Where to Ground, That is the Question

[spenceronehalf]

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!

Spencer

[brokedown]

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.

[cadillackid]

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?
-Christopher

[spenceronehalf]

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.

[turf]

the bus is not your AC ground, however, the bus needs to be grounded to your AC.

[spenceronehalf]

I like how you put that. Now just to get down into the battery box and lock in the ground wire

[family wagon]

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.

[spenceronehalf]

Hmmmm, I see your points. That would be nice and clean

[Rusty]

Originally Posted by family wagon

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

[PNW_Steve]

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?

[family wagon]

Certainly I won't say it's wrong to choose the vehicle frame as the ground point. It makes some sense that an OEM might choose to do it that way, and we can probably assume (?) that they detailed the connection for corrosion and vibration resistance as well as connection from vehicle frame to metal body.

PNW_Steve, I read that doc too. After reading I came away with the understanding that OSHA is hyper-vigilant about having the ground conductor connected through cord-and-plug equipment and the generator frame. What seemed glaringly lacking was discussion about the ground-neutral bond. The "Bonding Versus Grounding" paragraph mentions, almost as if it were a footnote, "Bonding is the intentional connection between the grounded circuit conductor (neutral) and the grounding means for the generator, which includes the generator’s frame. Thus, effective bonding of the neutral conductor to the generator’s frame is also a concern for the safe use of the equipment." By this I think the author means that bonding is right -- but since bonding from the factory is anything but standardized, I'm surprised they don't make a bigger deal of it. It seems to me that all the fuss over grounding in that fact sheet is for naught if the bond isn't present.

[Rusty]

I don't know the definitive answer- just adding to discussion.


I think one of these might be a good idea. I imagine most RV shore power is pretty dirty and electronics like clean power.

Hughes RV Autoformer Voltage Boosters & Surge Protector, 30 Amp
Catalog Item # 102449 $380



3600 watt. 2400 joules surge protection.

Park voltage drops as more RVs are plugged in and demand for power increases, causing appliances and electronics to draw more amps and create more heat due to inadequate voltage. Overheating results in shortened appliance life. Patented Hughes Autoformer constantly boosts power 2%. When shore power drops below 113 volts, it boosts power 10% to keep appliances operating at the correct voltage.

Monitors and analyzes shore power
Monitors for open neutral and ground
Tells you when it’s boosting power
Provides surge and spike protection
Tells you when to replace surge protection unit
Prevents low voltage circuit breaker pops
Keeps appliance motors from slowly burning out
Increases air conditioner air flow
Brightens lights
Prevents blackouts and brownouts
Easy to see indicator lights
Includes digital voltage meter and cable lock
Mfr. 2 year guarantee
Engineered and made in USA

[PNW_Steve]

Good addition Rusty,

When we were down in Mexico with our 5th wheel we saw a LOT of those units and heard many stories of fried electronics from "before we got the power protector".

Lot's of happy customers.

[Drop out]

I don't think anyone has brought up the topic of lightning.

I imagine when traveling and boondocking the closest a bus might get to an earth ground is dragging a bit of copper braid.

If I park somewhere for a few months, I would be tempted to sink an earth ground and make sure I have a nice thick connection to the chassis (star) ground.

I don't know all the details of doing that yet but I imagine if I design to try and make a lightning strike somewhat survivable, that ground should be just fine for everything else. I plan on trying to consolidate the electrical as much as possible to prevent ground loops and IR drop. I also want to keep the conduit runs and junction boxes easily accessible so I can pull new wire if I have to.

One thing I know is that a star ground is a good idea. Consolidation makes it a lot easier to avoid a daisy chain.

I'll draw a schematic and layout my devices to create clean wire runs, no spaghetti. I'll mix up automotive and residential wiring techniques where appropriate and I'll consult with a few electrical engineers I know to make sure my GFCIs, surge suppression, breakers and grounding are up to snuff.

Planning and a clean installation are going to pay off in terms of space used, trouble shooting and safety. I see a lot of hobbyist electronics that are a jumbled mess, if you do that, look at how a good electrician wires up a factory floor and try to raise your game.

[dan-fox]

You could ask the campground when the last time was that anybody put a megger on their ground. And watch them look at you like you were from Mars.

That brings up a point. What good is it to read everything on the Net about 12VDC vs 120VAC grounding issues if you end up trusting a ground that's not a ground? And the next guy over energizes it?