Car Fuses and Wiring

Is there a fuse that fixes itself?

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Wiki User
2011-05-25 14:53:16

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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