An Arc Fault Circuit Interrupter (AFCI) is circuit breaker designed to prevent fires by detecting an unintended electrical arc and disconnecting the power before the arc starts a fire. An AFCI must distinguish between a harmless arc that occurs incidental to when switches are operated or snapped, plugs are disconnected from appliances, or an undesirable arc that can occur, for example, in a lamp cord that has a broken conductor in the cord.
Arc faults in a home are one of the leading causes for household fires. The National Fire Protection Agency (NFPA) estimated that in 2010, in the United States, over 40,000 fires are attributed to home electrical wiring defects. These fires resulted in over 1.5 billion dollars in property damage, in over 400 deaths and over 1,500 injuries that year.
Ordinary conventional circuit breakers only respond to overloads and short circuits. They do not protect against arcing conditions that can produce an instantaneous peak current with temperatures of several thousand degrees. The circuit breaker reads the averaged heat over the full cycle of current rather than the concentrated heat that occur at the point of the arc. Even though the arc has occurred, there will be less current drawn than is necessary to trip a conventional breaker. This is the origin of many house fires.
An AFCI is selective so that normal arcs do not cause it to trip. The AFCI circuitry continuously monitors the current and discriminates between normal and unwanted arcing conditions. Once an unwanted arcing condition is detected, the AFCI opens its internal contacts, thus de-energizing the circuit and reducing the potential for a fire to occur. An AFCI should not trip during normal arcing conditions, which can occur when a switch is opened or a plug is pulled from a receptacle.
AFCIs resemble a (GFCI) (Ground-Fault Circuit Interrupter Device) in that they both have a test button although it is important to distinguish between the two. GFCIs are designed to protect against electrical shock of a person, while AFCIs are primarily designed to protect against arcing and fire.