What is a key functional difference between a fuse and a circuit breaker?

The key functional difference highlighted in the correct answer lies in the operational mechanisms of fuses and circuit breakers. A fuse operates by melting a wire within itself when excessive current flows through it, effectively interrupting the electrical circuit and preventing damage or fire. Once a fuse has melted, it cannot be reused and must be physically replaced to restore the circuit.

On the other hand, a circuit breaker is designed to protect electrical systems by automatically switching off when a fault is detected, such as an overload or short circuit. After tripping, a circuit breaker can be easily reset with a switch, allowing the circuit to return to normal operation without needing physical replacement.

This distinction is fundamental in understanding how each device functions in electrical safety systems. The other choices do not accurately describe the core differences; for example, while both fuses and circuit breakers interrupt current, the nature of resetting or replacing is what sets them apart significantly.