I have pos/neg 4/0 cables running from my multiples 3000 12/120 to my positive/Negative busbars. The run for the positive is 20 feet due to the way the conduit runs, Does anyone think I should run 2X70mm (2/0) cable instead of the one 4/0? the new batteries are 2 X Victron Smart 12.8v 200 amp.
At 300 amps (which is about the most you're likely to pull for more than a very brief burst), you're still just under 5% voltage drop over that length. And 4/0 is adequate ampacity-wise as well (4/0 with 105* C insulation is good for 445 amps, assuming no bundling, engine room derates or other factors).
2x2/0 is not significantly different than a single 4/0 (80% the resistance).
5% drop could be a factor: low DC voltage at the Multi or high ripple. But you'd need to go to 2x4/0 to make any significant improvement in these areas.
