Circuit Breaker Another device used for overcurrent protection is a circuit breaker. The NEC ® defines a circuit breaker as a device designed to open and close a circuit by non automatic means, and to open the circuit automatically on a predetermined over current without damage to itself when properly applied within its rating. Circuit breakers provide a manual means of energizing and deenergizing a circuit. In addition, circuit breakers provide automatic overcurrent protection of a circuit. A circuit breaker allows a circuit to be reactivated quickly after a short circuit or overload is cleared. Unlike fuses which must be replaced when they open, a simple flip of the breaker’s handle restores the circuit. Ampere Rating Like fuses, every circuit breaker has a specific ampere, voltage, and fault current interruption rating. The ampere rating is the maximum continuous current a circuit breaker can carry without exceeding its rating. As a general rule, the circuit breaker ampere rating s...