What safety device protects circuits by interrupting excessive current?

• A. A resistor
• B. A switch
• C. A diode
• D. A fuse or circuit breaker

Answer: (D)

Overcurrent protection is about stopping the flow of too much current to prevent overheating and possible fire. A fuse or circuit breaker does exactly that by interrupting the circuit when current exceeds a safe level. A fuse has a thin metal link that melts when the current gets too high, opening the circuit permanently until the fuse is replaced. A circuit breaker senses overcurrent and trips a mechanism to open the circuit, and it can be reset after the fault is cleared. This automatic interruption is what provides safety during faults. In contrast, a resistor simply limits current but doesn’t shut the circuit off, a switch is a manual disconnect, and a diode controls current direction rather than providing protection.