AFCI (Arc Fault Circuit Interrupter)
Also known as: arc fault circuit interrupter
Breaker that detects dangerous electrical arcs and trips the circuit. Required by NEC in most residential bedrooms, living areas, and habitable rooms since 2014.
An AFCI detects the unique electrical signature of arcing — sparks caused by damaged wiring, loose connections, or pinched cords — and trips the breaker before the arc can ignite a fire. AFCI protection is distinct from GFCI: GFCI protects against shock, AFCI protects against fire.
NEC has progressively expanded AFCI requirements since 2002. Current code requires AFCI protection on most 15A and 20A circuits in habitable rooms — bedrooms, living rooms, dining rooms, kitchens, hallways, closets. Combination AFCI/GFCI breakers (dual-function) cover both requirements in a single device, increasingly common for areas requiring both.
AFCIs are nuisance-trip-prone with some appliances (older vacuum cleaners, certain motors, some fluorescent fixtures) and with marginal connection quality (loose wirenuts, partial cable damage from drywall installation). For service businesses, troubleshooting AFCI nuisance trips is increasingly common work — usually requires investigating the entire downstream wiring path. Newer AFCI breakers have improved nuisance-tripping behavior compared to first-generation devices.
Related terms
GFCI (Ground Fault Circuit Interrupter)
Outlet or breaker that detects current leakage to ground and trips the circuit within milliseconds. Required by code in wet locations (kitchens, baths, outdoors).
Electrical conduit
Tube or pipe protecting electrical wiring. Required in commercial installations and exposed-to-damage residential locations. Material affects cost, flexibility, and code compliance.