AFCI (Arc Fault Circuit Interruptor) circuit breakers detect minor arcing in an electrical circuit due to a fault condition and preventing fires. A common example of this would be a nail driven into a wall to hang a mirror that comes in very close proximity to a home wiring system. The nail may not cause the breaker to trip, but, under conditions of high humidity the electrical charge may arc (think tiny lightning). The level of electrical current flowing isn’t enough to trip a conventional breaker, however, it could heat up and cause a fire. A poor connection in the wiring system could cause the same thing.