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Title: Grounding stage sections?
Post by: frank kayser on March 02, 2014, 10:24:37 pm
So I was describing the all-aluminum stage sections our city puts up for various events, and it occurred to me that I don't know if these should be grounded or not. 


The city supplies about ten 4x8 sections of staging on approximately 2' legs with vinyl/rubber caps.


The sections do not bolt or clamp together - there is some motion among the sections.


If I need to ground them, I'd guess the first task would to be to electrically connect all the platforms together.
I would also assume the safety ground on the 20A GFI feeding the plaza would not be the appropriate place to ground the stage, but to drive a ground rod and connect the stage to the ground rod using heavy copper wire.


I can't say I've ever seen something like that grounded (bleachers at the ball park?).  If these things are not to be grounded, I'd love to hear why not.


frank
Title: Re: Grounding stage sections?
Post by: Cailen Waddell on March 02, 2014, 10:45:30 pm
I'm not an electrician.  There may be many things I am not considering.  That said - if all the equipment on the stage is properly grounded, the the chance of the stage becoming a better ground path seems unlikely.   

If it gets struck by lightning - everyone is dead anyway. 
Title: Re: Grounding stage sections?
Post by: Craig Hauber on March 02, 2014, 10:56:42 pm
So I was describing the all-aluminum stage sections our city puts up for various events, and it occurred to me that I don't know if these should be grounded or not. 


The city supplies about ten 4x8 sections of staging on approximately 2' legs with vinyl/rubber caps.


The sections do not bolt or clamp together - there is some motion among the sections.


If I need to ground them, I'd guess the first task would to be to electrically connect all the platforms together.
I would also assume the safety ground on the 20A GFI feeding the plaza would not be the appropriate place to ground the stage, but to drive a ground rod and connect the stage to the ground rod using heavy copper wire.


I can't say I've ever seen something like that grounded (bleachers at the ball park?).  If these things are not to be grounded, I'd love to hear why not.


frank

Is it bare aluminum on top?  Most of the ones I've seen are still plywood or some kind of textured coating that's generally of insulating quality.  Just clamping a plugged-in but unused lighting fixture to one of the legs would probably suffice.  I also don't see why the grounding of that GFI receptacle wouldn't work either?
If it's fully floating then grounding could help with with static buildup (like the kind you get shuffling across a large carpeted hotel ballroom and touching the console with an audible 'snap' heard through the rig)
Title: Re: Grounding stage sections?
Post by: frank kayser on March 02, 2014, 11:01:16 pm
I'm not an electrician.  There may be many things I am not considering.  That said - if all the equipment on the stage is properly grounded, the the chance of the stage becoming a better ground path seems unlikely.   

If it gets struck by lightning - everyone is dead anyway.


A VERY big if... 
And I'm not sure a grounded stage would mitigate a lightening strike. 


However, I would think a well-grounded roof grid, or lighting truss would offer a fair amount of protection from lightening.  Like a lightening rod on a house, or like a mast in a sailboat - it provides a cone of protection to those on deck.


Is it bare aluminum on top?  Most of the ones I've seen are still plywood or some kind of textured coating that's generally of insulating quality.  Just clamping a plugged-in but unused lighting fixture to one of the legs would probably suffice.  I also don't see why the grounding of that GFI receptacle wouldn't work either?
If it's fully floating then grounding could help with with static buildup (like the kind you get shuffling across a large carpeted hotel ballroom and touching the console with an audible 'snap' heard through the rig)



The aluminum decking has SOME anti-slip coating left, but not what I'd call thick enough or complete enough to be considered an insulator.
Title: Re: Grounding stage sections?
Post by: Stephen Swaffer on March 04, 2014, 09:19:33 am
The NEC specifies that any metal object that is "likely" to become energized should be bonded to ground.  Bonded is defined as "intentionally connected" and the usual standard is with a "listed" connector.  I am not sure you can get  "listed" clamp for aluminum tubing-you could use a lug under a bolt. The bonding conductor size would be determined by the largest breaker capable of energizing the platform-ie if only 20 amp brreakers feeding a #12 would suffice.  And bondng needs to be to the service ground-NOT a ground rod.

