GFCI's are available either as an outlet or as a circuit breaker. The outlets are installed similar to a standard outlet and, depending on how they are wired, can protect just their one location, or be used to protect other standard outlets downstream from the GFCI in the circuit.

The GFCI circuit breaker is installed in the electrical system breaker box and protects every plug or device connected to its particular circuit. The GFCI circuit breaker looks similar to a normal circuit breaker except for the test button on the front of the breaker. When the GFCI breaker trips, it does not indicate whether the breaker tripped from an overload or excessive leakage in the circuit.

Protecting Downstream Outlets GraphicOne feature of the GFCI outlet is that it can be wired to protect all the standard outlets further downstream in the circuit. If an electrical problem develops on a piece of equipment plugged into a standard outlet with a GFCI upstream, the GFCI trips and shuts off power from the GFCI to everything connected downstream. When GFCI's are wired like this, it is sometimes difficult to tell where the leak in the circuit is, since any outlet or piece of equipment downstream from the GFCI could cause it to trip.

Since GFCI's do not rely on a grounding wire to operate, they can be installed in older homes having two prong non-grounded outlets, and provide a level of safety heretofore unattainable. The National Electrical Code allows GFCI's to replace a two-prong outlet for this reason. Since a GFCI receptacle has a third grounding plug as a standard feature, this eliminates the need for using grounding adapters.