What is an AFCI?
Updated August 2026
An AFCI, or arc fault circuit interrupter, is a protective device that listens for the erratic electrical signature of arcing inside damaged or loose wiring and opens the circuit before that arc can set a wall on fire. Nearly all of them are breakers in the panel, identifiable by a Test button on the face and a white pigtail wire. An arc jumping a loose screw terminal or a nicked cable reaches thousands of degrees while drawing only a few amps, far too little to bother an ordinary breaker.
Where it is
Open the panel door and look for breakers with a small white or yellow Test button. Requirements arrived in stages: bedroom circuits in the early 2000s, then most living-area circuits by the 2014 code cycle, covering bedrooms, living rooms, hallways, dens, kitchens, and laundry. A house wired before 2000 almost certainly has none, and nothing forces a retrofit until you replace the panel or rewire a circuit. Combination AFCI and GFCI breakers exist and earn the extra $15–25 on circuits that need both. Start with how the panel itself is laid out if the rows look unfamiliar.
What it does
Three devices, three hazards, and homeowners mix them up constantly. A standard breaker stops too much current. A GFCI stops current leaking through a person. An AFCI stops the sputtering arc from a stapled-through cable, a chewed lamp cord, or a decades-old push-in connection working loose behind an outlet. Electrical failures remain one of the leading causes of home structure fires in the U.S., and those failures usually begin as arcs rather than overloads. The tradeoff is nuisance tripping: universal motors in vacuums and treadmills, certain older dimmers, and neutrals shared between circuits all generate noise an AFCI can read as an arc. Newer generation breakers separate the two far better, so a chronic tripper is often a 2005-era device rather than a wiring fault.
Maintenance
Press the Test button on each AFCI breaker twice a year, at the daylight saving changes if that anchors it for you. The breaker should snap off; reset it and the circuit returns. A breaker that will not trip on Test has stopped protecting and needs replacing, and one that trips constantly needs an electrician with a tracer, not a lighter load. The routine is spelled out in how often to test AFCI breakers. While the panel door is open, put your CO alarms and smoke alarms on the same list, since the three cover different ways a house hurts you.
What it costs to replace
A replacement AFCI runs $40–60 for an AFCI breaker against $5–15 for a standard one, or $150–350 installed.
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Frequently asked questions
What is the difference between AFCI and GFCI?
Different hazards entirely. A GFCI watches for current escaping to ground and protects people from electrocution, which is why code puts them near water. An AFCI reads the waveform for the chaotic signature of arcing and protects the building from fire, which is why code puts them in bedrooms and living spaces. Neither substitutes for the other, and a dual-function breaker that does both runs about $55–80. Both still include the plain overcurrent protection of a normal breaker.
Why does my AFCI breaker trip when nothing is plugged in?
Two usual suspects, and neither is an appliance. The first is a shared neutral: two circuits splitting a single neutral wire confuse the sensing electronics, and the fix is separating them or fitting a two-pole AFCI. The second is a genuine fault, most often a nail or screw driven through cable during a remodel, or a loose push-in connection at a receptacle. An electrician can isolate the run in an hour or two, usually $150–350.
Do I have to add AFCIs to an older house?
No. Codes apply to new work, so existing wiring is grandfathered until you replace the panel, add a circuit, or do a major remodel. Retrofitting is still one of the better safety dollars in an older home: $40–60 a breaker plus labor, and the panel is already open during any upgrade. Houses with 1970s aluminum branch wiring or a history of flickering lights are the strongest candidates, because both point straight at the loose connections AFCIs catch.