Arc-fault circuit interrupter

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An arc fault circuit interrupter (AFCI) is a circuit breaker designed to prevent fires by detecting non-working electrical arcs and disconnect power before the arc starts a fire. Advanced electronics inside an AFCI breaker detect sudden bursts of electrical current in milliseconds, long before they would trip a regular overcurrent circuit breaker or fuse. The AFCI should distinguish between a working arc that may occur in the brushes of a vacuum sweeper, light switch, or other household devices and a non-working arc that can occur, for instance, in a lamp cord that has a broken conductor in the cord from overuse. Arc faults in a home is one of the leading causes for household fires.

AFCIs resemble a GFCI/RCD (Ground-Fault Circuit Interrupt/Residual-Current Device) in that they both have a test button, though it is important to distinguish between the two. GFCIs are designed to protect against electrical shock, while AFCIs are primarily designed to protect against fire

[edit] Electrical Code Requirements

Starting with the 1999 version of the National Electrical Code in the United States and the 2002 version of the Canadian Electrical Code in Canada, AFCI are now required in all circuits that feed receptacles in bedrooms of dwelling units. The National Electrical Code is an industry consensus document adopted by many U.S. municipalities. This requirement of the NEC is typically accomplished by using a kind of circuit-breaker (defined by UL 1699) in the breaker panel that provides combined arc-fault, ground-fault, and over-current protection. The ground-fault protection is intended to prevent fire from arcs to ground and works at a higher threshold (30 mA) than the GFCI/RCD (Ground-Fault Circuit Interrupt/Residual-Current Device) implementations protecting against the safety hazard of electric shock (which operate at 6 mA). Combined devices are available which trip at the lower, 6 mA threshold of a true GFCI/RCD.

[edit] Limitations

Even AFCIs, however, do not provide protection against all of the possible circuit faults that could ignite a fire. In particular, they provide no special protection against so-called "glow faults" where a relatively low-resistance short circuit draws a modest amount of current (within the trip limits of the circuit breaker) but heats the localized area of the fault to red heat. Glow faults also can occur where a connection in series with a load suddenly develops a high resistance; this might be the result of a now-defective switch, socket, plug, or wire connection. No practical circuit breaker could detect either such fault as there is no measurable characteristic that any circuit breaker could employ to distinguish a glow fault from the normal operation of a branch circuit.