Tuesday, November 30, 2010

Anatomy of an Electrical Service Panel

A service panel must conduct electricity to individual breakers, must receive and
route the current being returned through the neutral conductor, and must provide a
grounding medium for the system. In a sense, it’s the most powerful electrical device
in your system. Remember, the conductors and cable that come into and leave your
service panel include …

➤ Two hot conductors.
➤ One neutral conductor.
➤ One grounding conductor that

originates in the panel. The two hot conductors energize the panel—and thus the breakers—via two hot bus bars, which are located in the center of the panel. The black or red outbound wires are connected to the circuit breakers that clip or slide into the hot bus bars. These wires supply the current to electrical loads throughout your house. The neutral wires are connected to the neutral bus with setscrew terminals. A grounding bus bar connects the various grounding conductors from the circuits to the panel’s main grounding conductor. The grounding bus bar is bonded to the neutral bus bar. This is the only place the neutral and grounding conductors are tied together. In addition to individual breakers, most service panels have a single main service disconnect in the form of an individual breaker or a series of high-amperage breakers connected together. The code requires that you be able to shut the entire panel down with a maximum of six hand movements. (That is, the panel can’t need more than six switches or breakers to disconnect all of your home’s electrical equipment.) An old panel might require up to six moves to shut everything down, but new service panels all have a single main shutoff, as previously described. The code requires that this main disconnect be as close as possible to the service conductors’ point of entry into the building. In other words, you can’t bring the service conductors into one corner of your basement and then install the service panel 15 feet away while exposing the conductors. (Certain exceptions do apply.)

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