CHAPTER TWO
BUILDING ELECTRICAL
MATERIALS AND EQUIPMENT
2.1 POWER GENERATION AND TRANSMISSION
 A power station is an industrial facility that houses equipment to generate electrical
energy.
 A generator is a mechanical device that converts mechanical energy into electrical
energy. A generator rotates an armature, a shaft with conductor windings wrapped
around an iron core, through a stationary magnetic field, to produce current flow.
 A rotary engine called a turbine is connected to the generator and drives the rotation of
the armature shaft.
2.2 BUILDING ELECTRICAL SERVICE EQUIPMENT
 In a steam turbine, high pressure steam moves through the turbine, driving rotation of
 Service Entrance Conductors - are those that run between the service point and
discs attached to the turbine shaft.
the service equipment.
 Steam is produced by heating water by burning coal, oil, or natural gas, or with heat
 Service Drop - is an overhead electrical line running from a utility pole, to a customer's
created by a nuclear reaction.
building or other premises.
 Service Lateral - consists of the underground service conductors between the street main
- including risers - and the first point of connection to the service-entrance conductors in
a terminal box, meter, or other enclosure.
 Service Entrance - includes the components that connect the utility-supplied wiring (the
service lateral or service drop) to the service disconnect, excluding the utility’s metering
equipment.
Figure 1: Power transmission and distribution.
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 Service entrance equipment - receives the service entrance conductors. The service
equipment includes a method of measuring power (metering equipment), a method of
cutting off power (main disconnect or switch gear), and overcurrent protection devices
(circuit breakers or fuses) that protect the service entrance conductors.
 Electric meter is an instrument that is used by the utility company to measure and record
electrical energy consumed. In building services rated up to about 400 A, a feed-through
meter is used.
 Switchboard is a large cabinet or assembly of metal cabinets in which is connected
disconnecting switches, overcorrect protection devices (fuses or circuit breakers), other
protective devices, and instruments designed to divide large amounts of electrical current
into smaller amounts of current used by electrical equipment.
 Panelboards is one or more metal cabinets that serve as a single unit, including buses,
automatic overcurrent protection devices (fuses or circuit breakers).
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
Impedance (if 25 kVA or larger)

Required clearances (if it has ventilating openings)
 Step-down transformer has a secondary voltage that is less than its primary voltage.
 Step-up transformer is one with a secondary voltage that is greater than its primary
voltage.
 Single-Phase transformer has a single primary winding and a single secondary winding.
The 7200/240/120 V AC, single-phase, three-wire transformer is used in most residential
and small commercial applications where 120 V and 240 V are required.
Building Transformers
 Transformers are used in transmitting and distributing power from the power plant to a
 Single-Phase transformer has a single primary winding and a single secondary winding.
substation. The operation of a large commercial installation depends on power
The 7200/240/120 V AC, single-phase, three-wire transformer is used in most residential
distribution that, in turn, depends on transformers used to change voltage, current, and
and small commercial applications where 120 V and 240 V are required.
phase of electrical power nearby and within a building. Building transformers are rated in
 Three-phase transformer has three primary and three secondary windings. There are
kVA. Typical sizes used in buildings include 3, 6, 9, 15, 25, 30, 37.5, 45, 50, 75, 112.5,
two main types of three phase transformers: delta and wye.
150, 225, 300, 500, 750, 1000, 1500 kVA, and larger.
Every transformer comes with a nameplate that typically identifies:
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
Rated kVA

Primary and secondary voltage
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2.3 OVERCURRENT PROTECTION: FUSES AND CIRCUIT BREAKERS
 Overcurrent protection (OCP) device safeguards the building service or an individual
circuit from excessive current flows.

It protects the circuit components from severe overheating when current flowing through
the circuit reaches amperage that will cause an excessive or dangerous temperature rise in
conductors.

Circuit Breaker is an overcurrent protection device that serves two purposes: It acts as a
switch that can be opened and closed manually, and most importantly, it automatically
“trips off,” which opens the circuit when current flowing through it exceeds the circuit
rating.

Fuse is an overcurrent protection device that consists of a strip of metal with a low
melting temperature. Under normal operation, electricity flows through the metal strip.
However, when its current rating is exceeded, the metal strip heats up and melt and the
circuit is opened, thereby interrupting current flow.
OCP Device Ratings
 Overcurrent Rating of an OCP device is the highest amperage it can carry continuously
without exceeding a specific temperature limit (e.g., without overheating).
 If the current (amperage) flowing through the protection device exceeds the device
setting for a significant period, the OCP device will open.
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 Interrupting Rating OCP devices must have an interrupting rating sufficient for the
 Plug is typically connected to a flexible cord that is attached to a portable appliance,
maximum possible fault-current (short-circuit).
light, or equipment. Receptacles and plugs offer a simple way to attach or detach an
 If the OCP is not rated to interrupt at the available fault-current, it could explode while
attempting to clear the fault and/or the downstream equipment could suffer serious
appliance or piece of equipment to/from an electrical outlet.
