Thread: Electrical Questions

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Should I use a circuit breaker or a fuse on my universal ignition switch?

What size?

Where exactly do I put it?

Thanks for the help.

Fuse or breaker, it's your choice. No real difference.
How big - add up all the amperage loads plus ten percent, that's your number.

Not all breakers will auto re-engage. Some are manual reset. Some can be toggled between auto and manual.

Again, it's your preference.

Bussman has some nice stuff.
It's nice to know about the different types.
I've not had to work on the type which requires the over current to be removed before it will reset, nor the type that requires power off to reset.

I'll bet those could really throw a wrench into the troubleshooting process.

I have a universal ignition switch that has nothing in the circuit to protect it.
ALL vehicles have something to protect a circuit.
So should I use a circuit breaker or a fuse?
And where inline should I put it?

Also, you need to know everything which will directly feed through the switch. It might be just the starter solenoid and the ignition, but it could be a whole lot more.

As for where, that has two answers: where the breaker or fuse is physically positioned (your preference) and where it is located in circuit.

Your electrical system will be most efficient if you have a distribution block, which feeds all. The alternator should reference system voltage from this junction also. Typically, the various circuit feeds go from the junction to a fuse block, then to the circuits. Some like a master breaker in front of the junction (distribution block).

Main (battery to starter) wire size is determined by actual total current load + 20% (to protect wire from damage)
Main fuse (when used) is rated at actual total load + 10% (10% less than wire capacity)
Alternator wire size is determined by maximum output + 20%
Alternator fuse is rated at maximum output + 10%
Ignition/Fuse box wire size is determined by total equipment load + 20%
Ignition/Fuse box fuse is rated at total equipment load + 10%

~Fuses should be placed as close to source as practical, i.e. Main at battery, Ignition/Alternator at starter
~Often, fusible link wires or breakers are used in-place of fuses
*Batteries mounted in engine bay with short cables do not always have fuses at Main
*Battery's remote mounted (trunk exc.), should always have a Main fuse and disconnect

TOTAL LOAD = everything electrical, including starter.
EQUIPMENT LOAD = everything electrical that comes from fuse box, excludes starter.

Wire sizing is typically sized large enough to safely carry more than the maximun load of the circuit without causing damage to the wire or its insulation (insulations are temperature and environment rated for their applications).
Fuse sizing is typically sized large enough to safely carry more than the maximun load of the circuit but less than the maximum rating of the wire's safe current capacity.

Circuit Wizard - Blue Sea Systems

OK, now that we have bombarded you with all of this information, lets make it simple for you to solve your problem. If in doubt about the circuit load, fuse to protect according to the wire size.
Wire Sizes and Fuses

36Sedan, good to see you're "handle" pop up.
And ( as always) thanks for all the great info!