DaveInDenver
Rising Sun Ham Guru
I don't have my NEC book with me, so I'd only be able to guess. But if memory serves (and see the Monday night radio thread to judge my memory), I wouldn't have guessed 1/0 cable to be good to 300A for any sort of length. So I'd probably fuse the battery side to limit the current through those cables to around that, probably something like a 250A time delay.Gee, pretty affordable too.
So Dave, how would you size them?
FYI, read following at risk of headache.
The code approaches fusing differently. You calculate the load, take some margin factor and size the fuse. Then you use cable sufficiently sized for that fused load. So you'd need to know the stalled motor current for your winch plus anticipated load and that will give you a value. My guess is the stall current is gonna be like 225A (around 4.25HP stalled) and so I would take 150% of that value plus the expected continuous loads like ECU, ignition, radios, etc. at 125%. So say 330A + 20A = 350A. I would use a regular blow fuse. If you have electric fans, I would call those a continuous load during wheeling, so take their max current at 125%. You can take non-continuous loads at 100%, so headlights for example could be included at 100% of max.
But I'm almost 100% certain 1/0 cable can't safely take 350A+ over 20 feet. So I would fuse at the 40C capacity for 1/0 and deal with nuisance tripping. I can get back to you with the ampacity of 1/0 for different ambient temps and insulation types tonight or tomorrow.