons from being pulled to one side of the
wire and stopping. Notice that there is never an
electron transfer from the conductor to the
magnet. Electron flow is induced not
conducted.
Electron flow induced by magnet
Obviously, the mechanical energy expended
in passing a single wire through a magnetic field is an inefficient means of energy
transfer. However, if a stationary mass of wires surrounds a rotating or oscillating
magnet driven by a waterfall, fuel-fired steam boilers or an internal combustion engine,
the effect is amplified and the current increases. A mass of wires rotating between two
opposite poles of a magnet may also be employed.
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Numerous loops of a wire rotated between a magnet generate continuous electricity.
A magnet rotated between loops of wire will achieve the same result and is the
more common method.
The resulting current can be AC or DC depending upon how the output wires are
connected to the conductor. The advantages and disadvantages of the transmission,
distribution and use of AC and DC will be discussed later in this Module.
Again, whatever energy can create electricity can itself be created by electricity. Thus,
electricity can become magnetic energy (electromagnets) and mechanical energy for use
in valves, automatic switches, motors, and transformers - all of which will be discussed
later in this Module.
AC Generator
On wiring diagrams, the symbol for a generator is seldom
employed for building wiring. Rather the two terminals that
complete the circuit back to the source enter from the left
or top of the page and are denoted as L1 or - or H (for Hot)
for the applied voltage line and + or N (for Neutral).
LI is the electrically charged line that will cause electron
flow while N is the return path home to the source of the
electrical imbalance. The direction of flow is always
considered to be from L1 to N - from charged to uncharged
or pressurized to unpressurized.
Wiring symbols for generator
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The electrical force and current in building wiring are constant but adjustable. The voltage
and current required to operate a stove are different from that required to operate a
doorbell and therefore different voltage is applied to each. In most cases the voltage and
current are significantly higher than a battery could produce so the added safety precaution
of a ground wire is employed to direct any unwanted electrical energy to be safely returned
to source.
Although the ground wire is seldom shown
on electrical diagrams, its symbol as shown
to the right is found on most diagrams to
remind installers to comply with this safety
and legal requirement.
Symbols for Ground and Chassis Ground
3. Friction as a source of static electricity is encountered almost daily. Walking across a
wool rug in dry winter conditions often results in a static electrical discharge when a
doorknob is touched. The removal of electrons from one body by another by means of
friction and resulting in stored electrically charged bodies is not an efficient source of
energy for electrical circuits.
Actually, the mechanical energy of friction only serves to bring two materials into close
contact that already have the property of losing or gaining electrons easily. Friction does
not move electrons.
Static electricity is not just a novelty or nuisance concern - especially if working around
explosive vapours which may be ignited by a static electrical discharge. Static electricity, by
definition, has no current until discharged. The voltage and current of that discharge can
range from negligible to deadly. Lightning is a static electrical discharge.
Static electrical discharges can be painful and provide an ignition source
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4. Heat produces the electrical current in thermocouples used as flame sensors in older
gas appliances. The low DC voltage (20mV to 30 mV) produced by the temperature
difference between the hot and cold junctions of dissimilar metals, as shown below, can
be employed for measurement or control devices.
Thermocouple and wiring symbol for thermocouple
A number of thermocouples linked together to form a thermopile can produce enough
voltage (100mV to 1V) to supply the operating and safety circuit of a small appliance fired
on natural gas or propane.
Thermopile and wiring symbol for thermopile.
Heat produced by electricity is, of course, a more common and useful transfer of energy.
Its purposeful production (e.g. the heat element of an electric range or hot water heater)
is actually accomplished by the friction of electrons passing through wires sized and
designed to resist electrical flow.
The result is the same when wires are incorrectly sized or damaged causing resistance
to flow, overheating and possible fires. Energy is lost in the form of heat as current
increases beyond the wire’s current carrying capacity.
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5. Light causes some atoms like selenium, silicon, and germanium to give up an
electron in a sealed photocell or solar cell. Widespread use of this source of
electricity has recently increased in popularity.
The DC output of a single photo cell is usually less than
a voltaic cell but given their small size they can be joined
together to produce a significant force at low current
levels.
The electrical wiring symbol for a photocell, as shown to
the right, is similar to a battery but with an arrow indicating
light.
Wiring symbol for photocell
The conversion of electrical energy to light energy is probably the most common use
of electricity. There are various means of producing “electric light" by friction and/or
chemical action of electron flow. For example, electron flow through the filament in an
incandescent bulb creates friction due to resistance resulting in light.
6. Pressure as a source of electricity may surprise you. If you are old enough to have
played a phonograph record, then you have heard the results of pressure being applied
to a crystal needle. The spark igniters for gas barbecues also employ the principle of
bending, twisting, or squeezing certain crystal to free electrons which then build up on
one side of the crystal.
Crystals are employed in some microphones
and hearing aids to produce electricity from
the pressure of sound waves. This minor
transfer of mechanical energy to electricity is
also reversible.
Sound waves
If electricity is applied to certain crystals, a
bending, twisting or vibration action is created
that is used in hearing aids, wristwatches,
and radio tuning.
Crystal in microphone produces electricity
With the above brief descriptions of the six methods of producing an electrical source, the
basis for understanding the various sources and uses of electricity is laid.
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5.5.2 Conductors (Connecting wires)
The wires§ used to connect the other four components of a simple circuit deserve our special
attention since their purpose is to contain, control and direct the electrical current and to provide
the necessary connecting pathway for that current. Safe and efficient use of electricity depends
upon the proper material, installation, and protection of connecting wires.
Copper or aluminum wires with lacquer and plastic insulating coatings are available in a variety
of sizes, types, and protective coverings. The person doing the job often must choose the
appropriate wire for the application.
Nonmetaillc and metallic cable
Non-Metallic Cable ^ 2
and 3 wire
Dry Indoor Locations
Most common type
Armoured BX Cable
Dry Indoor Locations
Last link to Furnace
Ground Wire from
Panel to Ground Rod
Service Entrance Cable
Lead Encased
Underground Use
Non-Metallic Sheathed
Moisture and Flame
Resistant
Outdoor Rated
NM Cable
I Extension and Appliance r
Cord
Thin Wall Steel
Conduit
Wires Pull Through
Low Voltage
Thermoplastic
2,3,4 or 5 wire
Examples of wire types and protective coverings
§ The term "wire” as used refers to both the conductor core and insulation / protective coating. In common usage,
“conductor” is used to refer to the core wire or to the entire wire. A distinction will be maintained here between
conductor and insulation/protective coating. Wire refers to both.
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As previously discussed, even conductors offer a resistance to flow resulting in the
production of heat. Transfer of electrical energy to heat energy increases as current
increases. However, heat reduces current in wires - a hot wire cannot carry as much
electrical current as a cool wire.
Limiting heat production in the wire to within the safe current carrying capacity or ampacity
rating of the wire is the main concern. The factors affecting heat production and thereby
determining the current carrying capacity of a wire include:
• Length - the longer the wire the less current it can carry given a constant applied
voltage. This becomes a concern with thermostat wires or unusually remote
installations.
• Size - diameter or area of the conductor and thickness of the insulation. Larger is
better in both cases but as we will discuss below under wire sizes the American
Wire Gauge (AWG) standard numbers are in reverse order so the lower the
AWG number the larger the wire - #10 wire is larger than #20 wire. This number
system is similar to that used for sheet metal sizes.
• Material - the properties of both the conductor and insulator material affect current
carrying capacity. Properties include: resistivity (measured in Q/1000’ for
conductors); oxidation; strength; malleability; solid or stranded core (where
flexibility is required); voltage rating; temperature rating; and environmental
considerations such as resistance to moisture, corrosive materials etc.
RQ Q
Resistance Proportional to Length
Longer Wire = More Resistance
RQ
2
Smaller Wire = More Resistance
Hotter Wire = More Resistance
Factors affecting the ability of a wire to conduct an electrical current.
70°F
170T
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Fortunately, all of these factors are organized into standardized rating systems under the
Ontario Electrical Code that directs us in our wire choice. The conditions limiting a wire’s
use are listed on the wire sheathing and/or packaging. Some minor interpretation of codes
or abbreviations and an appreciation of the safety concerns underlying the rating systems
are all that is required to make an informed choice of wire type.
The wire size is the first standard of concern. The
size Is printed on the protective sheathing or can be
determined by a wire gauge tool as shown to the
right. As previously mentioned, the smaller the wire
# on the AWG scale the larger the wire size.
Wire sizes most commonly encountered include:
# 12 & #14 - 120-volt building circuit wiring
# 16
- 120-volt lamp cord
# 18 & #20 - 24-volt control wiring in appliances
Wire gauge sizing tool.
The maximum voltage rating of the wire along with
the amperage draw of all the loads on the circuit must be considered when choosing the
wire size. Given the importance of heating appliances, a dedicated supply wire that only
serves the furnace is required.
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In most residential installations, a #14 copper wire (or #12 aluminum wire) usually
supplies electricity to the furnace since its voltage rating of 300V or 600V is more than
sufficient for the maximum 15-amp draw of the circuit. A smaller wire (i.e. #16 or higher)
may cause overheating, insufficient current and possibly a fire. Occasionally a #12 copper
wire (or #10 aluminum) is required for long runs.
The smaller wires employed in the control wiring of the appliance are separated from the
main supply by a step-down transformer or solid-state control. Nevertheless, these #18 to
#20 wires are also rated on their sheathing - usually for a maximum of 30V. The same
results of overheating and reduced current flow will occur on a smaller scale if the rating
of the control wiring is exceeded. Although manufacturers can use #20 wire, installers are
required by Code to use #18 or larger.
The number of circuit wires in the sheathing will be printed on the sheathing after the wire
gauge number - such as 14/2 or 14/3. Only the insulated wires are counted so 14/2 has a
black, white, and bare ground wire in the sheathing and 14/3 has an added red wire.
Thermostat wires could have 2, 3, 4, or 5 wires depending on the added functions of the
thermostat (air conditioner, humidifier, fan functions etc.)
The CSA type designation as printed on the sheathing (see illustration at the top of the
previous page) gives the allowable location and maximum conductor wire temperature in
code form. Some of the common codes on wires used include: NMD90, NMW90,
NMWU60, T90 NYLON, T90, TW60, AC90, ACL, RA90, RW75, Ml, LVT60 and ELC60.
The first two are the most common types used in the building wiring to the furnace and the
last two are the most common for the control and thermostat wires.
The various codes are easily interpreted once you realize that the letters refer to the
sheathing material or allowable location while the two numbers refer to the maximum
allowable conductor temperature in °C.
A
Aluminum-sheathed cable
NM
Non-metallic
AC
Armoured cable
NYLON
Nylon jacketed
D
Dry locations
O
Oil Resistant
E
Elasoplastic
R
Rubber
L
Lead
S
Service Cable
LV
Low voltage
T
Thermoplastic
Ml
Mineral-insulated cable
W
Wet locations
u
Underground
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Thus, NMD90 has a non-metallic sheathing and can be used for dry (indoor) locations
where the conductor temperature will not exceed 90^0. NMW90 can be used in wet
locations. For full interpretation, reference to the Electrical Code is recommended.
It is worth noting that older wiring may not have the same (or any) code designations. Pre1950 construction may still have “knob and tube" wiring where the hot and neutral wires
are run separately with supporting clamps of porcelain and sheathing of woven material
and/or asbestos covering. Care must be taken when working around knob and tube wiring
- not only due to the asbestos covering but also due to the lack of a ground fault wire and
identification.
Common terms used in the industry in place of the CSA designations include ROMEX and
BX. Romex was the best-known manufacturer of NM cable so all non-metallic or
polyethylene plastic insulated wire may be referred to by that name. BX is armoured cable
(AC) used to protect exposed wiring between a junction box and the gas-fired appliance.
The minimum temperature rating of the wire is commonly given in brackets at the end of
the printed rating on the sheathing. Inside the sheathing, various conductor coatings,
wraps and fillers will be found depending on the allowable use locations and temperature
ratings.
The colour coding of the conductor coatings is standardized for easy identification:
Ground:
Bare or green
Neutral:
White or natural grey
Source or Hot:
Black, red, blue, yellow in that order
Always use the correct colour coding for any wiring that you install BUT never depend on
the colour coating as proof that the wire serves the function indicated by the wire colour.
An untrained installer may have used white wires as the source line.
Some wiring configurations require the neutral line to be used as a source wire such as
wiring a remote switch. In these cases, black electrical tape or permanent marker is used
to identify the change in function of the white wire at each junction point.
The junction and termination points of wiring are the “weak links” in the circuit so care
must be taken to ensure proper secure connections. All connections must be in a junction
box or protected control box with clamps at the entrance and exit to ensure that stress is
not placed on the connections if the wires are accidentally pulled.
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NM Cable Installation
1. Strip back -6" of wire covering
Ensure insulation is not cut.
2. Remove any wrapping
4. Install junction box connector. Use
type approved for NM cable.
3 Strip ~1" of insulation with proper tools.
5. Tighten cable into connector.
Tighten connector into box.
BX Armour Cable Installation
1. Use hacksaw to cut -6” of armour covering.
Ensure insulation is not cut.
2. Insert insulating bushing to protect wire
Strip ~1" of insulation with proper tools.
Electrical junction box with clamps
Joining wire to wire can be accomplished in a number of ways including soldering, crimpon connectors, splicing or the more common Marrette (or Marr) connectors. Screw
terminal connections and Marrette connectors with rattail joints, as shown below, are the
most common and reliable means of joining wires.
Marrette connectors with rat-tail joints and terminal screw connections.
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To secure a wire to a threaded terminal a hook is made in the wire pointing in the same
direction as the tightening action (clockwise) as shown above. Only the minimum
necessary amount of wire is exposed using wire strippers that leave the proper taper on
the insulation and help prevent damage to the wire.
Nicks created by
use of improper
tool results in
reduced current
carrying capacity,
overheating and
weakens the conductor.
Proper methods of stripping wires and
connecting to terminal screws
Connections may become dirty or corroded if exposed to adverse conditions such as high
heat and humidity. Always check exposed connections (like the terminal block on primary
controls) and seal hidden connection using electrical tape if adverse conditions are
possible.
Aluminum wire connections are a special concern due to aluminum’s tendency to oxidize,
breakdown chemically when in contact with other metals, and shrink over time. Antioxidizing chemicals for bared conductors and special aluminum to aluminum connectors
or terminals are required when using aluminum wires.
Compared to copper wires, aluminum wires are always two sizes larger for the same
ampacity (e.g. #14 copper carries the same as #12 aluminum wire). For all of these
reasons, copper wire is recommended for all appliance installations.
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Although conductor wire is flexible it is not to be installed such that it flexes back and forth.
Proper supports every 5 feet and within 1 foot of a junction box or turn in direction are
required. All bends in wires must be gradual arches - never sharp turns. Armoured cable
is especially susceptible to breaking if bent or twisted. As a general rule, make all bends
in armoured cable with a radius at least 6 times the diameter of the cable.
Electrical Code requirements will be discussed later in this Module. Further concerns
related to conductors and connections will be reviewed at that time.
On electrical diagrams, conductors are represented in a variety of ways. Some
standardized symbols have also changed over the years. Correct interpretation of wiring
diagrams requires close attention to these symbols.
General Wiring Diagram
Line Voltage Conductor
Low-voltage conductor
Appliance Manufacturer’s Schematics
Factory Installed Wiring
Field Installed Wiring (i.e. installer
supplies and installs it)
Connected Wires
Not Connected Wires
(Crossovers)
Old System
New System
Old System
New System
Connectors
Plug Jack
Junction Plug
(Wiring Harness)
Conductor and connector wiring symbols
Multiple Junction Plug
(Engaged)
Use and interpretation of electrical schematics is an import part of the work. The schematic
symbols shown throughout this text are intended as an introduction to the subject. Wiring
diagrams are simply electrical "road maps”. The conductors are the roads and the
electrical devices the destinations. To install or service electrical devices you must be able
to read the road map.
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5.5.3 Fuses and Circuit Breakers
Continuing with our examination of the simple circuit, the essential safety device to protect
the conductors and equipment from overload or short circuit conditions is the automatic
disconnect fuse or circuit breaker. Fuses are one-time-use only devices and must be
replaced when they "blow” while circuit breakers are manually resetable.
An overload is a low-level excessive current draw beyond the design ampacity of the
circuit. Common causes for overloads include:
•
too many appliances on the circuit
•
appliances being made to work harder than they are designed to
•
damaged or worn-out appliances (e.g. loose motor pulley)
•
current surge when a motor starts
A fuse element that melts due to overload seldom shows any signs of intense heat or
burning. Burn or soot marks on the glass front or contacts of the fuse are indicative of a
short circuit.
A short circuit or overcurrent condition is a sudden excessive current draw well beyond
the design ampacity of the circuit. The resistance of the load(s) is either removed or
becomes a minor factor in the current draw in a short circuit. Direct and unrestricted
current flow to ground may be caused by:
•
conductors contacting grounded metal
•
source conductor contacting neutral conductor
Examples of a short circuit condition
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The end result will be the same whether it is the slow, steady deterioration of an overload
condition or the immediate arcing of a short circuit. Excessive amperage-draw causes
overheating, damage to the components and possible fires.
A fuse located as close as possible to the electrical source with an amperage rating the
same or less than any component in the circuit can prevent the damaging effects of
excessive current draws. The fuse consists of a fire protection enclosure containing a strip
of heat-sensitive metal that has a lower melting point than copper or aluminum.
