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Old 09-10-2017, 05:47 PM   #1
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Where to Ground, That is the Question

I've been reading a lot about how and where people ground their AC systems, and there seems to be general agreement that it's "on the chassis" or "on the frame" that the ground is attached.

So that makes me think that I would run my ground wire out of my breaker box, through the floor, and bolt the ground wire onto the frame of the vehicle.

But what about just grinding down a spot on the metal walls of the bus, up in the passenger compartment (much easier!), and grounding the bus there?

I guess this all comes down to how you define "chassis." Is the chassis comprised of only the massive metal beams under the bus? Or is does the chassis extend to other struts in the metal frame?

Thoughts and pics would be appreciated!

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Old 09-10-2017, 06:50 PM   #2
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I have my DC circuits grounded to chassis. I'm an advocate of not having a big enough AC system to need to consider grounding it.
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Old 09-10-2017, 08:09 PM   #3
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if you are on shore power wouldnt you ground through shore? and on inverter, doesnt the inverter likely tie the AC ground to the input DC ground? or is the AC always isolated and can float?
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Old 09-10-2017, 08:32 PM   #4
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Yes, shore would be the ground when on AC, and that will ground the metal panel box itself ... but I'm thinking that also grounding the bus body would be good, on AC, as a 110 AC short that connected to the bus body could lead to hot bus. But maybe I could be wrong there.
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Old 09-10-2017, 09:47 PM   #5
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the bus is not your AC ground, however, the bus needs to be grounded to your AC.
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Old 09-10-2017, 10:15 PM   #6
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I like how you put that. Now just to get down into the battery box and lock in the ground wire
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Old 09-10-2017, 10:22 PM   #7
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Right, so your question is where on all that frame, sheet metal, etc should the wire attach. I would advocate for the body rather than the truck chassis for a few reasons, all of which kind of say the same thing in different ways:
  • is the electrical connection from the truck chassis to the bus body obvious and intentional? Or is it more of an assumed thing, ie a collection of clips distributed along its length that may or may not be painted, or rusty, or loose, etc?
  • most (all?) of the ac wiring will be routed around and through the body. If a wire-to-body fault happens, a good low-resistance path is needed to ensure that a protective device (over-current or ground fault) activates.
  • cleanliness and accessibility of the connection is important. If it's in a place exposed to the elements it'll be more likely to rust. If it's in a place that's out of the way it could get loose and go unnoticed. In both cases the connection could deteriorate to where it's no longer effective.
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Old 09-11-2017, 06:27 AM   #8
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Hmmmm, I see your points. That would be nice and clean
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Old 09-11-2017, 06:41 AM   #9
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some info

Quote:
Originally Posted by family wagon View Post
Right, so your question is where on all that frame, sheet metal, etc should the wire attach. I would advocate for the body rather than the truck chassis for a few reasons, all of which kind of say the same thing in different ways:
I'd go to the frame. My bus came with 10K generator and 100 amp service wired-in by coachbuilder. They went to the frame on mine. I have not found a ground jumper to the body yet, but may be there somewhere.

https://www.osha.gov/OshDoc/data_Hur..._generator.pdf

found this: My trailer came OEM with 120v ground and battery negative attached to the frame.
Fuses and switches on the 12v positive.
No bond (connection) between 120v neutral and ground in the trailer.
I would only have it this way. RVIA standards. NEC considers an RV to be a secondary panel, thus no 120v neutral to ground bond allowed.

120 VAC in your RV
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Old 09-11-2017, 09:34 AM   #10
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Rusty,

That link has some good info. But.... I did see see some things that gave me pause.

The author states that bonding neutral and ground in your generator is wrong.

That runs contrary to my understanding of NEC.

Did you get the same from the article?
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