A GFCI (ground-fault circuit interrupter) protects people from electric shock by cutting power when current leaks to ground, for example through water or a person. An AFCI (arc-fault circuit interrupter) protects the building from fire by cutting power when it detects dangerous electrical arcing in the wiring or a cord. They solve different problems, and many modern circuits need one, the other, or a dual-function breaker that does both.
Side-by-side
| GFCI | AFCI | |
|---|---|---|
| Protects against | Shock and electrocution | Fire from arcing wiring or cords |
| Detects | Current leaking out of the circuit (a few milliamps) | Irregular arc signatures in the current |
| Typical places | Bathrooms, kitchens, garages, outdoors, basements, laundry | Bedrooms, living areas and, in newer codes, many other rooms |
| Comes as | Outlet (receptacle) or breaker | Breaker (some outlet types exist) |
| Test button | Yes, test monthly | Yes, test monthly |
What a GFCI does
A GFCI compares the current going out on the hot wire with the current returning on the neutral. If a few thousandths of an amp go missing (through a person, or via water to ground), it shuts the circuit off in a fraction of a second. That is why GFCIs are required wherever electricity and water meet. If one will not reset, see GFCI won’t reset and how to reset a GFCI outlet.
What an AFCI does
An arc is a spark across a damaged wire, a loose connection or a crushed cord. It may not draw enough current to trip a normal breaker, but it generates enough heat to start a fire. An AFCI monitors the current pattern for the signature of dangerous arcing and trips when it sees it. Typical causes include a nail through a cable, a chewed wire, or a loose terminal.
Where each is used
Requirements depend on the local electrical code and the edition adopted, and have expanded over time. As a general rule, GFCI protection applies in wet or damp locations and AFCI protection applies to living spaces such as bedrooms and, in newer codes, kitchens, laundry areas and more. Your local building authority or an electrician can tell you what applies to your home, and what is needed when you renovate.
Dual-function breakers and outlets
A dual-function breaker combines AFCI and GFCI protection in a single device, which is useful for circuits such as kitchens and laundry areas where both are needed. They cost more than a standard breaker but save space in the panel.
Testing them
- Press the TEST button
A GFCI outlet or breaker, and an AFCI or dual-function breaker, each has one. It should trip with a click.
- Reset it
Push a breaker fully to OFF then back to ON; press RESET on an outlet. If a breaker will not reset at all, see circuit breaker won’t reset.
- Do this monthly
Test regularly, and replace any device that fails to trip or will not reset.
Tell everyone in the house which outlets are GFCI-protected, because one GFCI can switch off several downstream outlets, including one in another room.
Why they trip
| Symptom | Likely cause |
|---|---|
| GFCI trips when something wet is used | Real ground fault: moisture in an appliance, outdoor outlet or cord |
| GFCI trips with a specific appliance | That appliance has a fault; unplug and test elsewhere |
| AFCI trips with a vacuum, drill or old appliance | Motor sparking can look like an arc to the breaker |
| AFCI trips with no obvious cause | A damaged cable, loose connection or faulty AFCI — get it checked |
| Either trips often with new appliances | Compatibility issue; ask an electrician |
For a breaker that keeps tripping for another reason, see why a breaker keeps tripping.
What you can do and what you should not
You can test GFCI outlets, reset breakers and unplug suspect devices yourself. Replacing a breaker means working inside the electrical panel, where the main lugs stay live even with the main breaker off, so leave that to a licensed electrician. Never bypass or tape over a tripping GFCI or AFCI; the trip is the device doing its job.
When to call an electrician
Call one for a breaker that trips repeatedly without a cause, a device that will not reset, any burning smell, or when you want to add protection. Our common household electrical problems guide covers other warning signs.
