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.
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.
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.
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.
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.
Fuses perform the same function as a breaker, except when a fuse blows, it has to be replaced.
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.