The National Electric Code requires certain locations like bathrooms or other places with wet or damp conditions to have special power receptacles called ground-fault circuit interrupters, or GFCIs. GFCI outlets prevent you from being electrocuted due to malfunctions or accidents involving an appliance. The NEC requires that any receptacles on a kitchen countertop, in a bathroom or within 6 feet of any sink be GFCIs.
Electricity and Circuits
Electricity flows through a circuit through a pair of wires--one "hot" and one neutral. The hot wire carries the current from the source--usually a circuit breaker or fuse box to the appliance or fixture. The neutral wire returns the "unused" electricity back to the source. Touching the wires in a circuit will cause a shock, but shocks can also happen due to overloaded or short circuits.
A ground fault occurs when, because of a short circuit or overload, an electric device becomes an unintended conductor of electricity. In most instances, a ground wire protects you from faults by providing a pathway back to the service panel or to an electrode contract with the earth. If the ground is connected to the service panel, the fault trips a breaker or blows a fuse.
The Danger of Faults
Ground faults can cause electric shocks that are painful, harmful or even deadly. Normally the flow of current between the hot and neutral wire is fairly equal. Faults occur when the flow of electricity through the neutral wire is less than that of the hot wire. Shocks occur when you come between the two wires and the current flows through your body. If you are in contact with water or dampness, the effect can be deadly.
Function of a GFCI
A GFCI outlet contains a microprocessor that constantly measures the current flow in both wires. When the GFCI senses a difference in the flow, it opens the circuit--interrupting the flow--in as little as four-hundredths of a second. When this happens, the red reset button on the GFCI pops out. Once the fault is corrected, pushing the reset button on the receptacle closes the circuit.
Installing a GFCI
GFCI receptacles are not more difficult to install than standard receptacles, although there are more terminals on the GFCI. One set of terminals is the Load; the other is the Line. Current comes into a GFCI through the Line. A GFCI installed as the first receptacle in a run provides protection for all standard receptacles in that circuit. The wiring for the rest of the run is connected to the Line terminals.
Shortcomings of a GFCI
A GFCI receptacle can only work when a fault occurs. If you come between the hot and neutral wires and are not grounded, the flow of current remains equal--except it is flowing through your body. Since the GFCI does not sense a fault, it does not trip.
- "Wiring, 7th ed."; Creative Homeowner; 2010.
- Photo Credit Bathroom image by Nikolay Okhitin from Fotolia.com
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