If you are using a B2B, the current in the cables between the B2B and the house battery will be limited by design, so you can set your cable size based on the B2B rating, plus some fudge factor. Say 60a for the 40a B2B. (I would think that the B2B Manual would have something to say about the cable size - - if so, certainly follow that recommendation over random advice on the internet.)
I used some 4ga welding wire from Windy Nation, they have reasonable prices and good quality.
You will also want some kind of a crimper, either a hydraulic crimper or a hammer crimper.
More random, free (and worth what you paid for it) advice: Don't buy the cheesey breakers from Amazon. Get some real Buss brand breakers from a reputable marine supply (West Marine, etc) or Del City.
I used some 4ga welding wire from Windy Nation, they have reasonable prices and good quality.
You will also want some kind of a crimper, either a hydraulic crimper or a hammer crimper.
More random, free (and worth what you paid for it) advice: Don't buy the cheesey breakers from Amazon. Get some real Buss brand breakers from a reputable marine supply (West Marine, etc) or Del City.
