AFCI (Arc-Fault Circuit Interrupter)
Affiliate link — we may earn a commissionAn AFCI breaker detects electrical arcs, the sparking that happens when a wire is damaged, a connection is loose, or a nail has pierced a cable inside a wall. Normal arcs happen when you flip a switch or unplug a tool. Dangerous arcs happen when insulation is cracked, a staple has nicked the wire, or a connection has worked loose. The AFCI analyzes the electrical signature to distinguish between the two and trips when it sees a dangerous arc pattern. The NEC has required AFCI protection in bedrooms since 1999, and the requirement has expanded to cover most habitable rooms in newer code cycles.
Why It Matters
Arcing faults cause about 30,000 house fires per year in the US. A standard breaker won't detect them because the current might be well below the trip threshold. The arc generates enough heat to ignite insulation, wood, or dust without ever pulling enough amps to trip a regular breaker. AFCIs catch this failure mode.