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Old 08-14-2022, 06:26 PM   #1
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Electrical Review

Would like any comments on my electrical diagram. I have left out the smaller draws on the AC and DC sides as I have those figured out. I will have a charge controller on the house batteries. I will have shore power available for my AC power only. so, questions:

1. Distance from the start batteries to the DC battery charger is 30'. That would be a total run of 60'. What size wire would you run? I was thinking 2/0.

2. Distance from DC fuse box to refrigerator is 35'. Total run of 70'. What size wire would you run? I was thinking 0. I don't know when I would use DC for the refrigerator, but I at least want it available.

3. The DC->DC charger looks like it will only take up to 6AWG wire. Any idea how to get bigger wires attached to it?

Thank you for your thoughts.
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Old 08-14-2022, 07:45 PM   #2
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Personally, I would separate the start battery entirely. Use it for its original purpose only. Make the living area completely separate...it's own battery bank, charger, etc..
If you feel you need to charge the bus battery, do it with a battery charger. I have a little 30w solar panel with a cheap controller to maintain my start battery.

I can't imagine a scenario where you'd need #0 wire for a DC refer
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Old 08-14-2022, 08:11 PM   #3
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Refrigerator pulls 20amps dc. Just going by AWG wire charts for 35'. Any other ideas?
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Old 08-15-2022, 02:52 AM   #4
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Refrigerator pulls 20amps dc. Just going by AWG wire charts for 35'. Any other ideas?
First off, you could use your chassis as a DC ground and not double your run length. Secondly, you could go with a 24 volt system. Just ideas
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Old 08-15-2022, 09:12 AM   #5
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Check out the ' Blue Sea Circuit Wizard' app (android or apple). Its an excellent tool so long as you do your part supplying the correct parameters.
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Old 08-15-2022, 12:26 PM   #6
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Have it set up for 12v. I'm great at ac wiring, so I'm gonna stick with bringing the ground back to the bus bar.

Blue Sea says I need wire capable of 180 amps.

Can welding wire be used for these long runs?
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Old 08-15-2022, 02:35 PM   #7
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Have it set up for 12v. I'm great at ac wiring, so I'm gonna stick with bringing the ground back to the bus bar.

Blue Sea says I need wire capable of 180 amps.

Can welding wire be used for these long runs?
Copper is copper, generally speaking. Welding wire is normally stranded, which is what you want for any kind of mobile application.
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Old 08-15-2022, 02:41 PM   #8
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First off, you could use your chassis as a DC ground and not double your run length. Secondly, you could go with a 24 volt system. Just ideas

I believe for engineering purposes using the chassis as ground doesn't reduce the "circuit distance" (thus size of wire) ONLY the amount of wire needed to make the circuit thus reducing cost and freeing space in the passages used to route the wire.
I could be wrong but I'd need to see a reference
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Old 08-15-2022, 03:05 PM   #9
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Originally Posted by Ranchorossa View Post
Would like any comments on my electrical diagram. I have left out the smaller draws on the AC and DC sides as I have those figured out. I will have a charge controller on the house batteries. I will have shore power available for my AC power only. so, questions:

1. Distance from the start batteries to the DC battery charger is 30'. That would be a total run of 60'. What size wire would you run? I was thinking 2/0.

2. Distance from DC fuse box to refrigerator is 35'. Total run of 70'. What size wire would you run? I was thinking 0. I don't know when I would use DC for the refrigerator, but I at least want it available.

3. The DC->DC charger looks like it will only take up to 6AWG wire. Any idea how to get bigger wires attached to it?

Thank you for your thoughts.
Not sure if you've already committed to some of the purchases, but if you haven't yet bought the components, here's my questions/thoughts.

-Your battery is only 200Ah. A 60 amp DCDC charger would completely recharge it in less than three hours. Do you really need that large a DCDC charger? It's going to drive up your installation costs significantly.

Depending on how you recharge, you may be able to use a (much) smaller DCDC charger and get what you need. I have a 20 amp unit because I'm assuming I'll use the device to recharge when I move from site to site, and usually that will be several hours driving. In your case, if you truly need fast recharging while driving, you may need a large DCDC charger, but it will come at a cost.


-These wire distances are killer for the 12 volt fridge. Why not consider a standard 120 volt AC appliance? If you increase the size of the inverter you could install a (cheaper) 120 volt fridge and put it almost anywhere on the bus. Typically, the concern about 120 volt fridges is the vampire load on the inverter, but as long as you're running 200Ah or greater I can't see that as a valid argument, especially with solar.

Also, with 12v DC the voltage drop on the line combined with the lower voltage at the battery when it's getting low on charge may cause the fridge to operate under greater stress. There are a lot of things that feed into this, but you're kind of fighting the laws of physics at these distances.

The #6 lug limitation is telling you that whatever size wire is coming from the alternator or going to the battery, if it is greater than #6 you'll need an intermediary bus bar to handle the termination on the bigger cable, then connect the DCDC charger to that with something much shorter-in the case of a 60A charger, a #6 no more than about a meter long.

edit: don't forget to add a fuse at the alternator, then again at the beginning of the wire from the dcdc charger to the battery bus.
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Old 08-15-2022, 03:17 PM   #10
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Quote:
Originally Posted by HamSkoolie View Post
I believe for engineering purposes using the chassis as ground doesn't reduce the "circuit distance" (thus size of wire) ONLY the amount of wire needed to make the circuit thus reducing cost and freeing space in the passages used to route the wire.
I could be wrong but I'd need to see a reference
My thinking on this is that you derate the for voltage drop in one direction. You don't need to derate the chassis. You do not need 1/0 for a refer.
I've dabbled with electricity for a while, don't make simple things, complex.
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Old 08-15-2022, 03:36 PM   #11
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The house battery is 300a. The refrigerator is a 3 way, already installed so 99% of the time it will run on ac or propane. Just came home from the rv repair shop. Recommended 4 or 6 for the refrigerator run and 2 for the run from batteries to the dc charger.

