Electrical Principals Chapter 5

Electrical Principals
Chapter 5
Switches, Fuses, Ground,
Receptacles, Basic Circuit
A Switch is a device that is used to start, stop,
or redirect the flow of electricity in an electrical
A Switch must be rated higher than (or equal to)
the voltage and current the Switch is controlling.
There are three manual types of Switches used
to control the ON/OFF current flow in a circuit
and they are two-way, three-way, and four-way
Two-Way Switch is a single-pole, singlethrow (SPST).
A Two-Way Switch has two positions and
they are ON and OFF
A Two-Way Switch is used to control a
circuit from one location.
Three-Way Switch is a single-pole,
double-throw (SPDT) switch.
A Three-Way Switch does not have an
ON – OFF position.
A Three-Way Switch is used to control a
circuit from two different locations.
A Four-Way Switch is s double-pole,
double-throw (DPDT) switch.
A Four-Way Switch changes the electrical
connections inside the switch from straight
to diagonal.
A Four-Way Switch does not have ON –
OFF positions.
A Four-Way Switch is used with ThreeWay switches to control a circuit from
three different locatrions.
A Fuse is an equipment protection device that
consists of a thin wire link within a casing.
All Fuses have a current rating and this
indicates what value of current will generate
enough heat to open the Fuse.
When the circuit current exceeds the rating of
the fuse, the fuse opens (wire link melts) and
prevents current from flowing in that part of the
Fuses come in a variety shapes, sizes,
Fuses are very low resistance devices
connected in series with the circuit’s
Fuses for DC current are different from
Fuses used in AC circuits. Fuses ARE
NOT Interchangeable between AC and
DC circuits.
Fuses also have a voltage rating that indicates
the maximum circuit voltage that can be applied
across the Fuses by the circuit in which the
Fuses resides.
This voltage rating, which is important after the
fuse has blown, prevents arcing across the
blown fuse contacts.
Once the fuse has blown, the circuits positive
and negative voltages are now connected
across the fuse contacts.
If the voltage is too great, an arc can jump
across the gap, causing a sudden surge of
current, damaging the connected equipment.
Fuses are mounted with Fuses holders and
normally are placed at the back of the
equipment for easy access.
When replacing Fuses ensure the power to the
equipment is turned OFF before replacing a
blown Fuses.
Ground is a term used to identify zero potential.
All potentials are either positive or negative with
respect to ground.
Ground, in electricity, is an electrical conductor
that is connected to Earth to complete a circuit.
In electrical equipment, such as household
appliances, the ground conducts electric current
that may build up in the appliance because of a
"leak" or a short circuit.
There are two types of Grounds: Earth and
In homes, offices, and buildings or AC circuits,
all electrical circuits and appliances are earth
In automobiles, the chassis becomes the ground
for all circuits. The ground serves as part of the
complete circuit.
In electronics, electrical ground serves a
different purpose: Ground is defined as the zero
reference point against which all voltages are
Basic Circuit Conditions
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