Glass Tube Low Amperage
Rase:
button
Type P Regular Type D Time Delay
Type S - Safety
Ferrule Cartridge Fuses up to 60 A Knife-blade Cartridge up to 600A
Various types of fuses
The current carrying capacity of the metal strip determines the fuse rating. Either 15, 20 or
30 amps are used in household branch circuits depending on the ampacity of the circuit.
A No.14 AWG wire is rated for 15-amp circuits; No. 12 AWG wires for 20 amps, and No.10
for 30-amp circuits. A 15-amp fuse usually protects our gas appliances, which are
connected with No. 14 wire.
To prevent nuisance or unnecessary destruction of the fuse due to momentary current
surges (such as when a motor starts), most modern fuses are equipped with a thermal
expansion element to absorb the sudden but short increase in heat. These are called time
delay fuses.
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Metal
link
Metal link
Standard and time delay fuses
po
t
Circuit breakers provide the same protection as fuses but are not discarded after they “trip”.
They act as automatic switches with a manual reset function. In place of the melting strip, a
circuit breaker employs a bi-metal element and/or a magnetic element to sense excessive
current draw and open a switch to prevent continued current draw.
Various types of circuit breakers
The operating principle of the bimetallic element is that two different metals are bonded together
and expand at different rates when exposed to heat so they bend and break a connection.
Excessive current flow through the fuse causes the bimetallic element to heat up, bend and open
a switch stopping current flow. The operating principle of the magnetic element is the same as
relay switches to be discussed in the next section covering switches.
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A time delay is built into the operation of most circuit breakers to prevent nuisance deactivation
of the circuit. A lever or stop prevents the resetting of the switch without manual attention. The
reset lever will move to the center position if the breaker is tripped and it must be turned to the
“off’ position before it can be reset.
Never reset a circuit breaker or replace a blown fuse until the cause of the tripped or
blown safety device is investigated and corrected. When replacing or resetting the device
care must be taken to ensure that the amperage rating of the fuse does not exceed that of any
of the components on the circuit.
Never increase the fuse size to "solve” a nuisance de-activation problem - you will create an
even greater problem by addressing the symptom rather than the cure. The Abe Lincoln fuse
(i.e. penny inserted in the fuse base) is a recipe for disaster - unrestricted current flow may result.
On wiring diagrams, various symbols are used for fuses and circuit breakers:
Fuse
Circuit Breaker - Open Circuit Breaker - Closed
Cartridge Type Fuse
Bimetal Overload
Thermal Overload with heater
Wiring symbols for fuses and circuit breakers
If a sub-branch circuit of the building wiring contains components that have a lower ampacity
than the rest of the circuit, an in-line fuse can be used to protect those components after the
reduction of voltage is achieved. Thus, 2-amp fuses may be found in appliance wiring to
protect 24V control components. Glass tube thermal link
fuses are commonly used for this purpose.
Multimeters usually have two fuses to protect the meter especially the sensitive ammeter components from excessive
current.
Most motors on gas-fired appliances also employ a heat
sensing or magnetic coil switch to protect against overloads.
These may be manually or automatically resetable.
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5.5.4 Switches
A switch is a device for making, breaking, or changing connections in a circuit. As might be
expected from such a wide definition, the variety of switch types is almost unlimited. We will
focus on the four basic types of switches and then the activating methods and purposes of
switches used on gas fired appliances. First, a few comments that apply to all switches.
A switch must be rated at or above the voltage and current rating of the circuit and fuse. The
connection and disconnection action must be fast-acting to prevent arcing and damage to the
components.
There should be no voltage drop across a closed switch. However, switches do wear
out - contacts oxidize or get dirty, travel mechanisms break or misalign
etc. Resistance through the switch will cause a reduction in voltage and
current to the load.
Any voltage drop or resistance reading across a closed switch indicates
that it must be cleaned or replaced. In either case the power to the switch
must first be shut off.
Dirty and corroded contacts
For a switch to safely control a load it must be located in the source or hot line - never in
the neutral line. As shown below and as discussed previously, switches in the neutral line will
turn the load on and off but will not allow work to be done on the load without a risk of electrical
shock.
Proper and improper location for a disconnect switch.
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Variations of the four basic types of switches (shown below) are found throughout the
electrical circuits of gas-fired appliances. The abbreviations and symbols for each type
will be used throughout the rest of this text as they are in manufacturer's literature and
drawings that you will encounter throughout your career.
Double Pole, Single Throw (DTSP)
Double Pole, Double Throw (DPDT)
Four basic types of switches
a) SPST switches are the simplest type since they are either on or off. The main
disconnect switch, limit switches, flame safeguard switches are all examples of SPST
devices either manually or automatically operated. There may be numerous SPST
switches in one line.
b) SPDT switches can energize one of two separate circuits from a single source such
that only one can operate at a time. A two-speed motor control switch or a thermostat
heat-cool switches are examples.
c) DPST switches make or break two independent circuits at the same time when
synchronous actions are required on two circuits such as the main power supply at the
electrical panel.
d) DPDT switches re-direct the power of two independent supplies lines to two circuits
simultaneously.
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Variations, additional poles, and different activating mechanisms may be added to the basic
types such as the rotary switch in a multimeter or the cad-cell light sensitive switch but the
basic functions are captured by the above types. That a switch can serve many functions is
critical to understand for interpreting wiring diagrams and actual circuits.
Methods of actuating switches used in the gas heat industry range from manual devices
to self-programmable computer circuits known as “fuzzy logic” controllers. Any device that can
create or respond to a mechanical motion, a change in physical condition or that can employ
the principles of electricity and electromagnetism can be used as a switch.
A brief overview of the types of switches that are commonly found in gas-fired appliances along
with their schematic symbols will allow you to identify them on diagrams and in the field.
Note that the positions of all switches in wiring diagrams are shown in their normal
position when the unit is not operating. This is called the “at rest” state. As such, the
switch will be shown as normally open (NO) or normally closed (NC)
Manual switches are, of course, activated by hand. Included in this category is the appliance
disconnect switch, the manual/auto fan or thermostat function switches, and the primary
control reset switches. As the last three indicate, a switch that is activated by other
mechanisms may also have a manual function.
CONTACTS
OPEN switches.
Examples of manual
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Sensing switches respond to a physical change in condition such as temperature, pressure, flow,
liquid level, light, humidity etc. Bi-metallic, bulb and bellows, rod and tube, sail, diaphragm, and float
switches all fall into this category.
The “at rest” position of the switch as shown in schematic diagrams will indicate whether the switch
opens or closes on a rise or fall in the sensed condition. The switch position (NO or NC) and the action
that causes it to open (rise or fall) are used to categorize switches.
If a switch opens because of a rise in the sensed condition, it is called a direct acting (DA) switch. If it
opens on a fall in the sensed condition it is called a reverse acting (RA) switch. Heating thermostats
and high limit switches are direct acting since they open on a rise in temperature while cooling
thermostats and the fan off switch on forced air furnaces are reverse acting switches that opens on a fall
in temperature
Thermostat and Aquastat: Normally Open direct acting switches open on temperature rise
Fan and Limit Control Switches
Examples of direct and reverse acting temperature control switches and wiring symbols.
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Examples of various types of sensing switches and their wiring symbols
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Relay switches found in primary controls employ an electromagnet to connect,
disconnect or change the direction of electricity in a circuit. The basic principles of
electromagnetism will be discussed in detail in section 5.9. Given the importance of relay
switches in gas-fired appliances it is worth briefly discussing their function here.
A magnetic field is created when electricity passes through a wire. If the wire is coiled
around a metal core the magnetic field is concentrated and the coil becomes an
electromagnet. This electrically activated magnet can be used to pull switch contacts
together or apart that are normally held in position by a spring. The advantage of this type
of switch is that low voltage wiring can be used in the electromagnet to make or break
contacts in a separate higher voltage circuit. When the electrical flow ceases in the coil
the magnetism immediately ceases and the spring returns the contacts to their normal
position. Remote switching and reduced arcing are two of the many advantages.
MOVABLE
CR1
STATIONARY
CONTACTS
CONTACTS
HORIZONTAL ACTION TYPE
BELL-CRANK TYPE
Coil will be shown as either of the above
symbols in location where it is powered. It will
be designated with a control relay number
(CR1) to correspond to contacts.
1K
Normally open contact. Number indicates
controlling relay
Normally closed relay contact.
Examples of relay switches and their wiring symbols
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Electronic switching devices are becoming more common in flame safeguard controls
and thermostats. Solid state and integrated control switches do not have moving parts.
They allow for tighter control of the operating sequence of components In a gas appliance.
Gate
Triacs used in thermostats
Integrated Controls
Examples of electronic switching devices and their wiring symbols
The principles of operation, testing and troubleshooting of each solid-state component are
not usually required since the flame safeguard control (relay module) is not repairable.
Your role is “simply” to determine if the control is energized and if it is receiving and
delivering electrical signals in the proper sequence.
Classroom demonstrations and lab sessions will supplement this brief introduction to the
various types of switches used on gas appliances. The variety of switching devices should
never obscure the fact that switches simply make, break or re-direct electrical power In a
circuit. The testing methods to determine electrical flow are essentially the same no matter
which actuating method is employed.
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5.5.5 Loads
The final component in the simple circuit achieves the end purpose of electrical flow by
converting electrical energy to another more useful form of energy. A load is anything that
uses an electrical current from a power source.
As highlighted in our discussion of the electrical supply methods, anything that can
produce electricity can itself be produced by electricity. The load converts electrical energy
into heat, light, magnetism, chemical actions, and mechanical motion. The loads found in
gas appliances, as shown below, include:
• motors - burner; circulating; venter; humidifier
• electromagnetic coils - relays; solenoid valves
• transformers - ignition; control
• heaters - primary control safety switch; thermostat heat anticipator
Motor
ELECTROMAGNET
SPRING
SEAT
VALVE DISC
Solenoid
Transformer (Step-down)
Examples of loads and their wiring symbols
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A load is a resistance opposing electrical flow. The simple circuit with only one load is ideal
for applying your understanding of the basic terms and conditions of electricity.
The information presented to this point should allow you to understand the following basic
concepts about electrical circuits.
>
Electricity requires a complete path from an electrical source back to that source.
>
Conductors offer less resistance to electrical current than insulators.
>
Voltage is the electrical pressure difference between two points in a circuit that causes
electricity to flow. That pressure difference is measured In volts.
>
Current is the rate of electron flow as measured in amperes.
>
Resistance is the opposition to electrical flow measured in ohms.
>
A load offers a resistance to electrical current that determines the current draw for any
voltage applied.
>
Only sufficient current will be drawn by the load to overcome that resistance.
>
Voltage applied is voltage consumed.
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5.6 Ohm’s Law and Watt’s Law
Electricity is a mathematical science. If you enjoy math there are electrical calculations that will
fascinate and challenge you. However, this is a basic electrical course for Gas Technicians so
only the necessary and useful math equations will be examined. In large part, it is the concepts
underlying the math equations and not the calculations that are of primary importance to
understand.
To a large extent, we have already discussed Ohm’s law in this text without naming it. In this
section, we will extend that knowledge of the relationship of voltage, current, resistance and
power or work. Using the principles underlying the simple formulas we can prevent and solve
the most common electrical problems found in gas-fired appliances.
5.6.1
Ohm’s Law
Ohm’s law is simply: it takes one volt to push one amp through one ohm. The proportional
relationships between force, current, and resistance are summed up in Ohm’s law.
1 amp of current
1 volt
1 ohm
of electrical pressure
f resistance
Wiring diagram of Ohm’s law
Current is directly proportional to voltage and inversely proportional to resistance.
If the voltage is doubled through the
same one ohm of resistance (as above),
the current must also double since
current is directly proportional to voltage.
If one volt is applied to two ohms, then the
current must be cut in half since current
is inversely proportional to resistance.
16
amp
1
volt
Increasing voltage increase current.
Increasing resistance decreases current.
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As long as we know two of the three values, we can figure out the third. If we know the
resistance of a load and the voltage applied to it then we can determine the current that
will pass through it: voltage * ohms = current. If we know the resistance and the current,
we can determine the voltage: amps X resistance = voltage.
Using the symbols for the three factors affecting electron flow the formulas are:
E = IxR
Voltage = Current X Resistance
I =E +R
Current = Voltage + Resistance
• R = E +1
Resistance = Voltage + Current
The following visual aid is helpful in remembering these useful formulas:
Simply cover up the missing value and
the formula appears for finding the
unknown value.
E = 1 x R or
Voltage = Amps X Ohms
I = E + R or
Amps = Voltage + Ohms
R = E + I or
Ohms = Voltage 4 Amps
Diagram of Ohm’s law. Even I Remember.
The above formulas can be applied directly to all DC circuits and AC resistive circuits. A
resistive circuit is one that poses only a fixed resistance to electrical flow - usually from
the type of material the electricity is flowing through. A heater is an example of a resistive
circuit.
AC circuits are seldom simply resistive (as will be discussed in the section 5.8 of this
Module). An AC circuit with an electromagnet, inductive coil or capacitor creates opposing
forces that affect current flow in these circuits. Therefore, Ohm's law cannot be applied
directly to most AC circuits - especially those with a motor, relay, or transformer.
Complicated formulas are available for calculations based on Ohm's Law for AC nonresistive circuits but they are seldom used in Gas Technician work.
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However, the principles and general relationship given in Ohm’s law can and should be
used on a regular basis. Those principles are quite simple and logical.
1. Voltage and current are directly proportional - whatever happens to one will happen
to the other. If voltage increases, current increases and vice versa. If current
decreases, voltage decreases and vice versa.
2. Current is inversely proportional to resistance - whatever happens to resistance will
cause the opposite reaction to current. If resistance increases, current decreases. If
resistance decreases current increases.
Although the mathematical accuracy of Ohm's law cannot be employed in most of our
circuits, the principles are extremely important for installation and troubleshooting of
electrical circuits in gas-fired equipment. Two examples will serve to illustrate the point:
1. You are helping a G.2 to replace a furnace. The new furnace uses a line- voltage (¡.e.
120V) thermostat but the old furnace used a 24V thermostat. The customer tells you
to use the existing thermostat wires that are installed in the hollow walls. This sounds
easier and quicker. Won’t the G.2 be impressed!
With your knowledge of Ohm’s law, you realize that increasing voltage by
approximately five times (24V to 120V) will cause a proportional increase in current.
Increased current causes increased heat. A quick check of the wire jacket reveals that
the #18 AWG wire is not rated for the increased current.
You explain to the customer why you cannot use the existing wires since this would
pose a fire hazard. The customer and supervising G.2 are duly impressed with your
expertise and recommend you for a raise (but more importantly, you have prevented
an unsafe condition).
2. You have conducted an annual maintenance on a furnace but when you try to reactivate the appliance the venter motor makes an unusual noise and the combustion
characteristics are improper and cannot be corrected.
You take a voltage reading across the activated venter motor and find that the voltage
is 120V as required. An ammeter test determines that the current draw is significantly
less than that specified on the rating plate of the venter motor. Using the principles of
Ohm’s law, you can easily determine that, given a constant supply voltage, the only
thing that could reduce current is an increase to resistance. In other words, the motor
is causing more electrical resistance than it was designed to.
Further investigation focuses on the cause of the motor's increased resistance and
quickly determines that the bearings are partially seized. The motor is replaced by a
G.2 who thanks you for efficiently and effectively troubleshooting the problem. Again,
you are recommended for a raise!
Safe installations and easy troubleshooting are made possible by using the principles
underlying Ohm’s law.
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5.6.2 Watt’s Law
Electrical power is the rate at which electrical energy is delivered to a load. Electrical work
is the rate at which electrical energy is consumed by a load. Electrical power is the same
as electrical work. The symbol for power is the letter P.
A load consumes electrical energy and that consumption or use is measured as power
consumption. Since electrical power is the rate at which electricity is delivered, the two
factors that determine delivery - voltage and current - also determine power or work.
Electrical power is equal to voltage (volts) multiplied by current (amps) or P = I X E.
Electrical Power is measured in WATTS.
One watt of power is the result of one ampere driven by one volt through a circuit.
This is known as Watt’s law, named after James Watt the inventor of the steam engine.
1 Amp of current
1 Watt of Power consumed
or converted to another form
of energy
1 Volt
Wiring diagram depicting Watt’s law.
If the above circuit is operated for one hour, then 1 watt-hour of electrical energy is used.
A watt-hour is a relatively small unit of energy consumption so it is more common to use
the term kilowatt-hour, which means that energy is used at a rate of 1000 watts per hour.
A 100-watt light bulb left on for 10 hours would consume 1 kilowatt of energy. The local
power supply company bills the customer based on how much power is consumed per
month. The meter at the point of entry for the electrical supply to the building measures
power consumption directly in kilowatts by measuring the varying current flow given a
constant voltage.
Watt’s law can be written and depicted in three ways similar to Ohm’s law:
• P = IxE
Power = Current X Voltage
• I =P +E
Current = Power * Voltage
• E = P +1
Voltage = Power + Current
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The following visual aid is helpful in remembering these useful formulas:
Simply cover up the missing value and the
formula appears for determining the
unknown value.
P = I x E or
Watts = Amps X
Volts
I = P + E or
Amps = Watts -r Volts
E = P + I or
Volts = Watts T Amps
Diagram of Watt’s law. The Power PIE.
Again, the above formulas can be applied directly to all DC circuits but require complicated
calculations when applied to AC circuits as we will discuss in section 5.8 on alternating
current. To avoid these complications the power rating may be given in Volt-amps (VA) often called apparent power.
