Circuit Protection Devices

Fuse check.

Circuit protection devices like fuses and circuit breakers are used to protect the circuit's wires and components from circuit overload. An overloaded circuit occurs when there's too much current flowing through the circuit. It can damage components and wiring that are sensitive to high current.

A circuit protection device like a fuse or circuit breaker opens the circuit before any other components are damaged. A short circuit results in a burned fuse. Do not replace the recommended fuse with one of a higher amperage rating. Installing a fuse with a higher amperage rating may damage the circuit. A higher rated fuse allows more current to flow through the circuit than it can handle.

Blade and Plug-in Fuses

Automotive blade plug-in fuse.

A fuse is a metal strip that melts if the circuit is overloaded. They're made of see-through plastic and come in different colors, shapes, and sizes. They come in different colors to quickly indicate the different amperage ratings. They also come in small, standard, and max sizes.

Maxi fuses separate the different circuits. It makes the diagnosis of the short or component, causing the overload much easier. An inline fuse may burn and separate, leaving a hot wire flopping around the engine compartment. This problem made maxi fuses popular with automobile manufacturers. When an inline fuse blew, the insulation around the wire would bubble around the open.

Many of today's vehicles contain a combination of mini and standard fuses. Mini fuses are small and conveniently fit into a small housing that takes up less space in a kick panel or under an instrument panel.

Circuit Breakers

Circuit breakers protect the circuit by creating an open just like a fuse does. The difference is that many circuit breakers can be reset and then placed back into service. Self-resetting breakers use a heating element that bends and creates an open until it cools, straightens, and completes the circuit again. When there's a circuit overload, it continues in a cycle of opening and closing until the short or the component creating the draw is found and repaired.