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Homes in North America typically are
powered with both 220-volt and 110-volt alternating
current (AC) electricity. Modern outlets have three
different shaped holes to assure plugs can only be
inserted in one way. Two of the holes are considered
grounds, for reasons of safety. Proper grounding and the
use of fuses are important to maintain electrical safety
in the home.
Questions you may have about AC home
wiring are:
-
What is the configuration of home
wiring?
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What do the holes in the wall
outlets represent?
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What safety features are necessary?
Home wiring
Typically, homes in North America
receive 220 volts of AC electricity. Certain high-power
devices, such as an electric stove, use the full 220
volts. The rest of the outlets in the house use 110
volts.
Usually, three copper wires come into
the home. Two are covered in black insulation and one
has white insulation. Sometimes one wire is red instead
of black. Each black or red wire is called a "hot" wire
and has 110-volt AC. The white wire is called the
"common" and is grounded at the power station. Measuring
across the two hot wires results in 220 volts. Measuring
the voltage between a black (or red) and white wire,
results in 110-volt AC.
Wiring configuration
Copper wire is used because it is a good
conductor of electricity. Materials that do not conduct
electricity as good usually have a higher resistance.
This results in wasted energy and the tendency to get
hot, which could be a safety hazard.
In the 1960s many electrical contractors
started to use aluminum wire instead of copper. Aluminum
is almost as good of a conductor as copper, but it is
much less expensive. After a number of years, it was
found that this type of wiring caused a potential fire
hazard. Problems due to expansion caused overheating at
connections between the wire and switches, outlets, or
splices. Many homes had to be re-wired, although there
still are many that still have aluminum wiring but have
never had problems.
Wall outlets
The wall outlets usually have a one wide
slot, one narrow slot and one round-with-flat-bottom
hole. This is to assure that each part of the plug will
be used as it is supposed to and to increase safety.
Older outlets have both slots the same size and no round
hole.
Typical wall outlet
The narrow slot is considered "hot" and
is where the alternating current power comes out. The
wiring behind the outlet to this slot is usually black
in the U.S. The wide slot is considered the "common" and
is supposed to be grounded. Using the white wire as a
common grounded wire, means that everyone is working
from the same zero voltage position.
The hole that is round on the top and
flat on the bottom is an extra ground. Usually the wire
behind the wall outlet has green insulation. Sometimes
it is a bare wire. This extra ground is to make sure
your utensils are properly grounded in the situation
that someone had improperly wired the house. It is an
extra safety measure.
Although the white wire is not supposed
to be a "hot" wire, in some cases it is used that way,
especially in older homes that have the old style
outlets. In general, this is acceptable, but it can
result in problems. If you touch a common wire that is
properly grounded, you should not get a shock. But if
that wiring has made it hot, you can get a shock. Also,
by using the white wire where the black should be used,
you may cause a short circuit.
Safety
Proper grounding and the use of fuses
are important for protection against shock, as well as
to prevent electrical overheating and fire hazards
Correct grounding is very important.
Often ground wires are connected to water pipes that
normally go into the ground. Connecting to a hot water
pipe means that the water heater is between the
connection and the ground. The water heater may have
plastic parts that would insulate the connection to
ground. Thus, using a hot water pipe is not a good idea.
Another consideration in using water
pipes to ground the circuit is that plastic piping is
often being used in plumbing. You must make sure there
are no plastic pipes between your connection and the
outside earth or ground.
Fuses and circuit breakers are used as a
safety measure in case of short circuits. A fuse or
circuit breaker will break the connection if more
current is passing through the wire than is considered
safe. This will prevent the house wiring to overheat and
start a fire.
Most homes now use circuit breakers
instead of fuses. One reason is because people with bad
wiring in their homes that constantly blow out fuses,
would then force pennies in the fuse receptacles, thus
bypassing the requirement for a fuse. This removed the
aggravation, as well as the expense of buying new fuses,
but it also often resulted in serious electrical fires
in the house.
Most homes use both 220- and 110-volt AC
electricity. Wires have black, red, white or green
insulation, depending on their use. The holes in modern
outlets assure plugs can only be inserted in one way.
Proper grounding and the use of fuses are important to
maintain electrical safety in the home. |
