Vehicle Mounted Generator Neutral Bond And Ground

SparkyInCanadaE

Maybe some of you have come across this before. I am to install a 85kw 3 phase 120/208 generator (diesel powered) on a truck (24 ft straight truck). I will be installing a loadcenter 100A 3 phase 4 wire for distribution. If the generator neutral is internally bonded to the frame of the generator than there should be no neutral bond at the loadcenter. Here is the question: Is this a sufficient ground? The way I look at it is: this "ground" is not "really" a ground in the normal sense. My concern would be if the gennie is running and there was a short or poor neutral connection than there is an opprortunity for current to flow to a person touching the truck and the earth at the same time. And grounding the frame of the genereator to the frame of the truck could further complicate this? Sorry if it's confusing, I'm struggling with getting this out.

mickeyco

I have no idea but I think you would want it completely isolated from the truck.

On a side note (why I looked at this post), we have a sub-division a few blocks away that has a truck with a giant generator that comes and plugs into a large receptacle whenever there's a power failure. I have no idea what it's for, no hospital or old folks home in the area, any ideas?

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__________________
Some people climb mountains. I take out the trash. But we both do it for the same reason.

jrclen

So that's where Dick Cheney is hiding. We can't find him anywhere.

playsinmud

Is the vehicle being driven or mobile while generator running?? I know Hydro here will have a seperate ground wire with a short rod and of course in summer push it into the ground, that or if you wanted to be safe use a ground plate and maybe just slide it up against the tire and earth.

InPhase277

Nah. 250.34(B)

Water or sewage pump station maybe.

InPhase277

InPhase277

I don't know about Canada, but NEC 250.34(B) doesn't require a grounding electrode for vehicle-mounted generators as long as the generator and vehicle frame are solidly bonded. This fellow is thinking that if there is a fault to the truck, that someone may get hurt if they touch the truck and the Earth at the same time. In reality, current will not flow to the Earth, because there isn't a complete path, because the generator is insulated from the ground by the truck tires. A common misconception about grounding is that electricity "goes to the ground". Not true.

InPhase277

jrclen

There is no restaurant in the ground that the electrons wish to go to. They wish to return to their source, and will use the ground to get there.
(One of my early instructors)

Mackie

Ahhh... something up my alley!

I work for a mobile AC power company and outfit trucks similar to what you've got going on.

We do bond the ground to the neutral in the load demand center. If it's good enough for Verizon, it should work for you!

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2 Cor 13:14

jrclen

Now there is a scary thought.

acrwc10

[quote=mickeyco; I have no idea
.[/quote]

This is the most accurate thing you have ever posted !!!!!!!!!!!!!!!!!

mickeyco

This may be true but I am able to properly quote someone (see above). I do have some questions maybe you or some else can answer them, I have no need to know other than curiosity. The question I have is about bonding the generator to the truck, I would guess that it probably happens just by attaching it to the truck (unless it's isolated), now depending on what the generator is being used to power couldn't the truck be a shock hazard? Say you were using it to power something that is already tied into or bonded to an existing earth ground, is there not then potential between the truck and the actual ground (the grass) or the truck and any of the hot lines?


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__________________
Some people climb mountains. I take out the trash. But we both do it for the same reason.

acrwc10

Keep up the good work , I know you are also an expert in "Cut and Paste".

mickeyco

It's "Copy and Paste". Although I have no idea what you are talking about. Any answers on my last question?

__________________
Some people climb mountains. I take out the trash. But we both do it for the same reason.

jrclen

If the generator was bonded, ground to neutral, and if the generator was bonded or in contact with the truck body, and if you were in contact with the truck body, yes. If you were down on the ground, not leaning on the truck, probably not. There would be no bond between the generator and earth.

Most generators now have GFCI protected receptacle outlets on the 120v circuits. So there would be little to worry about.