Homes 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 include:
- What is the configuration of home wiring?
- What do the holes in the wall outlets represent?
- What safety features are necessary?
This lesson will answer those questions.
Home wiring
Typically, homes 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.
Wires into home
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
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
Outlet slots
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.
Round hole
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.
Common wire
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
Grounding
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
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.
Summary
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.
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