Master Electrician Exam (NEC)Overcurrent ProtectionMedium
A residential garage circuit requires AFCI protection. Which of the following conditions is specifically addressed and protected against by an Arc-Fault Circuit Interrupter (AFCI) that a standard circuit breaker would not typically detect?
- AA sustained overload exceeding the circuit breaker's rating.
- BA bolted short-circuit between line and neutral conductors.
- CA low-level series or parallel arc fault caused by damaged insulation.
- DA ground fault current of 5 milliamperes to a human body.
Show answer & explanationAnswer & explanation
Correct answer: C. A low-level series or parallel arc fault caused by damaged insulation.
AFCIs are specifically designed to detect and interrupt hazardous arc faults (both series and parallel) that are not typically detected by standard overcurrent protective devices (which respond to overcurrents and short circuits) or GFCIs (which respond to ground faults). These arc faults can occur due to damaged insulation, loose connections, or frayed wires.
Why the other options are wrong
- A. A sustained overload is the primary function of a standard thermal-magnetic circuit breaker.
- B. A bolted short-circuit would be detected and cleared by a standard circuit breaker or fuse.
- D. This condition is specifically addressed by a Ground-Fault Circuit Interrupter (GFCI), not an AFCI.
AFCI Protection
An Arc-Fault Circuit Interrupter (AFCI) is a circuit breaker designed to detect and trip on potentially dangerous electrical arcs, thereby reducing the risk of electrical fires.
- Detects both series and parallel arc faults.
- Protects against fire hazards from damaged wiring.
- Required in specific dwelling unit locations by NEC 210.12.
Memory trick: AFCI is an 'ARC'itect of safety, building a 'FIRE'wall against sparks.