A.Master electrician Rex Cauldwell responds: According to the National Electrical Code, these little babies will be required for bedroom receptacle circuits, beginning in 2002. An arc-fault circuit interrupter (AFCI) is like a common 15-amp or 20-amp single-phase circuit breaker with a twist. It will sense any arc on the circuit that is 75 amps or higher. The arc can be a short to ground or to neutral, or an arc across itself as the wire opens and closes. Such an arc might occur in a wire beginning to break, or in a loose wiring connection. Since AFCIs are designed to sense at 75 amps, you should not get any nuisance tripping. And yes, they are expensive (about $75 to $125 each), although prices are expected to drop as they become more common.