Arc-Fault Circuit Interrupter (AFCI)
Definition
A circuit protection device required by NFPA 70 (US NEC) in specified residential circuits, designed to detect the signature current waveform of series arcing in degraded wiring and interrupt the circuit before ignition-level heat is generated.
- Standard
- NFPA 70 (US National Electrical Code)
- Function
- Detects series-arc waveform signature
- Application
- Specified residential circuits
- Purpose
- Interrupt circuit before ignition-level heat
Common questions
How does an AFCI differ from a standard circuit breaker?+
A standard breaker trips on sustained overcurrent, which a low-level series arc from degraded insulation often does not produce, while an AFCI analyzes the current waveform for the erratic, high-frequency signature characteristic of arcing and trips before enough heat accumulates to ignite nearby material.
Does the presence of an AFCI on a circuit rule out electrical arcing as a fire cause?+
No, because AFCIs can fail, be miswired, bypassed, or simply not cover the specific circuit involved, so investigators still document the device's presence and test its function rather than assuming it prevented an arc fault.
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