The principles are more important than the actual measurement for our purposes. As
current or voltage increases, the power consumption and work performed increases. This
is important to consider since every load has a power rating based on its being supplied
with a certain voltage and current. Failure to supply those specified values results in a
change to the load's power consumption and performance.
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5.6.3 Other Measurements of Work and Power
Loads are often given a specific power rating as well as an amp rating. The power rating
may be given in watts, Btus, joules or horsepower. The first two are most commonly
used with heating loads and the latter with motors. Joules are the units of power in the
metric system.
Horsepower is a common unit of measurement for mechanical power or work. James
Watt, in trying to market his steam engine as an improvement over using horses,
determined that the average horse working at a steady rate could do 550-foot pounds of
work per second (550 ft.-lb./s). A foot pound is the amount of force required to raise a onepound weight one foot. The power delivered by one horse is thus 550 ft.- Ib./second or
33,000 ft.lb. /hour.
1 Horsepower = 550 ft.-lb./s
= 33,000 ft.-lbVhour
1 Horsepower = 746 Watts
Joules are becoming a common unit of measurement for electrical power and mechanical
power. They are the metric equivalent of watts and horsepower. A joule is the amount
of work done by a coulomb flowing through a potential of 1 volt or, in different terms,
the amount of work done by one watt for one second.
1 Joule = 1 Watt/second
Btu’s are also employed as a unit of power consumption or energy production. The
following chart gives some common conversions for different quantities of energy, which
can be used to calculate different values.
1 Horsepower
1 Watt
1 Watt
1 Watt/second
=
=
=
=
746 Watts1 Btu/h X 0.293 =
Watts
0.00134 Horsepower1 Ft.-lb./s
=
Watts
3.412 Btu/h1 Btu=
1050Joules
1 Joule
Ohm’s law and Watt’s law are employed to make an installation safe and to help a Gas
Technician troubleshoot and correct an electrical problem. They are tools of our trade and
should be used as such rather than feared and neglected, as is commonly the case.
The laws governing the simple circuit will be explored in labs related to other types of
circuits. By understanding the relationship between voltage, amperage, resistance and
power, the time and energy required to install or service an appliance will be not only be
greatly reduced but also more successful.
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5.7 Types of Circuits
The simple circuit has only one load. When more than one load is attached to a circuit
there are three methods of connecting the components with three very different results.
• Series circuits
• Parallel circuits
• Series-parallel circuits.
The type of circuit along with voltage, current and resistance will determine how the
individual load will perform and how the other loads in the circuit will affect or be affected
by it. Proper installation and easy troubleshooting depend on a sound understanding of
the types of circuits.
5.7.1 Series Circuit
When there is only one path from source back to source, the components are wired in
series. The simple circuit is wired in series with the only available pathway through the
connecting wires, fuse, switch, and load. If any one of the components is disconnected the
circuit is broken and current stops. The load is dependent on the other components to
complete the circuit and function.
Simple Circuit wired in series (left). Series circuit with three loads (right)
Attach other loads in series with the other components and that dependence remains. If
any one load is not operating, then the other loads cannot operate. Like the cheaper
Christmas tree lights, remove one bulb and they all go out.
Loads in a series circuit are interdependent and share the applied voltage
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Series wiring is useful for controlling the operation of a load through one or more switches
actuated for different reasons such as the disconnect switch wired in series with the high limit
and burner. However, series circuits are not intentionally used in gas-fired appliances because
of the affect on voltage and current caused by more than one load in a circuit.
Since voltage applied to a circuit is voltage consumed, more than one load in the same pathway
will share the supply voltage. The other loads in the same pathway reduce the voltage drop
across each load as well as the current through the entire circuit.
L1
120 V
20
ohms
N
Simple Circuit wired in series (left). Series circuit with three loads (right). Voltage applied is
voltage consumed. The total resistance of the circuit determines current draw.
Just as the current in any part of the simple circuit is the same no matter where it is measured
so too in the series circuit because the resistance of all the loads together affects the current
draw. The total resistance in the above series circuit is 60 ohms (20 + 20 + 20). Given the
relationship between voltage, current and resistance established by Ohm’s law, current in every
part of the circuit is 2 amps (120 V : 60 ohms = 2 amps)
Although series circuits are not commonly used, it is worth knowing the effects on loads wired
in series for troubleshooting purposes. Two examples will serve to illustrate the rules that apply
to a series circuit and how they could help you solve a problem.
Example #1: The burner motor in the diagram to the right is not functioning properly. As a result,
the air delivery is improper so incomplete combustion is occurring.
Before replacing the burner, a competent
technician checks the voltage drop across
the load and finds 100 V. The applied voltage
is tested and proven to be 120V. So, what’s
the problem?
Problem circuit
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Gas Technician 3
The reduced voltage indicates that there is another load wired in series with the motor. In
this case, the second load is the resistance created by the corroded switch, which would
indicate a voltage drop of 20 volts. An amperage reading would indicate insufficient current
since the resistance of the dirty switch would be added to that of the motor. The motor is
designed to operate at 120 V; replacing the motor would not correct the problem.
Example #2: The same conditions as
example #1 with the same result of
incomplete combustion.
120
V
Before replacing the burner, a competent
technician will check the voltage drop
across the load and recognize that the
reduced voltage indicates that there is
another load wired in series.
Problem circuit
In this case, the loads are the excessive lengths of wire. A voltage drop of 10 volts would
be found from either side of the motor back to source. An amperage reading would indicate
insufficient current since the resistance of the long wires would be added to that of the
motor. Again, replacing the motor would not solve the problem.
By applying Ohm's and Watt’s laws to all DC circuits and to AC resistive series circuits,
three simple and informative characteristics of a series circuit are evident:
1. The total resistance is equal to the sum of all the individual resistors.
2. The current flowing in all parts of the circuit is the same.
3. The sum of the voltage drops is equal to the applied voltage.
These characteristics also apply to other AC circuits (non-resistive) although the resistance
reading measured at each load cannot be simply added to determine the total resistance.
The opposing forces created by alternating current affect total resistance in these circuits.
Again, it is the principle underlying Ohm’s and Watt’s laws that is of primary importance, not
the math calculations.
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Module 5
Basic Electricity
5.7.2 Parallel Circuits
A parallel circuit has two or more loads and each load has its own path from a common source
line back to a common neutral line. The source voltage is applied to each load individually.
L1
120 V
Voltmeter
N -----------------Supply voltage is applied to each load individually in a parallel circuit
The loads work independently. If one load is not operating, the other loads are not affected.
This is the major advantage of parallel circuits over series circuits and the reason that
parallel circuits are the most commonly encountered circuits.
120 V
Each load operates independently of the other loads in a parallel circuit
Often the branch circuits are individually controlled by their own switch.
Individual branch circuits may be controlled by a separate switch wired in series
with the load
The current in each branch circuit is determined by the resistance of the load in that branch
circuit. The current in the common lines is equal to the sum of all the current flowing in the
branch circuits served by that section of the common line. Thus, current varies in different
parts of a parallel circuit unlike current in a series circuit.
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Gas Technician 3
Each load in the following example is the same. Each offers a resistance of 100 ohms.
120 V
Current in each part of a parallel circuit varies depending on the resistance of the
load in the branch lines and the sum of the resistance served by the common
lines.
As the number of branch circuits increases the total current draw will be increased. The current
carrying capacity of the common line may be exceeded resulting in overheating, overload fuse
activation or a fire. A classic example of this dangerous condition is when too many electrical
devices are plugged into a #16 AWG lamp cord - known as an octopus connection.
Total current draw exceeds lamp cord’s
current carrying capacity resulting in
overheated wires
Dangerous overloading of a lamp cord
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Basic Electricity
As the current carrying capacity of the conductor is approached the conductor will heat
up. A hot conductor does not conduct electricity as well as a cool conductor so current
decreases. The conductor essentially becomes a significant resistance in the circuit and
can be considered a load in series with the other loads. As such the effects of loads in
series will result in reduced voltage to the intended load as discussed in the section on
problem series circuits.
Obviously, it is important to calculate the total current of a parallel circuit and to ensure
that this total current does not exceed the ampacity rating of the conductor. Ohm’s law
and Watt’s law can be used in all DC parallel circuits and AC resistive parallel circuits.
For most gas-fired appliance installations it is sufficient to ensure that the heating
appliance is on its own dedicated circuit. Additional loads connected in parallel to the
heating appliance may cause an overload or reduction of current to our appliance.
Resistance in a parallel circuit varies like current in different parts of the circuit. However,
since Ohm’s law states that current is inversely proportional to resistance it is not
surprising that resistance decreases in the common sections of the circuit whereas current
increases.
Resistance in the individual branch circuits is simply the resistance of the load. As such,
determining the current draw of the branch circuits is no different than for a simple circuit.
Total current (IT) = 1.2 + .6 + .4 = 2.2 amps
Total resistance (RT) = 54.5 ohms
L1
120 V
1.2 amps-*
.6 amps ~*
.4 amps “
Ri = 100
Ohms
R2 = 200<
Ohms
R3 = 300
Ohms
1.2 amps —►
.6 amps —►
.4 amps —►
Total current = 2.2 amps
IR: & a = .6 + .4 = 1 amp
Total resistance = 54.5 ohms R2& s = 120 ohms
Resistance varies in each part of a parallel circuit depending on the load in the
branch lines and the sum of the resistance served by the common lines.
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Gas Technician 3
Notice that the resistance in the common lines is less than the resistance in any of the
branch lines served by the common line. The total resistance in a parallel circuit will
always be less than the smallest resistance in the circuit because the total circuit
current is always greater than the current through the branch circuits.
Unlike series circuits, resistance in a parallel circuit cannot be added to yield the total
resistance. For an introductory electrical course, it is sufficient to understand that total
resistance in a parallel circuit will always be less than the smallest resistance. However,
for those students who wish to know how total resistance is determined in a parallel circuit
the following three formulas are briefly presented.
If all loads are of equal resistance (as shown below) the total resistance is easily
determined by dividing the resistance value of one resistor by the number of resistors. The
formula is RT = R + N where RT = Total resistance; R = the value of any one resistor; and
N = the number of resistors.
In the following diagram, RT at source = 100 : 3 or 33.33... ohms.
Total current = 3.6 amps
Total resistance = 33.3 ohms
T
1.2 amps
1.2 amps
R1 = 100
Ohms
R2= 100
Ohms
R3 = 100
Ohms
1.2 amps
1.2 amps —►
1.2 amps
120 V
Total resistance = 33.3 ohms
Total current = 3.6 amps
1.2 amps
50 ohms
2.4 amps
Total resistance in a parallel circuit with loads of equal resistance is easily
determined by dividing the single resistance value by the number of resistors in
the circuit.
If the loads are of different resistance (as shown in the diagram on the previous page) the
total resistance is usually determined by the conductance method using the following
formula:
1
+
1
R2
R3 etc.
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Page 5-94
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Module 5
Basic Electricity
Using the resistor values in circuit shown on page 5-90, the total resistance can be
calculated using the following equations.
RT = 1 = 1
=1
1
100
RT =
+1
200
1 X 600
11 X 600
600
+1
300
=
6 +3 + 2
600
600
600
11
=
600
11
600
54.5 ohms
The total resistance of a circuit is worth calculating to determine current draw. In most
cases, we will know the voltage for the circuit (120 V or 24 V) and we can easily measure
the resistance of each load with our ohmmeter. Given a known voltage and resistance we
can easily calculate amperage using Ohm’s law.
Using the circuit on the last page, a voltage of 120 V applied to a total resistance of 54.5
ohms would produce a current of 2.2 amps.
I = E + R = 120 : 54.5 = 2.2 amps
Although the math calculations based on simple total resistance cannot be applied
straightforwardly to non-resistive AC circuit, the following three simple and informative
characteristics of a parallel circuit do apply to all circuits:
1. The voltage drop across each load is equal to the applied voltage.
2. The total current flowing in the circuit is the sum of the current flowing in each
branch circuit.
3. The total resistance is always less than the smallest resistance in the circuit
Lab exercises will allow you to develop and confirm your understanding of parallel circuits.
Given that the parallel circuit is the most common type of circuit used in gas- fired
appliances, a solid understanding the operating principles and expected electrical
readings will be rewarded with trouble-free installations and easy troubleshooting.
Basic Electricity
© NRG Resources Inc.
Page 5-95
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Gas Technician 3
5.7.3 Series-Parallel Circuits
A circuit that contains some loads connected in series and other loads connected in
parallel is called a series-parallel circuit.
In this series-parallel circuit, R1, R2 and the combination of R3 and R4 are
connected in parallel while R3 and R4 are connected in series with each other.
Due to the inefficiency and problems created by loads connected in series it is not
surprising that series-parallel circuits are not intentionally used in gas-fired appliances
except in some minor cases in the electronic control circuitry of some controls. The later
exceptions are not serviced since control circuits are non-repairable.
Nevertheless, a basic understanding of how series-parallel circuits operate assists in
identifying those unintentional cases when a parallel circuit functions as a seriesparallel
circuit due to a problem connection or fault.
The operating principles and expected electrical readings that we have discussed for
series circuits and parallel circuits separately are applicable to series-parallel circuits.
In the above diagram, R1, R2 and the combination of R3 and R4 will function as a parallel
circuit. The supply voltage is applied to each branch circuit separately so they function
independently. The current in each branch is determined by the load(s) in that branch and
the total current (IT) will be the sum of the current draw in each branch. However, the
current will not vary in the branch circuit with two loads (R3 and R4) just as it did not vary
in a separate series circuit.
The total resistance in a series parallel circuit can be calculated like a parallel circuit once
the series branch circuit's total resistance is calculated by adding the resistance of the
loads in series. The end result will show a total resistance less than the smallest branch
circuit but not necessarily less than the smallest resistor in the series circuit.
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Module 5
Basic Electricity
The values that would be determined for the above circuit using Ohm's law or electrical
measurement devices are given in the following diagram based on:
Es = 120 V; Ri = 50; R2 = 100; R3 = 175; and R4 = 25.
IT = 2.4 + 1.2 + .6 = 4.2 amps
R = 28.6 ohms
L1
IR1 = 2.4 amps
|R2= 1.2 amps
IR3&4= .6 amps
> ERI = 105 V
Ra = 175 Ohms
R2 = 100 Ohms
Ri = 50 Ohms
120 V
ERi = 120 V.
ER1 = 120 V.
ER1 = 15 V
R4 = 25 Ohms
L2
IR2,3 & 4 = 1.2 + .6 = 1.8 amps 1R3 a 4 = .6 amps
R23&4 = 66.7 ohms R3&4 = 200 ohms
Total current = 4.2 amps
Total resistance = 28.6 ohms
Values given in this series-parallel circuit show that the separate branches
operate as individual circuits and the common lines function on the principles of
the parallel circuit
Identifying a parallel circuit that is functioning like a series-parallel circuit is the most common
use of the above information. Consider the following diagram, which is similar to the above
one, except that it was built to operate as a parallel circuit but R3 is not operating properly
Es = 120 V; Ri = 50; R2 = 100; Rs = 175
IT = 2.4 + 1.2 + .6 = 4.2 amps
120 V
A parallel circuit with one load (R3) operating like it is in series.
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Basic Electricity
The ^ indicates the wiring fault that is causing R3 to malfunction. If electrical readings were
not taken and understood it would have been easy (but not very productive or
professional) to replace the R3 load.
Ohm’s law and Watt’s law can be applied to each branch circuit separately in a seriesparallel circuit. The three defining characteristics of a series-parallel circuit are:
1. The voltage drop across each branch circuit is equal to the applied voltage.
2. The total current flowing in the circuit is the sum of the current flowing in each branch
circuit.
3. The total resistance is always less than the smallest resistance of any branch circuit
but not necessarily less than the smallest resistor.
Lab exercises will allow you to develop and confirm your understanding of seriesparallel
circuits. Given that the parallel circuit is the most common type of circuit used in gas-fired
appliances, it is not surprising that a common electrical fault is a parallel circuit functioning
like a series-parallel circuit.
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Module 5
Basic Electricity
NOTES:
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Gas Technician 3
5.8 Alternating Current
Both direct current (DC) and alternating current (AC) are used in heating appliances.
Direct current is an electron flow in only one direction. Alternating current is an electron
flow that reverses back and forth many times a second.
The use of direct current in heating appliances is becoming more common. Battery
operated test equipment and the programmable functions of some thermostats utilize
direct current. DC motors are now used on air circulating fans as well as venter and
combustion blowers. Appliance controls and electronic igniters often employ DC current.
In most cases, the DC current is created by the rectification of the AC supply in electronic
controls, which are non-repairable devices.
The following overview of factors affecting AC voltage and current in circuits concludes
with a brief look at the distribution and building wiring systems that deliver AC power to
our appliances. In the next section of this Module on solenoids, relays, motors, and
transformers we will apply this knowledge of AC electricity.
5.8.1 Phases
Phase is the number of voltage/current alternations in an electrical supply. We commonly
use single-phase electrical supply to our residential appliances but the Power Company
generates three-phase electrical supply.
As depicted on the following page, three-phase electrical supply has three separate
voltages alternating at the same frequency occurring in sequence. This increases power
delivery and is commonly used in industrial electrical devices for this reason. A transformer
can change the three-phase transmission supply into single-phase for use in single-phase
wiring systems.
Basic single-phase generator wiring configuration and resulting sine wave.
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Basic Electricity
Basic three-phase generator wiring configuration and resulting sine waves.
