Which device is primarily used for over-current protection in electrical systems?

The fuse is primarily used for over-current protection in electrical systems because it acts as a safety device designed to prevent excessive current from flowing through the circuit. When the current exceeds a predetermined level, the fuse’s conductive element melts, breaking the circuit and thereby stopping the flow of electricity. This protects the wires and devices in the circuit from damage that can be caused by overheating due to over-current conditions.

In contrast, a resistor is used to limit current and manage voltage levels in a circuit but does not provide protection against over-current events. A transistor can act as a switch or amplifier in circuits but does not perform over-current protection duties. A capacitor stores energy and smooths out fluctuations in voltage but does not directly provide protection from over-current scenarios. Therefore, the fuse stands out as the appropriate device for maintaining safety and integrity in electrical systems by ensuring that excessive current does not cause harm.