Short definition
A GFCI (Ground Fault Circuit Interrupter) is an outlet or breaker that compares current flowing through hot and neutral conductors. If the difference exceeds about 5 milliamps — the threshold below which current through a person’s body remains survivable — it disconnects power within roughly 25 milliseconds. Required by NEC and adopted in Washington for receptacles in wet and damp locations.
What it is
A GFCI continuously measures hot-side current and neutral-side current. In a normal circuit, those are equal. When current “leaks” — for example, through a person standing on a wet floor and touching a faulted appliance — some of it returns through the body to ground rather than through the neutral. The GFCI sees the imbalance and trips.
The personnel-protection trip threshold is 4–6 milliamps (Class A devices, per UL 943). Trip time is roughly 25 milliseconds. That’s fast enough that the cumulative current passing through the body stays below the level required to cause ventricular fibrillation in a healthy adult.
The UK calls the equivalent device an RCD (Residual Current Device), typically set at 30 mA for whole-circuit protection — not the same as US 5 mA personnel-protection.
Why it matters to a homeowner
Wet areas of a home — bathroom counters, kitchen counters, garages, exterior outlets, basements, laundry rooms — are where electrical faults most often kill people. The combination of water on the floor and an appliance with compromised insulation is the textbook scenario. GFCIs prevent the fatal pathway.
For homeowners, GFCIs show up in two ways: as receptacles (the outlet itself has the test/reset buttons) or as breakers (the entire branch circuit is GFCI-protected at the panel). Both are code-acceptable; the receptacle is usually cheaper for retrofits. Either way, monthly testing — pressing the TEST button to verify the unit trips — is the maintenance step that separates “device that works” from “device that’s been broken since 2014.”
When you’ll encounter this term
- Pre-1980 home with ungrounded 2-prong outlets in kitchen/bathroom — replace with GFCI receptacles, which allow grounded plugs without re-wiring (label “no equipment ground” required by NEC)
- A bathroom outlet trips when running a hair dryer — dryer leakage or end-of-life GFCI
- Outdoor outlets failing repeatedly after rain — weather-resistant in-use covers required
- New jetted tub install — dedicated GFCI-protected circuit per NEC 680
- Adding a kitchen island with a sink — countertop receptacles GFCI-protected
Common variants and disambiguation
- GFCI receptacle (point-of-use, $15–$30) vs. GFCI breaker (whole-circuit, $40–$80). Both are code-acceptable; receptacle is usually cheaper for retrofits.
- GFCI vs. AFCI vs. dual-function. GFCI protects against ground-fault electrocution. AFCI (NEC 210.12) protects against arc-fault fire. Some locations require dual-function (combined GFCI + AFCI).
- GFCI vs. GFPE (ground-fault protection of equipment). GFPE trips at higher currents (30 mA typical), used for equipment protection, not personnel.
- GFCI on a 240V circuit. Used for water heaters and similar; uses a 2-pole GFCI breaker.
Common failure modes
- Nuisance tripping. Old appliance with high leakage (older fridge, old well pump, certain LED drivers), wet outdoor outlet, miswired daisy chain.
- No reset / dead receptacle. Homeowner replaces non-GFCI with cheap unit that won’t trip-test correctly.
- Reverse-wired (line/load swapped). Common DIY error; GFCI doesn’t protect the load side correctly.
- Open ground fault. GFCI still functions to protect persons (it works without a ground), but a tester should signal “no ground.”
- End-of-life electronics. GFCI internal electronics fail; many manufacturers self-test and indicate failure with an LED.
- Painted-over reset button. Disabled during a remodel.
Cost data
| Item | Cost |
|---|---|
| GFCI receptacle | $15–$30 retail |
| GFCI breaker | $40–$80 retail |
| Whole-circuit GFCI breaker install | $100–$250 with electrician |
| Outlet replacement (single location) | $50–$150 with electrician |
| Whole-house bringing up to current code | $500–$2,500 depending on age and wiring access |
Washington note
Washington adopts the National Electrical Code via WAC 296-46B with state amendments. NEC 210.8(A) requires GFCI for receptacles in residential bathrooms, kitchens, garages, accessory buildings, outdoors, crawl spaces, unfinished basements, laundry areas, and other listed locations. The exact list expands with each NEC cycle (2017, 2020, 2023).
WA L&I administers the electrical permit and inspection program. For paid electrical work, a licensed electrician (EL01 or EL06 specialty) is required. Washington has specific owner-occupied DIY electrical permit rules — verify with L&I before doing any electrical work yourself.
FAQ
Why did my GFCI trip when nothing’s wrong?
Nuisance tripping has a few common causes: an aging appliance with elevated leakage current, a wet outdoor outlet without weatherproof cover, a miswired daisy chain, or an end-of-life GFCI itself. Try unplugging everything from the protected circuit, then resetting; if it holds, plug devices back in one at a time to find the culprit. If it trips immediately with nothing plugged in, the GFCI itself may have failed.
Do I need a GFCI breaker or a GFCI receptacle?
Either is code-acceptable. A GFCI receptacle protects the receptacle itself plus any downstream outlets wired in series (“load side”); a GFCI breaker protects the entire branch circuit. For retrofits with one or two wet-area outlets, the receptacle is usually cheaper. For new construction protecting many outlets on a circuit, the breaker is often the cleaner answer.
Should I push the test button on my GFCI outlets?
Yes — monthly. Press TEST; the outlet should click off. Press RESET; it should click back on. If it doesn’t trip during TEST, replace the device. UL 943 GFCIs are designed for monthly testing as the maintenance protocol.