Which device melts and opens the circuit when the current becomes too high?

Which device melts and opens the circuit when the current becomes too high?

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

Answer: (D)

Overcurrent protection that uses a thin metal link designed to melt when the current is too large. The fusible link heats up as current flows (heat scales with I^2R), and when the current exceeds its rating the link melts, breaking the circuit to prevent damage. Fuses are single-use protection devices; once they blow, they must be replaced. A switch is just a manual on/off control, so it doesn’t automatically respond to overcurrent. A resistor isn’t a protective device and won’t automatically interrupt a fault. A circuit breaker also protects against overcurrent, but it operates by tripping a mechanism (thermal or magnetic) to interrupt current and can be reset, rather than melting a link.

Overcurrent protection that uses a thin metal link designed to melt when the current is too large. The fusible link heats up as current flows (heat scales with I^2R), and when the current exceeds its rating the link melts, breaking the circuit to prevent damage. Fuses are single-use protection devices; once they blow, they must be replaced.

A switch is just a manual on/off control, so it doesn’t automatically respond to overcurrent. A resistor isn’t a protective device and won’t automatically interrupt a fault. A circuit breaker also protects against overcurrent, but it operates by tripping a mechanism (thermal or magnetic) to interrupt current and can be reset, rather than melting a link.