Let's start with 20 ft of #8 AWG wire, which has a total resistance of .6282 * (20/1000) = 0.0125 ohms. The Temperature Coefficient of Copper is .39 % per degree C. Let's heat it up from 20 to 30C (68F to 86F), and we will find the resistance will increase by (0.0039 * 10) ohms and become 0.0125 + 0.039 = 0.0515 ohms. If we were running 15A through that #8 wire, then the difference would be [E=I*R] (15 * .0515) - (15 * 0.0125) = .59 volt additional loss due to higher temp. If on a 12 volt system, this is .59/12 = 4.9% change due to temperature. Hot stuff!
I found the physical # wires limit also interesting.
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