 Switch is a device placed between two or more electrical conductors in a circuit to safely
damage, causing possible hazards to occupants and property.
and intentionally open or close the circuit or to redirect the path of current in a circuit.
2.4 UTILIZATION EQUIPMENT AND DEVICES
 Utilization equipment is a broad category of electrical or electronic machine or
instrument designed to perform a specific mechanical, chemical, heating, or lighting
function through the use of electrical energy.
 Appliance is an end-use piece of utilization equipment designed to perform a specific
function such as cooking, cleaning, cooling, or heating.
 Fixed appliances are permanently attached installations such as a built-in electric cook
top or oven.
 Stationary appliances are situated and used at a specific location but can be moved to
another outlet such as a refrigerator, clothes washer, or clothes dryer.
 Portable appliances are appliances that can be easily carried or moved such as a hair
dryer or toaster.
 Electrical device is a component in an electrical system that is designed to carry but not
use electricity. This includes components such as switches, receptacles, and relays.
Outlets, Receptacles, and Plugs
 Outlet is the location in a branch circuit where electricity is used. For example, a lighting
outlet is the location in a branch circuit where conductors provide power to a light fixture.
 Receptacle is a female connecting device with slotted contacts. It is installed at an outlet
or on equipment, where it is intended to easily establish an electrical connection with an
inserted plug.
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Specialty Switches
In addition to the standard switches, there are many types of switches that perform
special functions. These are as follows:
Automatic switches deactivate a circuit after a preset time period has lapsed. They are
available as a twist-turn device where the operator determines the operating time interval by how
far the switch is twisted or as an electronic device that looks like a normal on/off switch but is
designed to automatically switch off after a preset time.
A dimmer switch (SD) is a device in the electrical circuit for varying power to a circuit.
Dimmers are usually included in a lighting installation to vary the intensity of light emitted by
the lights.
Time clocks can be used to control the time period that a piece of equipment or a lighting
installation operates. Traditionally, a time clock is an electrical-mechanical device that controls
time of operation by pin placement on a moving time wheel that repeats a daily cycle as the
wheel rotates. Electronic timers allow greater flexibility as they can easily be set for 7-day
cycles. They do require relay switching on large loads.
Photocell controls sense light and open or close a circuit with the presence of light. They
can be used to control night lighting in lieu of a time clock. Recent advancements in photocell
technology allow them to be used effectively to control illumination levels in spaces that have
daylight available. As illumination levels from daylighting increases, the photocell dims the
lights.
Occupancy sensors control a lighting or equipment installation by sensing occupants in a
space.
Infrared sensors respond to the motion of an infrared heat source, such as a person or
animal. The field of view of the detector’s lens is divided into several zones. Motion is detected
when the heat source moves from one zone to another. The sensor must have a direct line of
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sight to the infrared heat source to detect motion. Relatively small movements, such as typing on
a keyboard, may not be sufficient to trigger the sensor.
Ultrasonic sensors emit a high-frequency sound that is in the range of 25 to 40 kilohertz
and well above the capacity of normal human hearing. Objects moving in the space shift the
frequency of the returning signal, which in turn is detected by the sensor. Ultrasonic sensors do
not require a direct line of sight to the occupant. They usually can detect small movements, but
extraneous signals from wind-blown curtains or people walking by in nearby spaces can trigger
the sensor. Both infrared and ultrasonic sensors work well in interior spaces such as classrooms
and offices. Occupancy sensors are usually mounted on the wall or ceiling.
2.5 CONDUCTORS
 Electrical conductor is any material that conducts electrical current.
 Wire is a common electrical conductor. Most conductors used in building applications are
classified according to a wire gauge standard and on the cross-sectional area of the wire
in units called circular mils. A mil is equal to 1>1000 inch, so one circular mil (cmil) is
equal to the cross-sectional area of a 0.001 in diameter circle.
 Bus bar, is an electrical conductor (usually copper or aluminum) that serves as a common
connection for two or more electrical circuits Buses are typically solid bars used for
power distribution. They are commonly found in panelboards, switchboards, and other
power distribution equipment.
 Buses are typically solid bars used for power distribution. They are commonly found in
panelboards, switchboards, and other power distribution equipment.
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Conductor Material
Underground Feeder Cable
Scientifically, silver is the best electrical conductor material (other than a superconductor
Underground feeder (UF) cables are flame retardant and moisture, fungus, and corrosion
material) because it has the least resistance of common materials. It works so well as a conductor
resistant. UF cable is available in No. 14 AWG copper and No. 12 aluminum AWG through No.
that several hundred pounds of silver wiring was used in the first mainframe computer. Gold is
4/0 AWG. It looks much like NM or NMC except that the sheathing fully encases the insulation-
also an excellent conductor. Both materials, however, are too costly for building installations.
covered conductors. UF cable is used in direct-burial applications as a feeder or branch circuit
provided it is protected by an overcurrent protection device (fuse or circuit breaker) before if
Conductor Insulation
leaves the panelboard.
