ECN Forum Forums General Topics of the Trade General Discussion Area Portable Generator Grounding

There is a long thread going on at one of the travel trailer forums right now. Seems a guy bought two small portable inverter generators (Ducar 2000) and the instructions are saying that they must be grounded to a ground rod. No exception is provided for a single travel trailer. I disagree with those instructions especially due to the fact that a shock hazard can be introduced when grounding a portable generator to earth.
Now if you carefully read the instructions they could be interpreted to mean that you must use the generator's ground terminal when using a ground rod as opposed to connecting it somewhere else. But it really appears to mean that you must ground the generator no matter what. Then in the Warning! box we see "Always connect the nut and ground terminal on the frame to an appropriate ground source" My gut feeling is that the instructions are at least partly incorrect.
(The Ducar 2000 is made in China)

Another note, the Ducar 2000 is CSA approved but not CSA/US

2nd note, going to post this on Mike Holt as well.

I would measure resistance between the Neutral and Ground on the generator outlet, and also to the lug. If N-G is Hi R, and G to Lug is Lo R, I would connect the genny lug to the trailer metal.
Joe4

When I read 250.4(A) it makes me wonder why we would ground a truly "portable" generator at all. What is the function of the ground or a main bonding jumper on a portable generator? It looks like you are simply adding a dangerous fault path that has no real good reason to even be there. I understand once you connect this to a structure it becomes a separately derived system or it uses the building grounding and MBJ (depending on your transfer equipment) and those rules change but if I am sitting at a camp site in the woods or prairie building away from PoCo power, what does grounding the generator or bonding the neutral accomplish?

Flame away.

I wonder why we earth ground a lot of things and I can't help but think it has a lot to do with the grounding equipment manufacturer's. However as far as my original post my conclusion is that the instructions are incorrect and following them actually creates a shock hazard as you noted, and there doesn't seem to be any exception to 110.3(B) which tells us to follow the manufacturer's instructions.

I agree. I doubt NFPA was thinking about every dumb thing an offshore manufacturer might write in an instruction manual.

OSHA has addressed this issue for portable generators and recognizes that, under certain circumstances (e.g. travel trailer), the frame doesn't need to be grounded, but itself can act as the ground. See the attached document - I circled the relevant information.

That's all very well, libellis, but OSHA doesn't really apply to places that aren't construction sites, sure it could be used as a guide, but it is what it is.
Personally, you should bond the ground of the genny to the metal on the trailer as well as the spike in the ground.
That is common sense, so that you don't end up with voltage differences between ground and people touching things with no shoes on.

Trumpy, given the opinions expressed in the thread, my post was only intended as a bit of information regarding how one regulatory safety agency viewed the issue, and was not meant to reflect my opinion (or that OSHA - which has relevance to work sites - has any authority in this situation). I should have been clearer in the post, and I never argue against the wisdom of minimizing potential differences (although implementation practicality vs real world risk can be a temptation).

Additional hazard created by ground rod

BigB,
How often would a situation like you've pictured occur?
I'm of the understanding that most tools and appliances these days are Class II (double insulated) and have no reference to ground, whereby they have a plastic body and no ground conductor.
Yes I can understand that there might be some Class I appliances still out there, but if people are going to use them, would they not use an in-line GFCI/RCD?

Libellis,
Sorry, don't think for a moment that I was having a go at you.
I should have been clearer as well.
Down here, we like to throw a GFCI/RCD on everything that might become a safety hazard either now or in the future,
it's not ideal, but when you have idiots working with electricity, there may be problems.
And with generators, there usually are........

I imagine it is rare to non-existent, but by the same token how often would the ground rod do anything beneficial? Yes GFCI protection is required but you can't control what Joe Public does. We still have kitchen re-modelers here who don't bother to install them.

Trumpy,

No, I didn't take any umbrage at all, and I know from your various posts the value you place on safety and common sense.

I suppose the point being made is by grounding a portable generator you are creating a fault path for no particularly good reason. Let's look again at why we ground electrical systems (250.4(A)(1))



You are not going to see line surges or contact with higher voltage lines if you are using a generator and if your generator gets hit by lightning you are toast anyway.