Electric power is generated by rotating turbines. The mechanical power to turn the turbines
may be supplied by waterfall, gas, oil, coal, or atomic power. The turbines actually turn a
massive winding of conductive wires surrounded by an electromagnetic field. The above,
simplified drawings of generators are representations of the basic principle of electric
power production. The following photo shows an actual alternator.
Generators used for the production of AC power
Understanding the means of producing AC electrical supply and the basic voltage - current
relationship that arises from that production will allow us to examine the factors affecting
voltage and current in various types of circuits in the next sub-section.
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5.8.2 Factors Effecting Alternating Current in a Circuit
Voltage and current are seldom in phase in an AC circuit. The relationship of current to
voltage depends on the type of load(s) in the circuits. Forces created by some loads have
a significant effect on the back and forth motion of electrons.
Before we examine these factors, let us revisit the meanings of voltage, current and
power to ensure that it is clearly understood what these opposing forces are affecting.
Voltage is simply electrical pressure. It is the potential difference between two points in a
circuit that provides the motive force to cause electrons to move. If voltage is reduced
given a constant opposing force (i.e. a given resistance) the current is reduced.
Power plants are not the only means of producing; it can be produced in the circuit itself
by magnetic fields and by devices that store and discharge large amounts of electrons.
Voltage is simply force so it is often necessary to state the origin of that force by identifying
it as supply voltage, induced voltage etc.
Current is simply the flow of electrons. Measured in amperes, it is the rate that a
standardized quantity of electrons flows past a fixed point in the circuit. The greater or
more intense the current, the greater the amount of electrical energy.
However, the greater the current the greater the magnetic field created around the
conductor. That magnetic field can act as a force to limit current by creating an opposing
force to the current flow caused by the source voltage. Current is not only caused by
voltage from the power plant; it is caused by any electromotive force that acts upon the
conductor. Current does not have to stay in phase with source voltage.
Power is simply the rate at which electrical energy is delivered to a load. There must be a
conversion (or consumption) of electrical energy before power can exist. The amount of
power, as measured in watts, is a product of voltage times current if the voltage and current
are in phase as occurs in DC circuits and purely resistive AC circuits.
If voltage and current are out-of-phase the calculation of voltage times current only yields
the apparent power not the true power. Voltage and current are not working together when
they are out-of-phase. As a result, the readings from a voltmeter or ammeter are not a true
indication of the rate of energy delivery to the load. True power must be measured by a
wattmeter or calculated using the power factor specific to the out-of-phase condition.
A review of sections 5.2, 5.3 and 5.6 is warranted if you are unsure of the meanings of
voltage, current, and power. Now to our examination of the factors affecting alternating
current in circuits.
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Basic Electricity
There are basically three types of loads in a circuit as given below with examples.
•
Resistive - heaters, incandescent lights
•
Inductive - motors, relays, solenoids, transformers
•
Capacitive - capacitors used on some motors.
A circuit may have one (in which case they are called pure) or a combination of these
types of loads as in the case of a motor with a capacitor, which is an inductive- capacitive
circuit. The type of load determines the phase relationship between voltage and current
by affecting the back and forth motions of the electrons. Since they affect voltage and
current, the type of load also affects the resulting power of the circuit.
In a purely resistive circuit, AC current rises and falls in phase with voltage. The amount
of current flow in the circuit is only dependent on the resistance in the circuit. There are
no other factors affecting current besides resistance and voltage.
Voltage and current are in phase in a purely resistive circuit.
Voltage and current are working together at every point in the cycle. Whenever voltage
has a positive value (i.e. acting in one direction), current also has a positive value (i.e.
flowing in the direction of the applied voltage). Whenever voltage is zero, current is zero.
This is how a DC supply works all the time - no matter what the load is.
The amplitude or rise and fall of current above the zero line are determined by the
resistance in the circuit. The amplitude of the voltage is determined by the electrical
source.
A measurement of effective voltage (as given by the meter) and the current can be
employed in a resistive AC circuit to determine power in watts by simple multiplication.
For example, a supply voltage of 120 VAC is applied to a 100-watt load resistor, which is
a purely resistive load. A measurement of current will find a .83-amp draw. Voltage times
current (120 X .83) yields true power (100 watts) in a resistive AC circuit.
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Gas Technician 3
.83 amps
100 Watts
120 VAC
Voltage times current equals power in a resistive circuit.
An inductive load in an AC circuit creates a magnetic field that acts upon current and
voltage in the circuit. If the load has a coil of wire it is an inductive load or inductor.
As current increases in a conductor the magnetic field around the conductor increases.
As current decreases the magnetic field collapses. The direction of flow determines the
polarity of the magnetic field. In an AC supply, current increases and decreases 120 times
a second in alternate directions (60 in the positive direction, 60 in the negative direction)
so a magnetic field builds, collapses and changes polarity 120 times per second.
Magnetic
Lines of Flux
and
Polarity
Direction of current
\
Magnetic/
Intensity of current
Lines of Flux'\,../' Apply
• Small Large counter force against supply voltage
Current produces a magnetic field - the polarity of which is determined by the
direction of flow and the strength of which is determined by the intensity of flow.
The effect of this magnetic field in a coil of wire is similar to the effect of the magnet rotating
in the AC generator. The magnetic lines of flux cut across the wires in the coil and induce
a voltage in the coil. This induced voltage is opposite that of the source voltage because
the strength of the magnetic field is building as the current increases and collapsing as
the current decreases.
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Page 5-104
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Basic Electricity
The induced voltage is often called back emf because it counteracts the applied
electromotive force (voltage). Induced voltage is electrical pressure pushing back against
the applied or source electrical pressure. Induced voltage is determined by various factors
including the number of turns in the coil. Manufacturer’s of electrical devices with colls use
these determining factors to design their devices for a certain current flow since current
will be determined by the difference between the applied voltage and the Induced voltage.
If there is no difference, there is no flow.
Induced voltage acts upon the current in the conductor to limit its flow. As such, inductance
is like resistance in that it limits current. However, resistance is a physical limitation
whereas induction is a limitation by counteracting force.
Inductance limits the current when current changes direction. The applied voltage is forcing
electrons in one direction while the induced voltage is forcing them in the opposite
direction. Depending on the strength of the induced voltage in relation to the applied
voltage, a lag time results in between the voltage change and current change in direction.
As shown in the graph, voltage leads current in an inductive circuit.
Voltage and current are out-of-phase with voltage leading current in an inductive
circuit.
Voltage and current are out-of-phase. They are not working together at all points in the
cycle. For example, at point A in the above graph the applied voltage is zero while current
is still decreasing toward zero. Just right of point A, voltage is being applied In the negative
direction but current is still decreasing in the positive direction.
The degree of phase shift between voltage and current is known as the phase angle as
identified in the graph. This angle is employed in calculations of the true power delivered
by the voltage and current working sometimes together and sometimes at counter
purposes of delivering electrical energy to the load.
Basic Electricity
©NRG Resources Inc.
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Basic Electricity
For our purposes, it is sufficient to note that the phase angle - the amount that the voltage
leads the current - is dependent on the difference between the applied voltage and the
induced voltage. Phase shift depends on the design and use of the inductor.
In a coil device such as a relay or solenoid, the difference between applied and induced
voltage may be quite small. The applied voltage of 120V may have to compete against an
induced voltage from the coil of 115V leaving only 5 volts to overcome the resistance of
the wiring in the coil. If the resistance of the coil is 10 ohms, this determines the current,
which as per Ohm's law, would be .5 amps (5 volts + 10 ohms = .5 amps).
Coil’s
Resistance
= 10Q
Applied Emf = 120V
Magnetic field around one wire coil creates back emf that limits applied emf.
Note: The amount of back emf depends on the design and use of the coil - the
above values are only an example
A more practical discussion of induced voltage in the following sections on solenoids,
relays, motors, and transformers will review and expand upon the theory presented here.
The purpose of this discussion is to explain the factors that affect AC circuits.
Induced voltage or back emf is a major factor affecting AC circuits with motors, relays,
solenoids, and transformers - basically every circuit in a gas appliance. The energy
delivered to the load (i.e. power) is not a product of applied voltage times current in an
inductive circuit. The actual voltage that causes current to flow through the resistance of
the coil is the difference between applied and induced voltage.
A DC circuit with a coil will also create a magnetic field and an induced current or back
emf. However, current does not change directions so flow is not affected by the back emf.
The induced voltage in a DC circuit acts like a resistance so voltage times current
determines true power even in an inductive DC circuit.
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A capacitive load can only exist in an AC circuit because it only functions with an
alternation of current. A capacitive load stores an electrical charge and converts it into a
more usable form of electricity by shifting the phase. As such it is an unusual type of load
in that it does not convert electricity into another form of energy. It is simply a
device that allows another load that is wired in series with it to work more effectively. It
cannot function as the only load in the circuit.
Capacitors used on electric motors are the most visible
example of a capacitive load although capacitors are also
used in some controls.
Briefly, a capacitor consists of two thin, long aluminum
plates that are rolled together with an insulating material
separating them. Voltage is applied from the electrical
source to one of the plates which, because of its large
capacity, stores the electrical charge during one half of the
alternation cycle and then releases those stored electrons
back into the supply wire on the other half of
the cycle.
Terminals
Dielectric Paper
Capacitor construction and wiring symbol for any type of capacitor
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The aluminum electrodes act as storage reservoirs for electrons. The dielectric papers
prevent electrons from flowing from one electrode to the other. All power is delivered by
means of the capacitor but no electricity flows from plate to plate. Capacitors are used to
boost the starting torque and/or running efficiency of single-phase motors.
When the capacitor is connected to an alternating current circuit, the rise in applied voltage
during half of the cycle forces one electrode to gain electrons while the other plate
“empties" of electrons. The source plate induces the opposite charge in the plate. When
the voltage reverses, the empty plate fills with electrons while the full plate discharges.
Electrons do not flow through the capacitor. Essentially one plate fills with electrons
causing the other plate to empty of electrons. During the second half of the alternation
cycle the flow in and out of the plates is reversed. Electrons flow in both wires attached to
the plates but electrons never flow between the plates.
Arrows indicate direction of electron flow
Capacitor
L1 during one half of the alternation cycle —O“ "&
N during one half of the alternation cycle
L1 during other half of the alternation cycle —O**&
N during other half of the alternation cycle
Capacitor in an AC motor circuit
A capacitor resists a change in voltage by storing an electrical charge that acts upon the
voltage as it changes direction. This opposition to voltage causes it to lag behind current
in an out-of-phase relationship. As a result, current leads voltage in a capacitive circuit.
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Again, voltage and current are not working together at all points in the cycle. This conflict
between voltage and current is put to advantage when the out-of-phase electrical supply from
the capacitor to the motor is employed to boost the magnetic field in one of the windings in
the motor allowing it to start or run easier.
Capacitors pose a significant safety hazard.
A capacitor will maintain its charge after the circuit has been deenergized. In some cases, a bleed resistor is visibly attached to
both terminals on the capacitor.
This resistor has no influence on the capacitor when it is
operating but will allow the plates to discharge at the end of
operation.
If a person touches a charged capacitor they will receive a severe shock. An electrical test
instrument that is connected to a “de-energized” circuit with a charged capacitor may be
destroyed by the discharge from the capacitor.
Care must be taken when working around motors with capacitors. The capacitor must be
discharged prior to working on any circuit that includes a capacitor. That discharge must be
restricted to prevent damage to the capacitor. Shorting the terminals with an insulated handle
screwdriver may damage the capacitor. A special function on some digital multimeters or a
20,000 Q 2-Watt resistor should be used.
The factors affecting alternating current are employed in our appliances to achieve useful
work. Understanding those factors allows us to interpret and troubleshoot problems that may
prevent that achievement of useful work. Theory and practical experience are a powerful
team if they function “in phase”. Allowing theory to lag practical experience (or vice versa)
usually results in a reduction in useful work.
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5.8.3 AC Power Distribution
Alternating current electricity is produced inside a power plant and then transferred
outside where it is boosted, by means of transformers, to very high voltages.
The neighbourhood transformer functions on the same principles as the transformers
found in our appliances as will be discussed in section 5.10.
The neighbourhood transformer on the hydro pole or surface box steps down the
4,800V transmission electricity to 240V single phase power for distribution to the
residences in the area. This transformer is “center grounded” for safety reasons and to
reduce electrical interference generated by a transformer.
Electrical power supply to electrical panel in residence
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The 240V supply is split between two busbars such that building circuits can be connected
to one or both supply lines. With a single fuse or breaker contacting one busbar 120 V is
supplied. If a doublewide fuse block or breaker is inserted, both busbars are connected
thus supplying 240V.
Some appliances such as stoves, dryers, etc. require 240V and are supplied through a
#12 or #10 AWG wire protected by a 20 or 30-amp fuse or breaker. Residential gas- fired
appliances must have their own dedicated 120V supply through a #14 AWG wire protected
by a 15-amp fuse or breaker.
Although G.3 certification does not allow the holder to change fuses or breakers in a panel,
it is crucial that you understand the wiring arrangement inside the panel.
As depicted below and on the previous page, the neutral wire from the center point of the
distribution transformer is grounded both outside at the pole and grounded inside through
the common neutral / ground busbars. The grounding rod attached to the electrical panel
is directly connected to the ground busbar which, in turn, is connected to the neutral
busbar.
The neutral wire (white) is the designated or controlled path home for electricity supplied
through the source wire (black). However, there are two alternate paths that can complete
the circuit between the transformer power wires and the transformer neutral wire. The
ground wire (green or bare) that accompanies the source and neutral is the preferred path
for any stray current but the physical ground (earth) is also an available path home.
Electrical panel, disconnect switch, and furnace motor wiring.
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The ground wire to the appliances and outlets in the building is never connected to the
electrical circuit. Its purpose is to serve as a safety outlet for electricity that strays from the
pathway consisting of the source and neutral lines through the loads.
In a junction box the ground wires must be connected together and screwed to the box. At
any junction with a component (switch, motor etc.), the ground wire must be connected to
the designated screw on the component and to the junction box.
To serve as a safety device, the ground wire must be continuous from the load back to the
panel. Any break in the line voids its safety value. The best way to check for a continuous
ground at any point in the circuit is to use a voltmeter with one lead on the source line and
the other on the ground wire. If the ground is proper a reading of applied voltage is given.
If the reading is zero, then you are either not connected to source or the ground wire is
broken. This test can also be conducted on the neutral line.
Never assume that a component is properly grounded until you test it. That a plug outlet
has a third slot for a ground prong does not mean that the connection is complete back to
the electrode driven into the ground outside. In the following two diagrams of short circuits
a slight “tingle" may be felt if you were to touch the grounded junction box on the left. A
severe shock would occur if you touch the ungrounded box on the right.
This section has introduced basic concepts about AC power. Knowledge of how AC
SHORT CIRCUIT.
energy is produced and distributed, why it works, and what safety features are in place if
it is not contained were the main points of the discussion. The more you know about it in
both theoretical and practical terms the safer and more efficient you will be.
The following two sections discuss electrical devices found in gas-fired appliances. You
SHORT CIRCUIT
will find the information presented in this section to be helpful for understanding how and
why those devices work and what the probable cause is if they do not work.
Common short circuits in electrical junction boxes
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NOTES:
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Electromagnetic Action
The conversion of mechanical and magnetic energy to electrical energy resulting in the
production of electricity can be reversed to create mechanical and magnetic energy from
electrical energy. This reverse process is known as electromagnetic action and it is
employed extensively in solenoid valves, relays, and motors used in gas-fired appliances.
In this section, we look at each of these uses individually to explain how electricity is
converted into mechanical and magnetic energy in valves, relays, and motors. In the latter
case, only the basic principles are introduced.
5.9.1 Solenoid Valves
As briefly discussed at numerous points in this text already, the flow of electrons through
a conductor creates a magnetic field around the conductor. The polarity of the magnetic
field depends upon the direction of the current flow while the strength of the magnetic field
depends on the intensity of the current.
Magnetic Lines
of Flux
U
Direction of current
Intensity of current
«—
Small Large ------------------------- >
।
1
▼
A magnetic field is created when current flows through a conductor
If the conductor is wound into a coil, the magnetic field becomes concentrated in the center
of the coil. A coil with ten turns of wire will produce a magnetic field that is ten times as
strong as the magnetic field around a single conductor.
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Magnetic field around one wire is increased and concentrated if wire is coiled.
The circuits illustrated appear to be dead shorts that would require low voltage and
current levels together with large size wires to prevent a dangerous overheating of the
conductor.
However, in a coiled AC circuit the alternation of voltage and current causes the magnetic
field to build and collapse around the wire 60 times per second. As the concentrated
magnetic lines of flux cut across the wires in the winding they induce a voltage into that
winding (as discussed in the last section).
In a properly designed induction coil this induced voltage is almost the same as the
applied voltage but is exerted in the opposite direction to the applied voltage. The induced
voltage acts to limit the applied or source voltage. The induced voltage is commonly called
back emf.
In a properly designed AC electromagnetic coil circuit, very little current will flow. There is
no short circuit due to the back emf. Current will only flow in the circuit wire if the magnetic
force that is limiting applied voltage is being used for another purpose and thus cannot
fully limit the applied voltage.
If an iron bar is partially inserted into the center of the coil of wire and voltage is applied
to the circuit, the electromagnetic force will be applied to the iron bar as well as the coil.
The magnetic force of attraction will pull and hold the magnetic bar into the center of the
coil. This is essentially what is happening with a solenoid valve.
If a spring is attached to the iron bar (or valve stem), it returns immediately to its original
position when the electricity is turned off to the coil and the magnetic field collapses.
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Electromagnetic field can pull an iron valve stem into Its center when activated.
