I am trying to figure out the size of wire I need to get for my new, 160 amp, alternator. I found this chart which shows the resistivity/length of different wire gauges. Chances are that I will not be using 160 amps but I want to make sure that my wiring is adequate in case I ever draw a large amount of current. If I need 4 feet of wire between my alternator and battery what size would be the safest?

Also, what is the difference between chassis wiring and "power transmission"?

enter image description here (source): http://www.powerstream.com/Wire_Size.htm


This is actually much simpler than that chart implies. Don't worry about ohms per thousand feet - for a four foot length this will be very very low. What is more important is the maximum current a wire is rated to.

So here the question is whether you will want the OO gauge as it is rated to 190A in the power transmission column, or the 2 gauge as it is rated to 181A in the chassis wiring column.

Update - a quick bit of research, that also agrees with Mike's answer: The chassis wiring column is the relevant one, so go for the 2 gauge.

Not 100% sure exactly what they mean by chassis and power categories in this context, to be honest.

  • I don't know either but it's copied from the site that was linked. – R.. GitHub STOP HELPING ICE Apr 15 '13 at 2:37
  • Yeah, I think that chassis wiring is when it is grounded to the chassis and there is only a positive cable. – Sponge Bob Apr 17 '13 at 2:47
  • @SpongeBob, the ground won't make a difference as it won't change the current in the wire. I suspect that the difference is that in a "power transmission" application a (more) continuous load is expected and thus more sustained heating of the wire. Ampacity ratings are often based on the insulation of the wire and its ability to withstand heat. – dlu Aug 8 '16 at 12:19

I use this guide. For 160amps you probably want at least a 2 gauge (as seen in power&ground cable specs) but you could probably get away with a 4 gauge run if it is short.

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