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Electrical Service in the Typical
American Home
Caution:
Please read our safety
information before attempting any testing, maintenance
or repairs.
The typical American home has a
primary circuit coming in from the electrical supplier with two
120 volt "hot" wires and one neutral wire. These wires
connect to the main electrical panel and then possibly from there to one
or more sub panels. The main panel or sub panel contain circuit
breakers (or fuses for older installations). One breaker is used
for each of the home's "branch" circuits. Occasionally
a breaker may be "double tapped" to control more than
one branch circuit, although this may be dangerous and likely
violates your local electrical codes. Most branch circuits have
one 120 volt hot wire, one neutral wire and one ground wire. A
few specialized branch circuits have two hot wires instead of
one. Each of the two hot wires carry 120 volts which results in
240 volts being supplied on the circuit. Such circuits are commonly
used for air conditioners, electric ranges and dryers.
You may have noticed that electrical
devices have ratings listed such as 120v, 115v or 110v. These
are all designed to run on a standard circuit in your home. Your
electrical supplier delivers 120 volt current to your home. However
as electricity travels through the wire, it dissipates
some of its energy and as a result the voltage drops. By the time
it gets to the farthest outlet in your home, the voltage may have
dropped from 120v down to 108v or so. Voltage drops over a distance
are normal and to be expected.
Electrical current is commonly measured in watts,
amps and volts. The voltage is analogous to water pressure; it
measures the "pressure" of the electricity being "pushed"
through the wire. Wattage is the quantity of electricity being
pushed through the wire. Amperage is the result of wattage divided by voltage. So if you see a device rated for "15 amps",
that means when supplied with 120 volt current, it is designed
to handle up to 1800 watts
(15 amps * 120 volts = 1800 watts).
Circuit breakers and fuses are important safety
devices. They work effectively as a switch and are designed to
stop the flow of electricity. While a circuit breaker is very
much like a switch, fuses have a one time usage and must be replaced
each time they protect a circuit. When too much load is placed
on a circuit, the breaker "trips" and interrupts the
flow of electricity. An excessive load may result from too many
devices simultaneously in use on a circuit, a faulty device or
a short circuit, amongst other possibilities.
Without a circuit breaker, an overloaded device
could be damaged , a fire could result from the heat generated
by the device or wiring or from electrical sparking. Circuit breakers
however are not very effective at protecting people from electrocution.
The problem is that they do not trip quickly enough to protect
you from harm. That is why most electrical codes now call for
GFCI outlets
in wet locations such as kitchens and bathrooms. GFCI outlets
trip very quickly reducing your exposure to dangerous electrical
current.
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