Which device is used to cut off excessive current automatically?

The device that is used to cut off excessive current automatically is a fuse. A fuse operates as a safety mechanism within electrical circuits. It is designed to protect the wiring and components by breaking the circuit when the current exceeds a certain threshold. This is accomplished by the fuse containing a metal wire or filament that melts when too much current flows through it, thereby interrupting the circuit and preventing overheating or potential fires.

While circuit breakers also serve a similar purpose by interrupting excessive current flow, they are resettable and can be used multiple times, unlike fuses which must be replaced once they have blown. The other devices, such as transistors and capacitors, serve different functions in electrical circuits and are not designed to automatically cut off current flow in the same protective manner as a fuse does.