Originally Posted by dirko
The answer is that wires are protected by circuit breakers, so if you have 20 amp breakers you need at least AWG 12 wires. 15 amp breaker requires at least AWG 14. The input wires should also be sized according to the fuse that protects them. This isn't something that you have to guess at. just look at the protection device to determine which wire size is needed. You can always increase the wire size, but you shouldn't use breakers larger than the associated wire sizes.
This is correct and just for example, I have a factory installed 2K watt inverter/charger with four 12v AGM batteries, connected in parallel. It uses 3/0 wire size throughout on the input side and is capable of delivering 166.6 amps at 12v.
Not that it might ever or going to make a habit of it, but the math has been done correctly.
One could get away with using smaller wire, I guess and especially with short runs, but then why upgrade to a 2000w in the first place?