Conductors are covered with insulation that provides electrical isolation and some
physical protection of the conductor material. It prevents loss of power and the danger of short
circuits and ground faults. The type of insulation protecting a conductor determines the
environment in which it can be used safely. Wires used indoors are subjected to less exposure to
the elements than those designed for outdoor use. Outdoor wiring is exposed to water and
ultraviolet light, so the insulation is designed to withstand these elements. Insulation on wires
buried in the ground must also be able to withstand the damp, corrosive environment of the soil.
Cable
A cable contains more than one conductor bundled together in a factory assembly of
wires. An outer sheathing encases and protects the conductors, simplifying installation of
multiple wiring.
Nonmetallic-Sheathed Cable
Nonmetallic-sheathed cable is classified as type NM or NMC and is commonly called by
its trade name, Romex. NM consists of two or more insulated conductors enclosed within a
moisture-resistant, flame-retardant outer sheathing or jacket that is very flexible. NMC has
conductors encased in the sheathing. NM is reserved for use in dry, indoor applications. NMC
can be used in dry and damp applications but not wet and exposed conditions. Type NM and
Type NMC cables can typically be used only in one- and two-family dwellings, and in
multifamily dwellings permitted to be of Type III, IV, and V construction.
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Service Entrance Cable
There are several conductors that can be used specifically for underground and overhead
service entrances. Service entrance (SE) cable is suitable for exposed above-grade conditions.
Underground service entrance (USE) cable is used in underground service applications. A
conductor marked with only type USE or USE-2 may not be installed in conduit inside buildings
because it does not have the necessary flame retardant. In many cases, USE cable is
accompanied by the RHW-type marking and USE-2 cables are dual marked with RHW-2. These
dual marked cables are suitable for use as exposed single-conductor cables and as cables inside
conduits in buildings.
Armored Cable
Armored cable, classified as either AC or ACT, is sometimes referred to by the trade
name, BX cable. This cable consists of two to four copper conductors between 14 AWG and 1
AWG in size that are enclosed within a flexible spiral-shaped metallic enclosure. Armored cable
is classified as type ACT if the conductor insulation is thermoplastic and AC if the insulation is
rubber. AC cable contains a 16 AWG bonding strip, which is in constant contact with the metal
armor, allowing the armor bonding strip combination to act as an equipment ground. Armored
(AC) installed in a steel-framed partition is shown in.
Metal-Clad Cable
Metal-clad (MC) cable is similar to armored cable except it is not limited to the number
sizes (from 18 AWG to 2000 kcmil) of conductors it can carry. The conductors in MC cable may
be copper, aluminum, or copper-clad aluminum. The metal armor may be a smooth tube,
corrugated tube, or interlocked metal armor. MC cable does not contain a bonding strip like AC
cable, and the armor cannot be used by itself as an equipment ground. However, it supplements
the internal grounding conductor. MC cable can be used in many locations not allowed with AC
cable.
Flat Conductor Cable
Flat conductor cable (FCC) is a wiring system composed of very thin cable with three or
more conductors and special connectors and terminals. It is designed to rest between the topside
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of a smooth continuous subfloor and carpet squares. It can serve general purpose and appliance
circuits up to 20 A and individual circuits up to 30 A, with a system voltage between the
ungrounded conductors not exceeding 300 V.
Thermostat Cable
Thermostat cable is used in applications with voltages less than 30 V, such as wiring to
doorbells, chimes, and thermostats. It generally contains No. 16 AWG or No. 18 AWG
conductors that are bundled in a thin plastic sheathing.
Cords
Cords are made of stranded conductors within a flexible insulated sheathing material.
They are designed for flexibility and bending. Cords are generally manufactured of a lighter
gauge (e.g., No. AWG 18 or No. AWG 16) stranded conductors. They are designed for use on
power tools, large stationary equipment, or detachable computer power cords. Extension cords
are made of stranded wires because they require flexibility, allowing the cord to be bent and
twisted without stressing the conductors.
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Concealed Knob-and-Tube Wiring
Concealed knob-and-tube (K&T) wiring consists of an old style wiring technique using
insulated conductors strung between glass or porcelain knobs and tubes. In this wiring method,
the ungrounded (hot) wire is run along one side of the joist/stud bay and the neutral is run along
the other. To secure it to the wood, the wire is wrapped around ceramic knobs spaced every 18 in
or so. To penetrate a joist/stud and prevent abrasion, the wire is separated from the wood
joist/stud by a ceramic tube. K&T wiring is installed in walls or ceilings so it is concealed from
view when finish materials such as plaster is applied. Loose or blown-in insulation in framing
cavities can encase the knob-and-tub conductors, causing heat build-up in walls or ceilings with
insulation. Therefore, concealed knob and- tube wiring is not permitted in framing cavities where
insulation presents this problem.
