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)
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.
Quote
(A) Grounded Systems.(1) Electrical System Grounding.Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation
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.
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).
