Arc Fault Interrupters

Arc Fault Circuit Interrupters (AFCIs) are special types of electrical outlets and circuit breakers designed to detect and respond to potentially dangerous electrical arcs in home branch wiring.

How do they work?

AFCIs function by monitoring the electrical waveform and promptly opening (interrupting) the circuit they serve if they detect changes in the wave pattern that are characteristic of a dangerous arc. They also must be capable of distinguishing safe, normal arcs, such as those created when a switch is turned on or a plug is pulled from a receptacle, from arcs that can cause fires. An AFCI can detect, recognize, and respond to very small changes in wave pattern such as loose connections in outlets, switches and light fixtures.

Where are AFCIs required?

Locations in which AFCIs are required depend on the building codes adopted by their jurisdiction. The 2006 International Residential Code (IRC) requires that AFCIs be installed within bedrooms in the following manner:

Arc-Fault Protection of Bedroom Outlets. All branch circuits that supply120-volt, single-phase, 15- and 20-amp outlets installed in bedrooms shall be protected by a combination-type or branch/feeder-type arc-fault circuit interrupter installed to provide protection of the entire branch circuit.

Arc Faults vs. Ground Faults

It is important to distinguish AFCI devices from Ground Fault Circuit Interrupter (GFCI) devices. GFCIs detect ground faults, which occur when current leaks from a hot (ungrounded) conductor to a grounded object as a result of a short-circuit. This situation can be hazardous when a person unintentionally becomes the current’s path to the ground. GFCIs function by constantly monitoring the current flow between hot and neutral (grounding) conductors, and activate when they sense a difference of 5 milliamps or more. Thus, GFCIs are intended to prevent personal injury due to electric shock, while AFCIs prevent personal injury and property damage due to structure fires.

In summary, AFCIs are designed to detect small arcs of electricity before they have a chance to lead to a structure fire. 

Hendrie Javier-CMI
House Mouse Inspection Services
PO Box 802735
Santa Clarita CA 91380

Ph: 661-294-9565

Fx: 661-702-1068