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An electrical service panel is the main distribution center of your house's electricity.
It's where the local utility's service lines hook up with the individual circuits
that run throughout the house. If
you don't feel comfortable working at the service panel, don't take chances --
hire a licensed electrician. In many areas, an electrician is also needed to hook up the service leads to the service panel and that's also a good time to have the branch circuits hooked up.
Here,
we'll explain the major parts of the service panel to give you a basic understanding
of how it functions. Three
utility service lines come into the panel. Two "hot" leads attach to a two-gang
main circuit breaker that connects to two "hot" buss bars. Individual
branch circuit breakers, rated to accept a fixed amperage of electricity,
clip or slide onto the hot buss bars. Each
breaker also connects with an outbound "hot" lead that supplies a circuit. The
service panel has a neutral buss bar where the incoming neutral service
line connects with the neutral leads of the branch circuits. The
panel should also have a ground buss bar where all the branch ground wires screw
in. In main service panels, the ground buss and neutral buss are connected together to provide a safe grounding path for both busses.
If
it hasn't been done already, you should label each breaker so you know just what
it controls. Circuit
breakers protect the wiring and fixtures by turning off the power. If a fixture
shorts out, or if a circuit gets overloaded, the breaker will "trip." That
cuts power to the circuit and protect the wires and fixtures from damage. The
most common reason for a breaker to trip is too many appliances and lights on
one circuit. A tripped breaker usually looks like it's between the ON and OFF positions. To reset a breaker, turn it OFF and then ON again. If a service panel doesn't have breakers, it probably has fuses.
There
are cartridge fuses and screw-in fuses. Cartridges look kind of
like a shotgun shell. They mount in a little rack that pulls in and out of a bracket
Screw-in
fuses screw in and out like light bulbs. Some have a glass window on top and metal
threads on bottom. When
a fuse blows, its internal metal strip breaks and the window may get discolored.
Be sure to replace a fuse with the exact same amperage-rated fuse. Fifteen
and 20 amp fuses are the most common size ratings. Some fuses have a smaller screw
base and are called "non-tamperable, type-S" fuses. The
threads vary in size so they can't be accidentally replaced by another type. When
you install a fuse, screw it in snug, then give an extra 1/4-turn to make a solid
connection. Other
fuses are rated as "slow-blow" or "time delay." They take a little
longer to blow and are made to withstand short, extra surges of power -- like
a motor starting. When buying replacements, be sure to get the right fuse types. It's also a good idea to get a couple extra fuses of each type to keep on hand when working on circuits. | |||
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This section is not designed to help a beginner start work on a service
panel. Remember, no one should attempt service panel work without having a firm
understanding of what it's all about. 
All newer homes, and many older ones that have been re-wired, will have circuit
breakers. Each breaker controls the power to a group of lights, outlets and appliances.
Fuses perform the same function as a breaker, except when a fuse blows,
it has to be replaced.