Conductor Power Loss
Heat generated by current flow through a conductor results in a loss of power. This lost
power is referred to as power loss or line loss. Power loss (Ploss) in a conductor can be
computed with amperage (I) or voltage (V) and resistance (R) by the following formula:
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Conductor Ampacity
Power loss is converted directly to heat. Power loss is equivalent to heat produced. The
A conductor’s ampacity is the maximum current (in amperes) it can carry continuously
relationship between power and heat is 1 W _ 3.413 Btu/hr. Heat produced (q) for a known
without exceeding the temperature limitations of the insulation and sheathing material. Simply, it
power loss (Ploss) can be computed by the following formula:
is a conductor’s maximum current-carrying capacity. Ampacity is based on the following:

Wire thickness (thicker wires have larger cross-sectional areas and can carry more
electrical current without overheating)

Type of conductor material (at a specific current and conductor size, aluminum produces
more heat than copper)

Insulation and sheathing type (some insulation materials handle heat better than others)

Number of conductors bundled in the sheathing or in proximity of one another (more
conductors concentrate heat in an area)

Temperature and exposure of the conductor (e.g., buried, in free air, in attic, in crawl
space, and so forth).
Voltage Drops in Conductors
Voltage drop is directly proportional to power loss. This is true because current flow (I)
through a conductor will not change. And, with the power equation P = EI, because power is lost
(wattage available is less), the voltage (E) must drop. Refer to Kirchhoff’s Current and Voltage
Laws introduced in Chapter 2.
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2.6 ENCLOSURES AND RACEWAYS
Enclosures
Enclosures are electrical boxes and cabinets made of metal (e.g., steel, galvanized steel,
aluminum, and so on) or nonmetallic (plastic) materials that provide protection for conductors,
connections, controls, and other electrical equipment. They protect the wiring, devices, and
equipment from damage and deterioration from accidental contact, wear, corrosive atmospheric
exposure, and sunlight.
Electrical boxes
Electrical boxes are metal and non-metallic (plastic) enclosures that hold devices such as
switches or outlets and safely permit wiring connections. Boxes are available in four primary
shapes: square, rectangular, octagonal, or round.
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Conduit and Other Raceways
 Liquid tight flexible nonmetallic conduit is a flexible plastic conduit used in a manner
similar to flexible metal conduit.
 Raceway is as an enclosed channel such as a conduit, tube, or gutter designed for holding
wires, cables, or bus bars.
 Cellular concrete floor raceways are hollow voids in floors made of precast concrete
slabs (core slabs) found in certain precast concrete buildings.
 Rigid metal conduit is a heavy galvanized steel or aluminum tube that looks like the
galvanized steel pipe used for plumbing applications except it is much smoother and is
 Busway is of a standardized, factory-assembled enclosure consists of outer duct-like
labeled with a UL Listed stamp or label.
housing, bus bars, and insulators. Busway systems are typically used in service
equipment or as feeders because these systems are designed to carry large amounts of
 Intermediate metal conduit (IMC) is a galvanized steel or aluminum tube that has a
current.
thinner wall than rigid metal conduit.
 Electrical metallic tubing (EMT) is a thin-walled galvanized steel or aluminum tube in
 Feeder busway is used to deliver large amounts of power with low voltage drop. It is
available in sizes from 600 A to several thousand amps.
nominal diameters up to 4 in.
 Electrical nonmetallic tubing (ENT) is a flame-retardant corrugated plastic tube that is
 Plug-in busway is used to provide power tap-offs at multiple points. It is available in 100
A to 3000 A sizes.
semiflexible such that it can be bent by hand.
 Rigid nonmetallic conduit is a thin-walled pipe of PVC. It is joined with fittings that are
solvent welded.
Wireways
Wire gutters or wireways are sheet metal or nonmetallic, flame-resistant plastic troughs
that serve as a housing that encloses and protects conductors. Access to the enclosure interior is
through a hinged door or removable cover. Wire gutters and wireways typically carry large
conductors.
 Flexible metal conduit is similar to armored cable, but it is installed without cables or
wiring in it; wiring must be pulled.
 Liquid tight flexible metal conduit is similar to flexible metal conduit, but it is covered
with a plastic, watertight jacket that is sunlight resistant.
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Types of Motors
2.7 ELECTRIC MOTORS
 Universal motor is a fractional horsepower (less than one horsepower) motor designed to
operate on both AC and DC power. Its rate of rotation varies considerably with load. It
Motor Ratings
Electric motors are found in refrigerators, freezers, dishwashers, kitchen sink waste
disposal, portable kitchen appliances, exhaust and ventilation fans, clothes washers and dryers,
operates at high speeds under light load and low speeds with heavy load.
 Split-phase motor operates on single-phase AC only. The motor windings are configured
so that single-phase AC power is split into two phases that are 1⁄2 out of phase. This type
furnaces, air conditioners, and paddle fans. Electric motors are rated in horsepower (hp). One
of motor starts slowly with low torque so it is not capable of starting heavy loads.
horsepower is equivalent to 33 000 foot-pounds (ft-lb) of work per minute (550 ft-lb/s). This is
about 1⁄8 the power an adult can produce continuously.
