GFCI and AFCI Protection in Your Home Explained

Why this matters

Two small devices in your home's electrical system do a large share of its safety work. A GFCI shuts off power fast enough to keep a shock from killing someone. An AFCI shuts off power when wiring starts to arc, before the arcing starts a fire. Both protect you quietly for years, and both cause the same mild confusion when they do their job: a bathroom outlet goes dead, nothing in the bathroom has a reset button, and the outlet that controls it turns out to be in the garage.

This card explains what each device protects against, where you will find them, why a dead outlet is often reset somewhere else, and the monthly test that keeps the protection honest.

What a GFCI does

GFCI stands for ground-fault circuit interrupter. It watches the current going out to a device on one wire and coming back on the other. Normally those are equal. If some of the current is leaking out by another path, such as through a person standing on a wet floor holding a faulty hair dryer, the two no longer match. When the difference reaches a few thousandths of an amp (about 4 to 6 milliamps for the kind used in homes, under the UL 943 safety standard), the GFCI cuts the power in a fraction of a second.

That is far less current than it takes to trip an ordinary breaker. A 20-amp breaker protects the wire from overheating; it does nothing about a shock that passes a small current through a person. The GFCI is the device that protects the person.

Where you will find them: bathrooms, kitchens, garages, outdoor outlets, unfinished basements, crawlspaces, laundry areas and outlets near sinks. The list in the electrical code (NEC 210.8) has grown with almost every edition, so a newer home has GFCI protection in more places than an older one. Which spots are required in your house depends on when it was built or rewired and which code edition your jurisdiction had adopted then.

What one looks like: a receptacle with two buttons in the middle, TEST and RESET. Or a breaker in the panel with a test button on its face, which protects the whole circuit from the panel.

What an AFCI does

AFCI stands for arc-fault circuit interrupter. An arc is electricity jumping a gap: a nail driven through a cable, a cord crushed under furniture, a loose connection inside an outlet box. Arcing generates intense heat at a small point and is a well-known cause of house fires. An AFCI listens to the electrical signature of the circuit and shuts it off when it recognizes the pattern of a dangerous arc.

Where you will find them: in newer homes, AFCI protection covers most living-area circuits, such as bedrooms, living rooms, hallways and often kitchens and laundry areas. It was first required by the electrical code (now NEC 210.12) for bedroom circuits around the turn of the century and has expanded since. In most homes it is a breaker in the panel with a test button; some homes use AFCI receptacles instead, at the first outlet on the circuit. Some breakers do both jobs and are labeled dual-function.

A GFCI does not do an AFCI's job, and the reverse is also true. One protects people from shock, the other protects the house from fire.

One GFCI, several outlets

A GFCI receptacle has two sets of terminals on its back. The incoming power connects to the LINE side. Any outlets wired from its LOAD side are protected by it too, and when it trips, they all lose power along with it. Electricians use this to protect a whole run of outlets with one device.

 PANEL
 [ 20 A breaker ]
        |
        v  LINE side
 [ GFCI RECEPTACLE ]  garage wall
        |              TEST / RESET buttons here
        v  LOAD side, everything below is protected
 [ outlet ]  main bathroom       no buttons
        |
        v
 [ outlet ]  hall bathroom       no buttons
        |
        v
 [ outlet ]  front porch         no buttons

When the GFCI in the garage trips, all four outlets go dead: the garage one, both bathrooms and the porch. The bathroom outlets look like ordinary outlets. Some installers put a small "GFCI protected" sticker on each downstream outlet, but not every installer does, and stickers fall off.

This layout was common in homes built in the 1970s and 1980s. In newer homes, each bathroom usually has its own GFCI, but a downstream outlet on another GFCI is still common for porches, garages and basements.

Worked example: the bathroom outlet that went dead

A homeowner plugs in a hair dryer in the main bathroom, and nothing happens. The bathroom light still works. Here is how she finds the answer.

Step 1: rule out the breaker. She opens the panel door and looks for a tripped handle. Everything is lined up. No breaker has tripped, which points to a GFCI somewhere. See related: Reading Your Electrical Panel and Its Breakers.

Step 2: look for buttons nearby. The dead outlet has no TEST and RESET buttons. The hall bathroom outlet has none either, and it is dead too. Two dead bathroom outlets with no buttons is the classic sign of a GFCI upstream.

