A GFCI compares the current going out against the current coming back. If more than a few milliamps go missing — because they found a path through a person, or through water — it opens in a fraction of a second. It is one of the highest-value safety devices per dollar in a house.
Where they are required
- Bathrooms — all receptacles
- Kitchens — countertop receptacles, and increasingly all of them
- Garages and accessory buildings
- Outdoors, including any receptacle on a deck or patio
- Unfinished basements and crawlspaces
- Laundry areas and utility sinks
- Within six feet of any sink, tub or shower
- Pool, spa and hot tub equipment — see hot tub electrical installation
Older homes are not required to retrofit retroactively, but adding GFCI protection is quick and inexpensive, and it is the single easiest safety upgrade in most houses. See GFCI outlet installation.
GFCI vs AFCI
They solve different problems and are not interchangeable. GFCI protects people from shock by detecting leakage to ground. AFCI protects the building from fire by detecting the electrical signature of arcing in damaged wiring. Modern code requires both in various places, and dual-function breakers do both jobs at the panel.
Why yours keeps tripping
- Moisture. Outdoor receptacles after rain, or a bathroom fan venting into an attic. Dry it out and retest.
- A failing appliance. Unplug everything downstream, reset, then reintroduce items one at a time. Old fridges, sump pumps and heaters are frequent culprits.
- Long circuit runs. Small natural leakage on a long run can add up past the threshold, particularly on older wiring.
- The GFCI itself. They wear out. If it will not reset with nothing plugged in and nothing downstream, replace the device.
- A genuine wiring fault. If it trips instantly with the load side disconnected, stop and get it traced.
Test them monthly
Press TEST, confirm power dies, press RESET. It takes ten seconds and a GFCI that fails this test is not protecting anyone. If yours will not reset at all, that is a troubleshooting call, not a mystery to live with.