This article is from the Car Audio FAQ, by Ian D. Bjorhovde (ianbjor@mobileaudio.com) with numerous contributions by others.
There is much debate over the benefit of certain wiring schemes
(oxygen-free, multistranded, braided, twisted, air core, you name it).
However, most people do agree that the most important factor in
selecting power wire is to use the proper size. Wire is generally
rated in size by American Wire Gauge, abbreviated AWG, or commonly just
"gauge". To determine the correct wire size for your application, you
should first determine the maximum current flow through the cable
(looking at the amplifier's fuse is a relatively simple and conservative
way to do this). Then determine the length of the cable that your will
use, and consult the following chart, taken from the IASCA handbook
(see Section 6.1),
Length of run (in feet) Current 0-4 4-7 7-10 10-13 13-16 16-19 19-22 22-28 0-20A 14 12 12 10 10 8 8 8 20-35A 12 10 8 8 6 6 6 4 35-50A 10 8 8 6 6 4 4 4 50-65A 8 8 6 4 4 4 4 2 65-85A 6 6 4 4 2 2 2 0 85-105A 6 6 4 2 2 2 2 0 105-125A 4 4 4 2 2 0 0 0 125-150A 2 2 2 2 0 0 0 00
 
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