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How-to Choose Wire Sizes DIY Camper Van Electrical System

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How-to Choose Wire Sizes DIY Camper Van Electrical System

There are many different sizes, shapes, colors, and ratings of wires.  It’s pretty confusing.  For this blog post, I’ll teach you to size wires for a DIY Camper Electrical setup and point you in the direction of the wires I recommend. Sizing the wires for your camper solar setup can get super complicated…if you let it.  So don’t let it…

Quick note before we get started.  This is just one part of an overarching “How to Install a DIY Camper Van Electrical System” series.  If you’ve just stumbled on this article directly without seeing that, there are likely some things we’ve already covered.  If you want to check out that step by step guide, you can do that here:

Also, we have interactive solar wiring diagrams that are a complete, A to Z solution for teaching you exactly what parts go where, what size wires to use, fuse size recommendations, wire lug sizes, and all kind of other stuff to help save you time and frustration.  You can check that out here:

How to Size Wires for your Solar Setup

  • Step 1: Read the instruction manual for the item you are attempting to wire.  Seriously… most of the time it tells you exactly what size of wire and fuse to use.  Trust it.  They’ve got electrical engineers backing those numbers.
  • Step 2: Use my wiring diagrams.  I have read those numbers found from step 1 and applied them to my wiring diagrams.
  • Step 3: Figure it out yourself. Which is what we are going to talk about now.

The following chart may look familiar if you’ve already been trying to find an answer to the question”How do I size my camper van wires”.  This chart, though, is a little different.

I didn’t like most of the diagrams already out there, so I made my own.  Here’s what you do.

  • Determine how many amps will be flowing to your appliance.  Find that number in the column on the left.
  • Determine how far your appliance will be from your power source.  Find that number on the top row.
    • (not round trip… this graph accounts for that)
  • Follow the column down and the row over to the appropriate box.
  • The two numbers are the wire gauges that will work for that run of wire.
    • Green = 3% voltage drop
    • Red = 10% voltage drop.
  • Try to stay closer to the ‘green’.  Red is still fine, but only for “Less important” things such as fans, lights, usb outlets, etc.
  • Consider ‘green’ as the Ideal wire gauge.
  • Consider ‘red’ as acceptable, but really try to go for green…

DIY Camper Electrical System Cheat Sheet:

Please verify using the above guidelines, but these wires will work for most situations.

Pro Tip: Be flexible in your wire sizes, if you need 3 feet of 2ga, 4ft of 4ga, and 4 ft of 6 ga; consider using 2ga for all of it and just buy a longer section of 2 ga rather than buffet style wires.

Now that you know what size of wire to use in your DIY camper van electrical system, it’s time to learn what type and size of fuses you’ll need to make sure your system doesn’t catch on fire in case of malfunction.  Check out how to size fuses here:

Everything that you are learning here is put to use in our FREE Interactive Solar Wiring Diagrams.  If you haven’t yet, check them out as they are a complete solution for a camper van electrical system.  Check them out here:

Remember, this is just one part of a full camper van electrical educational series.  To see all of the individual guides, click here:

Finally, If you found this guide helpful, It’d truly mean the world to us if you’d share it with somebody who can use it, pin it to pinterest for later reference, or share it to a facebook group when somebody has a question about this subject.  Click the bubble in the lower right corner to subscribe to be notified of future updates and as always, leave any questions you’ve got in the comments below.

How-to Install a Battery Monitor in a DIY Camper Van Electrical System
How-to Size Fuses in a DIY Camper Van Electrical System


Wednesday 28th of April 2021

My dad has a small trailer and I am trying I size everything perfect for him he just needs lighting a wather heater and water pump I just want I make sure I do it right for him especially if I do a solar to make him to make hit proud.

Billy Koichopolos

Thursday 18th of February 2021

Hi Nate,

How do you determine the prober size wire and fuse for your battery bank? For example if I have 2 x 12 Volt 100 amp hour lithium batteries how do determine the wire size to connect those in parallel and then fuse it as it leaves the battery bank?

cory cantrell

Wednesday 17th of February 2021

Hi Nate,

First I would like to say I have been following your work for a while now, your content and ability to present concise, clear, and informative information is unmatched. Thank you for all the help you have provided over the years via sharing your knowledge.

