Re: Elec-tricky-ty Dilema - Battery Wiring
The proper way to approach it is to figure out what you need from the banks in terms of current and work backwards from there.
You should set your system up so you can start from either bank, this will almost certainly be your largest load and this will inform your wiring decision. Whatever gauge wire is needed for that starting load should be carried all the way back to both banks (through battery switches) AND should be used for the wiring between batteries within the bank for both safety and simplicity.
Normally your 3 pairs of 6-volt batteries in parallel in the house bank will see only 1/3 total bank current each, however unless you have fuses enforcing this it can't be guaranteed. That's why I'd use the same wire throughout the whole bank, for both safety and simplicity.
As for fusing, I think you want one fuse for each bank as close to the bank as possible assuming the batteries within the bank are close to one another - if you have any crazy, long runs within the bank you'd want to consider fusing those in addition. I'm not positive of the code here but I think that's right. Again the fuse is sized to protect the wire and both wire and fuse should be sized larger than your largest draw (again, probably the starter).
EDIT: Also consider getting an automatic charge relay so you don't have to do any manual switching between banks. There's lots written about that here.
Last edited by asdf38; 10-11-2012 at 02:01 PM.