"Likely" is a pretty vague term.  Bottom line is someone is going to be held responsible if something bad happens.  If you are in a lawyers potential target field, might be wise to consider.  IF all equipment is grounded, you should be ok-but do you have a broken ground pin in the chain?  Are you SURE you don't?
Title: Re: Grounding stage sections?
Post by: TJ (Tom) Cornish on March 04, 2014, 10:11:58 am
There are a few different things to consider here: as others have said, grounding is not the same thing as bonding.  Grounding implies a connection back to earth, and if the legs are aluminum, you already have some amount of "grounding" just by them being on the ground.  If the ground is wet and the aluminum is unpainted and in direct contact with the earth, you already have an excellent ground, whether you want it or not.  I disagree with Cailen about being sure that the stage would be a less-preferable path than the actual ground wire - there's potentially a lot of metal with a lot of ground contact, not to mention that there's no way to ensure that every piece of equipment is always properly grounded; - an SO cord could become pinched between stage sections causing a fault during the actual performance, even if the cord was in perfect condition a moment ago.

For life safety, you need to think about the potential for fault currents.  If a metallic object has the potential to be energized - something very possible with lots of power distribution and instruments of unknown condition right on your conductive deck, then it should be bonded to the electrical service, such that GFCIs and OCPDs will function.  This likely also means the metallic object is grounded, but not necessarily (see below).

There are some nuances here depending on the nature of your power source.  The small Honda EU-series generators are unbonded - no ground to neutral connection at the generator.  The EU6500 can be externally bonded, but the 120v-only models cannot be bonded, as they make "balanced power" - 60V hot to ground, 60v neutral to ground.  For these small generators, the ground screw goes basically nowhere, - especially the EU6500. 

If you are using a 120v only Honda generator, your protection comes from the fact that the supply is isolated - there's only one power source - the hot wire of the single circuit, and only one power sink - the neutral wire.  There's actually no way to have a ground fault, as there can be no completed circuit to ground.  A dangerous situation with this type of supply would require two faults - one fault to hot, and the other to neutral.  This could potentially happen with two cord failures - a hot to one deck, and a neutral to another deck.  Touching these two decks would complete the circuit.  Bonding the decks together would eliminate this risk.

If you are using an EU6500 with an external distro, your distro should bond neutral->ground, as this is not present internally on the EU6500.  Per NEC2014, the receptacles must be GFCI, and I would want to bond the deck sections to each other, and to the distro, which creates a fault current path back to the generator that would enable GFCIs and OCPDs to function.

Code requires generators greater than 5KW to have an earth ground rod, I believe.

If you are using shore power, receptacles should be GFCI, and the decks should be bonded together and to ground.
Title: Re: Grounding stage sections?
Post by: Tim McCulloch on March 04, 2014, 10:18:09 am
So I was describing the all-aluminum stage sections our city puts up for various events, and it occurred to me that I don't know if these should be grounded or not. 


The city supplies about ten 4x8 sections of staging on approximately 2' legs with vinyl/rubber caps.


The sections do not bolt or clamp together - there is some motion among the sections.


If I need to ground them, I'd guess the first task would to be to electrically connect all the platforms together.
I would also assume the safety ground on the 20A GFI feeding the plaza would not be the appropriate place to ground the stage, but to drive a ground rod and connect the stage to the ground rod using heavy copper wire.


I can't say I've ever seen something like that grounded (bleachers at the ball park?).  If these things are not to be grounded, I'd love to hear why not.


frank

Ask your city manager and inspection department if they've heard of Salina, Kansas and the 12 year old girl who was electrocuted because of apparent non-bonding.  The first lawsuit has been filed, and my guess is the City of Salina or their insurance company will be paying out.  See topic elsewhere in this forum.
Title: Re: Grounding stage sections?
Post by: frank kayser on March 04, 2014, 12:23:59 pm
Ask your city manager and inspection department if they've heard of Salina, Kansas and the 12 year old girl who was electrocuted because of apparent non-bonding.  The first lawsuit has been filed, and my guess is the City of Salina or their insurance company will be paying out.  See topic elsewhere in this forum.
Tim,
It was precisely that article that got me thinking about the safety of our staging.  As the outdoor season is rapidly approaching, I would like to be able to put the City Manager on notice of a potential safety issue and be able to state the case in some "intelligent" fashion, and use the Salina, Kansas as an incentive for them to pay attention and act.


