ELECTRIC CIRCUIT PROTECTION

Each electrical circuit and item must be protection by electrical protection. Protection can be in the form of an automotive fuse, a resettable circuit breaker or a thermally activated circuit breaker. Each protection device should be installed into a circuit that is rated for the current that it will carry, as well as be able to handle any surges during starting or increases in load as voltage drops and current rises. Resettable circuit breakers generally have an indicator that shows when it has been activated and  this normally doubles up as the rest button while thermally activated circuit breakers like those fitted on electrical trailer  brake circuit will automatically rest when the internal temperature has lowered to the set value. These types of circuit breakers activate after the temperature has risen due to excessive current passing through it and they will reset themselves.

Blade fuses provide a one off protection of the circuit. They can be checked visually for an open circuit though the more accurate and preferred method is to use a multimeter to check across the fuse. A blade fuse has two small test points on the top, allowing the test probes to make contact with the steel posts either side of the trigger wire. This is extremely beneficial when testing fuses in your fuse box, as modern defender have a number of things that piggyback off other designated circuits, meaning that reading the fuse panel label alone may not highlight the specific fuse in question.