Which component is designed to protect equipment by interrupting current when a fault occurs?

• A. Fuse
• B. Relay
• C. Circuit breaker
• D. Switch

Answer: (C)

When a fault occurs, protecting equipment means stopping the fault current quickly and reliably. A circuit breaker is designed for this purpose: it detects abnormal current (like an overcurrent, short circuit, or ground fault) and automatically opens the circuit to stop the flow of electricity. It can be reset after the fault is cleared, which is essential for returning to service without replacing parts.

Fuses also interrupt current, but they are sacrificial and must be replaced after they blow; they aren’t resettable. Relays are sensing devices that trigger protective actions, such as signaling a breaker to trip, but they don’t themselves interrupt current. A switch merely opens or closes a circuit for normal operation and isn’t intended to respond automatically to faults.