 Capacitor motor operates on single-phase AC only. Capacitor-star motors have a
capacitor that stores and discharges energy to help start the motor rotor.
 Induction motors use electromagnetic induction to cause the motor rotor to turn.
Repulsion-start induction motors are capable of handling heavy starting loads.
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 Motor controller is a switching device designed to start, stop, and protect the motor.
 Variable-frequency drive (VFD) is a solid-state electronic power conversion device used
for controlling the rotational speed of an AC electric motor by controlling the frequency
of the electrical power supplied to the motor.
allows the shutters to slide and open up access to the receptacle contacts. The plug becomes fully
inserted and securely fits into the receptacle. When the plug is removed, the shutters instantly
close, covering the contact openings. When a foreign object, such as a paper clip or small bladed
screwdriver, is inserted into only one of the openings, the safety shutter will not allow access to
the live contact. For these receptacles, the safety mechanism covers only the line and load
2.8 OCCUPANT PROTECTION
Need for Occupant Protection
contacts, and not the ground. Because they accept a two pronged plug, these receptacles can be
used with standard household and office appliances like light fixtures, clocks, and radios.
In the United States, hundreds of people are accidentally electrocuted each year.
Electrocution occurs when a small amount of electrical current flows through the heart for 1 to 3
Ground Fault Interruption
A ground fault is the unintentional flow of electrical current between a power source,
s. The amount of 0.006 to 0.2 A (6 to 200 milliamps, or mA) of current flowing through the heart
disrupts the normal coordination of heart muscles. These muscles lose their vital rhythm and
begin to fibrillate. Death soon follows. To provide an example of how small an amount of
such as an ungrounded (hot) wire, and a grounded surface. A ground fault occurs when electrical
current leaks or escapes to ground.
current it takes to kill: a 15 W nightlight on a 120 V circuit draws about 13 mA, enough
amperage to cause electrocution.
A ground fault circuit interrupter (GFCI)
Is an electrical device that detects an extremely low leak (6 mA) of electrical current
Tamper-Resistant Receptacles
According to U.S. Consumer Product Safety Commission data, approximately 2400
children suffer electrical injuries each year from incidents involving electrical outlets or
receptacles. Tamper-resistant receptacles have built-in shutter systems that prevent foreign
objects from touching electrically live components when these are inserted into the slots. The
shutters protect against electrical burns without impairing normal plug insertion, removal, or
(called ground faults) and acts quickly to shut off power. It is designed to protect the user of an
electrical appliance much like a circuit breaker or fuse safeguards the wiring in an electrical
system. A GFCI continuously monitors the current drawn through the ungrounded (hot) and
neutral conductors of an electrical circuit. When a leakage to ground that exceeds 6 mA is
detected, the GFCI instantaneously switches off power to the branch circuit or appliance, thereby
protecting a person from the dangerous effects of electrical shock.
function. Tamper-resistant receptacles have emerged because of the tendency of children to
Three types of GFCIs are commonly available for use in a building.
unwittingly endanger themselves by inserting keys, pins, paper clips, or other items into
unprotected receptacles. Products such as plastic plug-in inserts and wall plates with contact
shutters are available for tamper resistance, but do not meet the requirements of a tamper-
Receptacle Outlet Type
This type is generally used in place of standard duplex convenience outlets that are
resistant receptacle.
There are several methods to achieve tamper-resistance operation, the most common
being the use of a spring-loaded shutter mechanism. Inside the face of the receptacle is a spring
loaded thermoplastic safety shutter. Under normal, unused conditions, the shutters are closed and
both contact openings are covered. Upon insertion of a grounded or ungrounded plug, the blades
commonly found throughout the house. A GFCI convenience outlet fits into the standard
electrical outlet box and protects the user against ground faults whenever an electrical appliance
is plugged into the outlet. Most convenience outlet-type GFCIs can be installed so that they will
also protect other electrical outlets further downstream in the branch circuit.
of the plug simultaneously compress the shutters against the spring. The simultaneous force
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Arc Fault Protection
An arc fault is an unintentional electrical discharge (an electrical arc) characterized by
low and erratic current. Arcing generates high-intensity heat and expels burning particles, which
can easily ignite combustible materials. Arc faults are caused by the breakdown of the protective
insulation that surrounds household wiring. These breakdowns occur naturally as the wiring ages
and can be exacerbated by dust, settling and shifting of a home’s foundation, or by rodents.
Types of arc faults common in building wiring are the following:
 Parallel arcing faults result from direct contact of two wires of opposite polarity.
Examples of this type of fault include appliance or extension cords that are frayed or
ruptured; staples or other fasteners that pierce or pinch insulation on construction wire
and appliance or extension cords; and wire or cord insulation that has cracked from age,
heat, corrosion, or bending stress.
