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Author Topic: URGENT: 24V between ground and neutral at festival event  (Read 18690 times)

Mark McFarlane

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Re: URGENT: 24V between ground and neutral at festival event
« Reply #30 on: December 13, 2013, 12:28:43 pm »

The earth conductivity (or lack of it) for the ground connection really has nothing to do with the G-N voltage since there should be a single G-N-E bonding point ... 

Thanks Mike as always for your thoughtful help.
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Mark McFarlane
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Mark McFarlane

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Re: URGENT: 24V between ground and neutral at festival event
« Reply #31 on: December 13, 2013, 12:45:11 pm »

Just to tie pretty bow on this, glad you got some informed help.  The fact that nothing caught fire suggests that the ground voltage was spurious low current leakage. Repeating my caveat that I am not a mains wiring expert, this was not like the home distribution panel, since the drop at the house panel has transformer isolation.

Connecting a floating ground to neutral at a sub panel is arguably better than having a floating ground only as long as the neutral line back to the power source is robust and properly attached. The reason this sub panel ground/neutral connection is not considered good practice is because of what happens if you get a bad/loose  connection in that neutral line back to the primary power drop. If neutral opens up back at the primary, the neutral and now connected ground can rise up to hot voltage. So you end up with hot voltage*** on all your product chassis.

The correct fix that your venue still needs to get right is to bond ground to neutral at the transformer/primary panel. Your band-aid ground bond at the sub panel could be more dangerous than the floating ground should the neutral path open up.   

Glad you didn't release any smoke or kill any meat puppets.

JR   

** The hot voltage from an open neutral bonded to ground is in series with all the loads so perhaps not full voltage, surely enough voltage to be life threatening.

Gene Power
To clarify, tomorrow I'll be running off the gene, not the mains and transformer.  I'll be the only load on this 170kva gene.  Still a chance to smoke some gear tomorrow.

The neutral connection from my sub panel to the gene connection panel is good, I had them pull it, clean it and reconnect it.  How that neutral connects inside the gene is anyone's guess.

Considering the the gene neutral and ground are not connected together (according to the gene tech who probably partially read the manual and that is about all he knows, but a really nice guy), would it have been better to bond neutral to ground at the gene versus the way we did it, bonding at the one and only breaker panel at the stage?

Land Power
Regarding the site land power, which I am not using, we have a plan to get someone qualified out over the next few weeks to look at the 24V neutral-ground problem, which was described in the opening post of this discussion.  For reference, the picture below shows where I was connected in. My sub panel was run from the panel on the left, which was 120V 3 phase. The sub panel on the right I think was marked 480V 3 phase.  The box between panels was a transformer and that is where the grounding rod was connected.

The guy who runs events at this site (and others) was very appreciative that I identified a problem and looks forward to getting it resolved.  He stuck around on and of for 3 days, probably 10 hours total just making sure I was happy with the stage power.  He was the one who brought in the gene when I complained about the land power.

Of course, the food vendors are all still using the land power.  I vowed to myself not to test any of their circuits :)
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Mark McFarlane
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Mac Kerr

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Re: URGENT: 24V between ground and neutral at festival event. Slightly OT
« Reply #32 on: December 13, 2013, 04:54:41 pm »

Considering the the gene neutral and ground are not connected together (according to the gene tech who probably partially read the manual and that is about all he knows, but a really nice guy), would it have been better to bond neutral to ground at the gene versus the way we did it, bonding at the one and only breaker panel at the stage?

Maybe I'm tired, and thinking clearly, but if the Neutral and  Ground are not bonded how does the safety ground blow a beaker? If the electricity can't return to its source because the safety ground circuit is not connected to the electrical circuit what is the current path that is low enough impedance to blow the breaker? The dirt that the ground rod may or may not be driven into is not an infinite sink for electrons.

Since this seems to be, from this discussion, common practice in Mark's locale, is everyone at risk?

Mac
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John Roberts {JR}

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Re: URGENT: 24V between ground and neutral at festival event
« Reply #33 on: December 13, 2013, 05:11:07 pm »

Perhaps they don't have as many lawyers there as we do here....

JR
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Rob Spence

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Re: URGENT: 24V between ground and neutral at festival event
« Reply #34 on: December 13, 2013, 05:38:52 pm »

One thing not specifically pointed out is that the primary reason for the ground rod is to have somewhere for a lightning strike to go.


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John Roberts {JR}

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Re: URGENT: 24V between ground and neutral at festival event
« Reply #35 on: December 13, 2013, 06:14:45 pm »

One thing not specifically pointed out is that the primary reason for the ground rod is to have somewhere for a lightning strike to go.


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Not since Mike said it this morning...

JR
Quote from: Mike posted
The ground rod in a power system is really there for lightning protection and keeping your local ground plane (G-N-E) close to earth voltage.
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Stephen Swaffer

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Re: URGENT: 24V between ground and neutral at festival event
« Reply #36 on: December 14, 2013, 01:16:37 am »

 Sounds like your engineer got more than just a piece of paper for the time and money he spent at school!  Sounds like a reasonably safe setup to me though I agree that bonding at the source would be a better option-but might step on toes too.

To clarify my earlier post regarding being more concerned about bonding than running the ground wire-that wire is actually an equipment bonding conductor and serves a different purpose than the ground rods.  It also more critical when there are other metallic paths between the source and the load-metal water lines-or more likely in this scenario a metal fence.  If a person cannot touch metal from both the source and the load, a voltage difference doesn't present a huge hazard.  Still best to have the equipment bonding conductor if there is any way to get it, but in my mind lack bonding is a deal breaker.

Code allows for impedance grounded systems in certain situations.  I have never worked with them, nor do I understand the advantages of them-however that might explain why the neutral is not bonded on the gen set-to allow for use on an impedance grounded system if necessary-the manufacturer leaving properly bonding the neutral up to the end user for flexibility.
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Steve Swaffer

Mark McFarlane

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Re: URGENT: 24V between ground and neutral at festival event
« Reply #37 on: December 14, 2013, 11:15:25 am »

My thanks again to everyone for your thoughtful assistance. I was really stressed out this week with my normal day job and two fairly large gigs. I've had <10 hours of sleep over the past 3 nights.

Anyway, the gig is over.  It turned out to be hotter than expected (I suspect it was in the mid-high 80s) but with a clear sky (i.e. no dust) which is unusual for this desert.  A long day, as festivals always are, but the bands played well and the rig sounded better than I expected for such a large outdoor space. I suspect we'll get some complaints from the food vendors, who were about 250' in front of the mains and the sound was still fairly loud.  Probably around 4,000 people came, I should get a count tomorrow.

This is my last gig with the 01V96, the new GLD is on its way.  I affectionately rolled up the copper snake and put it to rest in my grandmothers steamer trunk.

Thanks again John, Mike, Tim, Chris, Stephen, Geoff, Lyle, Steve and Rob for your kindness and support.

I'm off to soak in the tub....
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Mark McFarlane
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Jeff Bankston

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Re: URGENT: 24V between ground and neutral at festival event
« Reply #38 on: December 14, 2013, 05:46:15 pm »

just because there was never a problem doesnt mean a thing. famous last words > the guy said he doesnt need an instrument rating to fly. the news said he had ben in trouble with the faa several times for flying in weather without an instrument rating. he took off in over cast and crashed about 2 miles from where i live. i heard the boom. the xo on the tranformer(s) needs to be grounded. this is the single most common screw up that i and my electrician buddies have seen.
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ProSoundWeb Community

Re: URGENT: 24V between ground and neutral at festival event
« Reply #38 on: December 14, 2013, 05:46:15 pm »


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