Circuit Protection Devices

Automotive fuse.

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 will create an open and protect the circuit. This can be thought of as a weak point that will fail before any other components are damaged. There are different kinds of devices used to protect circuits. A short circuit will result in a burned fuse. Do not replace the recommended fuse with one of a higher amperage rating.

Fuses: A fuse is a metal strip that melts when 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 easily indicate the different amperage ratings. They also come in small, standard, and max sizes. Maxi fuses replaced inline fuses because they separate the different circuits. This helps when diagnosing an open circuit.

Maxi fuses separate the different circuits. This makes 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 made maxi fuses popular with automobile manufacturers. Usually 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. The fuse boxes are located in different locations depending on the manufacturer. 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 would. The difference is that some circuit breakers can be reset and then placed back into service. Many circuits contain self-resetting breakers. These breakers use a heat element that bends and creates an open until it cools. When the circuit breaker cools, its contacts reset and complete the circuit again. When there’s a circuit overload, it will continue in a cycle of opening and closing until the short or the component creating the draw is found and repaired.