I have a bit of an odd ball question I am hoping you can help me out with. Here goes:

I purchased an RV new from the factory, I asked them to run a 6 gauge wire from the roof solar panel (single panel) to the charge controller and a 6 gauge wire from the charge controller to the battery bank. This was due to the fact I was going to expand the solar system substantially and I wanted to not have to re-run wires or put any holes in the roof. I got my RV and unfortunately they only ran the 6 gauge wire from the charge controller to the battery. The solar panel to the charge controller wire (10 gauge I believe) is about 5 feet in length, and the wire from the charge controller to the battery (6 gauge wire) is about 11 feet in length (could be shorter I am overestimating for caution).

I want to put a something like this to join the wires (if you don’t want to click the link I understand, so I will explain). When I say join the wires I mean take the 10 gauge wire off the charge controller and connect it to the 6 gauge to basically extend the wire. That wire would then be a 10 gauge wire 5 feet long connect to a 6 gauge wire 11 feet to make a total of 16 feet wire that would ultimately be the wire going from Solar Panels to the Victron 150/100 charge controller. Then a 6 gauge from the charge controller to the battery bank. I plan to ultimately have a 4s3p setup with 13.39 volts per panel and 9.21 amps per panel so that would make a 53.56v 27.63a system. I realize the charge controller I bought is overkill but want to be able to add more panels on the ground and more on the roof of my RV so went with a bigger charge controller.

Back to the question finally, will this wire setup be substantial for the current load above of 4s3p? I was not able to figure out how to mathematically figure out the change in gauge along the path to tell if this will be sufficient in my setup. I am trying my best to not have to re-run the wire on my roof as all the panels are flexible and do not require any holes in my RV roof, which I am terrified of doing on a new RV 😊. Years down the road I will be adding additional panels and then I think I will have to replace the wire, but for now to support the 1,474 Watts of power my 12 panels will provide (max) I am trying to avoid running new wire.

Panels are the FXT24R and FXT24L by Merlin Solar - 115w flexible panels Thank you!

Nate Yarbrough

Wednesday 17th of February 2021

Hey Cory!

Okay... I'm going to sidestep your question a bit...because it's not necessary to use 6 AWG from a solar array given the array is properly configured. My recommendation... Wire that array 6s 2p into a 2-1 MC4 combiner and run that through the 10AWG wire to the charge controller. That would be about 96Voc and would knock your array amperage down to 18A. That would be well within amperage spec and the boost in voltage would get rid of any potential voltage drop for a 10 AWG wire.

I would recommend making the 6 AWG from charge controller to Battery bank larger, though. Feel free to run the numbers, but I always run 2 AWG for that circuit as that is the biggest wire that the charge controller can handle.


Saturday 5th of December 2020

Hey Nate, thanks for all the resources. I'm a little confused between the wiring chart and the calculator. I'm looking at my shore power inlet wire for example: When I calculate 20' at 30 amps at 120 V using the calculator, it tells me 14 AWG. However, the chart would tell me 6-8 AWG. Seems like a big difference. When I look up some "standard" charts for NM-B, it tells me 10 AWG for 30A service. Is there a mistake in the calculator? 14 gauge seems way too small for 30 amps. Thanks, Steve

Nate Yarbrough

Monday 7th of December 2020

AC and DC wiring is a little different. This blog post (and my calculator) are for DC wiring. For AC wiring & sizes... it's much easier. This blog post explains:


Monday 23rd of November 2020

Nate, I am hung up because I can’t arrive at a consensus on the size and type of wiring for the A/C side of the system. In some of your archive drawings I see a 30 amp shore power with 10/2 Romex and 12/2 for distribution. You referrer to an automotive electrical code saying that stranded wire must be used. Isn’t Romex synonymous with solid copper core?

Nate Yarbrough

Tuesday 24th of November 2020

Correct. This blog post should address ALL of those issues: