Electrical devices in homes, cars, airplanes, and other complex machines must be protected from higher voltage than the wires designed to take. Otherwise, the devices can break and even catch fire.

In real life electrical circuits, wires (conductors) may lose their insulation and come into contact with the ground or other conductors. If that happens, the voltage in the wire will have no resistor (load), and the same high voltage will be returned to the source of power.

That can result in overheating, as there is way too much voltage than the wires can take. Overheating will then cause melting and eventually, a break (open) in the circuit.

One way to protect a circuit is to add a fuse, circuit breaker, or thermal breaker to the circuit.

These work in similar ways, but let us consider a fuse in more detail:

A Fuse
A fuse is simply a strip of alloy wire (made of bismuth and tin) connected to the circuit. The fuse is designed to take specific volumes of electricity (voltage). For example, if a 3amp fuse is fixed into a circuit — it cannot take any more than 3amps of electricity. If for any reason, there is a surge or increase in the voltage, the fuse will melt immediately and break. This will stop the flow of high voltage and prevent any potential damage to the circuit or device.