Which device, after it clears an overload, cannot be reset?

The fuse is the correct answer because it is designed to protect electrical circuits by melting and breaking the circuit when an overload occurs. This irreversible action means that once a fuse has blown to clear an overload, it cannot be reset or reused; it must be replaced with a new one to restore functionality.

In contrast, circuit breakers can be reset after they trip due to an overload, allowing them to be reused without replacement. Relays and contactors also have the ability to be reset or activated again after the condition causing their deactivation is resolved. Thus, the unique nature of fuses makes them the only device in the list that cannot be reset after clearing an overload.