Which term describes a device that interrupts current to protect circuits by opening the path when fault current occurs?

• A. Bus bar
• B. Circuit breaker
• C. Capacitor
• D. Commuter

Answer: (B)

The device that interrupts current to protect circuits by opening the path when fault current occurs is a circuit breaker. It detects abnormal current and automatically trips, breaking the circuit to stop the flow and prevent damage, overheating, or fire. Circuit breakers use a thermal mechanism for slower overloads and a magnetic mechanism for fast, high faults, and they can be reset after tripping to restore service once the fault is cleared.

Other terms don’t fit this protective function. A bus bar is a conductor that distributes power to multiple circuits, not a breaker. A capacitor stores energy and helps with voltage stability or power factor, but it does not interrupt fault current. A commutator is a rotating part in DC machines used to switch current direction, not to protect circuits.