Electric wire common ground question

Jun 12, 2010
936
Oday 22 Orleans Marina, NOLA
Since I'm rewiring the battery/solar charger 'panel' on my O'day 22 (in the locker) I thought I would replace the wire running from the batteries to the distribution panel (DC only) in the cabin, about a 6 ft one way run. When I did the work originally I used a section of an old extension cord I had laying around, it's 12-3 I think, cut to length and used the white for battery 1, black for battery 2, and green for a common ground. The panel has a A/B/Both switch and powers just a few cricuts - VFH, AM/FM, Auto Tiller, Nav lights (non-led), and that's it. Max load with everything on is probably 4 amps, and that's mostly the nav lights. I do have an inverter I never use but it's connected directly to the battery (somehow, need to look at that).

I was thinking of using Anchor's marine grade 12 AWG 3-wire using the same wiring scheme, but then I wondered if I should use 2 runs of 2-wire instead and not have a common ground. The only time it would matter I think is if I had the battery selector on 'Both' (which I never do and can't image why I would...), so this is mostly a best practice question. The battery and solar grounds are all connected in the locker.

One complication I forsee with two 2-wire runs is wire color, with the 3 wire I can tell battery 1 from battery 2, if I used 2 wire I would be tempted to use red-black for 1 and red-yellow for the other so I could tell them apart in the panel, essentially doubling the cost.

So any issues with using a common ground wire to deliver power to the distribution panel?
 

leo310

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Dec 15, 2006
649
Catalina 310 44 Campbell River BC
I would use #4 wire Red for pos and Yellow for Neg if you want a ground busbar it would be Green. Remember to place a fuse to protect the wire from the battery to your DC panel. From the DC panel I would use #10. All wire would be tin coated with proper fuses. Yes this would cost more but then I rather be safe.
 
May 17, 2004
5,740
Beneteau Oceanis 37 Havre de Grace
A common ground wire should be fine. The 1-2-B switch only switches the positive, so you wouldn’t have any way to switch the negative anyway. As Leo says, be sure to size the wire based on the load, and fuse at the battery based on wire size.

Only other consideration I would have is that technically cable ampacity is reduced when you bundle them because their heat is concentrated. When you bundle three cables you should technically increase the wire size by 30%. Probably not a big deal if you only ever run low amperage, and voltage drop is probably a bigger issue than maximum ampacity, but just something to keep in mind when fusing.
 

Ward H

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Nov 7, 2011
3,792
Catalina 30 Mk II Cedar Creek, Bayville NJ
One complication I forsee with two 2-wire runs is wire color, with the 3 wire I can tell battery 1 from battery 2, if I used 2 wire I would be tempted to use red-black for 1 and red-yellow for the other so I could tell them apart in the panel, essentially doubling the cost.
Keep the cost down and just label the wire ends. You can use a label maker or just a perm marker pen. I'd probably use a black perm marker pen and put a 1 on batt one cable and 11 on batt two cable. Then put a piece of clear heat shrink over it.
 
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Likes: LloydB
Jun 12, 2010
936
Oday 22 Orleans Marina, NOLA
Cool, thanks. I have fuses on the batteries (30A) and the panel itself has fuses (size varies by use). I may go up a size since I'm bundling; loads are low except if a short occurs!

My original wire job lasted, what, 10 years now? And it still works fine but the solar panel connector stopped working and when I went to fix that I just kept going. Sigh.