Reply posted by Gene Pink on July 22, 2000

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 fellow that first brought up the problem with two gennies using a common ground rod obviously had something wrong somewhere else downstream of the gennies. Your answer to that was correct, but then you replied again about it being wrong, under the assumption that your electrician friend knows more than you do. I disagree, you had it right the first time. This is where I jumped in, to challenge the opinion of this electrician.

"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."

If I understand this premise, the ground rod was at the distro instead of the usual place near the gennie? This is one way to do it, sink the rod near the distro, bond the neutral and ground in the distro instead of at the genny, and ground the frame of the genny through the green wire in the feeder back to the distro/rod. Techically this may well meet code if there is a main breaker either coming into the distro or at the output of the gennie, not really sure though, but in this case you would refer to your distro as the service entrance, and watch the fire marshall scratch his head trying to get the gist of it all. But I believe it is plenty safe.

In thinking about the original problem of breakers popping, perhaps they were the ground fault type? If the neutral and ground are bonded in more than one place, the voltage drop on the neutral will show up as a voltage on the ground and trip them.

"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..."

I should hope so, a bad connection on a set of contacts used for a neutral could over-voltage one of the legs and blow up a lot of stuff in a building. There is no need to disconnect the neutrals from each other.

Importance of connections:

Lose a ground, lose a life.

Lose a neutral, lose some gear.

Lose a leg, show stops, fix it, no harm done.

"The neutral is not switched. This would be the same , I would think, as two generators grounded to the same rod."

I'll buy that.

"Electrical items sure generate a lot of interest on this forum. And we're supposed to be sound guys."

Does with me. :-)

"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."

Yeah, typical "pass the buck" bullshit, he just didn't want to stick around, or maybe he didn't have a clue himself and didn't want the responsibility. I highly doubt that every sound company in existance has the knowlege to tie into a gennie, or even a power box, safely. Just around here in the past few years, I know of at least four tie ins that resulted in 208 on a leg, frying a lot of gear. In half these cases, the people on site were quite competent, they just didn't bother to meter it before they plugged in.

I caught one myself a few months ago, a well respected but sometimes careless employee that is pretty sharp with power was instructed to run the feeder but not to tie in, I'll do that when I get over there. I got there in the nick of time, he went ahead and tied in and was about to throw the two-pole breaker, with the black and white on the neutral/ground buss, and the red and green on the two hots. Sonovabitch. His excuse: his maglite was about dead and the green looked like the black.

I renewed my liability insurance the following Monday.

Gene

Reply posted by Weogo Reed on July 22, 2000

Hi Gene,

"In thinking about the original problem of breakers popping, perhaps they were the ground fault type? If the neutral and ground are bonded in more than one place, the voltage drop on the neutral will show up as a voltage on the ground and trip them."

So with a properly wired PD and sound system, GFCIs can be a good thing?

Are GFCIs best located at the breaker box or outlet?
I do know not to use the cheapo GFCIs.

Thanks and good health, Weogo

Reply posted by Gene Pink on July 23, 2000

An anal inspector that didn't get laid last night may well require them on an outdoor show. I have nothing against them, but I don't use them. It has been my experience that backline stage amps with two prong power cords and three-position ground/power switch (center-off), will relentlessly trip these things, due to a capacitor in the amps that couples either leg to ground, ie, makes leakage current on purpose if set the wrong way in relation to which way they are plugged in. The original Fender Twin comes to mind.

A case of old technology and new technology not working together, even though each is functioning as designed.

"Are GFCIs best located at the breaker box or outlet?
I do know not to use the cheapo GFCIs."

Good question, that I don't have an answer for. At the outlet, you have to buy more of them than if you just got GFI breakers. On the other hand, if each outlet is a GFI, it makes finding the offending power leakage a lot faster, and won't leave other gear wthout power if it goes.

A few words about GFI workings: They don't actually sense ground current directly, they look at the current in the neutral and the hot leg and compare the two. Both should be the same, anything that goes out on the hot should come back on the neutral. If they are not within a few milliamps of each other, they make the assumption that some of the current is getting back to the neutral buss through another path, possibly through your arms and legs to wet dirt, so they trip. Perfect for residential kitchens and bathrooms around water, but many false trips on stage. Some are more sensitive than others, and can be prone to tripping way too early. (In my opinion. A little tingle now and then is good for ya...) I hate having to cross my fingers that the stage will stay powered until loadout.

Gene

Reply posted by D. Parker on July 22, 2000

"In thinking about the original problem of breakers popping, perhaps they were the ground fault type?"
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I had considered this possibility.
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In half these cases, the people on site were quite competent, they just didn't bother to meter it before they plugged in.
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That's a biggie. Last thing I do is meter at the distro, the actual edisons I will be plugging into.

David