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Wiring Gooroos: Determine Wiring Load

keith_b00ne

NAXJA Forum User
Location
Kentuckiana
I have an AWG 10 wire going from the battery to an aux fuse box by the drivers feet. The wire is approximately 8' long. The wire feeds 3 glass fuses. Based on my calculator, the wire can handle 60 amps with only a 1/2 volt drop. (right?) So I have 2 - 100 watt lights pulling about 17-20 amps from one of the fuses, does this leave me able to pull about 40 more amps from that circuit on the other 2 fuses?

Does anyone know how many amps a starter pulls?

I assume this math also works out for wiring lights in a series. You calculate the load on each wire section?
 
A starter pulls way more amps than you ever wanna put on that 10awg wire. Hundreds. Typical stall current for a car starter is between 300-500. Remember that's AMPS, not watts.

Yes, your calculations are correct. But it looks like you're nearing the limits of the wire. At some point everything is going to start getting nice and hot. Why not bump up to 8awg and know that you're safe?
 
A starter pulls way more amps than you ever wanna put on that 10awg wire. Hundreds. Typical stall current for a car starter is between 300-500. Remember that's AMPS, not watts.

I will have to look at my wiring. The guy before me has a 14 gauge wire running from the battery to a push button start to the starter. Been like that for years and works. I was thinking about cleaning it up and running it to my new aux panel, but now I am second guessing his wiring.

Yes, your calculations are correct. But it looks like you're nearing the limits of the wire. At some point everything is going to start getting nice and hot. Why not bump up to 8awg and know that you're safe?

I wanted to go up to 8 awg, but I can get 10 and 14 in 10' lengths free from work. Is 1/2 volt drop safe to keep things from getting hot?
 
I have an AWG 10 wire going from the battery to an aux fuse box by the drivers feet. The wire is approximately 8' long. The wire feeds 3 glass fuses. Based on my calculator, the wire can handle 60 amps with only a 1/2 volt drop. (right?) So I have 2 - 100 watt lights pulling about 17-20 amps from one of the fuses, does this leave me able to pull about 40 more amps from that circuit on the other 2 fuses?

Does anyone know how many amps a starter pulls?

I assume this math also works out for wiring lights in a series. You calculate the load on each wire section?

Starter can pull 300+ amps. Depends on age of engine, age of starter, etc...

I will have to look at my wiring. The guy before me has a 14 gauge wire running from the battery to a push button start to the starter. Been like that for years and works. I was thinking about cleaning it up and running it to my new aux panel, but now I am second guessing his wiring.

That is most likely just triggering the starter solenoid. The big heavy battery cable still feeds the power for spinning the starter.

I wanted to go up to 8 awg, but I can get 10 and 14 in 10' lengths free from work. Is 1/2 volt drop safe to keep things from getting hot?

There is an electrical term called "thermal run-away". As things heat up, resistance goes up. More resistance and you get more heat which gives more resistance which generates more heat... Not a good situation. Heat in the engine bay will heat that wire also and contribute to the problem. Personally I would not run 60 amps through 8' of 10ga. I would go with 8ga to that aux panel. When I wire our race cars, I calculate the load then go 1 size larger on the wire to compensate for heat.

P=IE -> watts = volts * amps -> amps = watts/volts

amps = 200 watts / 13.6 volts = 14.7.
 
I would also want to know what the aux fuse panel is rated for. Some of the blocks I looked at are only 50 or 60A total; depending on your accessories, you can exceed that figure pretty easily.
 
I would also want to know what the aux fuse panel is rated for. Some of the blocks I looked at are only 50 or 60A total; depending on your accessories, you can exceed that figure pretty easily.

The fuse box came out of a 70's Dodge D100. It does not have a hot feed for the entire panel, but is broken down into quadrants. Each quadrant has about 3 fuses on it. I'm not sure the rating.
 
For a fuse box such as the one I installed, how would you divert your power for multiple accessories? Would you run larger wire from the battery to the fuse panel and split from there using a distribution block or run multiple lines off the battery to each fused zone?
 
I have an AWG 10 wire going from the battery to an aux fuse box by the drivers feet. The wire is approximately 8' long. The wire feeds 3 glass fuses. Based on my calculator, the wire can handle 60 amps with only a 1/2 volt drop. (right?) So I have 2 - 100 watt lights pulling about 17-20 amps from one of the fuses, does this leave me able to pull about 40 more amps from that circuit on the other 2 fuses?

I assume this math also works out for wiring lights in a series. You calculate the load on each wire section?

Not sure how you calculated that a 10 gauge wire will handle 60 amps...
Generally the rule of thumb would be 14 gauge/15A, 12 gauge/20A and 10 gauge/30A.
To supply an auxiliary fuse box that is rated for 60A; you should use a minimum of 8 gauge wire.
If you are wiring up two 100W lights with a power source of 13.6V you should draw 15A continuous.
 
Not sure how you calculated that a 10 gauge wire will handle 60 amps...
Generally the rule of thumb would be 14 gauge/15A, 12 gauge/20A and 10 gauge/30A.
To supply an auxiliary fuse box that is rated for 60A; you should use a minimum of 8 gauge wire.
If you are wiring up two 100W lights with a power source of 13.6V you should draw 15A continuous.

This isn't what I used, but it will clarify the situation. This websites says 55 max amps for chassis wiring, but other guidelines lists 60 amps.

http://www.powerstream.com/Wire_Size.htm
 
That is most likely just triggering the starter solenoid. The big heavy battery cable still feeds the power for spinning the starter.

Any idea how many amps the starter solenoid pulls?

FYI - I tried to wire a relay to my backup lights tonight and realized my stock backup lights are not working. Of course. Guess it is time to trouble shoot those before I move forward.
 
Generally the rule of thumb would be 14 gauge/15A, 12 gauge/20A and 10 gauge/30A.
That's the standard max rating for 120V AC - House wiring. Automotive is 12-14V DC. The amp rating will go way up(8 -8.5 times as much) for the same sized wire.

There's a huge difference in switching also, but it goes the other way. It isn't unusual to see a switch rated at 20 amps AC, but only 1/2 amp DC.
 
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