The way I recall with electric motors, it has to do with the Full Load Amps (FLA) rating when you initially put power to them versus the the Run Load Amps (RLA) when an electric motor is actually running. The FLA draw is huge, albeit it only last for a second or 2 (why capacitors on some). Wire is sized by amperage so you go with the FLA rating of the motor. If you are going to do yourself, don't skimp on the crimper as suggested (would not recommend the type you 'hammer' shut), use commercial grade crimper as suggested. That was most memorable, and perhaps best, piece of advice I got on this forum 12 years ago from BoatsB when I was installing an inverter and dealing with allot of 4/0 wire. With inverters, way I recall, large wire size has to do with impedance. As aside, I always go at least one wire size larger then recommended with everything, saves allot of nuisance trips (like windlass) from happening.
As another aside - when you look at wire charts based on amperage and length, you take the full circuit round trip length, not just one way.
