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Circuit Circuit refers to the course electric current travels, from the point where power enters your house (the service entrance panel or a subpanel wired to it) through wires to a device using electricity (such as a light fixture) and back to its starting point. How Your Home is Wired Today, most homes have what's called "three-wire service." The utility company connects three wires - two "hot," one neutral - through a meter to your service entrance panel. These wires provide both 120-volt and 240-volt capabilities. One hot wire and the neutral wire combined supply 120 volts, the amount used for most household applications, such as lights and small appliances. Both hot wires and the neutral wire can form a 120/240-volt circuit for such needs as a range and dryer. Service Entrance Panel and Distribution Center The wires from the master connect to the service entrance panel, the control center for your electrical service. Housed in a cabinet or box, the panel is often located outside your home, below the electric meter. Or it can be on an inside wall, directly behind the meter. In this panel you'll usually find the main disconnect - the main fuses or main circuit breakers to which the wires connect. After passing through the main disconnect, the wires enter a distribution center housed in the service entrance panel or in a separate subpanel. Here the current is divided into branch circuits, each protected by a fuse or circuit breaker. The branch circuits run to lights, switches, receptacles, and permanently wired appliances. Grounding to Prevent Shock The National Electrical Code requires that every circuit have a grounding system. Grounding ensures that, in the event of a short circuit, all metal parts of the wiring system or of lamps or appliances connected to it will be maintained at zero volts. The grounding wire for each circuit is connected to the distribution center and then is run with the hot and neutral wires in the branch circuits. Wire Connections Connections between wires are made inside plastic or metal boxes mounted in the walls or ceiling. Switches, receptacles, and wall or ceiling-mounted light fixtures all have their own boxes. Individual wires are wrapped in color-coded insulation for easy identification. Though hot wires are usually black or red, they may be any color other than white, gray or green. Neutral wires are white or gray. Grounding wires are bare or green. Safety Tip Occasionally, a white wire will be used as a hot wire. For easy identification, it should be taped or painted black where it's close to terminals and splices. Safeguards in the System The service entrance panel and distribution center in your home are equipped with either fuses or circuit breakers. These are the weak points of each circuit - the safety devices that keep the branch circuits and anything connected to them from overheating and catching fire. If there's an overload or a short circuit, a fuse will blow or a circuit breaker will trip, shutting off the flow of current. Circuit breakers Circuit breakers are heavy-duty switches that serve the same purpose as fuses. When a circuit is carrying more current than is safe, the breaker switches to Reset. On most breakers, the switch has to be pushed to Off and then to On after the circuit trips. Ground Fault Circuit Interrupter (GFCI) The GFCI is a special kind of circuit breaker that is installed in bathroom, outdoor and garage locations. If there's a current leakage, or "ground fault," the GFCI opens the circuit instantly, cutting off the electricity. When a GFCI is tripped, reset it as you would a regular circuit breaker. For a receptacle GFCI, push the Reset button. Saving Electricity
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