Circuit Breaker Type
 Ground arcing faults are arcs between a single conductor and ground, such as in the cases
of wire or cords that touch vibrating metal; in appliances, wall plugs or switches where
A GFCI circuit breaker can be installed in the panelboard in buildings equipped with
the internal wires were not installed properly; and where connections became loose.
circuit breakers. The GFCI circuit breaker gives protection to the entire branch circuit. The
wiring and each outlet that is served by the branch circuit is protected by the GFCI breaker. By
providing overcurrent protection as a circuit breaker and serving to provide GFCI protection, the
 Series arcing faults occur across the break of a single conductor—for example, in the
case of an electrical wire cut by a nail or screw used to mount a wall hanging.
GFCI circuit breaker serves a dual purpose: it will interrupt power in the event of a ground fault
and it will trip when a short circuit or a power overload occurs.
A safety device, called an arc fault circuit interrupter (AFCI), provides enhanced protection
Portable Type
Where permanent GFCIs are not possible or practical, portable GFCIs may be used. One
type contains the GFCI circuitry in a plastic enclosure with plug blades in the back and
convenience outlet slots in the front. It can be plugged into a convenience outlet so an electrical
appliance plugged into the GFCI is protected. Another type of portable GFCI is one that is part
from fires resulting from arc faults. This device uses electronics to recognize an arc fault and
interrupts the circuit when the fault occurs. Essentially, an AFCI continuously monitors the
current and voltage characteristics in a circuit, senses variations in these characteristics, and
automatically opens the circuit (trips the AFCI breaker) when arc fault characteristics are
detected.
An AFCI detects low-level arc faults that traditional overcurrent protective devices (fuses
of an extension cord, such as those required on new-model hair dryers.
and circuit breakers) cannot detect. Traditional overcurrent protection perceives a low-level arc
fault as a normal load unless the current flow exceeds its rating. As a result, fuses and circuit
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breakers do not respond to early arcing and sparking conditions in building wiring. By the time a
Extremely Low-Frequency Electromagnetic Fields
fuse or circuit breaker opens a circuit to stop these conditions; a fire may already have begun.
Extremely low-frequency electromagnetic fields (EMF) are silent, invisible magnetic
fields produced any time electricity runs through a wire, an appliance, or piece of equipment. In
There are four basic types of AFCIs.
buildings, higher levels of EMF can cause computer monitor interference and raise potential
health concerns. High levels of EMF produce electromagnetic interference (EMI), which reveals
Circuit Breaker Type
A branch/feeder AFCI breaker with protection provided to branch-circuit wiring
itself as visible screen jitter in video displays, humming in telephone/audio equipment, and data
errors in magnetic media or digital signals.
in the form of a circuit breaker.
2.9 EQUIPMENT PROTECTION
Convenience Outlet Type
An outlet AFCI for protecting connected cord sets and power supply cords in the
Ground Fault Protection of Equipment
form of an outlet receptacle.
Ground fault protection (GFP) is designed to detect and rapidly interrupt low-level
equipment ground faults. A GFP operates on the same principle as GFCI protection, by
Portable Type
A portable AFCI for protecting connected cord sets and power supply cords that
can be moved from outlet to outlet.
monitoring the current drawn through the conductors of an electrical circuit and quickly shutting
off power when current is not equal. A special type of sensing transformer, called a current
transformer (CT), encircles the conductors in the switchboard or panelboard and produces a lowcurrent output signal if all current flowing to the load does not return to the source through the
Cord-Mounted type
phase or neutral conductors.
A cord-mounted AFCI for protecting the power-supply cord connected to it (in
the form of an attachment plug on a power supply cord).
Surge Protection
A power surge is a sudden increase in electrical current or voltage that is very short in
Nuisance Tripping
duration. This increase may be caused by a lightning strike or from a sudden power spike caused
Because GFCIs and AFCIs are extremely sensitive, they have a tendency to trip
by a problem in the utility transmission and generating system. The switching of fluorescent light
frequently. This repeated tripping is referred to as nuisance tripping, as the general public sees it
fixtures or other heavy equipment can also cause a power surge. A power surge can damage
only as a nuisance. Appliances that are beginning to fail can cause nuisance tripping. They
sensitive electronic equipment such as computers, fax machines, televisions, stereos, VCRs, and
should be repaired or replaced. Lightning can also cause nuisance tripping. For this reason, it is
electronic phone systems.
not a recommended practice to connect essential equipment and appliances containing perishable
products (e.g., refrigerators, freezers) into an outlet with GFCI or AFCI protection.
A surge protection device (SPD)
Is an electrical device that prevents power surges from reaching electric and electronic
equipment or other device. SPDs work by instantaneously limiting the transient voltage from a
power surge to a level that is safe for the equipment they protect by diverting the large surge
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current safely to ground. The SPD diverts the surge by allowing the current to flow past rather
than through the protected equipment.
Inrush current can also be reduced by an inrush current
circuits that encounter high inrush loads
limiter,
which
protects
up to 30 times the rated current for one-half cycle at
60 Hz and eliminate nuisance tripping.
Types of SPD include the following.
