Second guessing myself on wire size for ARB CKMA12 (Single Compressor)

[JeepOfTheseus]

I'm in the process of redoing all my wiring, and I'm starting to question what is the actual wire gauge size needed to support this compressor. The official tech specs rate the draw at 14.2A under no load, 25.2A under load, and 32.0A max. For this reason, I previously used a 40/30A rated relay (so rated at 40A for NO operation) with a 40A inline fuse on the main wire from the battery (I believe this is what comes with the original wiring loom included with the compressor as well).

The relay has 12ga leads, so I assumed/figured that was the safe size to go with. Reading around (here and Internet in general), I'm getting mixed results on what's required - anywhere from 12ga up to 8ga. Relay will be right next to the battery, so the main wire w/inline fuse will be 8-10" in length, but the compressor is in the driver fender area so that run is closer to 5.5' long.

I don't recall what is the wire size of the leads coming off the compressor itself (and don't have access at the moment because I'm not pulling the fender till I'm ready), nor the size of the wire in their provided harness. Given the length, though, is 12ga still okay? I can't even seem to find pre-assembled waterproof SPST relays with 10ga leads.

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[sharpsicle]

8 gauge is overkill. You'd be generally fine with 12 gauge but you'd be at or slightly over it's technical limit. Could go 10 gauge to give cushion to safely carry the max amperage consistently. No reason to go above 10 though.

And for a reference, the factory aux switches rated for 40 amps use 12 gauge wire.

 

[Sandevino]

10 gauge and a 30A fuse. Bring a few spares but if you routinely blow them you need to evaluate how you’re using the pump. Airing up tires shouldn’t draw 30A but filling a tank might with back pressure.

The aux switches are rated for 15A and 40A fed through relays.

 

[Radio Guy]

I would use 10ga minimum and prefer 8ga. Nothing will break or overheat with 12ga but at 30A there will be about 1V drop in a 10ft run, which is actually 20ft of wire and that is not including a noticeable drop through the fuse and its holder or the relay contacts. This means the compressor will run slower and produce less CFM and tires will take longer to inflate.

With 8ga wire there will be about .38V drop, which would be noticeable and you would hear the difference when the compressor is running.

 

[JeepOfTheseus]

I would use 10ga minimum and prefer 8ga. Nothing will break or overheat with 12ga but at 30A there will be about 1V drop in a 10ft run, which is actually 20ft of wire and that is not including a noticeable drop through the fuse and its holder or the relay contacts. This means the compressor will run slower and produce less CFM and tires will take longer to inflate.

With 8ga wire there will be about .38V drop, which would be noticeable and you would hear the difference when the compressor is running.

Makes sense. Voltage drop has to factor in length of power and ground or just power?

In my current configuration (12 ga wire), it took about 38 seconds to fill up my KO2 37” from about 16/18-32 psi. I can live with those times. I just want it to be safe.

 

[Radio Guy]

If the device being powered has a chassis common with the negative lead and its screwed into the vehicle body it will be grounded and much of the current will flow back to the battery through the body. In this case any extra negative lead from the battery to the device will share some of the current depending on size, length, etc. So in this case most of the voltage drop will be in the hot lead.

If the device being powered is isolated then add the resistance of both the hot and negative lead.

Makes sense. Voltage drop has to factor in length of power and ground or just power?

In my current configuration (12 ga wire), it took about 38 seconds to fill up my KO2 37” from about 16/18-32 psi. I can live with those times. I just want it to be safe.

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