GROUND FAULT CIRCUIT INTERRUPTERS (GFCIs)
The outlets with the "Test" and "Reset" buttons are specially designed to protect people better than ordinary outlets. GFCIs have been used in houses since the 1970s.
WHY ARE THEY USED?
GFCIs are designed to shut power off if there is a very small leak of electricity (a ground fault) which ordinary outlets do not notice. Normal outlets are shut off by a fuse or breaker if more than 15 amps flow. This helps prevent a fire. However, since people can be killed by 1 amp or less, GFCIs shut off power if a leak as small as .005 amp occurs.
HOW DO THEY WORK?
A GFCI detects a leak by comparing how much electricity comes back through the white wire to how much was sent in the black wire. When everything is working correctly, the current flow is the same. If a little electricity is leaking out, it may be going through a ground wire or through part of the house. If this happens, the black wire will have more electricity than the white wire. Electricity, like most people, will follow the path of least resistance. If a person touches a leaky electrical system, they may present a better route to ground for electricity since they may offer very little resistance. Another way of saying this is that the person may be a very good conductor, so the electricity will flow through the person giving them a shock or worse. Without a GFCI, this can be fatal. With a GFCI, the little leak would be detected and the power would be shut off.
WHERE SHOULD THEY USED AND WHERE SHOULD THEY NOT BE USED?
In the United States, GFCIs are now required by code for outdoor outlets, bathroom outlets, all kitchen outlets at counter height or on an island, whirlpool outlets, and electrical systems for swimming pools. They should not be used for refrigerators or freezers since during the time that the power is off, food can spoil. They should not be used for automatic garage door openers because it may prevent someone from being able to escape during a house fire or to enter a home using the car remote or keypad during a power outage.
CAN THE OUTLET BE GFCI PROTECTED IF THERE IS NO BUTTON?
Yes, IF the circuit breaker back at the panel has a "Test" button, it is a GFCI breaker. This will protect everything on that particular circuit. Any outlets wired downstream of a GFCI outlet are also protected if the GFCI is wired correctly.
CAN THEY BE ADDED TO OLDER HOMES?
Yes, GFCIs can be added to any electrical system. They are more expensive than regular outlets (average $15-$20), but may be viewed as inexpensive insurance. While they do not replace grounding systems exactly, some codes do allow GFCIs in lieu of grounding in some cases. It is safe to say that a circuit protected by a GFCI is better protected than one without.