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Author Topic: Grounding stage sections?  (Read 1949 times)

TJ (Tom) Cornish

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Re: Grounding stage sections?
« Reply #20 on: March 05, 2014, 09:13:25 am »

Grounding the stage creates an opportunity for electrocution.  It is hoped that the opportunity for electrocution pops a breaker or trips an RCD/GFCI before electrocution occurs.  Percentage wise, across lots of incidents, this is absolutely a good thing.  On a case by case basis YMMV.

The stage needs to be built according to the manufacturers specs and local regs.  If there are concerns these should be raised with the installers/manufacturer/engineer/site electrician.
You raise a good point - if the stage is truly floating, in some cases that could be better than a strong ground/bond connection, but I agree that the majority of situations, making a known current path - both between deck sections and the distribution ground for bonding purposes is a good thing.

Something that has not been mentioned yet in this thread is that it is important to test that the GFCI receptacles are functioning.  Maybe Mike or someone else has data on this, but I would suspect that the failure rate for GFCIs that live outdoors in closer proximity to water and lightning strikes is statistically high.  So far we have all assumed that the GFCIs will work.  It would be good to carry an inline GFCI device like this http://www.amazon.com/Voltec-04-00103-Adapter-Lighted-3-Foot/dp/B00279LG50/ref=sr_1_11?ie=UTF8&qid=1394028650&sr=8-11&keywords=gfci+cord in case you run into a dead GFCI.
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Tim McCulloch

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Re: Grounding stage sections?
« Reply #21 on: March 05, 2014, 10:04:51 am »

Grounding the stage creates an opportunity for electrocution.  It is hoped that the opportunity for electrocution pops a breaker or trips an RCD/GFCI before electrocution occurs.  Percentage wise, across lots of incidents, this is absolutely a good thing.  On a case by case basis YMMV.

The stage needs to be built according to the manufacturers specs and local regs.  If there are concerns these should be raised with the installers/manufacturer/engineer/site electrician.

Code requires all structures with metal framework to have that framework bonded to the building's ground electrode system.  Temporary demountable entertainment structures are not exempt from the requirement.
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Mike Sokol

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Re: Grounding stage sections?
« Reply #22 on: March 05, 2014, 10:26:45 am »

*Disclaimer - I haven't actually measured the impedance between neutral and ground on the EU2000 - there may indeed be a low enough impedance for a GFCI trip to generator frame ground, but I suspect they're just coupling capacitors - I'll try to borrow a generator and measure that sometime.  I do know for sure that the EU6500 has virtually an infinite impedance between neutral and ground.

It's actually quite high on a EU2000, perhaps a few 100K ohms. Here's an article I wrote about building a Ground-Neutral bonding plug for powering an RV (with it's properly isolated ground and neutral). http://www.noshockzone.org/generator-ground-neutral-bonding/

I've just sent a formal proposal to Honda to see if they'll send me an EU2000i generator (and maybe the Companion version) so I can do my own experiments. I already know a lot about how these generators work according to all the published tech sheets, but nothing's quite as good as measuring it yourself. Should be a lot of fun. I do know that hundreds of RV users are running using the G-N bonding plug I detail on this article. The problem with using a portable floated neutral generator on an RV is that many of them have a voltage monitoring system that will shut down if the differential between the ground and neutral is more than a few volts. As someone posted earlier, these portable generators will try to put out 60-60 volts on the hot and neutral unless you tie the neutral to chassis ground. While that's not an issue for a power tool at a worksite, my position is that an RV is basically a portable house, and thus should follow basic G-N bonding code. But because the entire system has a floated ground plane, they don't require a ground rod. Stages are something different, so I'm currently of the opinion that your portable generator should be G-N bonded as well as tied to a ground rod. I have personal experience to back up this opinion, but I'll need to do more studying as to code compliance. More to study... ;)

Ray Aberle

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Re: Grounding stage sections?
« Reply #23 on: March 05, 2014, 05:54:28 pm »

It's actually quite high on a EU2000, perhaps a few 100K ohms. Here's an article I wrote about building a Ground-Neutral bonding plug for powering an RV (with it's properly isolated ground and neutral). http://www.noshockzone.org/generator-ground-neutral-bonding/

I've just sent a formal proposal to Honda to see if they'll send me an EU2000i generator (and maybe the Companion version) so I can do my own experiments.
Surely someone on here has one that you could use...? If you were on the WEST coast, instead of Maryland, I would let you borrow mine in a heartbeat.

-Ray
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Mike Sokol

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Re: Grounding stage sections?
« Reply #24 on: March 05, 2014, 06:49:13 pm »

Surely someone on here has one that you could use...? If you were on the WEST coast, instead of Maryland, I would let you borrow mine in a heartbeat.

-Ray

Honda just emailed this afternoon and offered to send me a free EU2000i to experiment with. That way if I do something stupid and destroy it, nobody will be out a generator. BTW: I sent them the link to this forum as well as my NoShockZone.org blog for examples of the type of questions we all have about grounding and bonding generators for stages and such. So keep those great questions and comments coming and I'll do my best to design a relevant experiment and gather some empirical data.  And remember that I'm counting on all of you to be my peer review on this stuff. This forum has a great mix of both theoretical and practical engineers, so it's always great to hear your opinion on a subject.
« Last Edit: March 05, 2014, 06:57:17 pm by Mike Sokol »
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Mike Sokol

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Re: Grounding stage sections?
« Reply #25 on: March 05, 2014, 07:40:44 pm »

Something that has not been mentioned yet in this thread is that it is important to test that the GFCI receptacles are functioning.  Maybe Mike or someone else has data on this, but I would suspect that the failure rate for GFCIs that live outdoors in closer proximity to water and lightning strikes is statistically high. 

You are correct. Somewhere I remember reading a white paper about the failure rate of GFCIs in outdoor locations to be something on the order of 50% or thereabouts. As you may have noticed, many GFCIs have a notice to check them monthly for proper operation, but I don't know ANYBODY who's ever tested them once the building inspector does a test (and that's not all the time either). I'll look for the white paper on GFCI failure rates tomorrow when I'm back in my office.   

Stephen Swaffer

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Re: Grounding stage sections?
« Reply #26 on: March 05, 2014, 07:51:52 pm »

I did actually initiate a PM program and check GFCI's in an industrial facility for several years.  We had somewhere in the neighborhood of 20  tested every 6 months.  Over a period of several years, I never completed a PM without at least one failure.  Most of these were not heavily used-just in place because of powering a drinking fountain, or near a wet location or water filled tank.  These were  "name brand"  GFCI's not big box cut rate ones.
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Lyle Williams

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Re: Grounding stage sections?
« Reply #27 on: March 06, 2014, 02:42:20 am »

I have read about high failure rates.  We have mandatory testing every 12 months (every three months is the gear is being hired out) in Oz.  I have probably done 200 tests and only had one fail.
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Lyle Williams

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Re: Grounding stage sections?
« Reply #28 on: March 06, 2014, 03:17:29 am »

Code requires all structures with metal framework to have that framework bonded to the building's ground electrode system.  Temporary demountable entertainment structures are not exempt from the requirement.

If code requires it, do it.  If code doesn't require it, be wary of doing something different without sharing the blame around amongst others.
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