GFCI and AFCI

Why it matters

Two small devices prevent a large share of electrical deaths and fires in homes. A GFCI (ground-fault circuit interrupter) protects people from shock. An AFCI (arc-fault circuit interrupter) protects buildings from fires started by arcing wires. The NEC has steadily expanded where each is required, and knowing those locations is a core skill for residential electricians and a regular exam topic.

Awareness level only. Installing, testing or replacing GFCI and AFCI devices on real circuits is electrical work. Do it only under a licensed electrician's supervision with employer training. Pressing the TEST button on an existing GFCI receptacle at home is the only thing a non-electrician should do.

How a GFCI works

A GFCI compares the current going out on the hot conductor with the current coming back on the neutral. Normally they are equal. If some current returns by another path (through water, a metal pipe or a person), the two no longer match. When the difference reaches about 4 to 6 mA, the GFCI opens the circuit in a fraction of a second, fast enough to prevent a fatal shock in most cases.

Points to remember:

• A GFCI does not need an equipment grounding conductor to protect people. That is why the code allows a GFCI as a fix for replacing ungrounded two-prong receptacles (marked "No Equipment Ground").
• A GFCI does not protect against a hot-to-neutral short or an overload; the breaker does that.
• GFCI protection can come from a GFCI receptacle (protecting itself and the downstream "load" receptacles), a GFCI breaker or a dead-front device.

How an AFCI works

An AFCI watches the current waveform for the signature of a dangerous arc: the irregular, high-frequency noise of a loose connection, a nail through a cable or a damaged cord. Normal arcing from switches and motor brushes looks different and is ignored. When it detects a dangerous arc, it trips. A combination-type AFCI detects both series arcs (along one conductor, such as a loose terminal) and parallel arcs (between conductors).

AFCIs are about fire, not shock. A GFCI and an AFCI do different jobs, which is why many circuits now need both, often in a single dual-function breaker or receptacle.

Where they are required (dwellings, in general terms)

The exact lists are in 210.8 (GFCI) and 210.12 (AFCI) and they change with almost every edition, so treat the summary below as general awareness and read the sections in your adopted edition.

GFCI protection (210.8) in dwellings has long covered receptacles in bathrooms, garages and accessory buildings, outdoors, crawl spaces, unfinished basements, kitchens (now including more than just countertop receptacles), within a set distance of sinks, bathtubs and showers, boathouses and laundry areas. Recent editions extended it to more locations and to some 240 V receptacles and specific appliances. Other articles add their own GFCI rules, for example Article 680 for pools and spas.

AFCI protection (210.12) in dwellings covers the 120 V, 15 and 20 A branch circuits supplying outlets and devices in most living areas: kitchens, family and living rooms, bedrooms, dining rooms, closets, hallways, laundry areas and similar rooms. It also applies when existing branch-circuit wiring in those areas is modified, replaced or extended, with some exceptions for short extensions.

Non-dwelling occupancies have their own GFCI lists in 210.8(B).

Worked example: reading a floor plan

A small house plan shows: kitchen with countertop receptacles and a dishwasher, a bathroom, a bedroom, a hallway, an attached garage and an outdoor receptacle by the back door.

• Kitchen countertop receptacles: GFCI and AFCI (often a dual-function breaker).
• Dishwasher outlet: GFCI in recent editions; AFCI as a kitchen outlet.
• Bathroom receptacle: GFCI (bathrooms are generally not on the AFCI list, but check your edition).
• Bedroom and hallway receptacles and lights: AFCI.
• Garage receptacles: GFCI.
• Outdoor receptacle: GFCI, plus the outdoor weather-resistant and in-use cover rules.

Then confirm each against your edition's 210.8 and 210.12 text.

Testing and nuisance trips

GFCIs and AFCIs have a TEST button; manufacturers recommend testing them monthly. A GFCI that will not reset may be wired with line and load reversed, or protecting a downstream fault. Frequent AFCI trips usually point to a real problem (a loose connection or damaged cable) or, less often, an incompatible appliance. Troubleshooting those circuits is for a qualified electrician.

Common mistakes

• Thinking a GFCI protects against overloads, or an AFCI against shock.
• Assuming a GFCI requires a ground wire.
• Using an old list of required locations from a previous edition.
• Forgetting that modifying existing circuits can trigger AFCI requirements.

Quick recap

GFCIs compare outgoing and returning current and trip at a few milliamps to protect people. AFCIs detect dangerous arc signatures to prevent fires. Required locations are in 210.8 and 210.12 and change every edition. More information: Electrical Safety Foundation (ESFI) and NFPA 70. Checked on 2026-10-23.