Of course, I'd like to know enough to be able to see if something is actually done, and done effectively.
thanks
frank

Title: Re: Grounding stage sections?
Post by: frank kayser on March 04, 2014, 01:31:21 pm
There are a few different things to consider here: as others have said, grounding is not the same thing as bonding.  Grounding implies a connection back to earth, and if the legs are aluminum, you already have some amount of "grounding" just by them being on the ground.  If the ground is wet and the aluminum is unpainted and in direct contact with the earth, you already have an excellent ground, whether you want it or not.


I disagree with Cailen about being sure that the stage would be a less-preferable path than the actual ground wire - there's potentially a lot of metal with a lot of ground contact, not to mention that there's no way to ensure that every piece of equipment is always properly grounded; - an SO cord could become pinched between stage sections causing a fault during the actual performance, even if the cord was in perfect condition a moment ago.

<snip - generator discussion>

For life safety, you need to think about the potential for fault currents.  If a metallic object has the potential to be energized - something very possible with lots of power distribution and instruments of unknown condition right on your conductive deck, then it should be bonded to the electrical service, such that GFCIs and OCPDs will function.  This likely also means the metallic object is grounded, but not necessarily (see below).

If you are using shore power, receptacles should be GFCI, and the decks should be bonded together and to ground.


Thanks, TJ, for some very salient points.  Some of it is a bit confusing, and some may, according to my reading here, may or may not be in conflict.  I'd like to explore the answer a bit, if you please. 


One thing that is confusing my direct situation is the generator discussion.  If you please, I am very interested in that, too, but I'd like to explore that a bit in a different post.


I'd like to explore the shore power aspect of your answer in this post.
First, I have to assume the staging in question (aluminum deck and legs) is poorly grounded as it sits.  I have never worked with the staging on anything but a slab of concrete.  (wet and dry). The legs have a vinyl cap to protect a surface from scratching, acting as an insulator.  The  square legs fit loosely into sockets.  Aluminum oxidizes quickly left open to the air, and creates a high resistance surface on the aluminum further degrading the natural grounding.


Second point is grounding vs. bonding.  As I understand it, and discussing only shore power, the safety ground in the GFCI eventually is connected to a ground rod somewhere (close to the power panel, I would assume).  Neutral would be bonded to ground in only the first panel (and only bonded once - not every panel/sub-panel) after the power leaves the pole.  (lay explanation)  So, in a shore power situation, bonding and grounding are the same, correct? (Understanding gennys are a different kettle of fish)


Third point: "... deck, then it should be bonded to the electrical service, such that GFCIs and OCPDs will function"  I'm assuming this is a comment for generators, as your last statement "If you are using shore power, receptacles should be GFCI, and the decks bonded together and to ground"


Fourth point: I fully agree - any cord on this type of stage can (and has) been caught between sections, though we've been lucky to have caught them before the cord insulation could be compromised.


Fifth point: I think I've read here, that just because metal is in contact with the ground (wet or dry), that constitutes a good ground.  I'm out on a limb here, but I'm thinking that just being in contact is inadequate given the length and composition of the grounding rod.


And thanks for helping me gain a better understanding.
frank
Title: Re: Grounding stage sections?
Post by: TJ (Tom) Cornish on March 04, 2014, 02:52:24 pm

Thanks, TJ, for some very salient points.  Some of it is a bit confusing, and some may, according to my reading here, may or may not be in conflict.  I'd like to explore the answer a bit, if you please. 


One thing that is confusing my direct situation is the generator discussion.  If you please, I am very interested in that, too, but I'd like to explore that a bit in a different post.


I'd like to explore the shore power aspect of your answer in this post.
First, I have to assume the staging in question (aluminum deck and legs) is poorly grounded as it sits.  I have never worked with the staging on anything but a slab of concrete.  (wet and dry). The legs have a vinyl cap to protect a surface from scratching, acting as an insulator.  The  square legs fit loosely into sockets.  Aluminum oxidizes quickly left open to the air, and creates a high resistance surface on the aluminum further degrading the natural grounding.
"Ground quality" is a continuum.  Leg caps or boots can frequently be compromised, and stage decking gets banged around all the time.  Aluminum Oxide cannot be depended on in any fashion as an insulator. Bottom line - you have to assume that in the absence of intentional insulators, any metal is conductive and potentially able to be energized.  The larger the metal and/or the larger the contact area with the ground, the larger the current potential.  There's nothing magic about a 6' or 8' ground rod in the ground - a few legs of an aluminum stage with compromised feet on wet grass may have a lower-impedance ground connection than an intentional ground rod in drier soil.



