Which safety device is activated when the current exceeds a specified level?

The safety device activated when the current exceeds a specified level is a fuse. A fuse is designed to protect electrical circuits by interrupting the flow of electricity when it detects an overload condition.

When excessive current flows through the fuse due to a fault or short circuit, the metal wire or strip inside the fuse melts due to the heat generated by the current exceeding its rated capacity. This melting disconnects the circuit, thereby preventing damage to electrical components and reducing the risk of fire.

While a circuit breaker also provides a similar protective function by tripping to stop the flow of electricity when an overload occurs, it is a resettable device, unlike a fuse, which must be replaced once it has blown. A switch simply controls the flow of electricity and does not respond to current levels, while a sensor monitors conditions but does not interrupt the circuit on its own. Thus, in contexts where a clear change in current level triggers a protective response, a fuse is the correct safety device.