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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.

Questions:

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!

  • Just looking up some cable, this #6 AWG two-conductor cable is rated for 99A, so you should have plenty of leeway in your current. – Felthry May 13 '18 at 17:36
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    Thanks @Felthry, but using a voltage drop calculator, a 6 AWG cable would have a 13% voltage drop over 50ft at 40A 12VDC - that's too high, I think. The rating that manufacturers / retailers often provide is over a much shorter run - for example, that cable will manage a voltage drop of just 4% at 99A, assuming the run is only 6ft long.... – Matt Knight May 13 '18 at 17:56
  • Well, you did say you were more concerned about heat than about voltage drop, so I didn't bother checking it. – Felthry May 13 '18 at 18:09
  • That’s fair enough. I’d like to keep the voltage drop reasonable though and that seems a little high to me. – Matt Knight May 13 '18 at 18:11
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    Consider whether it would be easier to install a battery near the back of the truck. Maybe with a solar trickle charger to keep it topped off. Obviously this will only work for occasional use. Also, consider using the truck chassis for ground return wire. The truck chassis has way less resistance than any wire you are going to install. – mkeith May 14 '18 at 2:37
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Consider running 2ga wire and connecting to the PowerPole with a “pigtail reducer”:

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2ga to 4ga is a standard item in US power wiring. You might have to look around for a 2 to 6, but try talking to a local electrical supply place, as they can often special order.

And make sure to use a suitably strong crimping tool. This is not something to mess around with, because even with fuses localized heating from load current can start a fire.

  • +1 Wow, what a cool adapter, one crimp and a stranded wire end. Also important to use the professional crimping tool. I vote for a bigger wire and using the earth as a return if the weight and cost are not an issue. 12V at 40A you want to save every volt you can for the accessory and not waste it in the cabling. – KalleMP May 14 '18 at 7:35
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As you also asked about tools specifications, I'd highly recommend a hydraulic crimper. It's very difficult to get a proper crimp just by hand-strength alone once you get larger than around 10awg. In the environment you're describing, you want the best crimps possible. Just make sure the included, or available, dies for the crimper will match what you're going to be working on. I've also found that a 20ft long vehicle can use up a LOT of wire in a hurry, trying to find a clean routing away from exhaust and moving components. Don't be surprised if you're 10ft longer on both sides of the run than you first expected.

  • Thanks! Is it possible to join 2 AWG to 6 AWG cable? So I could do the majority of the run with 2 gauge then reduce it to 6 gauge for the connector. If so, how would you join those two different gauges together? – Matt Knight May 13 '18 at 23:48
  • Physically possible? Yes, with the correct butt splice and if correctly insulated. But I personally wouldn't do it. It adds two more splices, and it's hard enough to prevent corrosion with under-vehicle wire runs. Then you'll have the negatives of a higher voltage drop due to the larger cable, but still be limited by the amperage capacity of the smaller one. – Hans May 13 '18 at 23:55
  • So you’d just run 6 AWG the full length? – Matt Knight May 13 '18 at 23:56
  • Since I don't know what you're powering with it, I can't answer that with any confidence. Though, depending on your vehicle, you may be able to look into chassis grounding instead of running a full-length ground cable. All depends on how new it is, anything with a CAN bus system starts getting tricky real quick with accessory wiring. – Hans May 14 '18 at 0:00
  • I’ll be bringing from the battery terminals (actually a negative post next to the shunt for negative) to the back on a 2016 F-150. I thought about chassis grounding, but (naively) felt it would be better to have specific cabling for it. Very open to advice though! I’m pretty sure I avoid complexities of the CAN-BUS and smart alternator this way. – Matt Knight May 14 '18 at 0:03

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