Your Homes Electrical System

Electricity is a mystery to many people, but there are rules that govern how your home's electrical system should work. Every house should have an electrical panel with a main shutoff, whether it’s circuit breakers or fuses. The number of circuits will vary with the electrical loads in the house.

According to the National Electric Code (NEC), 240 volt – 100 amp service is now the minimum standard for residential use. Older homes may need to be upgraded to that standard to accommodate the electric demand common to today's lifestyle. Although older electric systems may be "grandfathered in," most communities require that all new electrical work meet code. That means, among other things, that the system must be grounded; all outdoor outlets, bath outlets, most kitchen outlets and basement outlets must be protected by Ground Fault Circuit Interrupters (GFCIs); and new work in other living areas of the house must be protected by Arc Fault Circuit Interrupters (AFCIs).

Ideally, your wiring should be color-coded to indicate the function of the wires (with black wires being "hot," white wires being "neutral," and green or bare wires being "ground.") But, with old knob-and-tube wiring (common in houses built prior to the 1950's), all of the wires may be black. Always check!

Using too high a fuse can allow the wires to heat up and burn their insulation before the fuse blows. For safety, all fuses or circuit breakers should be correctly sized to the wire they control -- and to the load on the circuit. Wire is assigned a number according to its thickness. That number ("gauge") corresponds to the maximum amps it can safely carry and determines the total wattage that can be used on that circuit. 12-gauge wire should carry no more than 2400 watts, and should be controlled by a 20-amp fuse or circuit breaker; 14-gauge wire, 1800 watts, controlled by a 15-amp fuse or circuit breaker. Unless you can determine the wire size, it's safest to assume any old knob-and-tube circuits to be 14-gauge, to prevent a fire hazard; if you put a 15-amp fuse on the circuit and it starts blowing, don't replace it with a bigger fuse -- unplug something from the circuit or upgrade the wiring.

Many household appliances use so much current that they are required by code to be on "dedicated" circuits (circuits with only a single item on them) to prevent nuisance tripping of the fuse or breaker. For example, a forced-air gas furnace should be on its own separate 20-amp circuit. Although the blower motor, when running, is rated at 1600 watts, a surge of 2200 watts is needed to get it to start spinning. If another appliance draws power from the same circuit as the furnace when it starts, the circuit breaker can trip.

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