Lightning Protection
The idea of protecting buildings and other structures from the effects of direct lightning
Metal Oxide Varistor (MOV)
A semiconductor device used mainly on AC power applications that has surge ratings
ranging from a few hundred to many thousands of amps.
strikes by the use of protective conductors was first suggested by Benjamin Franklin. The theory
presented has not changed. Simply put, lightning protection must provide a direct path for the
lightning bolt to follow to ground and it must prevent destruction, injury, or death as the current
Gas Discharge Tubes (GDT)
travels that path.
A primary surge protection component with a surge rating of several thousand amps that
Vertical lightning rods, sometimes called air terminals, are placed at the top of the
is comprised of a sealed tube containing a special gas that breaks down at a given voltage rise
protected structure. These lightning rods are equally spaced a maximum of 20 ft apart along the
time.
high points on the structure. Rods are also placed within 2 ft of the building ends and on the top
of cupolas, chimneys, antenna mast, and towers.
Zener Diode
A secondary surge protection component used for accurate clamping of surge voltages. It
Equipment for Hazardous Locations
has a quicker response time than the GDTs and provides a more accurate clamping voltage than
MOVs.
In a hazardous location, such as a gasoline station, paint spray booth, or factory,
explosion-proof or explosion-resistant equipment and wiring must be used. A hazardous location
is a location in which fire or explosion hazards may exist because of the presence of flammable
Hybrid Circuit
A circuit comprising different types of surge protection component, taking advantage of
gases or vapors, flammable liquids, combustible dust, or easily ignited fibers under normal
operation or abnormal operating conditions.
each component’s strengths. For example, a hybrid may combine the high surge capability of a
GDT with the accurate voltage clamping of a surge diode.
Technically, the definitions of explosion-proof and explosion-resistant differ. Explosionproof receptacles, switches, enclosures, fixtures, equipment are specially designed to withstand
an explosion that may occur within it and of preventing the ignition of a specified gas or vapor
Inrush Current Protection
Inrush current or input surge current refers to the peak instantaneous current, measured
in amperes (A), drawn by an electrical appliance or piece of equipment (e.g., power supplies, AC
surrounding the enclosure. Conduit that is used in an explosion-proof location must be sealed so
that gas may not move from one enclosure to another. In contrast, explosion-resistant equipment
is designed to prevent ignition of an explosive or flammable material.
motors, lamps, and lighting ballasts) when it is first turned on. Current can be as high as 100
times the normal steady state current.
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REVIEW UESTIONS
26. How are electric motors rated?
1. What are power generation, transmission, and distribution?
27. With regard to electric motors, what are LRA, RLA, and FLA?
2. What is the service entrance of a building electrical system and what are its components?
28. What are the types of motors used in building electrical systems?
3. What are the functions and differences of switchboards and panelboards?
29. What does a motor service factor indicate?
4. What is the difference between a wye-connected and delta-connected transformer?
30. What is a motor controller?
5. What is the difference between a step-down and step up transformer?
31. What is a variable-frequency drive (VFD) and what is its advantage?
6. What is a circuit breaker and where is it used in a building electrical system?
32. What is a tamper-resistant receptacle?
7. What is a fuse and where is it used in a building electrical system?
33. What is a GFCI, how does it function, and where is it used?
8. What types of fuses are used in building electrical systems?
34. What is an AFCI, how does it function, and where is it used?
9. What is the difference between a receptacle and plug-in building electrical systems?
35. What is a surge protection device (SPD), how does it function, and where is it used?
10. Distinguish between the terms appliance and device. Give examples of each.
36. What is GFP, how does it function, and where is it used?
11. What types of switching configuration is used to control a lighting installation from two
37. What is lightning protection, how does it function and where is it used?
points? What types of switches are used and how are switches arranged in the circuit?
12. What types of switching configuration is used to control a lighting installation from three
points? What types of switches are used and how are switches arranged in the circuit?
38. What is EMF and why is it a potential concern in buildings?
39. What is an inrush current limiter, and where is it used?
40. In a single panelboard, what is the maximum number of overcurrent protection devices
that may be used for protecting lighting/appliance branch circuits?
13. What types of switching configuration is used to control a lighting installation from four
points? What types of switches are used and how are switches arranged in the circuit?
41. It is referred to in the trade by several names: power panel, load center, distribution
center, or main power panel. Code refers to it by a single name. Identify this name.
14. Describe series and parallel circuit. Which is used in building electrical systems?
15. What are the types of specialty switches?
16. What are types of conductor (wire) materials and where are they used in building
PROBLEM SOLVING
electrical systems?
