Quick answer
A ground-fault circuit interrupter (GFCI) is a safety device that shuts off power in a fraction of a second when it senses current leaking out of a circuit, such as through a person to ground.
It compares the current going out on the hot wire with the current coming back on the neutral. A gap as small as 0.006 amps trips it.
Quick facts
The key facts about GFCI (Ground-Fault Circuit Interrupter), with sources:
Key takeaways
- A GFCI protects people from shock; a regular breaker protects wires from overheating.
- It trips when outgoing and returning current differ by as little as 6 milliamps 1.
- You can get GFCI protection from an outlet, a breaker or a plug-in portable unit.
- NEC 2023 210.8 requires it in bathrooms, kitchens, garages, outdoors, basements and more 1 4.
- Press TEST every month; if the power does not cut off, call an electrician.
What a GFCI does
A GFCI watches for one kind of problem: a ground fault. That is when electricity leaks out of its normal path and finds another way to the ground. Sometimes that other path is a person. The GFCI cuts power before the current can do lasting harm.
CPSC calls it a device built to protect people from severe or fatal shocks. Because it detects ground faults, it can also stop some electrical fires 1.
You may also see it called a GFI. The terms mean the same thing. Most people meet a GFCI as a GFCI outlet with TEST and RESET buttons in a bathroom or kitchen. That outlet is only one of three forms, covered below.
How a GFCI works
In a normal circuit, every bit of current that goes out on the hot wire comes back on the neutral wire. A GFCI has a small sensing coil that both wires pass through. If the two currents match, nothing happens.
If some current is missing on the way back, it went somewhere else. The GFCI notices a gap as small as 0.006 amps and opens the circuit "faster than a blink of an eye," in CPSC's words 1. It is designed to act before the shock can affect your heartbeat.
CPSC gives a plain example. A bare wire inside an appliance touches its metal case, so the case becomes live.
You touch the case with one hand and a metal faucet with the other. Current flows through you to ground.
On a GFCI circuit, the power shuts off before a fatal shock can occur 1.
- Current flows out on the hot wireand normally returns on the neutral
- Sensing coil compares the twoboth wires pass through it
- Some current leaks to groundthrough a damaged cord, water or a person
- Gap reaches about 6 mAthe coil signals the trip circuit
- Contacts openpower to the outlet and downstream outlets stops
Source: [1]
Types of GFCI protection
| Type | Where it sits | What it protects | Notes |
|---|---|---|---|
| GFCI receptacle (outlet) | Replaces a standard outlet | That outlet and outlets wired after it on the circuit | Most common in homes; can replace a two-slot outlet with a "No equipment ground" label 1 |
| GFCI circuit breaker | In the electrical panel | The whole branch circuit, including lights and hard-wired loads | Also protects against overload 1 |
| Portable GFCI | Plugs into any outlet, or built into an extension cord | Whatever is plugged into it | Good for yard tools and power tools where outlets lack GFCI 1 |
| Dual-function (AFCI/GFCI) | Panel or outlet | Shock and arcing faults | Combines a GFCI with arc-fault protection 2 |
Worked example: how small 6 mA is
Current through the body, not voltage alone, decides how bad a shock is. These thresholds come from the Merck Manual and CPSC. They show why a GFCI trips at such a low level.
| Current | What it means | Source |
|---|---|---|
| 6 mA (0.006 A) | GFCI trip point | CPSC 1 |
| About 15 mA AC | "Let-go" current for an average 70 kg adult; above it, muscles lock and you may not release the source | Merck 3 |
| 60 to 100 mA AC | Can cause ventricular fibrillation (a deadly heart rhythm) if it crosses the chest, even for a fraction of a second | Merck 3 |
| 15 A | A common household circuit breaker rating | Typical breaker size |
A 15-amp breaker allows about 2,500 times more current than the GFCI trip point before it reacts. That is why a breaker alone does not protect you from shock. It protects the wire.
Where GFCI protection is required
| Location (dwelling) | First required by the NEC | Notes |
|---|---|---|
| Underwater pool lighting | 1968 | The first GFCI rule 1 |
| Outdoor receptacles | 1973 | Expanded in 2023 to all outdoor outlets, with limits 6 |
| Bathrooms | 1975 | 1 |
| Garages | 1978 | 1 |
| Kitchens | 1987 | Countertop outlets first; NEC 2023 covers kitchen receptacles more broadly 4 |
| Crawl spaces and unfinished basements | 1990 | 1 |
| Wet bar sinks | 1993 | 1 |
| Laundry and utility sinks | 2005 | 1 |
| Dishwashers, ranges, wall ovens, dryers, microwaves | NEC 2023 210.8(D) | Specific appliances rated 150 V or less to ground and 60 A or less 5 |
Older homes
CPSC notes that the NEC usually applies to new construction and major renovations 1. A 1970s bathroom may have no GFCI at all. Adding one is often worth it, but an electrician should do the work.
Strengths and limits of a GFCI
What a GFCI does well
What it cannot do
- Does not stop a shock between hot and neutral, since no current is missing.
- Does not detect arcing in walls; that is the AFCI's job 2.
