You can gage a man by his wiring…
Lets talk wire gage as it is used around the truck. I may have gone overboard in a few places, but at least I won’t have power robbing voltage drops everywhere.
All the wiring in my truck is stranded. I am told that solid wire would not stand up to the vibration. Speaking as the guy who has to make all the connections, stranded is more difficult to deal with, but I guess it is necessary.
All of the wiring, both DC and AC is a full loop, meaning both out to the load and back. I do not rely on the truck chassis to carry any ground return currents. There are some ground return currents related to the original truck wiring, tail lights, turn signals, marker lights, things like that, but nothing related to the house wiring.
The battery to the inverter uses about a 4ft loop of 2/0 (spoken “double aught” where aught is pronounced like “not” without the “n”). It’s very heavy stuff, and expensive too, but it handles lots of current. I measured only 94mV drop at 141A. That’s less than 0.1V for the milli-challenged.
My house batteries connect to my starter batteries through a heavy duty (250A) switch and about a 7 foot loop of 1/0 (single aught) wire. 1/0 is still very heavy wire, though not as heavy as 2/0, about the same size as the wire from the starter batteries to the truck starter motor. If I ever need to “jump” the truck from the house batteries it should have plenty of punch to get her started.
The 2 foot loop from the battery charger to the inverter carries up to 90A and looks to be about 1 AWG (American Wire Gauge). I don’t really know for sure as I just used the wire that came with the power supply.
I used 8 AWG for the 3 foot loop from the inverter up to the DC distribution bus. 8AWG is rated for 73A over short runs, and it has a 60A breaker in line, so it should be OK. In practice I expect it will never see more than 20A.
The 3 each DC branch circuits that carry 12V throughout the truck are wired with 12 AWG dual conductor wire that is sold for low voltage outdoor lighting. It looks like lamp chord, with a seam down the middle that can be split. It was a little easier pushing a single pair of wire through the conduit though I am sure I could have made individual wires work. The insulation on the wire is tough and overall it was pretty cheap. The disadvantage is that it isn’t color coded. It has a ribbed conductor and a smooth conductor, just like lamp chord. In my case I decided to make Ribbed = Red = 12V, and smooth or Blank = Black = Ground. The thick insulation does make it tough to stuff into a small handi-box with a cigarette lighter socket and a couple of wire nuts though.
12 AWG is rated for 41A maximum, but more importantly it is 1.588 ohms per 1,000 ft. In my case the longest run is about 60 foot total loop length so that amounts to 0.095 ohms, which equates to a voltage drop of 1.9V at 20A, which is the value of the breaker on the branch lines. 1.9V is also 38W of power dissipated in the wires. That would definitely be enough to make them slightly warm, but no more than that. As a practical matter I doubt that the DC branch lines will ever see more than 10A. My refrigerator only draws 4.3A when the compressor is running flat out. Two 40W DC electric blankets (on a different branch circuit from the refrigerator) will draw less than 7A combined.
The AC wiring from the inverter on each of the three branch circuits is 12 AWG for the most part, with some 14 AWG out near the end of the run. In this case I literally used outdoor extension chord with 3 wires, black, white, and green. The longest loop length is about 40 feet. The two breakers on the inverter are limited to 15A so these wires will never be stressed.
The single run from the generator to the battery charger is also 12 AWG with a loop length of about 35 ft. The generator is only rated at 13.3A continuous and has a front panel breaker at 20A. Shore power also feeds through that line with an unknown current limit, but the battery charger will never draw more than 11.7A and it is the only thing connected through that line.
There is a little tiny “extension chord” that runs from a water tight covered plug that is accessible from the outside of the truck to the inside of the generator bay that allows me to plug into shore power and still have my generator bay locked up tight. It is 12 AWG, only runs about a foot and has a 15A fuse in line. Whatever shore power line I might be connected to will presumably have a breaker or fuse as well, but I have no idea what current it might be so I need to protect myself.
To be continued…
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