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Old 01-22-2021, 09:25 AM   #1
Rivet Master
 
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Ground.

Are the DC circuits ground buss common to the AC grounds?

I need a DC ground wire and I could tap into an AC outlet ground nearby.

My intuition says yes, but I'd thought I'd try an expert before I allowed smoke to escape equipment.

Both schematics show a ground.
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Old 01-22-2021, 10:08 AM   #2
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There is a publication called RV Travel. There is a section called Just ask Mike (JAM) he specialty is RV electric.
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Old 01-22-2021, 10:09 AM   #3
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Ground.

One of my degrees and training includes electrical power distribution. Hereís how it works in an Airstream.

Both the DC negative buss bar and the AC safety earth (bare copper or green ground wire) are tied together to a common point. On my Airstream they are separately run to a big ground lug bolted on the frame back by the bumper. Therefore they are tied to one point, but are not to be used as a common connection. Note that checking the integrity of that ground lug is a preventative maintenance check done at least once a year.

Note that the AC neutral (white wire in an outlet) is not and cannot be tied to the bare or green safety earth AC wire inside the Airstream anywhere, ever. Thatís required by code. It gets tied to safety earth in a power pedestal or home power panel, or at the generator with a bonding plug if needed.

The proper way to get a DC ground in your case would be to run a wire to the shell of the Airstream or the frame. The safety earth for an AC circuit is there for safety, to protect you from a hot wire to airstream shell short circuit and blow the breaker if it happens. Itís NOT there as a DC ground connection.

The short answer is NO, run the DC ground to the shell or frame if a home run to the negative DC buss bar is not possible. Donít use the AC safety earth. Thatís not why it is there.
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Old 01-22-2021, 10:10 AM   #4
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The AC ground (green and uninsulated) are grounded to the chassis. The AC neutral (white) is not and should not. Edit, beat me to it. Carry on.
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Old 01-22-2021, 10:25 AM   #5
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One of the slightly dumb things US electrical codes and electricians tend to do is call the green or bare wire in AC circuits Ďgroundí. The European standard refers to it as Ďsafety earthí which is a better name for what it is used for.

As I noted, itís there to blow the breaker if you get a hot wire short to the shell. Itís usually a lighter gauge wire, designed to blow the breaker, but not routinely carry any current.

The isolation in an Airstream (or any travel trailer) between safety earth and neutral is so GFCI devices will operate properly and to keep excess current out of the safety earth. Thatís why they are not tied in the Airstream electrical panel. They do get tied external to the Airstream as required by electrical code. Itís a safety thing that looks different on the schematic.
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Old 01-22-2021, 11:05 AM   #6
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Looks like more research is needed. There's no way to run a wire to the skin from where my need is.
BTW, I never suggested anything about the Neutral???
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Old 01-22-2021, 01:32 PM   #7
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Ground.

How much DC current do you actually need at the location?

Understand you didnít ask about neutral. I have a rotten long-standing engineering tendency to give very complete answers...
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