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Old 02-22-2015, 07:46 PM   #1
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trekerboy's Avatar

1979 31' Excella 500
Charlevoix , Michigan
Join Date: Aug 2014
Posts: 257
Is this bad? AC and DC Chassis Grounding Question

I'm in the process of creating an electrical control center for our '79 Excella 500 renovation and have a question about grounding the AC and DC electrical systems.

Let me start off by saying that all the DC loads in my AS are grounded to the frame (lights, etc...), which means I need the DC negative to attach to the frame as well.

I have the WFCO 8930 AC/DC distribution panel and I guess at a high level my question is if I can use a single copper grounding cable (connected to the chassis) to ground both the DC Negative and AC Ground Bus Bars by putting a jumper between them (see the Cyan/Teal outline in the image below; I added this jumper, it wasn't like this from the manufacturer). Is this a bad idea for any reason?

The alternative would be to run 2 separate grounding cables to the frame for each system (one for the AC Ground Bus Bar and one for the DC Negative Bus Bar) but I don't see the point in that since they both get connected to the frame.

Click image for larger version

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Here's a diagram of the distribution panel too if my image wasn't clear:

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Any guidance would be appreciated, thank you!!!

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Old 02-22-2015, 10:11 PM   #2
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2007 22' International CCD
Corona , California
Join Date: Jul 2013
Posts: 2,258
IMHO DC negative bar should have a heavy cable back to battery area and ground on the chassis at the same point the battery does. I would not depend only on the chassis of the AS for the DC ground if at all possible. There's a lot of current involved, and you want to minimize the voltage drop.

For AC ground (NOT Neutral) it's more accurately referred to in Europe as "safety earth". It's there to pop breakers or GFCI device in case of leakage to the chassis. That does not need to be as heavy as the DC ground, but should be run separately. Interestingly there are two AC safety earth leads connected to the chassis in my AS. Dunno just why.

I'd go with appropriately sized separate ground leads, personally.

Lewster needs to weigh in on this one as well--he knows the RV wiring requirements better than I do. I'm just a semi-retired Boeing engineer, home improvement wonk 😄 and ham radio operator.

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Old 02-23-2015, 12:35 AM   #3
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1972 31' Sovereign
1975 31' Excella 500
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Benton , Arkansas
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I would ground the 120v and the 12v to the chassis separately.

Mainly because an open at the frame could in the perfect storm (a fault condition) back 120v into the 12v system.

It would be unlikely for a confluence of circumstance to cause a problem, but remotely possible.

Avoid the situation and run the grounds separately.

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