Is there a fuse that fixes itself?

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1165105

2026-04-30 06:25

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Fuses do not fix themselves. They burn out, when you blow a fuse, and cannot be fixed. However, circuit breakers are designed so that they turn off the current when it exceeds a safe level, but afterwards they can be reset. This is much more convenient than using fuses. But even circuit breakers usually do not reset themselves, someone has to reset them.

You probably shouldn't use one.

The single most important job of a fuse is to prevent the flow of electrical current when some condition occurs. That condition may be the maximum safe amount of current flowing in a circuit. It could be the maximum safe temperature around the fuse being reached. Inside an ECM or BCM (vehicle computer) fuses may be set(conducting) at the factory allowing the module to be programmed and cleared(not conducting) when the module is ready to be delivered to a customer. These firmware fuses are sometimes resetable with specialized equipment. Temperature controlled fuses, often called PTC(positive temperature coefficient) or NTC(positive temperature coefficient) are almost always resettable automatically when the temperature returns to normal.

The most common fuse one thinks of is the glass tube or plastic square containing a short wire and labeled with a number representing the amps(current) it will allow to flow before that wire burns up stopping current flow. That type of fuse is a one time use protection device that sacrifices itself to protect more complex and expensive equipment it is connected too. The circuits these fuses are designed for will only blow a fuse if something elsewhere in the circuit has gone wrong. The fuse is only the indicator that something has gone wrong, it is almost never the root cause of a problem. Because the fuse takes a certain amount of time to blow after the excess current condition occurs, it can still allow damaging levels of current to reach the protected equipment for brief periods. Therefore it is very unwise to just keep replacing fuses in a circuit that blows them. It is even worse to replace the fuse with a resettable device such as a circuit breaker or automatically resettable circuit breaker.

These devices do exist. They operate on the principle of a temperature controlled fuse. Higher levels of current through a fixed resistance cause increased heat production. A bimetalic strip expands and breaks contact instead of burning an internal wire. When the bimetalic strip cools, the contacts can be reconnected. The major problem that can occur with these devices is the spark produced at the contacts when they make or break. The contacts can weld themselves together with the heat from this spark, unnoticed by anyone. This results in an unprotected circuit and possible fire condition.

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