Size of wire for a 12 volt run.

[chrisrosenb]

When the contractors cap was installed on my truck, they ran small fused power & ground wires from the battery back to the cap for interior lighting. I am now installing air bags on the rear axle. I am installing a small compressor in the cap to operate the air bags.

The compressor also requires fused wiring to be run to the battery for power.

Many times I would have like to have had access to 12 volt outlets at the back of the truck.
Instead of having several wires running from the battery to the back of the truck, I am considering running 2 larger wires.
One fused line for the power & one for the ground. I would then put a ganged fuse block in the cap. The block I have found is rated for a total of 65 amps & has 6 separate fused power connections.

The problem I am having, is the size wire I need to make the run from the battery to the rear. The run is about 25 feet.
I have found several charts online, but they do not agree. Some charts list wire length as total of hot & ground & others just give a length. Wire sizes are all over the place.

I need help.   

 

[shed9]

How many amps do you expect to run on this circuit? This will define the cable size.

 

[richy3333]

Cable size is predominantly dictated by the loading it will carry and the installation method (what it's run through).

 

[wow]

From Engineering toolbox:

Amps=5 10 15 20 25 30 40 50 60 70
Feet      AWG wire size needed
15- 16 12 10 10   8   8   6   6   4   4
20- 14 12 10   8   8   6   6   4   4   4
25- 14 10   8   8   6   6   4   4   2   2
30- 12 10   8   6   6   4   4   2   2   2
40- 12   8   6   6   4   4   2   2   1   1/0
50- 10   8   6   4   4   2   2   1 1/0  1/0
60- 10   6   6   4   2   2   1 1/0  2/0  2/0

At 25 feet for a circuit drawing 25-30 amps you'd want 6 ga wire.
At 25 feet for a circuit drawing 40-50 amps you'd want 4 ga wire.

Make sense?

 

[carlb40]

While it might seem overkill to a lot of people, and i always over engineer things. Personally i would just go for Zero gauge cable.

2 reasons

1 - Do the job once and do it right. No point using smaller gauge only to find you want to add something else later and having to swap / add 2nd cable.

2 - You will be covered for future additions - cable permitting.

If there was something bigger than Zero gauge i would probably even go for that.  ;D

 

[wow]

If there was something bigger than Zero gauge i would probably even go for that.  ;D

There is - see table above. After 0 gauge comes:
1/0
2/0

and so forth...

 

[sae]

I tend to opt for the smallest wire that suffices. 0 gauge is like the size of your average pointer finger, 00 is like the size of a thumb, both suck for turning corners, and are much more difficult to hide.

That's 00 (or 2/0), 0 (1/0), 4, and 8 AWG.

A few more things,

#1, you should fuse the +12v as close to the battery as possible so the whole run of the wire is fused, not just from the block onwards. Kinda sounds like you were planning on that, but just wanted to make sure.

#2, you don't need to run a separate ground wire, just use the chassis as ground (be sure it's a solid connection though, paint usually isn't conductive and you should chip away some paint to make a good connection if necessary).

 

[wow]

#2, you don't need to run a separate ground wire, just use the chassis as ground (be sure it's a solid connection though, paint usually isn't conductive and you should chip away some paint to make a good connection if necessary).

I used to install two-way radio systems for a living, and failing to provide an adequate ground can lead to all sorts of nasty problems. My experience is that - at least for wiring of this ampacity - you should ABSOLUTELY run a separate ground wire. You SHOULD NOT rely on the chassis to provide an adequate ground.

My  [2cents]

 

[polarsea1]

If there was something bigger than Zero gauge i would probably even go for that.  ;D

There is - see table above. After 0 gauge comes:
1/0
2/0

and so forth...

Ahem, after 4/0 you get into MCM - million circular mils.  [smile]

 

[shed9]

...you should ABSOLUTELY run a separate ground wire. You SHOULD NOT rely on the chassis to provide an adequate ground.

+1