GFCI and AFCI: What They Do and Where the 2023 NEC Wants Them

GFCI and AFCI devices look similar, a breaker or receptacle with a test button, but they guard against very different problems. Many circuits now need both, and combination devices exist that do both jobs.

How a GFCI works

In a healthy circuit, every bit of current that goes out on the hot wire comes back on the neutral. A ground-fault circuit interrupter measures both at once. If some current is missing, it is leaking somewhere else, possibly through a person to ground. When the difference reaches roughly 4 to 6 milliamps (thousandths of an amp), a people-protection (Class A) GFCI opens the circuit in a fraction of a second, fast enough to help prevent a serious shock.

A GFCI does not limit normal current, so it won’t stop an overload, and it doesn’t protect against a shock between hot and neutral. That is why a GFCI works alongside the breaker, not instead of it.

Where homes need GFCI protection (NEC 210.8(A), 2023)

Paraphrasing the 2023 NEC, dwelling-unit receptacles rated 125 through 250 V in these places need GFCI protection:

• Bathrooms, garages and accessory buildings, outdoors, crawl spaces, basements
• Kitchens: in 2023 this grew from countertop receptacles to all receptacles in the kitchen
• Other areas with a sink and permanent provisions for food or drink prep or cooking (new in 2023)
• Within 6 feet of a sink, bathtub or shower; laundry areas; boathouses
• Indoor damp and wet locations

Section 210.8(D) adds specific appliances such as ranges, wall ovens, cooktops, dryers and microwaves, and 210.8(F) covers outdoor outlets, with an exception for HVAC equipment. The exact list has exceptions, so read 210.8 itself for a real project.

How an AFCI works

An arc-fault circuit interrupter listens to the current waveform for the pattern made by dangerous arcing, such as a nail through a cable, a crushed cord behind furniture, or a loose connection. Normal arcs, like a switch opening or a motor running, have different signatures. When it detects a hazardous arc, it trips before the arc can start a fire.

Where homes need AFCI protection (NEC 210.12, 2023)

In dwelling units, 120 V, single-phase, 10, 15 and 20 A branch circuits supplying outlets or devices in kitchens, family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closets, hallways, laundry areas and similar rooms need AFCI protection. When circuits in those areas are modified, replaced or extended, protection usually has to be added too, with some exceptions.

Practical tips

• Press the TEST button monthly, as most makers recommend, and replace a device that won’t trip or reset.
• Frequent GFCI trips usually point to moisture or a failing appliance, not a bad GFCI.
• Frequent AFCI trips can mean a real wiring problem. It is worth having it traced instead of swapping in a standard breaker.

Our homeowner guide on breakers that keep tripping walks through the safe first checks.