Safety first. Working inside an outlet box means working on house wiring. Turn off the breaker, confirm the outlet is dead with a non-contact voltage tester, and check whether your area needs a permit or a licensed electrician before you start. If you’re not sure, stop here and call one. Testing the GFCIs you already have, below, needs no tools and no permit.
What a GFCI does
A ground fault circuit interrupter (GFCI, or GFI) watches the current going out on a circuit and the current coming back. The US Consumer Product Safety Commission (CPSC) explains that if the two differ by as little as 0.006 amperes, the GFCI cuts the power faster than a blink, before the shock can affect your heartbeat. That leak is a ground fault: current finding a path to ground through a damaged appliance, water or a person.
A GFCI is not a circuit breaker. It doesn’t protect against an overloaded circuit, unless it’s a GFCI breaker, which does both.
Where they’re required
In the US, the National Electrical Code (NEC) decides which circuits need GFCI protection, and it has added locations over the years. The CPSC lists when each one started:
| Location | Required since |
|---|---|
| Outdoor receptacles | 1973 |
| Bathrooms | 1975 |
| Garages | 1978 |
| Kitchens | 1987 |
| Crawl spaces and unfinished basements | 1990 |
| Wet bar sinks | 1993 |
| Laundry and utility sinks | 2005 |
Two things to know about that list:
- The code applies to new work. The CPSC notes that the NEC typically applies to new construction and major renovations, so an older home may have none of these, and that’s not a violation in itself. It is worth fixing.
- Your local code is what counts. States and cities adopt their own edition, sometimes with changes, and in Canada each province sets its own electrical rules. Ask your local electrical inspector, or see our permit guide.
One GFCI can protect a whole run
A GFCI outlet has two pairs of terminals, marked LINE and LOAD. Power from the panel goes to LINE. Anything wired to LOAD is protected too. The CPSC says a GFCI receptacle protects whatever is plugged into it and the outlets “down stream” on the same circuit.
That’s why a bathroom outlet with no buttons can stop working when a GFCI in another room trips. Before you replace a dead outlet, look for a tripped GFCI in the bathroom, kitchen, garage, basement or outside, and press its RESET button. Then check the breaker panel. Our Outlet not working page walks through the order.
How to test a GFCI
The CPSC says to test every GFCI after it’s installed, at least once a month and after a power failure. Leviton, a GFCI maker, says that even its self-testing models should still be tested by hand each month.
- Plug a lamp into the outlet and turn it on.
- Press TEST. The lamp should go out.
- Press RESET. The lamp should come back on.
If the lamp doesn’t go out when you press TEST, the GFCI isn’t working or isn’t wired correctly. If it won’t come back on with RESET, replace the GFCI. In either case, don’t rely on that outlet for protection until it’s fixed.
Replacing a regular outlet with a GFCI
The CPSC says receptacle-type GFCIs can be installed by people who have the knowledge to follow proper wiring practice and the device’s instructions, and that if you’re in doubt, you should have a qualified electrician do it. GFCI breakers go in the panel, and panel work is for an electrician.
A few points the instructions will cover:
- LINE and LOAD matter. The cable coming from the panel goes on LINE. Wired the wrong way round, the GFCI may not protect the outlets after it. If you can’t tell which cable is the incoming one, call an electrician.
- Two-slot outlets with no ground can be replaced with a GFCI. The CPSC says to apply the “No equipment ground” label that comes with it.
- Box space. A GFCI is deeper than a standard outlet. A crowded box may need a larger one.
In Ontario, the Electrical Safety Authority says homeowners may do electrical work in their own home only after filing a notification of work with ESA, even for small jobs. Other places may require a licensed electrician. See when to call a licensed pro.
When to call an electrician
- A GFCI trips again as soon as you reset it, with nothing plugged in.
- An outlet or cover plate is warm, buzzing or scorched.
- A breaker keeps tripping.
- You don’t have the wiring the instructions describe, or you find aluminum wire.
Watch it done
Install a GFCI outlet and Replace an outlet collect videos from licensed sources. If one won’t reset, see GFCI won’t reset. More under Electrical.