This principle is used extensively in gas-fired appliances and accessory components such
as solenoid valves, zone control valves and boiler feed-water valves. The position of the
valve stem is often critical since the force required by the electromagnet and spring to
move the valve stem may be restricted by the force of gravity. Always position a solenoid
valve in accordance with manufacturer's instructions.
Two factors that affect the strength of the electromagnet are:
1. The intensity of the current in the coil.
2. The number of turns of wire in the coil.
Electromagnets are therefore rated in amp-turns. The greater the amps and/or the greater
the number of turns, the greater the strength of the electromagnet. The amp rating on a
solenoid valve is based on its designed amp-turns.
Failure to supply sufficient voltage to achieve the amp rating or a short in the coil resulting
in a reduction in the number of turns will result in a reduction in strength of the
electromagnet. The valve will either not operate or will chatter as the magnetic field builds
and collapses but does not have sufficient strength to overcome the spring or weight of the
valve stem.
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Occasionally the valve stem may fail to move due to a restriction in its travel path,
blockage at the valve seat or because the spring fails. Solenoid valves are nonrepairable
components so your role in assessing a problem is to determine if replacement will solve
the problem or just the symptom.
To make this assessment take a voltage reading on the activated valve to ensure proper
input - remember that a voltage drop less than the applied voltage indicates that another
load is in series with the valve. Fix the circuit and you’ll solve the problem; replace the
valve and you’ll only “solve” the symptom.
An ohmmeter reading can be taken across the coil to determine if there is continuity
throughout the winding or across the coil to valve body to determine if there is a short.
The power must be turned off during these tests.
Some solenoid valves have a delay action function incorporated into the valve or it may
be a function in the flame safeguard control’s circuit to the valve. A semi-conductor called
a thermistor is wired in series with the coil such that power is supplied through the
thermistor. A small current flow through the thermistor is not sufficient to activate the coil
but is sufficient to heat up the thermistor.
The resistance of a semi-conductor decreases with heat so after a short delay the
thermistor allows full application of voltage to the coil. Be aware that on short cycling of
the burner the thermistor may still be hot on the next call for heat and will not provide a
time delayed action.
ELECTROMAGNET
VALVE STEM
SPRING
SEAT
VALVE DISC
Solenoid valve
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5.9.2 Relays
The magnetic field generated by a coil can be intensified by coiling the wire around an iron
core. Iron is a magnetic conductor unlike air, so the magnetic lines of flux are intensified
in the iron core. The core becomes a very powerful magnet that can be turned on and off
with the flow of electricity to the coil.
Operation of an electromagnet in a normally open relay switch
Electromagnets are employed on gas-fired appliances to make and break switch contacts
in line-voltage circuits using low-voltage control wiring. The electromagnet attracts a metal
plate on the armature defeating the force of a spring that holds the armature in its normally
open or normally closed position.
An electromagnetic relay can make or break one or more connections depending on the
configuration of the armature and contacts. In some cases, the action of the relay may
break a connection and pull the same contact into connection with another circuit. Relays
are used in all older and some new flame safeguard controls. Most new flame safeguard
controls employ solid-state components or microprocessor circuits to do the work of relays.
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Fan Relay
Relays
Honeywell R8182A Flame Safeguard
Control and Aquastat
Examples of electromagnetic relay switches used in heating appliances
Relays are normally powered by the low voltage from the control transformer. Depending on
the manufacturer and use, the input voltage may be 9 VAC to 46 VAC. Smaller wires can be
employed in the relay coil. Employing low voltage for the thermostat and primary control
circuits increases safety and reduces the cost and size of control component.
Line voltage can be employed in an electromagnetic relay designed for the purpose. Line
voltage relays are much larger and are called contactors. They are just big relays.
All of the issues previously discussed about solenoid coils also apply to relay coils. Although
the core does not move in the relay, similar problems can be experienced with the movement
of the armature. The reduction of the magnetic field in the relay coil due to improper voltage
input or a shorted coil can result in chattering of the contacts - similar to valve chatter.
The most common problem related to relays is not in the electromagnet but rather in the
contacts. Dirty or corroded contacts will add resistance to the switched circuit resulting in
reduced voltage to the load. A relay is simply a switch so the easiest check for a problem in
the contacts is to measure the voltage drop across the closed switch - there should not be
any.
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in older style controls the relay contacts are open and can be visually
checked. A clean, thin cardboard (business card or match book cover)
can be drawn across the contacts to clean them.
In ladder wiring diagrams, the relay’s coil is shown in the low-voltage
circuit while the relay contacts are shown in both the low and linevoltage circuit. The relay coil will be designated by a number - CR1,
CR2 or simply 1K, 2K. A corresponding number such as 1K1, 1K2 will
designate the contacts that are controlled by a similarly numbered coil.
CR1
Normally open
Normally Closed Contacts
Wiring diagram symbols for a relay coil (left) and relay contacts (right)
Wiring diagrams show switch positions in the de-energized circuit so a switch is either
normally open (NO) or normally closed (NC). This is important to consider when reading a
diagram. A wiring diagram for an older flame safeguard control is given below for general
reference. Can you identify and interpret the location of the relay coil and contacts?
L2 L1
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5.9.3 Motors
Electric generators convert mechanical energy into electrical energy using magnetism.
Electric motors convert electric energy into mechanical energy using electromagnetism.
Electrical energy is converted into mechanical energy in order to create a rotating motion
to drive fans, pumps, and other devices in heating systems.
The following brief introduction to motors focuses on the basic principles of split-phase
AC induction motors commonly found on gas-fired appliances. Motor operation and
starting methods will be discussed. If and when you continue your training to the Gas
Technician 2 level, you will learn about other types of motors such as capacitor-start/
induction run motors and DC motors.
The operating principle of split-phase AC induction motors is based on the laws of
magnetism - like poles repel and unlike poles attract. If a magnet is mounted on a pivot
and placed between the poles of two magnets, mechanical energy will be created as the
pivoting magnet moves to align itself with the opposite poles of the permanent magnet
(Figure A below). Once aligned, the motion will stop (Figure B).
Figure A
Figure B
Magnetic energy converted to mechanical energy is the basic principle of electric
motors
If the stationary magnetic poles could be made to reverse just as the opposite poles come
into alignment, the pivoting magnet would continue to spin in an attempt to align with its
opposite pole. Essentially, this is the operation of an electric motor except that
electromagnets are employed for the stationary and pivoting magnets.
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Stationary electromagnets change polarity to maintain movement of rotating magnet.
The stationary electromagnet in the above motor is called a stator. The pivoting or rotating
magnet, which can also be an electromagnet, is called a rotor.
An electromagnet created by an alternating current reverses polarity 120 times per second.
Before the rotor can stop in alignment with the stator poles, the current in the stator windings
changes direction causing a change in the magnetic polarity. The momentum of the rotating
rotor will carry it pass the alignment position. The change in magnetic polarity causes the like
poles of the stator and rotor to repel each other and the rotating motion is maintained as long
as power is supplied.
Unfortunately, when the motor stops, the rotor and stator
may stop in alignment with each other as shown to the right.
When the power is turned on again, the magnetic force will
not be sufficient to start the movement of the rotor.
Starting the rotation of the rotor is a major problem with
single-phase electric motors. Not only due to the position of
the rotor but also because of the inertia of the load attached
to the motor shaft. It is always harder to start something
moving than it is to keep it moving.
Alignment makes motor start difficult
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If the rotor in the above diagram was turned slightly, the electromagnetic forces could act
upon it and keep it rotating. A second stationary electromagnet is added to motors for this
purpose. This second winding is called the start winding.
It may be powered continuously or, as is the case with most motors on gas-fired appliances,
it may only be powered for a short time at the start of motor operation. The main winding is
called the run winding.
Start Winding
Start windings take the rotor out of alignment with the run windings to start the
motor
This type of motor is called a split phase motor.
Two speeds are common. In 1725 RPM motors,
there are four electromagnetic poles for each of the
run and start windings. In 3425 RPM motors, there
are two Run poles each.
The wiring configuration shown In the diagram to
the right is for 1725 RPM. The run windings are
indicated by an “A”, the start windings by a “B” and
the rotor by a "C”. Notice that both drawings on this
page show there are more turns on the start
windings than on the run windings.
Wiring layout of a split-phase motor
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As the name split-phase motor suggests, the current phases of the start and run windings
are “split” i.e. out-of-phase with each other by 45° to 90°.
Start Winding
Run Winding
Voltage and current phases of start and run winding are out of alignment or phase.
The wires in the start winding are smaller and have more turns. This produces greater
resistance to flow in the start windings so the run windings generate a greater magnetic
field. This larger magnetic field acts upon the current in the run winding by induction causing
the current in the run winding to lag behind the current in the start winding.
During one half of the alternation cycle the start windings produce a greater magnetic field
while in the other half of the cycle the run windings produce a greater magnetic field. The
current phases of the two parallel wired windings is split to start the rotor turning and provide
more starting power.
Run Winding
Start Winding
Winding
locations
(top). Stator
and rotor (bottom)
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The rotor is constructed of copper and aluminum bars evenly spaced in steel on an iron core
and connected to the shaft by aluminum or copper end rings. The squirrel cage rotor as shown
at the bottom of the previous page is the most common design of rotor.
The rotor produces an induced magnetic field within itself when the stator is energized. The
polarity of the rotor’s magnetic field does not alternate. It is a constant polarity induced
electromagnet.
The force necessary to produce rotation is called torque. The starting torque for a motor is the
force necessary to overcome the Inertia of the rotor and the mechanical load attached to it the fan, fuel unit, water pump etc. This starting force is many times the force necessary to
maintain the rotor and load in motion.
To overcome this significant starting torque, additional electrical energy is required. If the
motor is properly sized for the load, this additional electrical energy is only required for a few
seconds. The start winding serves the purpose of delivering this added electrical energy in the
form of increased current to the motor during activation. If the motor only employs start and
run windings to overcome starting torque it is called a split phase resistance-start-inductionrun motor.
After the motor reaches appropriately 75% of its normal speed, a centrifugal switch on the
shaft opens the circuit to the start winding. The motor continues to operate on only the run
winding.
Direction spool travels when shaft
slows down
Direction spool travels when shaft
speeds up
Centrifugal switch on motor shaft opens contacts when motor is spinning at 75% rate
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Location and wiring of a centrifugal switch
If the centrifugal switch fails in the open position the motor may not start since the start
windings that provide the split phase drive are not powered. If the centrifugal switch fails
in the closed position the start windings stay powered throughout the motor operation. This
may cause the motor to “burn-out” because the magnetic fields of the start and run
windings conflict after the 75% rotational speed is reached.
It is worth mention here that there are basically three trouble spots in the split phase
resistance-start-induction-run motor: the bearings, the windings, and the centrifugal
switch.
Bearings wear with age and use. Some motors have permanently lubricated bearings that
require no maintenance while others require lubrication with light oil annually. Check the
manufacturer’s instructions and look for lubrication ports on the motor. A seized bearing is
easy to identify by turning the shaft by hand. It should turn easily.
Windings on a motor can be easily checked for faults using an ohmmeter. Remember to
disconnect the power prior to the tests. There should be a measurable resistance on each
of the start and run windings with the start wiring resistance being slightly higher. A
continuity test between each lead and the motor housing will indicate a short if continuity
is found.
The centrifugal switch only stays in the circuit for a short period of time so it is the most
difficult to troubleshoot. If the motor only starts when the shaft is rotated slightly by hand
or a loop of string attached like a lawn motor starter, then the centrifugal switch has failed
in the open position. The centrifugal switch can usually be heard when it drops closed after
the motor is shut off. A high current draw during operation indicates that the centrifugal
switch has not opened. Replacement of the switch or motor is required.
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One final issue related to induction motors before we leave this introduction to motors.
Many fan motors in forced air furnaces have multi-speed motor functions. Two to five
speeds may be selected by wiring configuration or remote switching devices to meet the
various demands for air circulation.
Low speed allows a minimal airflow through the air cleaner and for circulation. Medium
speeds (or medium low and medium high speeds) allow for setting the correct air velocity
for the heating operation cycle to match the installation. High speed usually serves the air
conditioning function of an “A” coil restriction in the plenum.
Each speed is a separate tap into the continuous run winding of the motor. As shown
below, the logic underlying the wiring configuration is quite simple:
• The longer the wire the greater the resistance
• The greater the resistance the lower the current flow
• The lower the current flow the lower the power
Wiring schematic of a multi-speed motor
The L1 location is set to the desired speed and may be controlled by a remote switch to
allow changes during heating/cooling operation or summer/winter settings. Comparative
resistance readings can be taken to determine which wire serves each function. The motor
tap with the lowest resistance will be the high speed and the one with the highest
resistance the lowest speed.
This brief introduction to solenoids, relays, and motors will be supplemented during your
field experience.
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5.10 Transformers
A transformer is a device used to transfer electrical power from one circuit to another
without the physical transfer of electrons. The circuits are magnetically not electrically
connected.
Transformers are employed extensively in AC circuits to isolate and change the voltage
and current from one circuit into another. Two transformers are commonly found on gasfired appliances: the ignition transformer and the control-wiring transformer. They serve
opposite purposes of increasing and decreasing the line voltage (120V AC) but share the
same underlying operating principles. A sound understanding of those principles is
necessary for safe and efficient installation and servicing of all transformers.
Various types of transformers found on gas fired
appliances.
As discussed in the previous section, a magnetic field is created when a current passes
through a wire. The polarity of the magnetic lines of flux depends upon which direction the
current is passing through the wire. With an alternating current, the magnetic field expands
creating a magnetic force with a given polarity (e.g. N-S) as the current in the wire rises to
its maximum strength. Then the field collapses as the current decreases to zero. The
alternating current then increases to its maximum in the opposite direction thus creating a
magnetic field with the opposite polarity (e.g. S-N).
This rising and falling of magnetic forces can act upon a separate wire by inducing a
voltage. If the source wire is coiled around a soft steel core, the magnetic induction is
concentrated and can act forcefully upon a separate coil of wire wrapped around the same
core.
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The source winding is called the primary winding while the induced current winding is
called the secondary winding.
Positive current créâtes maximum magnetic force and induction in one direction
Négative current créâtes maximum magnetic force and induction in opposite direction
Primary Winding Secondary Winding
Simplified drawing of a step-up transformer
This induced reaction cannot occur in straight DC circuits since there is no alternation of
the magnetic field. Exposing a secondary winding to the constant magnetic field created
by a DC supply would be like holding a conductor stationary in a magnetic field. No
magnetic lines of flux would cut across the conductor so no voltage or current would be
induced. However, a pulsating DC voltage can be employed in a transformer, as we will
discuss below in relation to electronic igniters.
With a 60 Hz AC supply the magnetic lines of flux are building and collapsing 120 times
per second causing the lines of flux to cut across the separate secondary winding. The
induced voltage and current are the opposite of that in the primary winding. As the primary
voltage and current peak at their maximum positive value the secondary voltage and
current will peak at their maximum negative value. The frequency of the primary circuit is
maintained in the secondary circuit.
Voltage and Current
in the
Primary Winding
_ —— ____ ________________________________________________ _____
Voltage and Current in the
Secondary Winding
Voltage and current are opposite in the induced circuit from a transformer.
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If the number of primary windings is the same as the number of secondary windings, the
secondary voltage is the same as the primary voltage. The advantage to this winding ratio
of 1 :1 (read 1 to 1) is that the secondary voltage and current are isolated from sudden
adverse changes in the primary voltage - such as power surges. Industrial equipment often
employs transformers to limit the effect of power surges.
If the number of windings is less on the primary winding than on the secondary winding,
as shown in illustration at the top of the previous page, then the voltage is increased on the
secondary winding. This is due to the greater current in the primary winding and the greater
surface area on the secondary winding that can be influenced by the magnetic field from
the primary winding.
In the same simplified illustration, there are 5 turns on the primary winding and 10 turns
on the secondary winding (normally there would be hundreds of turns). The ratio of primary
to secondary windings is 1 : 2. With a primary voltage of 120V the secondary voltage would
be 240V. This increase in voltage identifies it as a step-up transformer.
The following diagram shows the reverse ratio of 2 : 1 with 10 turns on the primary
winding and 5 on the secondary winding. This is known as a step-down transformer. In
this case with a primary voltage of 120V the secondary induced voltage would be 60V.
Primary Winding Secondary Winding
Simplified drawing of a step-down transformer
The wires used in transformers have a lacquer coating to insulate them from each other
and from a short to the soft steel core, which is usually grounded. Under high heat conditions
this lacquer coating may melt resulting in a short circuit. Transformers are commonly
insulated to protect against high heat and humidity. This is the purpose of the tar-like
compound found in ignition transformers.
The core is normally constructed of thin stamped soft-steel plates laminated together. The
laminations help reduce the influence of the magnetic field on the core and focus that
influence on the secondary winding.
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Various configurations are employed for the core. It is neither necessary nor common to
wrap the windings on opposite sides of a hollow block as shown in the above diagrams
for reasons of simplicity. Smaller transformers commonly wrap the primary over the
secondary windings around the same center core in a “shell type” transformer.
Shell type transformer.
Transformers are very efficient transfer devices. The power output is very close to the
power input. It is important to understand that the transformer does not create power - it
is not an electrical source. Given the transformer’s efficiency, a general rule governing
transformers is that power input is equal to power output.
Since power is a product of voltage times current this rule results in the following formula.