- Does not protect wiring from overload unless it is a GFCI breaker.
- Can wear out; the test button is the only way you will know.
When a GFCI will not save you
A GFCI only reacts to current that leaks to ground. If a person touches both the hot and the neutral wire and is not touching anything grounded, the current goes out and comes back as usual. The GFCI sees no difference and does not trip.
It also cannot help on a circuit it does not cover. A bathroom outlet may be protected by a GFCI outlet in another room, or by a breaker in the panel. If that upstream device has failed, the bathroom outlet is not protected even though it looks normal.
Some equipment trips GFCIs often, such as older motors or long outdoor runs. Repeated trips are a signal, not a nuisance. Have an electrical repair visit find the cause instead of swapping the GFCI for a plain outlet.
What drives the cost of adding GFCI protection
We do not publish prices for this job, because local quotes vary too much. The things that move the price are clear, though.
Outlet or breaker: one GFCI outlet can protect several outlets after it, while a GFCI breaker protects a whole circuit from the panel.
Panel brand and age: a breaker must be listed for your panel, and some older panels have limited choices. Number of rooms: a whole-home update costs more than one bathroom.
Wiring problems found along the way, such as no ground or loose connections, add time. Permit fees vary by town.
See electrical cost guides or estimate a job with the project cost tool. Like any electronic device, a GFCI does not last forever. The monthly test tells you when it has failed.
How an electrician adds GFCI protection
- Map which outlets are on each circuit and which ones need protection under your local code.
- Choose the form: GFCI outlet at the first outlet, GFCI breaker in the panel, or both where needed.
- Pull a permit where your town requires one for outlet or breaker work.
- Install with the power off, matching the "line" and "load" terminals so downstream outlets are covered.
- Label protected outlets, and use the "No equipment ground" label where there is no ground wire 1.
- Test each device, then test each downstream outlet with a GFCI tester.
CPSC says breaker and outlet GFCIs may be installed by a qualified electrician, and to call one when in doubt 1. Work in a panel is never a homeowner task.
How to test a GFCI (the safe owner task)
CPSC says to test every GFCI after installation, at least once a month, after a power failure and as the maker directs 1.
- 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 stays on after TEST, the GFCI is not protecting you. Stop using the outlet and call an electrician.
- If RESET does not restore power, the device has failed and needs replacing by a pro.
- For a GFCI breaker, press the TEST button on the breaker; reset it once if it trips.
Warning signs to act on
- The GFCI will not trip when you press TEST.
- It trips again right after you reset it.
- It trips every time a certain appliance runs; unplug that appliance and have it checked.
- The outlet face is warm, discolored or smells like burning plastic.
- You felt a tingle from an appliance, faucet or tub. Treat this as urgent.
- Outdoor GFCIs trip after rain; water may be getting into a box or cover.
Do not bypass a GFCI
Never replace a GFCI that trips with a plain outlet, and never open an outlet box or panel yourself. A GFCI that keeps tripping is reporting a real leak. If anyone felt a shock, stop using the circuit and call a licensed electrician. If someone is hurt, call 911.
GFCI rules in the NEC
NEC 2023 210.8(A), dwelling units. GFCI protection is required for receptacles in listed areas, including bathrooms, garages, outdoors, basements, laundry areas and areas near sinks. The 2023 edition expanded kitchen coverage to all 125 to 250 V receptacles there, not only countertop ones, and added areas with sinks and food or drink prep 4.
NEC 2023 210.8(D), specific appliances. Branch circuits or outlets for appliances such as dishwashers, electric ranges, wall ovens, cooktops, clothes dryers, microwaves and sump pumps need GFCI protection when rated 150 V or less to ground and 60 A or less 5.
NEC 2023 210.8(F), outdoor outlets. All outdoor outlets at dwellings on single-phase circuits of 150 V to ground or less and 50 A or less, including garages with floors at or below grade, accessory buildings and boathouses. An exception for listed HVAC equipment expired on 1 September 2026 6.
The NEC is NFPA 70, a model code 7. It only becomes law when a state or city adopts it, often with changes. Check which edition applies to your address before relying on any rule here.
GFCI vs AFCI vs standard breaker
| Device | Protects | Trips on | Typical place |
|---|---|---|---|
| GFCI | People, from shock | Current leaking to ground (about 6 mA) | Wet and outdoor areas |
| AFCI breaker | The home, from fire | Arcing patterns in wiring and cords | Bedrooms, living areas, kitchens |
| Standard breaker | Wiring, from overheating | Overload and short circuit | Every circuit |
| Dual-function | Shock and fire | Both ground faults and arcs | Where both rules apply |
Common GFCI myths
- Myth A GFCI and a circuit breaker do the same job.
- Reality A breaker protects wire from too much current. A GFCI protects people from small leaks to ground 1.
- Myth You need a ground wire for a GFCI to work.
- Reality A GFCI works on two-slot outlets with no ground; it must be labeled "No equipment ground" 1.
- Myth If the outlet has power, the GFCI is fine.
- Reality A failed GFCI can still pass power. Only the TEST button shows if it still trips.