Second point is grounding vs. bonding.  As I understand it, and discussing only shore power, the safety ground in the GFCI eventually is connected to a ground rod somewhere (close to the power panel, I would assume).  Neutral would be bonded to ground in only the first panel (and only bonded once - not every panel/sub-panel) after the power leaves the pole.  (lay explanation)  So, in a shore power situation, bonding and grounding are the same, correct? (Understanding gennys are a different kettle of fish)
My language may not have been precise enough to fully explain this - an unfortunate reality of this not being billable time.  Two points here that could be expanded on later:

Point 1:
 GFCIs absolutely need a ground connection to function.  This is implemented by the G->N bond in the service entrance, which has the function of completing the circuit of the earth back to the neutral wire.  This is required, otherwise if you touch the hot terminal of your GFCI protected outlet and ground, there is no completed circuit path for the leakage current to go - your body and the ground you're standing on (or the generator, depending on your perspective) would just float at the potential of the hot wire.  This is exactly the isolating scenario of the 120v only Honda Generators I mentioned - a GFCI would never trip, as there is nowhere else for the current to go, since the only possible current sink is the neutral wire. 

Note 1: A GFCI receptacle itself does not necessarily need to be grounded - they are often used to retrofit homes with no ground wire at the receptacle, however the GFCI depends on the environment - the house, stage, etc., being bonded to neutral (done at the service entrance) for there to be a leakage current sink back to the panel.

Note 2: The intent of a GFCI receptacle is to provide a measure of life safety for currents that leak from hot to ground.  A GFCI receptacle provides no safety for a hot -> neutral fault.

Point 2 (Re: in a shore power situation are bonding and grounding the same thing):
From a cord and plug device standpoint, yes.  The green wire in the cord provides the path to earth ground as well as the bonded path back to neutral.  I used the language I did because in the example of staging given, some may think it would be acceptable to drive a ground rod in at the stage and then it would be "grounded".  This is inadequate, as there needs to be a low-impedance path from the conductive stage back to the G/N bond point at the service entrance to sink fault currents sufficiently well to trip the OCPD.  This, functionally, is bonding -  accomplished with a ground wire.



Third point: "... deck, then it should be bonded to the electrical service, such that GFCIs and OCPDs will function"  I'm assuming this is a comment for generators, as your last statement "If you are using shore power, receptacles should be GFCI, and the decks bonded together and to ground"


Fourth point: I fully agree - any cord on this type of stage can (and has) been caught between sections, though we've been lucky to have caught them before the cord insulation could be compromised.


Fifth point: I think I've read here, that just because metal is in contact with the ground (wet or dry), that constitutes a good ground.  I'm out on a limb here, but I'm thinking that just being in contact is inadequate given the length and composition of the grounding rod.


And thanks for helping me gain a better understanding.
frank
I don't understand your third point question, but absolutely the stage deck should be grounded and bonded in a shore power situation, or any time you have more than a single circuit generator.
Title: Re: Grounding stage sections?
Post by: frank kayser on March 04, 2014, 03:51:33 pm
"Ground quality" is a continuum.  Leg caps or boots can frequently be compromised, and stage decking gets banged around all the time.  Aluminum Oxide cannot be depended on in any fashion as an insulator. Bottom line - you have to assume that in the absence of intentional insulators, any metal is conductive and potentially able to be energized.  The larger the metal and/or the larger the contact area with the ground, the larger the current potential.  There's nothing magic about a 6' or 8' ground rod in the ground - a few legs of an aluminum stage with compromised feet on wet grass may have a lower-impedance ground connection than an intentional ground rod in drier soil.

