Ground fault circuit interrupter: the trip that will save your life
When are GFCIs required?
A ground-fault occurs when there is a break in the grounding path from a tool or electrical system. When a ground fault happens, the electrical current takes an alternative path to ground. If a person is part of that path, an electric shock results.
The ground-fault circuit interrupter, or GFCI, is a fast-acting circuit breaker that shuts off electric power if a ground-fault is detected. The GFCI breaks the circuit within 1/40 of a second, quick enough to prevent an injury. It works by comparing the current going to and returning from the tool or equipment. When the amount differs by more than 5 milliamps, the GFCI breaks the circuit.
A GFCI does not provide protection from line contact hazards, i.e. a person holding two “hot” wires, a hot and a neutral wire in each hand, or contacting an overhead power line. (Note that direct line contact is a less common hazard.) However, a GFCI – in addition to protecting against the most common form of electrical shock hazard, also protects against fires, overheating, and destruction of wire insulation.
It’s a good practice to test GFCIs on a regular basis. Check the manufacturer’s recommendations for testing and testing frequency.
GFCI protection is required on outdoor temporary circuits (extension cords used for power tools) and in wet locations. Also, they need to be attached at the power source and not to the tool-end of an extension cord.
GFCIs will provide protection when needed, but only when they are used correctly and tested.