I'm trying to install an Anderson Powerpole connector on the back of my truck. Ideally I'd like to go with the Anderson SB50 (rated to 50A) as it is widely used and compatible with various accessories including an Australian-produced spring-closing weatherproof cover.
The truck is just over 20ft long, so the cable run from the truck battery to the rear bumper is approximately 20ft. I'm looking principally to ensure that the cables can endure 40A continuous current draw (either for a DC-DC battery charger or a portable air compressor). Assume another 10ft total cable length for the accessory on the other side of the connector, so full circuit length is around 50ft.
I'd like to also connect this via a relay to ensure it's only active when the ignition is on - I have a convenient 12V line available in the engine bay for this, so that's not an issue. Obviously I'll fuse (or use a breaker on) the positive line near the battery too.
My question is specifically around the wire gauge. For a run this long, I'd like to be using 2 AWG cable, but the SB50 connectors only support up to 6 AWG. They do have a larger connector that supports 2 AWG, but the connector is physically larger which isn't ideal for me - it means I can't locate it where I was planning to, and it isn't compatible with the weatherproof cover.
1) What cable gauge would you advise for running 20ft (in each direction) along the frame rail of the truck? Is 2 AWG excessive? I'm less concerned about the voltage drop than I am about heat.
2) If I do go with larger than 6 AWG, what's the best way to reduce this down to 6AWG to fit in the SB50 connector? Can I just use a reducing splicer, heat shrink it and secure it to the frame rail?
3) What type of terminals do I need to use to connect a cable like this to a relay?
I have experience in microelectronics and some experience in automotive electronics - I've wired in relays, lights, etc before. I've no experience with any cabling as thick as this though!
My primary concern on all of these is safety. I either have or am happy to buy the tools required to do this job properly. Specific recommendations for components / tools are also much appreciated!