The results are given in Volt-Amps (VA) rather than watts to avoid the complications of
determining true power in an AC circuit:
Primary Voltage X Primary Current = Secondary Voltage X Secondary Current
For example, if the primary current is 1 amp to the step-down transformer depicted on the
last page, then the current in the secondary circuit could be determined by the simple
application of the formula.
120V Primary X 1 Amp Primary = 60V Secondary X ? Amp Secondary
120VA
60V
=
? Amp Secondary =
2 Amps Secondary
For a step-up transformer, this power equation means that given the voltage is increased
(stepped-up) on the secondary side, the current will be less in the secondary circuit
compared to the primary circuit. Less current means that the conductors on the secondary
circuit do not have to be as large as on the primary side. The large number of turns on the
secondary winding can be made with smaller diameter wire.
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Transformers are self-regulating devices. As current in the secondary winding changes,
the current in the primary circuit changes. If the secondary current stops due to an open
switch or broken secondary circuit, the primary current stops. The primary voltage induces
an opposing voltage in the iron core that effectively counteracts the primary voltage thus
stopping flow. The back emf from the primary coil regulates the current in the primary
winding.
Current only flows in the primary circuit when the primary voltage induces a voltage and
current in the secondary circuit. As such, current draw in the primary circuit depends upon
power consumption in the secondary circuit. As power (voltage X current) is consumed in
the secondary circuit, a proportional change in current flow will occur in the primary circuit.
Both circuits must be considered if the current is increased on the secondary circuit.
5.10.1 Ignition Transformers on Gas-fired Appliances
The ignition transformer used on most gas appliances is a step-up transformer. The ratio
of windings on an ignition transformer is approximately 1 : 50 resulting in an increase in
voltage from 120V primary to 6,000V secondary. This high voltage is necessary to
overcome the resistance to current flow across an air gap at the electrode tips.
Cutaway of an ignition transformer.
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The proper electrode gap poses a significant resistance to flow so the current draw on the
secondary side is only 23 milliamps (23/1000,h of an amp). However, if the gap is reduced
or the current finds an easier pathway to ground through a cracked or dirty insulator, the
current flow will be increased in both the primary and secondary circuits. Dangerous
overheating of the wires may occur.
As depicted on the previous page, the ignition transformer consists of one primary winding
of 120V and two secondary windings that each produces 3000V. The windings are
connected and grounded to the iron core, which in turn is grounded through the metal
casing and burner to the building ground wire.
This type of transformer is referred to as “mid-point grounded", since the secondary coils
are grounded. This grounding method eliminates interference with radio and TV signals
caused by high voltage arcing. If such interference occurs, it indicates a loss of ground or
faulty transformer.
Heat, humidity, corroded or loose contacts and improper electrode gap settings are the
major causes of problems with ignition transformers. The transformer casing is filled with
a tar-like substance to protect against the first two and it is important to check for the
contacts and electrode gap on every service call.
Checking the ignition transformer for proper operation is a simple and logical process
given an understanding of transformer functions.
1. Check the physical condition of the transformer, connections, and electrodes. Tar
leaking out of the casing, evidence of corrosion, cracking or stray arcing warrants
further investigation as to the cause along with possible replacement of the unit.
2. Check for proper line voltage input (a nominal 120V). Reduced input voltage below
105V usually indicates dirty or corroded contacts in the primary control circuit.
3. If you have a high voltage meter the actual voltage reading across the secondary
output terminals (6,000V) or across each terminal to ground (3000V) provides the
best indication of the transformer’s condition. A reading of less than 5000V with an
input of over 110V indicates a faulty transformer.
4. An ohmmeter test to determine the continuity of the three windings in the transformer
can also be conducted to determine the location of the fault as shown below. The
transformer must be disconnected from the power source for this test.
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Proper resistance readings taken on an ignition transformer
Most new appliances are replacing the iron core transformer with an integrated electronic
ignitor. These solid-state components convert the AC voltage into a rapid pulsating DC
voltage through a rectifier transistor. The frequency is changed from 60 Hz to 15,000 30,000Hz and sent through a small internal transformer. The secondary coil of this
specialized high frequency transformer produces a high voltage output of 8,000V to
17,500V depending on the manufacturer. Peak voltages can reach 30,000 VDC.
Iron core Transformer
Electronic ignitor
Output Voltage
Output Voltage
Output voltage graphs for iron core transformer and electronic igniter
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Electronic igniters have numerous advantages over the step-up transformer including:
•
Size - !4 to % as large
•
Weight - 1 lb. compared to 8 lb.
•
Output currents and peak voltages exceed that of an iron core transformer 8,000 VDC to 30,000 VDC
•
Less sensitive to line voltage fluctuations (functions even at 80V input)
•
Consumes less power - 45 watts compared to 300 watts
• Epoxy sealed in plastic enclosures for greater resistance to moisture
Standard iron core transformer (left) and new electronic igniters (right)
Like iron core transformers, electronic igniters must be grounded. To check for proper
grounding using an ohmmeter, follow these steps:
1.
Turn off the power to the burner.
2.
Check the ohmmeter resistance between the electrode terminal or cable and
the exposed metal of the burner (copper line or bolt - not painted metal).
3.
The resistance should be less than 2000 ohms. If the resistance is infinite, the
ignitor is not grounded.
4.
Check the resistance from the other electrode terminal or cable (if so equipped)
to ground. The two readings should not differ by more than 20% and should be
!6 of the terminal to terminal resistance.
Neither iron core transformers nor electronic igniters are repairable components. If they
fail the output tests or grounding tests but have the proper input, they are simply replaced.
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5.10.2 Control Transformers
Control transformers found inside flame safeguard controls, mounted separately, or in
auxiliary components such as humidifiers are step-down transformers. The 120V line
voltage is reduced to a nominal 24V normally although different manufacturers may
employ 9V to 50V.
The low voltage output of these transformers allows for the use of smaller wires and less
expensive control components. The safety advantages of employing lower voltage circuits
that are isolated from the main supply are also a prime concern.
The operation of these small transformers is usually assessed by determining whether the
proper input and output voltages are present at the terminals on the control. The
manufacturers often identify the output test terminals in their troubleshooting guides.
The primary control transformer supplies power to the relays through the thermostat and
safety control switches that activate the burner and ignition transformer. A failure of the
control transformer results in a stoppage of the complete burner circuit.
R8182H Combo Aquastat & Flame Safeguard Control
Examples of step-down transformers
The same principles and checks previously discussed for other transformers also apply to
control transformers. The input and output voltage tests are the most critical.
Newer controls often require the correct polarity for the output voltage from control
transformers. A simple voltage test from L1 on the primary side to one of the output wires
on the secondary side can quickly identify the “negative” or “source” output wire on the
secondary side. With reference to the diagram on the following page, the polarity test
consists of:
1. Determine which input wire is the L1 or source line. Do not depend on colour coding
- test for a voltage drop from the line to ground. Only the hot wire will show a 120V
drop.
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2. With the polarity-sensitive controls disconnected and power supplied to the
transformer, connect one lead from the voltmeter to L1 and the other lead to either
of the secondary output wires.
3. If the voltage reading is less than 120V you are connected to the negative or source
output wire. If the reading is more than 120V you are connected to the positive or
neutral output wire. The actual reading should be the difference or the sum of the
input and output voltages as shown below.
Pos.
Voltmeter tests to determine polarity of secondary output wires.
The above test must not be conducted on ignition transformers unless your meter is rated
for over 6,000V. If the test is conducted on a step-up transformer, the negative secondary
wire will indicate a higher voltage reading than the positive wire.
On ladder wiring diagrams, the symbol for a
transformer is as shown in the diagram to the
right. The above diagrams showing more
windings on one side are provided for
illustrative purposes only. If polarity is important
for the secondary circuit, the negative pole will
be indicated by a dot.
24 VAC
Symbol for a transformer
The VA rating (volt-amp) of a step-down transformer is important to consider when
replacing a separately mounted transformer. The lower the VA rating the lower the current
available in the secondary circuit. The VA rating is largely dependent on the wire size in
the transformer.
In most cases, following the appliance manufacturer’s requirements for the replacement
transformer is all that is required.
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5.11 Code Requirements Related to Electrical Work
The intent of this training course is to help you gain the knowledge, ability, and authority
(in the form of a certificate of qualification) to work on gas-fired appliances. With that ability
and authority comes responsibility to comply with the rules governing that work.
Here, the focus is on the rules governing electrical work. The text presentation is a
framework for a classroom discussion of the documents with some requirements
highlighted. It is not a complete list of the rules related to electrical work. The intent is as
much to inform you about the types of requirements and where to find them as it is to
infornryou about specific rules. Reference to the origin documents is required.
There are five sets of “rule books” that establish the minimum standards that we must
comply with when working on electrical circuits. They were created by industry to
standardize and regulate the industry to ensure safe practices and installations. In large
part, the rules were created in response to unsafe conditions and accidents. As such they
are instructional as well as mandatory requirements. Those rule books are the:
•
•
•
•
•
Fuel Industry Certificates Regulation
B149 Gas Codes
Standards accepted by the above Code concerning electrical components
on appliances and their installation
Manufacturer's certified installation instructions
Ontario Electrical Code
5.11.1 Certificates Regulation
For your own safety, the safety of your co-workers and customers as well as for reasons
of liability, it is essential that you comply with the limitation of your certificate of qualification.
Certain qualifications allow you to conduct a limited set of activities involving electrical
functions of an appliance. The applicable sections are as follows:
4. Maintain, service or replace a mechanical or electrical component or accessory that
forms part of an appliance or that is essential to the operation of the appliance.
5. Perform such tasks as are necessary to replace controls and components that form
part of an appliance.
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6. Install, service, remove or replace components and accessories that form part of the
gas-side of a refrigerating or air-conditioning unit, but the person shall not perform any
work beyond the gas-side unless he or she is the holder of a certificate of qualification as
a refrigeration and air-conditioning mechanic issued under the Trades Qualification and
Apprenticeship Act.
7. Install, repair, service and maintain electrical wiring from an existing branch circuit
containing overcurrent protection to appliances in order to exchange, service, repair or
install an approved appliance and carry out the replacement of electrical wiring necessary
to complete the reconnection or installation of controls, control systems, components and
accessories that are essential to the operation of the appliance, but the person shall not
run wiring back to the electrical supply panel or perform any additional wiring unless he or
she is also the holder of a valid certificate of qualification as an electrician issued under
the Trades Qualification and Apprenticeship Act.
Continued training in the field under the supervision of an electrician should be
supplemented by self-study and manufacturer-specific training on electrical components.
Your Gas Technician certificate gives you limited authority to work on electrical circuits; it
is your responsibility to ensure that your abilities match the work undertaken.
5.11.2 B149 Codes
All three B149 Codes require compliance with the Ontario Electrical Code as paraphrased
below from the B149.1. Refer directly to these clauses in the code.
5.11.3 Electrical Connections and Components
4.7.1
Compliance with the Ontario Electrical Code is required.
4.7.2 The appliance wiring for the gas valve, operating control, safety limit control, or
associated electrical device shall comply with the approved appliance wiring diagram.
Although many of the specific code requirements related to electrical work will be
highlighted in future training courses where they are applicable, it is worth noting some of
these requirements here. The following paraphrased clause appears in the B149.1. Refer
directly to the Code.:
6.14.6 Piping or tubing shall not be used for an electrical ground except for a low voltage
control circuit such as an ignition circuit or flame detection device circuit forming part of an
appliance.
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The B149.3 Code provides the following important clause as paraphrased below. Refer
directly to the Code.
6.14.7 Each safety control circuit shall be an isolated two-wire single-phase circuit of
not more than 120 V. One side shall be grounded and all breaking contacts shall be in
the power side - not the neutral side.
5.11.3 Standards and Manufacturer’s Certified Installation Instructions
A key safety requirement related to electrical work on appliances is to comply with the
wiring diagram that comes with the appliance. Those diagrams and the electrical
requirements in the manufacturer’s instructions form the basis for the approval
requirements set by the Standards for that particular type of appliance.
Our role as technicians is to respect the requirements placed on manufacturers by
Standards and only install equipment that has been built to and tested to those
Standards. Labels are the easiest means of ensuring compliance with Standards. Always
look for a CSA or equivalent label on electrical components.
Specific requirements from the Standards and manufacturer's instructions that are
applicable to electrical work will be addressed in during your G.2 training session.
5.11.4 Ontario Electrical Code
The vast majority of electrical installation work supplying power to
gas appliances will be conducted by qualified electricians who will
apply the Ontario Electrical Code as required.
All electrical installations and modifications to electrical systems
are subject to the approval of the inspection authority - the
Electrical Safety Authority (ESA). This private not-for-profit
company was formed in 1999 with the privatization of Ontario
Hydro’s Inspection Department. It is similar to TSSA that regulates
the gas industry.
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It is the responsibility of the company carrying out the work on building electrical systems
to:
1.
Notify ESA of the impending work. This initially requires a phone call in most areas
to the local office of ESA - they will send out an application. Completion and
submission of the application meets this requirement. In some pre-authorized cases,
notification only has to be by phone.
2.
Post the permit issued by ESA at the work site and keep it posted throughout the
time that the work is underway. In some pre-authorized cases, no physical permit is
issued - check with ESA for details.
3.
Comply with Inspector’s requirements resulting from an inspection. Not all
permitted worksites are inspected. However, there are hundreds of ESA inspectors
in the province so the likelihood of being inspected is high.
Local municipalities as well as your place of employment may have additional notification
and inspection requirements for electrical work. It Is recommended that you become
familiar with the permit and inspection requirements in your area.
Compliance with the Electrical Code is required whether you know the specific
requirements or not. Ignorance is no excuse before the law. A full discussion of even
the applicable sections of the Code would take a week-long course in itself. A few
important sections are listed below with the intent of highlighting specific requirements
and to give you a sense of what Information is available in the Electrical Code.
The Electrical Code is a detailed technical document that addresses all electrical
installations. There are sections focused directly on heating appliances but most the
requirements are arranged under general headings such as Wiring Methods, Fuses,
Transformers etc.
The Code should be available at your place of work for easy access but, failing that, the
local library will have a copy. Review it regularly. The following requirements are
paraphrased from the 27th Edition of the Ontario Electrical Code 2018. Direct reference to
the Code is required:
Section 2 This general section outlines the permit and inspection requirements and
powers. The requirements for equipment approval and labeling are
specified. Some individual clauses are worth highlighting:
2-032 It is the responsibility of the person carrying out any repairs involving electrical
components to ensure that the electrical installation is left in a safe
operating condition.
2-122 Electrical equipment shall be so installed as to ensure ready access to equipment
nameplates and parts that require maintenance.
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2-128
Openings made for electrical wiring through a fire stop shall not create a
potential fire-spread problem.
2-136
Wire installations, when completed, shall have no short circuits.
2-200/2
Guarding of electrical equipment is required. Any bare wires or terminals
must be in approved cabinets or enclosures.
2-300
Electrical equipment shall be maintained in a safe condition or permanently
disconnected.
2-304
Lock-out requirements are specified in this clause.
2-308
The minimum allowed working space around electrical equipment is specified
in this clause. Generally, 1 meter (3 feet) clearance is required.
Section 4
This section on Conductors gives valuable information as well as setting
minimum requirements for conductor size, current ratings, types of insulation
and allowable locations and use. Special requirements apply to conductors
in a raceway - the number and total ampacity of conductors in a conduit or
raceway are limited by the Code.
4-010
Flexible cord shall not be smaller than No. 18 AWG copper. Some
exemptions apply but this is a reasonable requirement for Gas Technician
uses.
4-032
The colour coding of conductors is given in this clause. See page 5-62 of this
Module.
Section 8
Section 10
10-506
This section entitled Circuit Loading and Demand Factors requires
calculation of the voltage and current demands of a branch circuit.
Entitled Grounding and Bonding, this section is very specific about grounding
requirements. As with the rest of the Code different requirements apply to
high voltage circuits (>750V), low-voltage circuits (750V to 30V), and extra
low-voltage circuits (< 30V). The intent and purpose of grounding are outlined
in 10-002.
Bonding conductors must be continuous with no switches.
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10-700/-708 Metal water piping and gas piping shall be bonded to ground using at least
No. 6 AWG copper conductor or No. 4 AWG aluminum conductor.
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Section 12 This section on Wiring Methods is full of helpful information on allowable
installation and jointing methods.
12-012 Underground wiring specifications are given in this clause including depth of
coverage and types of conductors.
12-118 Requirements specific to terminating and joining aluminum wires are given in this
clause. These include: using an anti-oxide compound on all stranded
aluminum conductors; only one conductor per screw terminal connection
is allowed unless approved connectors are used.
12-208 Open wiring shall be supported at least every 1.5 m (5').
12-500 to 526 These clauses deal specifically with non-metallic cable, which is
commonly used in gas installations. Requirements include:
• NM cable must not to be used in buildings that are required to be noncombustible;
• A separate hole shall be used for each cable entering a junction box;
• 1" clearance is required between cable and heating ducts or pipes;
• Shall not be stapled on its edge;
• Shall be supported at intervals of 5’ and within T from junction box;
• Shall be recessed at least 1%" when installed in concealed locations;
• Only one conductor per screw terminal is permitted unless approved
connectors are used.
12-600 to 618 Requirements specific to armoured cable, which is commonly used for
final connection to appliances, include:
• Aluminum armoured cable shall not be embedded in concrete;
• Continuity of metal sheathing is required - mechanical and electrical
joining is required at every junction box;
• Bends in aluminum cable shall have a radius at least 6 times the
diameter of the cable.
12-3000 Requirements are provided concerning installation of electrical boxes, cabinets,
outlets, and terminal fittings are very specific as to the types and installation
methods.
