Arc-fault circuit interrupter

An arc-fault circuit interrupter detects electrical arcing patterns that may start fires and disconnects the circuit to stop current flow.

Electrical arc: An electrical arc is a sustained discharge of current through an insulating medium, often producing intense heat and light. The hazardous discharge pattern the interrupter is designed to detect.
Series arc fault: A series arc fault occurs when an arc forms along a break or loose connection in a single current path. AFCIs are designed to detect this arcing within a conductor or connection.
Branch circuit: A branch circuit is the portion of an electrical system extending from its final overcurrent device to outlets or loads. AFCIs are installed to protect designated branch circuits in buildings.
Thermal-magnetic circuit breaker: A thermal-magnetic circuit breaker trips through heat-sensitive and magnetic mechanisms when current exceeds safe limits. It responds to overcurrent, which may not reveal a hazardous arc fault.
Arc signature analysis: Arc signature analysis identifies arcing by examining electrical signals such as current fluctuations and high-frequency noise. AFCIs use signal patterns to separate hazardous arcing from normal switching.
Parallel arc fault: A parallel arc fault occurs when current arcs between conductors at different electrical potentials. This fault can produce intense heat without necessarily drawing enough current to trip an ordinary breaker.
Combination AFCI: A combination AFCI is designed to detect both series and parallel arc faults. This device type covers the two principal wiring arc-fault patterns.
Fuse: A fuse is a sacrificial overcurrent-protection device whose element melts when excessive current flows. Unlike an AFCI, a conventional fuse does not analyze electrical signals for arcing.
Current transformer: A current transformer produces a smaller proportional current for measuring alternating current in a conductor. It can provide the current signal an AFCI evaluates for arc patterns.
Short circuit: A short circuit is an unintended low-resistance path that allows excessive current to flow. It is a different fault that conventional overcurrent protection is designed to interrupt.

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