I have not bought the dc/dc charger yet. When we boondocks, wanted to run the engine as little as possible to charge the batteries, hence the big charger. I do have a small generator if needed. I'd rather have overkill and do it once, than to have to do it over again, or even worse, have a melt down.
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Old 08-15-2022, 03:50 PM   #12
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Refrigerator pulls 20amps dc. Just going by AWG wire charts for 35'. Any other ideas?
You mention that its a 3-way refer. Is the heater in it 240 watt? Or...is that the recommended circuit ampacity? Real time numbers make a difference in these calculations.
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Old 08-15-2022, 03:52 PM   #13
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Voltage drop at those long distances is definitely a concern. It's one reason our plan includes a 24 volt "main line" feeding several 12 volt fuse panels via 24 to 12 volt converters. The idea being that voltage drop is minimized by the larger main line running higher voltage and then smaller gauge wires from each of the 12 volt panels to the individual points of use.
The main line will be run from the batteries up and then forward and back to the different panels and be of large enough gauge to handle the necessary loads. From there smaller wires can carry the small individual loads and be a lot easier to run between the insulation and interior panels.

Part of the reasoning is that, being a pack rat when it comes to such things as wire, I already have a good amount of pure copper heavy gauge stranded wire but I'd have bought wire if it seemed the better option. We will be buying new metal clad cable for everything in the 120 circuitry even though I have hundreds of feet of 12 gauge solid core romex on hand because the metal clad is stranded wire and offers superior protection against penetration without having to install nail guards and/or conduit.


Just the way we're designing our system.... YMMV
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Old 08-15-2022, 04:05 PM   #14
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Good ideas. I'm already set up for 12v. I too have a junk ton of 12 and 14 Romex for the 120. Also have a couple hundred feet of conduit sitting around. So, Romex in conduit = super safe. Overkill I know.
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Old 08-15-2022, 04:08 PM   #15
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Good ideas. I'm already set up for 12v. I too have a junk ton of 12 and 14 Romex for the 120. Also have a couple hundred feet of conduit sitting around. So, Romex in conduit = super safe. Overkill I know.

I don't think romex is supposed to be in conduit. Conduit is for individual wires.
Not an electrician, just a guy that's done a lot of home repairs to wiring, not all of which was installed by an electrician (exposed splices laying around in the attic, extension cords used to run circuits, etc.
For the 120 side of things, see if you can find a "green book". They're pretty handy.
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Old 08-15-2022, 04:26 PM   #16
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Good ideas. I'm already set up for 12v. I too have a junk ton of 12 and 14 Romex for the 120. Also have a couple hundred feet of conduit sitting around. So, Romex in conduit = super safe. Overkill I know.
Romex in conduit is highly controversial. There are rules that prevent it and others saying it's OK as protection (in certain cases). Either way, it will be a nightmare to pull in. I'm using stranded #12 MC, 12/2 & 12/3 cable, it doesn't easily kink and it's what I use at work. I know the owner, so it's cheap . If you're going to run conduit just pull in individual wire. Be mindful of derating..."more than 3 current carrying conductors..."
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Old 08-15-2022, 05:29 PM   #17
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At least in our county, don't know about in skoolies, Romex can go into conduit. For long runs, I thread wire through individual sections of conduit. When all the wire is where it needs to be, I glue the sections together. Super easy, no fish tape needed.
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Old 08-15-2022, 06:10 PM   #18
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While the National Electrical Code does not expressly forbid inserting NM cable inside conduit, it is, in practice, very difficult to do so and very few professional electricians will do such an installation.
Like you said, it's up to you. If you have a method that works, and you have free materials, go for it.
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Old 08-15-2022, 07:18 PM   #19
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Great Choice for Wire Protection

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Romex in conduit is highly controversial. There are rules that prevent it and others saying it's OK as protection (in certain cases). Either way, it will be a nightmare to pull in. I'm using stranded #12 MC, 12/2 & 12/3 cable, it doesn't easily kink and it's what I use at work. I know the owner, so it's cheap . If you're going to run conduit just pull in individual wire. Be mindful of derating..."more than 3 current carrying conductors..."
Agreed:
Conduit fill adds up fast, too. Bump to 3/4"+ for those runs with two or more cables, plus derating, if applicable. Where they pass through boxes, twice as many neutrals. Plus double the grounds to bond, at each junction. Unless each cable is in their own raceway. Then landing all the conduit in the panel might be exciting. Just connecting the pipe to j-boxes, in a bus, is fun.

The conduit protects the conductors from damage, per its classification. (NEC 300.4 Protection Against Physical Damage)
Idk what additional protections the Romex offers over THHN, once inside of the conduit. Aside from conversely holding in the heat.

I put cable into conduit, too. Sometimes, there's no way around it. Romex free-air (stapled) in an attic, then pipe down a wall's surface to a j-box. UF wire, too. Kitchen appliance gfci down through pvc in dirt/concrete to island recepts. Just not my ideal plan for an entire facility. Vacuuming a string, then pulling thhn is quick, easy & economical.


On our rig, where I switch from mc to emt, I use a 3/8" flex to 1/2" emt changeover. Strip out the req'd length, add an anti-short & push.
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