Step 3: walk the likely spots. She checks, in order, the places a GFCI is usually found: the kitchen counter outlets (working, not the cause), the garage, the outdoor outlets, the basement. In the garage, behind a shelf, she finds a GFCI receptacle with the RESET button popped out.

Step 4: reset once. She unplugs the hair dryer upstairs first, then presses RESET in the garage. It clicks and stays in. The bathroom outlets have power again.

Step 5: think about why it tripped. The hair dryer had been plugged in when the outlet died, but it is not clear it caused the trip; GFCIs also trip on moisture in an outdoor outlet after rain. The porch outlet is downstream of this GFCI, and it rained the night before. She checks the porch outlet's cover: it is a flip cover that was left open. She closes it.

What would change the outcome.

• If RESET would not stay in, or tripped again right away, she would leave it off, unplug everything on all four outlets, including anything on the porch, and call an electrician. A trip that repeats with the obvious load already unplugged points to the wiring, a wet outlet box or another device on the circuit, and that is the electrician's to find. She would not keep pressing RESET.
• If the GFCI shows a red or flashing light, or RESET will not engage at all, a GFCI made in roughly the last decade may be signaling that it has failed. GFCI receptacles made since about mid-2015 are required by their safety standard to monitor themselves, and many shut off power or show a light when their protection stops working. A failed GFCI gets replaced by an electrician.
• If there were no GFCI anywhere, she would look for a breaker in the panel with a test button, since the GFCI could be in the breaker instead.

The detail worth writing down. She labels the garage GFCI "also feeds both bathrooms and the porch" and adds a line to her panel directory. The next person to hunt for it will not need to.

The monthly test

Manufacturers recommend testing GFCIs and AFCIs monthly.

• GFCI receptacle: plug in a small lamp, press TEST. The lamp should go off. Check each downstream outlet you know about; they should be dead too. Press RESET; the lamp should come back on.
• GFCI or AFCI breaker: press the test button on the breaker. The breaker should trip, cutting power to that circuit. Reset it by pushing the handle to off, then on.

If pressing TEST does not cut the power, the device is not protecting you. Have an electrician replace it.

Warn the household before testing a breaker, since it shuts off a whole circuit. And remember what is on it: a refrigerator, freezer or sump pump on a GFCI will stop running while it is tripped, so reset promptly and check it came back.

If your home has little or no protection

Older homes were not built with GFCIs or AFCIs, and the code does not usually require an existing home to be brought up to the current edition just because it is old. Protection is generally required when a circuit is added, replaced or extended, or when an outlet in a required location is replaced, under the code your jurisdiction has adopted. That leaves many houses with gaps.

Finding the gaps yourself. Walk the bathrooms, kitchen counters, garage, outdoor outlets, laundry, and any unfinished basement or crawlspace. For each outlet, look for TEST and RESET buttons on it, or press TEST on the nearest GFCI and see whether it goes dead. An outlet in one of those spots that never goes dead when any GFCI is tested, and has no GFCI breaker feeding it, is unprotected. Write the list down.

What an electrician can do. Add GFCI receptacles or GFCI breakers where they are missing. Add AFCI or dual-function breakers to bedroom and living-area circuits. In older homes with two-prong outlets and no ground wire, a GFCI can add shock protection even without a ground, with a label saying there is no equipment ground; that is a choice for the electrician to make with you, since it does not do everything a ground does.

Have an electrician install them. A GFCI wired with LINE and LOAD reversed can look like it works and protect nothing downstream.

When protection trips and you should not just reset it

• A GFCI or AFCI that trips repeatedly, especially with the same appliance. The appliance may have a fault; stop using it.
• An AFCI that trips and you smell something hot. Leave it off and call an electrician.
• Any device that is warm, discolored or crackling.
• A trip that happens when water is present near the outlet or on the floor. Do not touch the outlet until the area is dry and the circuit is off.

References

• UL 943, Standard for Ground-Fault Circuit-Interrupters, which sets the trip threshold and self-test requirement and binds the device manufacturer
• National Electrical Code (NFPA 70) sections 210.8 and 210.12, in the edition your jurisdiction has adopted, for where GFCI and AFCI protection is required
• U.S. Consumer Product Safety Commission and Electrical Safety Foundation International guidance on GFCI and AFCI testing
• See related: GFCI and AFCI Troubleshooting Reference
• See related: How to Reset a Tripped GFCI Outlet