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Section 14
Overcurrent protection device requirements are given in this Protection and
Control section. For residential heating equipment, compliance with this
section is easily achieved by using an approved 15-amp fused circuit of No.
14 AWG conductor dedicated to the heating appliance.
Section 26
Entitled Installation of Electrical Equipment, this section has numerous subsections directly applicable to Gas Technician work including: Capacitors,
Transformers, and Heating Equipment. Items worthy of note in the latter
sub-section include:
26-802
All conductors within 1.5 m (5') of the floor shall be protected from
mechanical injury.
26-806
A suitable disconnecting means shall be provided for the branch circuit to
the heating unit. This switch must not be located on the furnace nor in a
location that requires passing close to the furnace. The switch shall be
clearly marked to indicate the equipment it controls.
26-808
One dedicated branch circuit shall supply power to the heating unit and
associated equipment. This branch circuit shall not be used for any other
purpose. However, equipment such as circulating pumps that are not
essential for the safe operation of the heating unit can be supplied by a
separate circuit.
Section 28
This section on Motors lists requirements on wiring methods, overload and
overheating protection and permitted locations.
The Electrical Code is approximately five times the size of the Gas Code so to condense it
would not do it justice. The Code book is doubled in size by the tables and appendices that
provide valuable technical information.
Hopefully, this brief presentation has sparked your interest enough to make you review the
codes directly. They contain valuable information gained from the “school of hard knocks”.
Like history books, Codes are boring to read if your imagination is not used. If we don’t read
and learn from them, we are condemned to repeat foolish mistakes.
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NOTES:
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5.12 Electrical Safety
There are three basic rules to successfully working with electricity.
1. Prepare a safe worksite
2. Conduct the work safely
3. Leave the worksite in a safe condition.
Safety is the first priority. Electrical safety is achieved by means of a proper safety attitude
and work practices.
Safety is of utmost importance to technicians and to our customers as well. Safe work
practices must always be followed. Workplace safety legislation is in place to ensure the
safety of workers and the public. In all cases, SAFETY MUST COME FIRST.
Electricity is energy in motion. Confined, controlled and respected, electricity is a safe form
of energy. Electrical energy can work for or against us only if it has a pathway to travel
from the source of the electrical force back to the source or to ground.
Metal objects and wires are the most common pathways but any wet object has enough
minerals in the water to provide a pathway if sufficient electrical energy is supplied. The
human body is 80% water and, especially when the skin is wet, will provide a pathway if
there is not an easier pathway.
Electrical energy can pass for short distances through air. When it does, the arc and flash
can cause burns, fires, and even explosions. Burns resulting from electrical arcs, such as
in a short circuit to ground, can be extensive and deep. More serious ones can even result
in amputation of the affected limb. Even small releases of electrical energy can have
serious health effects.
A shock occurs when the person becomes part of an electrical circuit. Electric current is
flowing through the person to the rest of the circuit, which may be a short circuit to ground.
The severity of the shock depends on 6 factors:
•
Amount of current
•
Path of travel through the body
•
Condition of the skin
•
Type of voltage AC or DC
•
Amount of voltage (higher is not necessarily worse)
•
Time duration of the shock
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Current level is the most important factor. As the diagram on the following page illustrates,
very low current levels well below one ampere can kill a person. The actual level
depends on the same factors that affect current flow in a circuit.
The amount of resistance in the pathway is determined by the travel path and condition of
the skin. The higher the resistance the lower the flow. From ear to ear, the resistance may
be as low as 100 ohms compared to 500 ohms from hand to foot. Dry skin can offer
resistance levels in the hundreds of thousands of ohms while wet, salty, or damaged skin
(cuts, abrasions) can lower the resistance to less than 50 ohms.
The most dangerous travel paths are those that pass through a person’s heart. A relatively
minor shock along the hand to hand pathway can send the heart muscles into spasms.
Surprisingly, victims of high voltage shocks respond better to resuscitation because high
voltage stops the heart while shocks of less than a 120V cause the heart to twitch
uncontrollably.
The electrician’s “rule-of-thumb” is to keep one hand in your pocket to prevent a hand to
hand shock.
On an equal voltage level comparison, direct current (DC) electricity is much more
dangerous than alternating current (AC) electricity. DC voltage and current is constant
while AC voltage and current rises and falls as it alternates.
The voltage level does matter. The higher the voltage applied against the resistance of
the skin, the greater the current. In addition, skin’s resistance decreases with voltage
increase.
The duration of the shock also influences the severity of the damage. The longer the shock
continues, the greater the damage.
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Danger
Less Than 1 Amp Can Kill
1000
1 Ampere
900
800
Required to operate a 100 Watt light
bulb
700
600
500
400
Risk of burns, severity of
which increases with
strength of current
300 Breathing stops
2001
100 > Normal pumping
90
of heart can stop
80 J
70
60
50
Breathing very difficult
suffocation possible
40
30 ----------- Severe shock
Muscle contractions.
20
"1
Breathing difficulty
begins
J
Cannot let go
10
9
8
Painful shock
7
6
_ _ —Trip setting for Ground Fault
5
Interrupter protection
4
3
2
Mild shock
1
1/1000’h of an amp
0
Effects of current levels on the human body
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A sound understanding of electricity is necessary to anticipate and avoid electrical shocks
and burns. If you are not comfortable In your understanding of electricity and electrical
safety, work with an electrician or ask for assistance. A few fundamental safety concerns
are raised below.
1.
Electricity will always follow the easiest pathway to ground; never allow that pathway
to be your body.
2.
Wear protective clothing for electrical work - including safety glasses, electrical
resistance rated safety boots (look for the Q tag), and, when working in an electrical
panel or on high voltage circuits, electrical rated rubber gloves.
All jewelry, watches, and metal objects in your pockets must be removed. Long
sleeve, fire-resistant shirts are recommended. All protective clothing must be kept in
good condition. An insulating mat may also be warranted.
3.
Most importantly, NEVER WORK AROUND LIVE ELECTRICAL CIRCUITS
WHEN YOU OR THE WORKPLACE ARE WET.
4.
Use the proper hand tools and power tools for the job and
maintain your tools in good condition.
o Use hand tools with insulated handles or grips when working on
electrical components. Specialty hand tools like insulated fuse
pullers are recommended.
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Basic Electricity
o Use grounded plugs or double insulated power tools that do not have
cracked casings. A portable Ground Fault Circuit Interrupter (GFCI)
outlet, as shown to the right, can detect a small current leak to
ground.
o Use the correct wire gauge for extension cords (14-gauge light use; 12gauge heavy use) to prevent overheating. Lamp cord (16 gauge)
should never be used. Protect cords from traffic, heat, or accidental
contact with power tools.
WHi
<V
o Never pick up a power tool by its cord or pull the plug from the outlet by
the cord.
o A tool or equipment that gives you a shock or tingle
should be immediately checked and repaired.
o Bulbs for temporary lighting should be protected from
damage in a bulb cage.
5.
Use a CSA approved meter rated for the application. For Gas Technician
work, a CAT III rating with a minimum working voltage (AC & DC) of 1000V
is recommended. Select a meter that can measure microamps. The
following graphic and tables identify the 4 categories.
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Basic Electricity
Category
CAT IV
CAT III
CATH
Module 5
Multimeter Categories and Uses
Examples of Uses
o Where connection is made to the utility power source
o Electrical meters, primary overcurrent protection equipment
o Outside the building and service entrance, service drop from the pole to building, run
between the meter and panel.
o Overhead line to detached building, underground line to well pump.
o Equipment in fixed installations such as switchgear and three phase motors o Bus and
feeder in industrial plants
o Feeder and short branch circuits, distribution panel services
o Lighting systems in larger buildings
o Appliance outlets with short connections to service entrance
o Appliance, portable tools, and other household and similar loads
o Receptacle outlets and long branch circuits
o Outlets at more than 30’ (10m) from CAT III source.
o Outlets more than 60’ (20m) from CAT IV source.
o Protected electronic equipment
o Equipment connected to source circuits in which measures are taken to limit transient
voltages to an appropriately low level
oAny high-voltage, low-energy source derived from a high-winding resistance transformer
such as a high-voltage section of a copier
CATI
Working Voltage de
or ac-rms to ground
CATI
CATI
CAT II
CATH
CAT III
CAT HI
CAT IV
6.
Gas Technician 3
Peak Impulse Transient (20 Test Source Ohms=
Repetitions)
V/A
600V
2500V
30 ohms source
1000V
4000V
30 ohms source
600V
4000V
12 ohms source
1000V
6000V
12 ohms source
600V
6000V
2 ohms source
1000V
8000V
2 ohms source
600V
8000V
2 ohms source
Treat all electrical wires and equipment as live until you test them and prove
otherwise. NEVER ASSUME that the disconnect switch is on the hot line. Higher
voltages (240V and above) and three phase circuits require tests to be conducted
between each leg of the circuit as well as from each leg to ground to ensure that the
circuit is de-energized.
DANGER
DO NOT on
ENERGIZE
OR
While work- proceeds
this system,
it OPERATE
has been 0
temporarily shut down.
7. At worksites where numerous trades are working or
anytime that a remote electrical switch could energize the
system that you are working on, the electrical switch should
be locked off and tagged.
Date:
Worker
Time:,
Employer
Front and back
The affected worker must retain the key. Tag must
identify the date, time, worker, and employer.
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Basic Electricity
8.
When working on electrical equipment, always observe the precautions in the service
literature, on tags, and on labels attached to or shipped with the unit. Perform all work
to meet the Ontario Electrical Code.
9.
If you must perform a test with power applied:
10.
o
Have only one hand in the unit.
o
Avoid working in poor light or when tired.
o
Unless required by the manufacturer's service procedure, do not bypass safety
devices such as a door interlock switch.
o
Make sure all grounds are connected properly.
Prior to drilling or cutting into a wall, ceiling, etc., check for indications of electrical
wires in the area.
5.12.1 Lockout/Tagout Procedures
In many commercial/industrial establishments there are detailed lockout and tagout
procedures which must be followed before beginning certain types of work on any
equipment. Become familiar with these procedures and follow them.
In some cases during normal appliance servicing procedures, you must have electrical
power to the appliance in order to diagnose problems. The following lockout / tagout
information only applies to situations where it would be dangerous for the equipment to
operate while it was being worked on. Cleaning of the air circulating blower on a forced air
furnace is one an example of this.
WORKING ON
EQUIPMENT DO
NOT START
SA MF
O*TE
COMAPNY NAME
STREET ADDRESS
CITY POSTAL CODE
TELEPHONE NUMBER
Your tool pouch should include a padlock and a lockout strip which you will use to lock an
electrical switch in the OFF position while the equipment is being worked on.
The lockout strip allows other workers to secure their locks to the switch at the same time.
The technician who puts a lock on a disconnect switch must be the only person with a key
to unlock it.
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Module 5
Gas Technician 3
When working on an appliance, shut off all energy supplies; tag and lockout both the gas
and electrical power. Attach a tag to any valve that must remain off during service to notify
others to check with you before attempting to restart the equipment. In some
circumstances, it may even be necessary to open a circuit breaker or remove a fuse and
then lock the electrical panel to ensure the circuits are not energized.
Unlike smaller residential equipment, the electrical panel at commercial/industrial sites
may have electrical power fed and controlled by SEVERAL sources. Use your multimeter
to verify that circuits are de-energized before reaching into the panel. Look at the electrical
schematic and verify all circuit and switch locations.
It cannot be emphasized too strongly that you should never "jumper" or
permanently remove any interlock or control in the system.
Limits and interlocks are there for a purpose -- to ensure safe operation.
Removing or disabling any safety control compromises that purpose.
Your first priority should be safety, with your second priority being the
re-activation of the appliance.
5.12.2 Responding to Electrical Emergencies
Current levels as low as 20 mA (20/1000ths of an amp) can make it impossible for the
shock victim to let go of the contact. If a co-worker is experiencing a shock, you must act
quickly to reduce the duration of the shock. The longer the duration of even a mild shock,
the greater the damage to the victim. If you touch the person - even a quick push - you
risk become a victim as well.
An emergency action plan must be in your mind already to act
with the required speed. A suggested action plan is as follows.
Make it your own by thinking it through and understanding the
logic of each step.
1. Disconnect the power if possible.
2. If disconnection is impractical, break the contact between
the victim and the source by using a dry board, rubber
hose, or dry polypropylene rope to move either the victim
or the energy source. If you don't know the voltage, treat
it as high voltage.
Be aware that wet insulators become conductors. With
sufficient voltage, electricity can arc across considerable
gaps. Stay well back from the victim if high voltage is
suspected.
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Basic Electricity
3. If the victim has stopped breathing, start artificial respiration at once. The victim’s heart
may be twitching but still working to pump some blood. Artificial respiration may have
to continue for hours under these conditions. If the victim's heart stops and you have
had the foresight to learn CPR, employ your skills.
4. As soon as possible send someone for help. Know
the numbers for your local emergency response
services.
5. Keep the victim warm to prevent physical shock from
setting in.
Pre-planning is the key to successful emergency response. Emergency procedures and
training should be available at your place of work. Learn and apply them.
Any workplace accident must be reported to the Ministry of Labour. The accident site must
be secured until the Labour inspector completes the investigation.
5.12.3 Electrical Fire Hazards
Fire is always a possibility when working with electrical circuits and equipment because
the potential energy in electricity can result in extreme heat transfer. At all times, the
technician should ensure his or her own personal safety.
In the event of an electrical fire:
1. IF IT IS SAFE TO DO SO, de-energize the electrical circuit.
2. Call the fire department or site authority.
3. IF IT IS SAFE TO DO SO, attempt to extinguish or control the fire.
Water or other conductive fluids must not be used on electrical fires. Only
carbon dioxide (CO;) or Class “C" dry chemical extinguishers should be
used. Class “C” extinguishers are indicated with a white letter C inside a
blue circle.
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Basic Electricity
Module 5
Gas Technician 3
SUMMARY
The length of this Module is an indication of the importance of electrical skills required of Gas
Technicians.
That a considerable amount of information has been covered is an indication of the diversity
of electrical energy. This is a basic course. Your continued training and work experience will
build upon the foundation laid here.
There is no value in memorizing the theories or the practical tips. “Memory workers” have to
work unsafely and inefficiently. They are blindfolded. They cannot see the signs in front of
them. Those signs may say stop - clanger! or they may say proceed to the next step. If they
don’t see the first sign, someone will get hurt. If they don’t see the ‘proceed sign’ then they
fix a symptom of a problem but not the problem itself. This latter mistake hurts the customer
and the industry.
Do not try to memorize the information presented in this training session. Do not become
discouraged by the apparent complexity or shear volume of the information. Understanding
takes time and field experience to develop. Apply the theories; use the knowledge gained
from this program and your instructor. Make the theories your own through practice.
Life is a lot safer, easier, and more enjoyable when you are in control.
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Module 5
Basic Electricity
REVIEW QUESTIONS
MODULE 5
BASIC ELECTRICITY
Questions #1 to #5 refer to Section 5.1 The Energy of the Atom
1.
The “Law of Electrical Charges” is:
a)
Protons are negatively charged electrical particles.
b)
Neutrons are positively charged electrical particles.
ci
Opposite charges attract each other; Like charges repel one another.
a)) Like charges attract each other; Opposite charges repel one another.
2.
State the defining difference between direct current electricity (DC) and
alternating current electricity (AC).
____ l>!L_^!i£lii-Jr4>i^!LtL^hi-^^L£L_J^
.^£tyi±ckiiy^y!\jtttfdaji!^^
Electricity can be defined as the movement of atoms.
3.
TRUE
FALSE
4. Electrical current (or the flow of electrons) in a wire may cause:
a)
b)
Friction and therefore heat in the wire.
The opposite electrical charge to be induced in another material.
A magnetic field around the wire.
All of the listed choices.
5. Materials that easily conduct electricity are called:
a)
d)
6.
insulators
conductors
grounds
ions
Materials that do not easily conduct electricity are called:
c)
d)
insulators
conductors
grounds
ions
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Module 5
Gas Technician 3
Questions #7 to #13 refer to Section 5.2 The Electrical Pathway
7.
Which of the following conditions will allow electricity to flow through a circuit?
a) An open switch
8.
Which of the following materials will allow the greatest electrical flow given the
same applied voltage?
a)
b)
c)
d)
9.
Silver
Aluminum
Copper
Ground
For electricity to flow through a wiring system there must be:
a)
b)
c)
d)
10.
b) A closed switch
a difference in electricalpressure between two connected points
a continuous pathway between the two points of flow
a circuit made of conductingmaterial
all of the listed choices.
Define the following terms and give at least one example of each.
Co nd u ctor: ____________________________________________________
I nsulator: ______________________________________________________
11.
Given the same applied electrical pressure, more electrical current will flow though:
(circle one of each of the following pairs)
a)
b)
c)
d)
12.
A hot wire
A conductor
A thin wire
A long wire
or
or
or
or
a cold wire
an insulator
a thick wire
a short wire
Define the following terms and give at least one example of each.
Conductance: _____________________
Resistance: _____________________________________________________
13.
There are no perfect electrical conductors or insulators.
TRUE FALSE
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Module 5
Basic Electricity
Questions #14 to #21 refer to Section 5.3 Electrical Terms and Relationships
14.
Electromotive force or emf is another term for:
a)
b)
c)
d)
15.
The voltage reading across an open switch of an energized electrical circuit should
be:
a)
b)
c)
d)
16.
