The basic monthly test (30 seconds)
- Push TEST. Button in the center of the GFCI outlet. You should hear/feel a click. The RESET button pops out.
- Verify power is off. Plug in a lamp or a plug-in tester at the GFCI and at any downstream outlet on the same circuit (GFCI protects downstream too). Confirm no power.
- Push RESET. Button back in flush. Click. Power restored.
If the test button doesn't trip the outlet — replace the GFCI. If RESET won't hold — see "Why won't my GFCI reset" below.
The trip-time test (annual, with a plug-in tester)
A plug-in GFCI tester (Klein RT250 or Fluke ST120+, $24-$35) does what the on-outlet button can't: measures the trip time. Plug it in, push the tester's trip button, and the LCD displays the actual trip time in milliseconds.
- Under 25 ms: within UL 943 spec. You're protected.
- 25-50 ms: trips, but slow. Replace soon.
- 50 ms+ or won't trip: replace now. Personnel protection is compromised.
Why won't my GFCI reset?
Three causes, in order of likelihood:
- Actual ground fault on the circuit. Unplug everything downstream and try RESET. If it holds, plug devices back in one at a time until you find the one that trips it. That's your faulty appliance or extension cord.
- GFCI is at end-of-life. Sealed-lithium-class GFCIs commonly fail at 10-15 years (less outdoor). UL 943 added end-of-life self-test requirements in 2015 — newer units have an indicator LED that blinks when they fail. If the LED blinks, replace.
- Wiring backwards. LINE and LOAD terminals reversed during install. Newer GFCIs auto-detect reversed wiring and refuse to reset. Power off at breaker, swap LINE and LOAD wires, restore power, RESET.
Where GFCI is required (NEC 210.8)
- All bathroom receptacles
- Kitchen receptacles serving counter surfaces (extended in NEC 2020 to all kitchen receptacles)
- Laundry / utility sinks
- All outdoor receptacles
- Garage receptacles
- Unfinished basement receptacles
- Within 6 ft of any sink, tub, or shower (NEC 2017+)
- Dishwashers (NEC 2014+)
- Bathtub + shower walls (NEC 2020+ — heated towel racks, etc.)
What GFCI does NOT protect against
- Short circuits. That's the breaker's job.
- Overloads. Also breaker.
- Arc faults. That's AFCI's job (NEC 210.12). Many modern circuits need BOTH GFCI and AFCI — DUAL-FUNCTION breakers solve this in the panel.
- Surges. See surge protectors.
- Standard 120V line-to-neutral hand-to-hand contact. GFCI protects against ground faults (line-to-ground through your body). It won't trip on a perfect line-to-neutral fault where you're touching both conductors at once. Rare scenario, but worth knowing.
FAQ
How often should I test my GFCI outlets?
Monthly per NEC and manufacturer recommendations. UL 943 requires trip in <25 ms at 6 mA.
Is the TEST button enough?
For mechanism check — yes. For trip-time verification — no. Use plug-in tester (Klein RT250, Fluke ST120+).
Why won't my GFCI reset?
(1) Real ground fault downstream — unplug things. (2) End-of-life — sealed-lithium GFCIs commonly fail at 10-15 yrs. (3) Wiring reversed.
How long do GFCI outlets last?
10-15 yrs indoor; 5-10 outdoor. UL 943 added self-test requirements in 2015 — newer units have indicator LEDs that flash at end of life.
Related guides
- GFCI keeps tripping for no reason — when the trip is real, not random
- Best home electrical tester kits 2026 — Klein RT250, Fluke ST120+
- Lights flickering — adjacent electrical diagnostic
Editorial standards: Cited authorities include UL 943 (GFCI standard) and NEC 210.8 (GFCI required locations) + NEC 210.12 (AFCI required). Reviewed by Al, Building Doctor — 18 years Class A commercial electrical Chief Engineer.