[BigLew]

Get yourself a West Marine catalog and there is usually a chart that will give you the proper gage wire needed based on the amperage being run and the length over which it is being run. Keep in mind the length is the total round trip of both the hot and return line. Usully two charts; one for 3% or less line drop and the other for 10% line drop. Intended purpose of the circuit determines which chart to use.

Example: 35' circuit at 250-300 amps or 50% of CCA's requires OO or O AWG wire. Big, stiff and heavy; also very expensive!