17. What are types of conductor insulation materials and where are they used in building
1. With respect to conductor insulation, interpret the following Conductor insulation
electrical systems?
designations:
18. What is a cable and where is it used in building electrical systems?
a. T
19. What is a cord and where is it used in building electrical systems?
b. N
20. What is a bus (bar)?
c. H
21. What are power loss and voltage drop and how are they related?
d. HH
22. What is ampacity?
e. W
23. What factors is the ampacity of a conductor based on?
2. With respect to conductors, interpret the following designations:
24. What are types of raceways used in building electrical systems? Explain each.
a. THHN
25. What is a busway and where is it used in building electrical systems?
b. THWN
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c. XHHW
11. From tables provided in this chapter, identify the NEMA designation for the following
d. AL
grounding-type devices used for clothes dryers:
e. CU
a. Receptacle
3. With respect to cable, interpret the following designations:
a. NM
b. Plug
12. From tables provided in this chapter, identify the NEMA designation for the following
b. ACTH
grounding-type devices used for a kitchen range requiring a 50 A, 125/250 V rating:
c. UF
a. Receptacle
d. USE
4. With respect to conductor insulation, describe the following location ratings:
b. Plug
13. From tables provided in this chapter, identify the NEMA designation for the following
a. Dry
grounding-type devices used for copy machines and air conditioners requiring a 50 A,
b. Damp
125 V rating:
c. Wet
a. Receptacle
5. A single-phase, three-wire panelboard must feed 30 circuits. From tables provided in this
chapter, identify the minimum frame size required.
b. Plug
14. From tables provided in this chapter, identify the NEMA designation for the following
6. A single-phase, three-wire panelboard must feed 36 circuits. From tables provided in this
grounding-type devices requiring a 20 A, 250 V four-pole, four-wire, three-phase rating:
chapter, identify the minimum frame size required.
a. Receptacle
7. A three-phase, four-wire panelboard must feed 42 circuits. From tables provided in this
chapter, identify the minimum frame size required.
b. Plug
15. From tables provided in this chapter, identify the NEMA designation for the following
8. A three-phase, four-wire panelboard must feed 42 circuits. From tables provided in this
grounding-type devices requiring a 20 A, 250 V four-pole, four-wire, three-phase rating:
chapter, identify the frame sizes available to meet this requirement.
a. Receptacle
9. From tables provided in this chapter, identify the NEMA designation for the following
wall-mounted, grounding-type devices used in a residence that are rated at 15 A, 125 V,
b. Plug
16. From tables provided in this chapter, identify the ampacity of the following conductors:
and serve as a connection method for a two-pole, three-wire circuit:
a. No. 8 AWG copper conductor with THHN insulation and a temperature rating of
a. Receptacle
60°C/140°F
b. Plug
b. No. 8 AWG copper conductor with THHN insulation and a temperature rating of
10. From tables provided in this chapter, identify the NEMA designation for the following
75°C/167°F
heavy-duty grounding-type devices that are rated at 20 A, 125 V, and serve as a
c. No. 8 AWG copper conductor with THHN insulation and a temperature rating of
connection method for a two-pole, three wire circuit:
90°C/194°F
a. Receptacle
d. No. 8 AWG aluminum conductor with THHN insulation and a temperature rating
b. Plug
of 75°C/167°F
17. From tables provided in this chapter, identify the ampacity of the following conductors:
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a. No. 4/0 AWG aluminum conductor with THHN insulation and a temperature
21. From tables provided in this chapter, approximate the full load rating for a 10 hp, 208 V,
rating of 60°C/140°F
b. No. 4/0 AWG aluminum conductor with THHN insulation and a temperature
three-phase electric motor, in amperes.
22. From tables provided in this chapter, approximate the full load rating for a 11⁄2 hp, 120
rating of 75°C/167°F
c. No. 4/0 AWG aluminum conductor with THHN insulation and a temperature
V, single-phase electric motor, in amperes.
23. From tables provided in this chapter, approximate the full load rating for a 100 hp, 460 V,
rating of 90°C/194°F
three-phase electric motor, in amperes
18. From tables provided in this chapter, identify the ampacity of the following conductors:
a. No. 500 kcmil aluminum conductor with XHHW-2 insulation and a temperature
rating of 60°C/140°F
b. No. 500 kcmil aluminum conductor with XHHW-2 insulation and a temperature
rating of 75°C/167°F
c. No. 500 kcmil aluminum conductor with XHHW-2 insulation and a temperature
rating of 90°C/194°F
19. Nonmetallic (NM-B) cable is commonly used in single family residential installations.
From tables provided in this chapter, identify the ampacity of the following conductors:
a. NM-B cable with three No. 14 AWG copper conductors having THHN or THWN
insulation
b. NM-B cable with three No. 12 AWG copper conductors having THHN or THWN
insulation
c. NM-B cable with three No. 10 AWG copper conductors having THHN or THWN
insulation
20. Armored cable (AC) is commonly used in commercial, industrial, institutional, and multi
residential installations. From tables provided in this chapter, identify the ampacity of the
following conductors:
a. AC cable with three No. 14 AWG copper conductors having THHN or THWN
insulation
b. AC cable with three No. 12 AWG copper conductors having THHN or THWN
insulation
c. AC cable with three No. 10 AWG copper conductors having THHN or THWN
insulation
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