Is Generator Grounding Necessary?

We need some help. DH was reading through the manual it talks about grounding the unit and connecting a ground lead, but no ground lead was provided. Is this a necessary component to run the generator safely - any thoughts or suggestions?

DH found a short discussion on an Airstream forum. Here is the link if anyone is interested. I guess we'll consider grounding it to a pipe if there is one around.

I did not see anything definative in that Airstream forum. I still wonder what the value would be of earth grounding the generator when the TT is isolated from ground.

The other concept that has not been really explained is why an onboard generator does not need to be grounded. I see those things fired up all the time and when did you see a ground rod anywhere around the TT?

I got this off another site with references to NEC. If someone has a new NEC manual maybe they could check to see if what I have is right.

250.34 Portable and Vehicle-Mounted Generators.
(A) Portable Generators. The frame of a portable generator shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by the generator under the following conditions:
(1) The generator supplies only equipment mounted on the generator, cord-and-plug-connected equipment through receptacles mounted on the generator, or both, and
(2) The non–current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.
(B) Vehicle-Mounted Generators. The frame of a vehicle shall not be required to be connected to a grounding electrode as defined in 250.52 for a system supplied by a generator located on this vehicle under the following conditions:
(1) The frame of the generator is bonded to the vehicle frame, and
(2) The generator supplies only equipment located on the vehicle or cord-and-plug-connected equipment through receptacles mounted on the vehicle, or both equipment located on the vehicle and cord-and-plug-connected equipment through receptacles mounted on the vehicle or on the generator, and
(3) The non–current-carrying metal parts of equipment and the equipment grounding conductor terminals of the receptacles are bonded to the generator frame.

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I am not an expert and I do not encourage you to do anything other than what the manuals say.
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From what I am reading there is a practical side to grounding. For one thing if you consider all the places you might go, the impedance of the earth could be quite high. Do where I live we have lots of wet earth so ground impedance is quite low. Out west where there is lots of sand, ground impedance is very high.

If you are going to try to get an 8-25 ohm ground circuit, you are going to have to work very hard at it. In order to have a ground circuit that will pop a fuse or breaker at 120VAC you need very low ground resistance.

The other thing I am reading is that what you do for a construction site is different than what you do for a trailer. I do not pretend to understand how that works, but I will. AND I WON'T TELL YOU (LAWYERS). It all makes some logical sense, but I am going to have to dig into my electrical books to better understand this.

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FIRST, I AM NOT AN ELECTRICIAN SO BEFORE YOU DO ANY OF THIS CHECK WITH A LICENSED ELECTRICIAN WHO HAS THE LIABILITY INSURANCE TO OFFER ADVICE.
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I talked to a few electricians I know about generator grounding and travel trailers. Here is a condensed version of what they told me.

According to NEC trailers do not require ground because they are a separately derived system. A separately derived system is essentially a system that has an isolated source. Assuming your trailer has one electrical source. That is one of the reasons why a trailer mounted generator does not require a ground rod to be driven into the ground. The same applies to a portable generator connected to a trailer.

NOW THE BIGGIE AND IMPORTAN ITEM

The generator must be bonded to trailer ground. That is the ground lug of the generator must be connected to trailer ground. A trailer mounted generator will have this done at the factory when the generator was installed. Likewise, with a portable generator you should (or as NEC would say "SHALL") do the same.

So what does bonding do? I have a ground installed in my power cable; doesn't that do the same thing?

The answer is yes, but for safety sake, bonding is a better way to go. For example, just suppose the ground wire came loose in the cable from the connector you would now have an ungrounded trailer. Not a safe thing to happen.

The solution is rather simple, ground the generator's ground lug to the trailer ground on a separate cable. As long as either ground (power main or the grounding bond) stays intact, the generator stays grounded with respect to the trailer.

This only applies to separately derived systems (trailers, for example). Houses are a different story, since they are typically not separately derived and usually require ground rods.

[Bill]

SS&FCN have done some real nice work here. The Internet is full of misinformation, guesses, and "my buddy says ..." stories, but very little real knowledge. This is especially troublesome to me, since I am an electrical engineer, and I didn't know the answer. I've spent hours drawing little diagrams and trying to find the issues.

The NEC is the gold standard. In its hundreds (thousands?) of pages, it covers everything about how to do electricity. SS&FCN have uncovered the parts that answer our questions. If I'm reading correctly, the important conculsions appear to be

• you DO NOT need to drive a ground rod or ground stake (thank goodness)
• you DO need to use a sufficiently-heavy three-wire extension cord, in good condition, between the generator and the trailer. A two-wire cord is absolutely forbidden.
• you SHOULD add a separate grounding wire between the generator ground lug and the trailer frame.

Thanks to you guys for straightening this out.

Bill

Originally Posted by Bill

...Thanks to you guys for straightening this out...

And gal...

One of the electrical people I talked to about this said the reason you see them grounding generators, is that they do not want their people to forget to ground when they should.

[Bill]

Sorry 'bout that. I use "guys" to mean plural people of any age and gender. I think I picked it up from my kids, who seem to have done it since birth.

Bill

[grill-n-go]

My 5 y/o grand daughter went to the same language school as yours', when she's the boss the rest of the family is "guys".

I hope everyone knows I was being tongue & cheek...though be aware wife hit 4 targets in 4 seconds with her shotgun...