- Myth An outlet with no buttons has no GFCI protection.
- Reality It may be protected by a GFCI outlet upstream or a GFCI breaker in the panel.
Which GFCI rules apply in your state
GFCI rules come from the edition of the NEC your state or city has adopted, and adoption varies.
One state may enforce NEC 2023 with its expanded kitchen and appliance rules, while a neighbor still uses an older edition. NFPA tracks where each edition is enforced 8.
Look up your state before planning a kitchen, laundry or outdoor project.
When GFCI protection matters to you
Check for GFCI protection if your home was built before the late 1980s, if you are remodeling a kitchen, bath or laundry, or if you use power tools and yard tools outdoors. These are the places shocks happen.
Next step: run the free home electrical safety check, then book an electrical inspection if outlets near water lack protection. For a broader view of household hazards, see our electrical safety page.
Outlet or breaker?
One room with one or two outlets near water: a GFCI outlet is usually simplest. A whole circuit with lights, hard-wired equipment or hard-to-reach outlets: a GFCI breaker covers it all from the panel. Your electrician confirms which fits your panel.
Questions about GFCI (Ground-Fault Circuit Interrupter)
What does a GFCI outlet do?
A GFCI outlet cuts power when it senses current leaking to ground, which can happen when electricity flows through a person. It compares outgoing and returning current and trips at a gap as small as 0.006 amps. It protects that outlet and, when wired that way, the outlets after it on the same circuit.
Why does my GFCI keep tripping?
Repeated tripping usually means there is a real leak to ground. Common causes are a damaged appliance cord, moisture in an outdoor box, or a worn motor. Unplug everything on the circuit, reset once, then add items back one at a time. If it still trips, or trips with nothing plugged in, call an electrician.
How often should I test a GFCI?
CPSC says to test every GFCI at least once a month, after a power failure and right after installation. Press TEST with a lamp plugged in. The lamp should go out.
Press RESET and it should come back. If the lamp stays on after TEST, the device is not protecting you and needs replacing by an electrician.
Where are GFCI outlets required?
In homes, the NEC requires GFCI protection in bathrooms, garages, outdoors, crawl spaces, unfinished basements, laundry areas, areas near sinks and kitchens, plus some appliances. NEC 2023 210.8 lists them. Rules depend on which code edition your state or city has adopted, so check locally.
Is a GFCI breaker better than a GFCI outlet?
Neither is better in every case. A GFCI breaker protects the whole circuit, including lights and hard-wired loads, from the panel. A GFCI outlet protects itself and downstream outlets and is easy to test where you use it. An electrician picks based on the circuit, the panel and the code.
Can a GFCI go bad?
Yes. A GFCI can fail and still pass power, so the outlet seems normal while it no longer protects you. That is why CPSC asks for monthly testing. A GFCI that will not trip on TEST, or will not reset, needs to be replaced by an electrician.
Do I need a GFCI if there is no ground wire?
A GFCI is one of the accepted ways to add shock protection to an old two-slot outlet with no ground. CPSC notes it works on two-slot receptacles. The outlet must carry a "No equipment ground" label. It still does not create a ground for surge protectors or equipment that needs one.
What is the difference between GFI and GFCI?
There is no difference. GFI is a short name for ground-fault interrupter, and GFCI is ground-fault circuit interrupter. Both describe the same shock-protection device. Codes and product listings use GFCI.
Does a GFCI protect against fire?
Partly. CPSC says a GFCI can prevent some electrical fires and reduce others by stopping ground-fault current. But it does not detect arcing between wires, which is a major fire cause. That is the job of an AFCI. Dual-function devices give both kinds of protection.
Why did my GFCI trip with nothing plugged in?
Something wired after it may be leaking current, such as an outdoor outlet with water in it or a damaged cable. A failing GFCI can also trip on its own. Reset it once. If it trips again with nothing plugged in, leave it off and have an electrician trace the circuit.
Sources
- U.S. Consumer Product Safety Commission, GFCI Fact Sheet (Publication 099), retrieved .
- U.S. CPSC, Preventing Home Fires: Arc Fault Circuit Interrupters (Publication 5133), retrieved .
- Merck Manual Professional Version, Electrical Injuries, retrieved .
- Leviton Captain Code 2023, NEC 2023 210.8(A) GFCI requirements in dwelling unit kitchens (quotes NFPA 70, 2023 edition), retrieved .
- Leviton Captain Code 2023, NEC 2023 210.8(D) GFCI protection for specific appliances, retrieved .
- Leviton Captain Code 2023, NEC 2023 210.8(F) dwelling unit outdoor outlets, retrieved .
- NFPA, NFPA 70 National Electrical Code standard development page, retrieved .
- NFPA, NEC enforcement maps (where each edition is in effect), retrieved .
Expert review
Written by the HyreElectrical Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: GFCI behavior, types, testing and NEC adoption years from the CPSC GFCI fact sheet; NEC 2023 210.8 text as quoted by Leviton from NFPA 70 (2023); shock thresholds from the Merck Manual. All read 10 October 2026.
Suggest a correction. We fix errors and say what changed.