Note; once you get over 200Amps of draw, you'll want to use 0+ size cabling. Having said that, if you are dealing with such amperage, its probably in your best interest to have a chat with an auto electrician to get some perspective. Few accessories will draw this much current, winches are one item that immediately comes to mind, and are typically wired up with the correct cabling out of the box anyhow.
Hope others find this a helpful tool.
