Thread: Questions--2 Electrical & 1 Hardware

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Questions:

1--What size (amps) circuit breaker do I need for the key switch circuit?

2--I have a headlight switch that has a 30 amp glass fuse under it---I want to use a 30 amp circuit breaker on it---
Can I use BOTH the glass fuse and the circuit breaker?

3--Is it OK to use both a lock nut and Locktite?

Thank you.

1. - what's the biggest load you expect to place on the circuit?
2. - Yes.
3. - Yes.

1 the max load for any circuit is ultimately decided by the wire guage. Put too much on it, and smoke appears.

2 you can use both, but why would you? If you put them in parallel, then you'll double the power load. With 30 A fuses, that would likely fry wires ( in case of a short ). In series, and then it's a contest to see which one goes first. Personally, I'd choose the breaker.

3 never use locktite on an electrical connection. It can act as an insulator, much better to use an electrical washer: they have little fins all around, like a star. They promote continuity, and function as a lock washer as well.

In both instances a circuit breaker is probably not the answer you should run relays to reduce the load,take some time and read this: Tips and click on "a current topic" this will explain why you should run relays.

On your #3, locktight can be used on any threaded fastener for extra holding power (guys, note that he said 2 electrical and 1 hardware question, so #3 is not an electrical question) but if you're talking about your steering tie rod ends again they need to be machined to make the castle head nuts work. You really don't want to use a nylock or crimp type lock nut in place of the cotter pin. You're risking your life with steering and brake connectors.

I bought a Haywire fuse/relay box for my car. In the ignition circuit, a neutral safety switch is most often used and there's a relay that transfers up to 30 amps from the neutral safety switch, whenever the neutral safety switch allows it. 12 gage wire is needed for 30 amps.

21 Fused Wiring System

A breaker or fuse only protects the wire that is upstream from it. If a wire was run to a headlight switch that has a fuse in it, then only the wire from the switch to the headlight is protected by the fuse at the switch. A fuse or breaker would be needed to protect the wire leading from the power source to the headlight switch. Without a fuse or breaker downstream from all of the wire, an accidental short to ground will fry the wire.

Originally Posted by daveS53

I bought a Haywire fuse/relay box for my car..... The headlight circuit does NOT use a relay, it just has a 30 amp fuse.

Dave, I don't believe that your statement is correct. Headlights are not fused, but instead run through a fast reset circuit breaker mounted in the fuse block. This is a safety feature, so that in the event of a short or over current situation your headlights will pulsate quickly vs simply going "black" if a fuse were to blow. I'm not sure when circuit breakers first appeared for headlights, but I know that it's at least fifty years ago.

Also, it is quite common to add a relay to the headlight circuit if high intensity, higher current lamps are used. The relay gives a shorter, higher gauge connection from the battery/charging circuit, allowing a more intense light without overloading existing headlight circuits. A relay is necessary if you opt for a HID (high intensity discharge) conversion. With the relay properly wired the circuit breaker still protects against a short, but the relay allows higher current to drive the lamps. I'm quite sure that your Haywire system has a small, rectangular headlight circuit breaker in the fuse block. You can Google/Bing "headlight circuit breaker" for a concise description of why this circuit is not fused, and you'll also find links to discussions of headlight relays.

Apparently, I have a circuit breaker, in the headlight switch.

GM Headlight Switch

http://www.haywireinc.com/index.cfm/...=prod/prd3.htm

Now I need to look again at the source wire, to see if it's fused. If not, then most of the wire is unprotected from a short.

Originally Posted by daveS53

....Now I need to look again at the source wire, to see if it's fused. If not, then most of the wire is unprotected from a short.

Your wiring is protected by the circuit breaker.....

As for the key switch circuit----

*it has an 8 gauge wire that leads from the starter to the key switch.
*How much current is flowing through this circuit?
*So what size fuse or circuit breaker do I need to protect this circuit?

Question 1; I'm not sure what your setup is, Stock GM, ford, etc. But the key switch normally powers the solenoid of the starter. I rewired my car with a Ron Francis harness and am using a GM steering column, ignition switch and high torque starter. I believe the solenoid on mine has a 30 amp fuse on it. Yours may be different.

Question 2; I am going to assume you would like to use a breaker so you don't have to replace a fuse if it blows. You could use both but in the event of excessively high current draw whichever device (fuse or breaker) is "weaker" will trigger. Even with both being rated at the same amperage there is a +/- tolerance. With a 5% tolerance @ 30 amps this could be as much as a 3 amp (1.5a for each) swing. A fuse over time will be affected by vibrations common in a car, especially the old glass tube type weakening them.

Question 3; As others have said, as long as your not using the bolt or nut as a ground or other electrical connecting point, I don't see why you couldn't use Locktite.

Triker - the total current will be the algebraic sum of all loads on the circuit.

So, if you have four headlights which pull four amps each, then that is sixteen amps.

There is really only one way to know exactly, and that is to create the circuit and put juice to it, and read the amps value with a meter in circuit. Then size the fuze between 110 - 150%.

Eight guage, are you sure you have that number right? That's beefy. I think my motorcycle and lawn mower each use that for battery cables.

Amps and Wire Gauge - 12V Circuit

The above link should show an amps chart for 12 V circuit. Although not specified, I'd expect it refers stranded wire.