What safety device contains a thin metal strip that melts when too much current flows through a circuit?

A fuse is a safety device designed to protect electrical circuits from excess current. It contains a thin metal strip or wire that is designed to melt or "blow" when the electrical current exceeds a specific level for which the fuse is rated. This melting occurs due to the heat generated by the increased current, effectively breaking the circuit and preventing potential damage to electrical components or even fire hazards.

In the context of electrical safety, fuses are essential because they provide a simple, passive way to interrupt the circuit, thereby safeguarding the equipment and the wiring. Once a fuse blows, it must be replaced to restore the circuit's functionality, which serves as an indication of an overcurrent condition that needs to be addressed.

Circuit breakers, while also used for similar protection, operate differently by using a mechanical mechanism to reset the circuit after interrupting it. Relays and diodes serve different functions in circuits, with relays controlling switch operations and diodes allowing current to flow in one direction only, rather than directly addressing overcurrent situations.