More distro info:
Do you guys tie neutral to ground on a single phase 50a distro on a "gennie" (generator)? If so, do you strap the Neutral lug to the chassis of the gennie, or do you tie it inside the box of the distro? It seems a little scary to strap the neutral lug to the frame of the gennie to me.

By the way, the NEC codebook apparently says that if you use the recepticles on the generator, the frame of the gennie does NOT have to be grounded to earth. Since I am using the lugs, however, I am running a ground rod to earth.

Reply posted by Jim Brooks on July 18, 2000

I thought that the neutral and earth ground were supposed to be tied together at the service entrance.
The generator would be the service entrance. The neutral and earth ground are not supposed to be tied togeather at a load center. I thought that the neutral and earth were already tied internally at the generator.

Hit this problem last year. two generators tied to the same earth ground. This ment that the neutrals were tied togeather. Had breakers with no load tripping. Very strange. Put them on seperate grounds, things calmed down.

Reply posted by D. Parker on July 19, 2000

And how many Earths do we have? I'd love to hear an explanation for this one. If I had set up 2 generators, I would have used one ground rod too. I'm gonna try to get in touch with my nephew who is a trouble-shooter for a large generator rental and sales company, see it he has run into this. He did the generators for a big show in Texas a couple of years back, they had a 350kw gennie for the sound and another just like it for the lights, I wonder if he used two ground rods.

David

Another reply posted by D. Parker on July 19, 2000

Boy was I ever wrong again. Asked an electrician friend. Grounding 2 gennies to the same ground rod is a major no-no. Explanation was over my head, but he said it would make the earthworms come out of the ground. He said a minimum of 20' between ground rods for separate gennies.

David "ever so humbled" Parker

Reply posted by Geri O on July 19, 2000

....Hear the "over the head" explanation the electrician gave you. Just to know.....

Geri O

Reply posted by Gene Pink on July 20, 2000

So would I, so I can refute it.

Unless I am missing something, two gennies feeding seperate load panels, say, one for sound and one for lights, each one having the neutral and ground bonded at the genny, and a wire coming from each genny's bonding point to a common ground rod... what's the problem with this? There won't be any current flow in the ground rod unless there is another connection to ground somewhere else, from a point that has a different voltage potential.

Ground rods aren't meant to carry any serious current, certainly not enough to trip a breaker on a genny, that's why the neutral gets bonded to the ground, when the hot wire in your Mackie power supply shorts to it's chassis, the ground wire carries the current through the ground wire back to the point where it is bonded to the neutral, and the neutral terminal takes it from there. The ground rod's only real purpose is to reference a floating neutral and ground connection to earth. The neutral wire carries the normal return currents back to the neutral source and the ground wire carries any fault currents back to that same neutral source.

One ground rod without another path somewhere else to the dirt does not a night-crawler harvest make.

As far as genny phasing/syncing goes, a common ground rod doesn't see it at all, as both neutral/ground bonding points are at earth, and the phasing of the hot legs is referenced off of that.

Gene

Reply posted by D. Parker on July 20, 2000

Have you tried it. I thought the same thing. The electrician that told me that has about 25 years experience in a refinery that has everything from 120v single phase to 138kv. Plus the guy who started this thread tried it and found out the hard way it wouldn't work.

David

Reply posted by Gene Pink on July 21, 2000

Yes, I have done it. Last saturday, a gennie for me and my tent and another one for the other two smaller tents. I raised holy hell when I got there, nice gennie but ungrounded. An electrician showed up and sunk a rod, and agreed with what I had already done, put my feeder neutral and ground on the gennies neutral lug, ran a short jumper to the frame of the gennie, and another longer wire from the neutral lug laying there on the dirt, waiting for a rod. Another company handling the other smaller tents saw this and decided he wanted a ground also, but the electrician only had the one rod. Since the gennies were 30 feet apart, I said to just ground it to the same rod. He did, and everything was quiet in all three tents, well under a volt between any chassis and the dirt below. Dry as it was, we dumped a gallon of water around the rod and it disappeared just as fast as we poured it.

Send this electrician around here, and I will be glad to give him an education. Sounds like there was another problem somewhere else that he didn't account for or wasn't aware of, and the easy fix was seperating the grounds, and using the dirt as a resistor to reduce the current flow. Which of course means there is a potential between the rods and for safety reasons is flat out wrong, similar to cutting off the ground pin on a power amp to get rid of a buzz.

Gene

Reply posted by D. Parker on July 21, 2000

Sounds like there was another problem somewhere else that he didn't account for or wasn't aware of, and the easy fix was seperating the grounds, and using the dirt as a resistor to reduce the current flow. Which of course means there is a potential between the rods and for safety reasons is flat out wrong, similar to cutting off the ground pin on a power amp to get rid of a buzz.

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The guy who started this thread said they had fixed the problem by grounding the distro from the gennie that they had lifted the ground at the gennie. The distro was at the stage. I would assume that this would be perfectly safe, I don't know about legal, but they didn't leave it ungrounded. I contacted my nephew who works for a company who does the emergency gennies for office buildings, hospitals, etc., and he said that the switch gear that transfers the power from the power company to the generator automatically has the neutral from the gennie and the neutral from the power company attached. The neutral is not switched. This would be the same , I would think, as two generators grounded to the same rod. Electrical items sure generate a lot of interest on this forum. And we're supposed to be sound guys. I did a generator job one time and the generator rental guy told the promoter of the concert, don't worry about the generator, the sound guy will know what to do, and he didn't know me, but he knew sound guys.

David