conductor is wired to the brass colored
screw terminal of the duplex outlet.
The neutral (sometimes called the cold)
wire is usually covered with white insula-
tion and completes the circuit to the device
plugged in. The neutral is termed this
because it will ultimately be connected to
an earth referenced ground. This ground
connection can be the cold water pipe (as
long as it is metal) or a copper rod pound-
ed into the ground (earth) near the home
electrical panel. The neutral wire is con-
nected to the silver colored screw terminal
on the duplex outlet. If you look carefully
at the front of an outlet, the neutral wire is
connected to the larger opening, the hot
wire to the smaller opening.
The safety ground wire, or ground, is
covered with green insulation. Its purpose
is to conduct electrical current away from
a fault or short circuit. Let’s suppose an
electrical heater that is made of metal
develops a problem or fault right where
the electric cord enters the device. The
insulation has been damaged, and the hot
wire is touching the metal cabinet. In this
unsafe situation, someone touching the
metal cabinet of the heater and an electri-
cal ground (another appliance, plumbing,
or any other device that may be grounded)
could receive a fatal electrical shock. The
safety ground takes this potential path of
current (from the metal case) to the earth
ground. The ground wire provides a low
resistance connection from the hot wire to
ground. In this way, an excessive amount
of current flows. Enough current should
flow that it will blow out a fuse or trip a
circuit breaker. For this system to function
properly, those who do the wiring, elec-
tricians, must follow strict codes and rules
for everyone’s safety. The National
Electrical Code specifies the rules that
must be followed by electricians who
work in homes and industries.
In Figure 7-14, no electric current is
being used because no appliance or light
(an electrical load) has been plugged in.
When a load is plugged in (R1
= 100 Ω),
a current flows, Figure 7-15.
I = = 1.1 A
and the power is:
P = I × E
or
P = 1.1 A × 110 V = 121 W
R1
(100 Ω) is the only resistance in the
circuit.
When R2
(also 100 Ω) is plugged in,
R1
and R2 are in parallel and the total
resistance is:
RT
= = 50 Ω
and the total current flowing is:
I = = 2.2 A
The power is:
P = 2.2 A × 110 V = 242 W
110 V
50 Ω
100 Ω
2
110 V
100 Ω
62
Electricity
Line
R2
R1
R1 = 100 Ω
R2 = 100 Ω
Figure 7-15.
Appliances plugged into convenience outlets
are in parallel across the line.