Snap, Crackle, Pop...

Most OE’s offer auto reset mechanical circuit breakers as an option to fuses in the power distribution box. For a few more dollars, the driver can rely on these breakers to protect the circuit from an overload.

When a fuse blows, the circuit remains cold until it is replaced. Certainly, there is more effort with finding the blown fuse and replacing it, especially if there are multiple power distribution boxes. One of the ‘benefits’ of a fuse is the finality of the failure which forces the operator to think about what caused the problem, because they do not want to have to replace it again. However, there is risk associated with increasing the size of the replaced fuse as ‘fix’, which could overload the wire, causing a thermal event.

When an overloaded circuit pops the breaker, it must cool before reconnecting the circuit. The breakers use contact points, typically made from precious or semi-precious metal). To resolve the problem, the device that overloaded the circuit must be removed, however there is no guarantee this step will occur (especially on the road). Most customers prefer breakers because they are simpler. However, if the points continue to open/close, and the load that causes the issue has not been removed, the chances of points welding increases. A welded circuit could cause a thermal event in the circuit it was designed to protect.

Two OE’s that I am aware of have designed Poly Switches into some of their chassis circuits. The poly switch serves as an over current protection alternative, using carbon black vs. points. As it heats up, it eventually opens the circuit and will close when the temperature drops, so it acts much like a common breaker, but has no points to fail/weld, thus is a much safer design.

All OE’s use 5 amp fuses on the limited circuits since they are more susceptible to overload.