Voltage
Current
Resistance
Electricity
applied current
applied voltage
zero volts
zero ohms
The voltage reading across a closed switch of an energized electrical circuit should
be zero volts.
FALSE
TRUE
17.
Which of the following tests on an energized circuit will give a reading of applied
voltage?
a)
b)
c)
d)
18.
An ampere is a unit for the measurement of:
a)
b)
c)
d)
19.
Electrical pressure
Electrical current
Electrical resistance
All of the listed choices
Electrical current is measured in:
a)
b)
c)
d)
20.
Across an open switch
Across a load
Across an energized line before the load and the return point of the source
All of the listed choices
volts
amps
ohms
watts
Electrical potential is measured in:
a)
b)
c)
d)
volts
amps
ohms
watts
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Basic Electricity
21.
Module 5
Gas Technician 3
Electrical resistance is measured in:
a)
b)
c)
d)
volts
amps
ohms
watts
Questions #22 to #34 refer to Section 5.4 Tools of Electrical Measurement
22.
When checking to determine an unknown supply voltage with an analog meter having
ranges of 0 - 50 volts, 0 - 200 volts, 0 - 600 volts, and 0 - 1000 volts, which range should
be selected?
a)
b)
c)
d)
23.
When it has been determined that the voltage to a unit is approximately 120 volts, which
range should an analog voltmeter be set at?
a)
b)
c)
d)
24.
ammeter
ohmmeter
voltmeter
power meter
Which meter is used to check for electrical continuity?
a)
b)
c)
d)
26.
0 - 30 V
0 - 250 V
0 - 600 V
0 - 1000 V
Which meter is used to check for electrical potential?
a)
b)
c)
d)
25.
0 - 50 V
0 - 200 V
0 - 600 V
0 -1000 V
ammeter
ohmmeter
voltmeter
power meter
When checking an electrical circuit with an ohmmeter meter, a reading of "OL” or “»”
indicates:
a)
b)
c)
d)
no resistance
a measurable resistance
closed circuit
open circuit
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Gas Technician 3
40.
Module 5 Basic Electricity
The ohmmeter reading across a blown fuse that is removed from the circuit, will be:
a) 0 volts b) 0 ohms c) 0 amps d) Infinity
41.
Match the following wiring schematic symbols for listed types of conductors. Draw lines
connecting the matches.
a) Connected wires
b) Not connected wires (crossover)
c) Field wired
d) Factory wired
42.
Define the following electrical terms and give one example for each.
Short Circuit:
Overload:
43.
A badly burned or charred fuse indicates:
a)
b)
c)
d)
44.
_____ ___
A short circuit.
Insufficient current.
An overload.
A good fuse.
A voltage drop never occurs across a switch.
TRUE FALSE
Basic Electricity
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Basic Electricity
45.
46.
Gas Technician 3
State the full names of the four types of electrical switches abbreviated below.
a)
DPST:.
b)
SPST:, ________________________________________
c)
DPDT: ________________________________________
d)
DPDT: _
____________
________
The line connection terminals on a 120-volt receptacle are:
a)
b)
c)
d)
47.
Module 5
green
gold
silver
black
the neutral connection terminals on a 120-volt receptacle are:
a)
b)
c)
d)
green
gold
silver
black
Questions #48 to #57 refer to Section 5.6 Ohm’s Law and Watt’s Law
48.
Ohm’s law is employed in electrical work to:
a)
b)
c)
d)
49.
Ohm’s law states:
a)
b)
c)
d)
50.
Determine the resistance of a circuit if the voltage and current are known,
Determine the voltage of a circuit if the resistance and current are known,
Determine the current of a circuit if the resistance andvoltage are known,
All of the listed choices.
Opposite charges attract and like charges repel
It takes one volt to push one amp through one ohm.
Resistance determines the applied voltage
Increasing voltage will increase resistance
If voltage is increased in a simple circuit, current will:
a)
b)
c)
d)
Increase
Decrease
Stay the same
Fluctuate.
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51.
Given a constant supply voltage, if resistance increases in a simple circuit, current will:
a)
b)
c)
d)
52.
An increase in resistance
A decrease in resistance
Back emf from a solenoid coil
All of the above
One watt equals Btuh.
a)
b)
c)
d)
57.
Current can be increased.
Resistance can be decreased
Voltage can be increased.
All of the listed choices.
If voltage is constant, what could cause current to increase?
a)
b)
c)
d)
56.
24
56
746
1346
Which of the following changes to an electrical circuit will increase power delivery to the
load?
a)
b)
c)
d)
55.
Ohms
Volts
Watts
Horsepower
One horsepower of mechanical power is equal to watts of electrical power.
a)
b)
c)
d)
54.
Increase
Decrease
Stay the same
Fluctuate
Electrical power is measured in units of:
a)
b)
c)
d)
53.
Module 5 Basic Electricity
0.5
3.41
3,412
5,020
What is the Btuh output of an electric heater rated at 20 kW?
a)
10
b)
68.2
c) 68,240
d) 100,400
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Module 5
Gas Technician 3
Questions #58 to #77 refer to Section 5.7 Types of Circuits
58.
Identify the type of circuit in the following diagrams:
59.
Which of the following statements is correct concerning a series electrical circuit?
a)
b)
c)
d)
60.
Which statement is correct?
a)
b)
c)
d)
61.
The loads in a series circuit operate independent of each other.
There is only one load in a series circuit.
The voltage drop across each load in a series circuit is always equal.
If one load fails in a series circuit then all loads will stop operating.
Current will flow with one load not operating in a series circuit
Current is not affected by varying voltage or resistance in a series circuit
Current will be the same throughout the series circuit
Current will be different after each load in a series circuit
With constant supply voltage, what will be the effect on total current if the resistance is
decreased in any one branch circuit of a parallel circuit?
a)
b)
c)
d)
No effect
Amperage will increase
Amperage will decrease
Amperage will fluctuate
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Basic Electricity
62. Answer the following questions using this circuit diagram:
R3= 80Q
a) The total resistance of the circuit is.
b) If the supply voltage is 100 V, the current in the circuit will be.
c) If the current in the circuit is 5 amps, the supply voltage must be.
63.
The total resistance of a series circuit that consists of two 10 Q loads is:
a)
b)
c)
d)
64.
The amperage reading at any point in a parallel circuit will be:
a)
b)
c)
d)
65.
0 amps
supply amperage
the same throughout the circuit
different on main line compared to each branch line
If the voltage drop across a load in a simple circuit is not the applied voltage, this indicates:
a)
b)
c)
d)
66.
20 0
5Q
10 Q
Depends on the supply voltage to the circuit.
There is more than one load wired in series with the tested load.
There are two loads wired in parallel with the tested load.
The load is faulty.
Nothing is the matter.
The equivalent resistance of two 20 W resistors connected in parallel is:
a)
b)
c)
d)
0.2 W
10.0 W
20.0 W
40.0 W
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Basic Electricity
67.
Gas Technician 3
The equivalent resistance of two 20 W resistors connected in series is:
a)
b)
c)
d)
68.
Module 5
0.2 W
10.0 W
20.0 W
40.0 W
Will the following circuits operate properly (i.e. will all bulbs glow)? Give your reasons
Yes
No
Reasons: _________________________________________________________
Yes
No
Reaso n s: ________________________________________________________
Yes
No
Reasons : _________________________________________________________
Yes
No
Reasons: _________________________________________________________
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Gas Technician 3
69.
The current required to operate a device rated for 1200 watts at 120 volts is:
a)
b)
c)
d)
70.
10 amps
12 amps
100 amps
15 amps
If a circuit is wired so that electrons can flow in only one possible path, the circuit is called
a/an:
a)
b)
c)
d)
71.
Module 5 Basic Electricity
parallel circuit.
broken circuit.
series circuit.
series-parallel circuit.
In a parallel circuit containing a 10 W, a 20 W and a 30 W resistor, the current flow is:
a)
b)
c)
d)
highest through the 10 W resistor.
highest through the 20 W resistor.
highest through the 30 W resistor.
equal through all three resistors.
72 Total resistance (RT) in a series circuit is equal to:
a)
b)
c)
d)
73.
The total current in a parallel circuit will be:
a)
b)
c)
d)
74.
Supply amperage
Supply voltage
Sum of each individual resistance in the circuit
The true RMS reading
120 Volts
0 Ohms
15 Amps
The sum of the current passing through each branch circuit
Which statement is correct concerning a parallel circuit?
a) The total resistance of the circuit is the sum of each individual resistance in the circuit
b) The total resistance of the circuit will be less than the smallest resistance in the circuit
c) The current reading will be the same throughout the circuit
d) Voltage drop across each load is more than the voltage supplied
75.
Which statement is correct?
a)
b)
c)
d)
The series-parallel circuit is commonly used in gas appliances
A corroded switch will cause a parallel circuit to act like a series-parallel
The series circuit is commonly used in gas appliances
The parallel circuit is never used in gas appliances
Basic Electricity
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Basic Electricity
76.
Module 5
Gas Technician 3
Given a constant supply voltage, which statement is correct?
a) The current through each branch circuit in a parallel circuit depends on the resistance of
the load in that branch circuit.
b) The current through each branch circuit in a parallel circuit is not affected by the
resistance of the load in that branch circuit.
c) The current through the main supply to all branch circuits in a parallel circuit will be less
than the current passing through any of the individual branch circuits.
d) The current through each branch in a parallel circuit is reduced by the resistance of the
loads in the other branches of the circuit.
77.
Which type of circuit will allow a load to deliver its design power rating if the load is
designed for 24V?
a)
b)
c)
d)
24V Series circuit with another load in series
24V Parallel circuit - no matter which branch line it is installed in
24V Series-parallel circuit - no matter which branch line it is installed in
120V Parallel circuit - no matter which branch line it is installed in
Questions #78 to #83 refer to Section 5.8 Alternating Current
78.
In North America, AC power is produced at a frequency of cycles per
second (also known as Hertz).
a)
60
b)
100
c) 50
d) 14
79.
Answer the following questions in reference to the sine wave graph below.
a) Are voltage and current in phase or out of phase? (Circle
one)
In phase Out of phase
b) If a circuit had this voltage and current relationship, what
type of load would you expect is connected to the circuit?
(Circle one)
Resistive Capacitive Inductive
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80.
Neutral wire
Ground wire
Electrical panel
All of the listed choices
Which of the following statements is correct concerning electrical installations?
a)
b)
c)
d)
83.
Positive applied voltage from the electrical supply
Induced voltage from the coil of an inductor that opposes applied voltage
Negative applied voltage from the electrical supply
A back flow of current produced by a conductive metal
Which of the following are connected to a grounding rod in a properly installed electrical
installation?
a)
b)
c)
d)
82.
Basic Electricity
Back emf is an electrical term that means:
a)
b)
c)
d)
81.
Module 5
The ground wire must be connected to the neutral wire at each junction box
The ground wire must be connected to each junction box
The ground wires must be connected together inside the junction box
Both b) and c)
Which statement is correct?
a) Batteries supply alternating current (AC).
b) Direct current flows from the positive to negative terminals.
c) Direct current electricity alternates polarity 60 times per second
d) Direct current measurements are polarity sensitive (i.e. black test probe must be on
negative terminal).
Questions #84 to #92 refer to Section 5.9 Electromagnetic Action
84.
The direction of the electrical current through a conductor determines:
a)
b)
c)
d)
85.
the voltage in the circuit
the resistance in the circuit
the polarity of the magnetic field around the conductor
the strength of the magnetic field around the conductor
The intensity of the electrical current through a conductor determines:
a)
b)
c)
d)
the voltage in the circuit
the resistance in the circuit
the polarity of the magnetic field around the conductor
the strength of the magnetic field around the conductor
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Basic Electricity
86.
Module 5
Gas Technician 3
A properly designed induction coil in an electromagnet will have very little current flowing
through it when the electromagnetic force is not doing any work.
TRUE FALSE
Explain your answer:
87.
An ohmmeter reading across the wires on a good induction coil will indicate:
a)
b)
c)
d)
88.
Infinite resistance
Measurable resistance
Zero resistance
Fluctuating resistance
An ohmmeter reading between a good solenoid coil and the solenoid casing will indicate:
a)
b)
c)
d)
89.
________________________________
Infinite resistance
Measurable resistance
Zero resistance
Fluctuating resistance
The current draw of an electric motor is consistent from start to finish.
TRUE FALSE
90.
A centrifugal switch on an electric motor:
a)
b)
c)
d)
91.
Controls the power to the start windings
Controls the power to the run windings
Increases voltage to the motor
Is a safety switch to protect the motor from overheating
Electrical current flows through a capacitor to increase starting torque on a motor
TRUE
92.
FALSE
A relay switch in most gas-fired appliances is activated by the low-voltage control circuit
but makes or breaks connections in the line voltage circuit.
TRUE
FALSE
Basic Electricity
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© NRG Resources Inc.
Gas Technician 3
Module 5 Basic Electricity
Questions #93 to #101 refer to Section 5.10 Transformers
93.
Transformers are very inefficient electrical devices that consume a lot of power.
FALSE
TRUE
94.
If there are more turns of wire on the primary windings of a transformer than on the
secondary winding, the transformer is called a:
a)
b)
c)
d)
95.
If there are fewer turns of wire on the primary windings of a transformer than on the
secondary winding, the transformer is called a:
a)
b)
c)
d)
96.
Relay
Step-up transformer
Step-down transformer
Solenoid
Relay
Step-up transformer
Step-down transformer
Solenoid
More electrical current will flow in the secondary circuit of a 40 VA transformer than will in
the secondary circuit of a 100 VA rated transformer.
TRUE
97.
If the primary winding of a transformer has an applied voltage of 120V and a current of 1
amp, the maximum current available on the 30V secondary side of the transformer would
be:
a)
b)
c)
d)
98.
3 amps
120 amps
4 amps
36 amps
A “VA" rating on a transformer indicates:
a)
b)
c)
d)
99.
FALSE
The available power to the secondary circuit
The available power to the primary circuit
The transformer uses varying amperage
The transformer can only be used with a DC power supply
Ignition transformers are:
a)
b)
c)
d)
Step-up transformers
Step-down transformers
Digital transformers
Auto transformers
Basic Electricity
© NRG Resources Inc.
Page 5-169
Basic Electricity
Module 5
Gas Technician 3
100. Transformers which produce a secondary voltage that is higher than the primary are called:
a)
b)
c)
d)
step down transformers.
step up transformers.
auto transformers.
neutral transformers.
101. Transformers which produce a secondary voltage which is lower than the primary are called
step down transformers.
TRUE FALSE
Questions #102 to #108 refer to Section 5.11 Codes Related to Electrical Work
102. Which of the following laws is a Gas Technician required to comply with when working on
electrical circuits?
a)
b)
c)
d)
Gas Code - OSA B149
Gas technician scope of certification in Ontario Regulation 215/01
Ontario Electrical Code
All of the listed choices
103. A G.3 certificate is authorized to install electrical wire from the electrical panel to the gasfired appliance if that work is conducted under the supervision of a G.1 or G.2.
TRUE
104.
FALSE
Whose responsibility is it to get an electrical work permit to install a gas-fired appliance?
a)
b)
c)
d)
The owner of the building where the appliance is to be installed
The installing contractor
A permit is not required
The manufacturer of the appliance
105. The Electrical Code requires that only one bare conductor is connected to a screw
terminal.
TRUE
106.
Electrical wires shall be supported:
a)
b)
c)
d)
107.
FALSE
Every 5 feet (1.5 m)
Every 10 feet (3 m)
Within one foot (300 mm) of a junction box or turn in direction
Both a) and c)
The branch electrical circuit to a heating appliance may be used to supply power to:
a)
b)
c)
d)
Lighting in the furnace room
Other electrical devices as long as the total amp draw is less than 15 amps
Accessories necessary for the safe operation of the appliance
Electrical outlets within 10 feet (3m) of the heating appliance.
Basic Electricity
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© NRG Resources Inc.
Gas Technician 3
108.
Module 5
Basic Electricity
How far into a junction box must conductors extend?
a)
b)
c)
d)
2 inches (50 mm)
6 inches (150 mm)
9 inches (225 mm)
12 inches (300 mm)
Questions #109 to #114 refer to Section 5.12 on Safety First
109.
Which of the following statements is correct?
a)
b)
c)
d)
110.
If a co-worker is suffering a shock from an electrical circuit and cannot let go of the circuit,
the first action to take is:
a)
b)
c)
d)
111.
A wet body has more resistance than a dry body.
A current of 15 amps is required to cause damage to the human body.
Electrical shock is caused by voltage.
Less than one ampere of electricity can kill a person.
Call the emergency response phone number
Give the co-worker a quick push to free him or her from the circuit
Disconnect the power to the electrical circuit
Grab the closest object and shove the person away from the circuit
Electricity can only flow through electrical wires.
TRUE
112.
Which of the following statements is correct concerning electrical shock?
a)
b)
c)
d)
113.
Voltage levels are more important than current levels
High voltage is always more deadly than low voltage
A wet body has less resistance than a dry body
AC voltage is more dangerous than DC voltage
Which class of fire extinguisher should be used to extinguish an electrical fire?
a)
b)
c)
d)
114.
FALSE
Class A
Class B
Class C
Class D
What will happen if you use water to extinguish an electrical fire?
a)
b)
c)
d)
Fire may be extinguished
Possible electrocution
Fire would spread
Fire would cause a short to ground
Basic Electricity
© NRG Resources Inc.
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Basic Electricity
Module 5
Gas Technician 3
NOTES:
Basic Electricity
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© NRG Resources Inc.