A ground fault occurs when an unintentional path is created between a source of current, such as a damaged electrical cord and the ground. Human beings can provide that path. The result can be a burn, shock or electrocution.

Ground-fault circuit interrupters (GFCI) protect against shock by measuring the current going into an appliance and coming out. Any discrepancy between the two indicates that electricity is passing where it shouldn’t - for instance, from a faulty electrical cord, extension cord or appliance.

The GFCI constantly monitors electricity flow in a circuit. When the GFCI detects leaking current, it switches off power before serious injury or damage can occur. A difference of only 5 milliamperes (5 thousandths of an ampere) is enough to trigger a GFCI.

There are three types of GFCI’s: The receptacle GFCI is used in place of the standard duplex receptacle. It fits into the standard outlet box. Most GFCI’s can be installed so that they also protect other electrical outlets further downstream in the branch circuit.

The circuit breaker GFCI is used in buildings that have circuit breakers rather than fuses. The GFCI is installed in a panel box to give protection to selected circuits. This type serves a dual purpose: it shuts off electricity in the event of a ground-fault, as well as when a short-circuit or overload occurs. The groundfault protection covers both the wiring and each individual outlet, lighting fixture or appliance served by the branch circuit protected by the GFCI.

Portable GFCI’s are used when working outdoors, or in other situations when a permanent GFCI is not practical. These can take two forms: either a single outlet adapter or an extension cord and GFCI combined.

GFCI protection is required, by code, for most outdoor receptacles, bathroom receptacle circuits, garage wall outlets, kitchen receptacles, and all receptacles in crawl spaces and unfinished basements.