They look similar, they both trip, and homeowners routinely confuse them. They protect against completely different things.
A ground fault circuit interrupter compares current going out on the hot with current coming back on the neutral. If more than a few milliamps goes missing, that current found another path to ground — often a person — and the device cuts power in a fraction of a second. This is why GFCIs live near water: kitchens, bathrooms, laundry, garages, basements, outdoors and near sinks.
An arc fault circuit interrupter listens for the electrical signature of arcing — a loose terminal, a nail through a cable, a cord chewed by a pet. Arcing generates enormous localized heat without necessarily drawing enough current to trip a normal breaker. That is how wiring starts a fire behind a wall while the breaker sits there unbothered. AFCI protection is required for most living-area circuits in new work.
GFCIs: moisture in an outdoor box is far and away the top cause. Also long circuit runs with natural leakage, old motors, and devices past their service life. A GFCI that will not reset with everything unplugged has usually failed itself.
AFCIs: some motors and older appliances produce arcing-like signatures. Shared neutrals between circuits are another classic cause. Before assuming nuisance, though, treat an AFCI trip as real — the loose backstab connection it just found is exactly what it is for.
Press the test button monthly. It should cut power. Press reset. If test does not trip it, or reset does not restore it, the device has failed and needs replacing — a small job that people put off for years.
In a house with no equipment ground, GFCI protection is the code-recognized way to put a three-prong receptacle in legally, with the required "No Equipment Ground" label. It protects you from shock. It does not create a ground, so surge protectors and equipment that need a ground will not perform as designed. Running a true ground is the better long-term answer, which is part of why rewiring comes up in older homes.
Device testing, replacement and circuit protection upgrades. See outlet and GFCI installation or call (866) 651-5242.
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