The purpose of circuit protection is to protect the wiring assembly during normal and overload conditions. An overload is defined as a current requirement that is higher than normal. This overload could be caused by a short circuit or system malfunction. The short circuit could be the result of a pinched or cut wire or an internal device short circuit, such as an electronic module failure.
The circuit protection device is only applied to protect the wiring assembly, and not the electrical load at the end of the assembly. For example, if an electronic component short circuits, the circuit protection device will assure a minimal amount of damage to the wiring assembly. However, it will not necessarily prevent damage to the component.
The vehicle's power distribution system consists of fuses, fusible links, circuit breakers and the ignition switch. Fusible links are short pieces of wire several sizes smaller than the circuit wire to which they supply power. They are covered with special high temperature insulation. When conducting an improperly high current flow, they will melt and stop current flow. They are designed to protect the vehicle's electrical system from electrical shorts in circuits not protected by circuit breakers or fuses.
There are three basic types of circuit protection device: Fuses, Fusible links and Circuit breakers.