What is a GFCI outlet?
Updated August 2026
A GFCI outlet, short for ground fault circuit interrupter, is a receptacle with Test and Reset buttons that compares the current leaving on the hot wire against the current returning on the neutral and cuts power in about 1/40 of a second if the two stop matching. An imbalance of roughly 5 milliamps means electricity has found another path to ground, and in a bathroom or a kitchen the most common alternate path is a person. Speed is the entire point: it opens faster than a shock can stop a heart.
Where it is
Look for the pair of small buttons on the face of a receptacle. Code puts them wherever water and electricity meet: kitchen countertops, bathrooms, laundry areas, garages, unfinished basements, crawl spaces, outdoors, and within 6 feet of any sink. One GFCI also protects everything wired downstream of it, so a plain-looking garage outlet may already be covered by a device in the bathroom or by a GFCI breaker in the panel. Map that before you go hunting: press Test on each device and note which ordinary receptacles die with it.
What it does
A GFCI protects people, which is a different assignment from the one your circuit breaker has. The breaker watches total current and saves the wire; the GFCI watches for leakage and saves whoever completes the circuit. Neither one covers the arcing an AFCI is built to catch. The failure mode nobody expects is the silent one. Devices made before the 2003 standard revision can lose their sensing electronics to surges and humidity while still feeding the plugs, so the outlet looks healthy and protects nothing at all. Units built since 2015 self-test continuously and refuse to reset once they fail, which is the behavior you want. Repeat tripping usually means real moisture in an exterior box rather than a bad device.
Maintenance
Press Test on every GFCI once a month. The Reset button should pop, whatever is plugged in should die, and Reset should bring it back with a firm click. Anything else, no pop, no loss of power, a reset that will not hold, means replace the device now. Ten seconds per outlet, and skipping it is the whole premise of what a dead GFCI eventually costs. Plan on 10–15 years of service, less outdoors or in a steamy bathroom, and see the replacement schedule for the details.
What it costs to replace
A replacement GFCI outlet runs $15–25 for the receptacle, or $130–250 per outlet installed by an electrician.
OnOtto's photo scan identifies parts like this in your home and builds the maintenance schedule for you. See how the scan works.
Frequently asked questions
Why did half my outlets stop working when no breaker tripped?
Odds are a GFCI you have forgotten about did trip, and it feeds the dead ones. A single device protects everything wired downstream, so a bathroom outlet can control a garage, a patio, and the receptacles behind a workbench. Check every GFCI in the house, including exterior walls and any hidden behind stored boxes, then check the panel for a breaker with its own Test button. Press Reset. If it will not hold, something on that run is wet or faulty.
Does a GFCI work without a ground wire?
Yes. It measures the difference between hot and neutral, so it never needs the ground conductor to do its job. That makes it the standard fix for two-wire homes wired before grounding was required: an electrician installs a GFCI and labels the outlet No Equipment Ground. You get shock protection and a legal three-prong receptacle, though surge protectors plugged into it will not work properly, because they need a real ground path to shunt into.
GFCI outlet or GFCI breaker: which is better?
The outlet costs less and is easier to test, since the buttons sit at eye level instead of in the panel. The breaker protects the entire circuit including the wiring in the wall, which matters for outdoor runs and pool equipment, and it costs $40–70 against $15–25. Most homes end up with a mix of both. If you keep forgetting to test, put the device where you will see it, which usually argues for the outlet.
Can I replace a GFCI outlet myself?
This one is within reach for a careful DIYer. Kill the breaker, verify with a non-contact tester, photograph the wiring, then land the incoming feed on the LINE terminals and any downstream wires on LOAD. Reversing LINE and LOAD is the classic mistake, and the outlet will power up while protecting nothing. Confirm the result with a $15 plug-in GFCI tester. If the box is crowded, wired in aluminum, or has no ground, call an electrician.