How to install ground fault interrupters
Electric shock protection. Fuses and circuit breakers protect against short circuits, but even a small current leakage in an electric appliance can cause serious shock if you are barefoot or standing on wet ground. For this reason, the National Electric Code requires that all receptacles in newly installed bathroom and outdoor circuits be equipped with a ground fault interrupter (GFI). This highly sensitive device monitors the current flowing through a circuit's black (hot) and white (neutral) wires. If there's no leakage, the currents will be the same. But a difference of .005 ampere or more causes the GFI to cut off power to the circuit within a fraction of a second, well before the current flow can harm you.
Three types of CFI's are available. A combination GFI - circuit breaker unit installed in the circuit breaker panel by an electrician protects an entire circuit. A portable GFI plugs into a standard three-prong receptacle. A permanent GFI receptacle is installed like a standard receptacle in a wall or outdoor box (see Electric receptacles). The GFI leads marked Line are connected to the feed cable wires, and those marked Load to the outgoing cable wires. Follow package directions or have an electrician install it.
A GFI has a test button, which simulates a current leak when pushed, and a reset button. Test a GFI monthly. If the reset button doesn't pop out when you push the test button, of if a test lamp lights when the reset button is out, turn off power to the circuit and call an electrician.