GFCI (Ground-Fault Circuit Interrupter)
Affiliate link — we may earn a commissionA GFCI monitors the current flowing out on the hot wire and returning on the neutral wire. If it detects an imbalance of 4 to 6 milliamps, it trips in about 1/25th of a second, cutting power before the current can cause a lethal shock. The imbalance means current is leaking through something it shouldn't, like your body, water, or a damaged cord. GFCIs come as outlets (the ones with TEST and RESET buttons), breakers (in the panel), or portable devices (the yellow boxes on job-site extension cords). The NEC requires GFCI protection in bathrooms, kitchens, garages, outdoors, and unfinished basements.
Why It Matters
A standard circuit breaker protects the wiring, not you. It trips at 15 or 20 amps. Your heart stops at about 0.1 amps. A GFCI trips at 0.005 amps, fast enough to stop a lethal shock. Any time you use a corded power tool near water, on concrete, or outdoors, run it through a GFCI outlet or portable GFCI. No exceptions.