How do circuit breaker keep the wires in a electrical circuit from overheating?

A circuit breaker is designed to 'break' in a circuit if a short circuit (or other malfunction) occurs. This prevents overheating (or burn-out) of the circuit wires. In older systems, you would need to find which fuse wire has fused and replace it. In a circuit breaker, once the fault has been found and corrected, the breaker is simply switched back on.