My language may not have been precise enough to fully explain this - an unfortunate reality of this not being billable time.  Two points here that could be expanded on later:

Point 1:
 GFCIs absolutely need a ground connection to function.  This is implemented by the G->N bond in the service entrance, which has the function of completing the circuit of the earth back to the neutral wire.  This is required, otherwise if you touch the hot terminal of your GFCI protected outlet and ground, there is no completed circuit path for the leakage current to go - your body and the ground you're standing on (or the generator, depending on your perspective) would just float at the potential of the hot wire.  This is exactly the isolating scenario of the 120v only Honda Generators I mentioned - a GFCI would never trip, as there is nowhere else for the current to go, since the only possible current sink is the neutral wire. 

Note 1: A GFCI receptacle itself does not necessarily need to be grounded - they are often used to retrofit homes with no ground wire at the receptacle, however the GFCI depends on the environment - the house, stage, etc., being bonded to neutral (done at the service entrance) for there to be a leakage current sink back to the panel.

Note 2: The intent of a GFCI receptacle is to provide a measure of life safety for currents that leak from hot to ground.  A GFCI receptacle provides no safety for a hot -> neutral fault.

Point 2 (Re: in a shore power situation are bonding and grounding the same thing):
From a cord and plug device standpoint, yes.  The green wire in the cord provides the path to earth ground as well as the bonded path back to neutral.  I used the language I did because in the example of staging given, some may think it would be acceptable to drive a ground rod in at the stage and then it would be "grounded".  This is inadequate, as there needs to be a low-impedance path from the conductive stage back to the G/N bond point at the service entrance to sink fault currents sufficiently well to trip the OCPD.  This, functionally, is bonding -  accomplished with a ground wire.


I don't understand your third point question, but absolutely the stage deck should be grounded and bonded in a shore power situation, or any time you have more than a single circuit generator.


Thanks TJ - my apologies for picking apart the language so literally - I do appreciate all I learned in this discussion and that you were spending your personal (non-billable) time.


I also did quite a bit of additional reading in the interim - "No Shock Zone" (Thanks Mike Sokol), and Phil Graham's three-part article in FOH Online.  http://www.fohonline.com/current-issue/74-tech-feature/8858-generators-and-portable-primer-part-1.html
Through your efforts and theirs, I have a much better understanding of grounding vs bonding - the ground rod vs the low impedance path back to the panel needed to trip a breaker and provide safety.


I also have a better handle on the Honda Gen floating neutral/ground issues.  (so I won't be bugging you here).  Still much to read and to sort out.  Thought I had a good handle on it, but it seems I have only scratched the surface.


As for the "ground quality" vis a vis aluminum oxide as an insulator - you're absolutely correct - trust aluminum oxide or a vinyl boot cap as insulators to keep us safe?  Never.  I was looking at these things not as a "protection from ground" but as an interference - high resistance point that could interfere with earth-ground quality.


I guess I had better start drafting a letter to the city manager...
- Speak in broad terms of electrical safety and the likelihood that the stage could become energized
- Refer them to Salina, Kansas
- Get their electrician to produce a plan and get that to the maintenance men who put the stage up.


It's a start...


And again, Thanks TJ!
frank
 
Title: Re: Grounding stage sections?
Post by: Mike Sokol on March 04, 2014, 04:15:59 pm
I also did quite a bit of additional reading in the interim - "No Shock Zone" (Thanks Mike Sokol), and Phil Graham's three-part article in FOH Online.  http://www.fohonline.com/current-issue/74-tech-feature/8858-generators-and-portable-primer-part-1.html
Through your efforts and theirs, I have a much better understanding of grounding vs bonding - the ground rod vs the low impedance path back to the panel needed to trip a breaker and provide safety.

I've not had time to jump in on this thread yet, but I have done a lot of thinking about the issue of generator and stage grounding/bonding in general. I've also discussed it at some length with a few generator manufacturers and electrical engineers in an attempt to get my head wrapped around the issues involved. I'll try to come up with a bullet-point list of how to handle stage and generator bonding/grounding, which I'll present here for your critique. Perhaps together we can come up with a basic SOP of how to handle these situations before the outside spring concerts get started. Could save a few lives, and that's a good thing...
Title: Re: Grounding stage sections?
Post by: Scott Wagner on March 04, 2014, 04:33:41 pm
The city supplies about ten 4x8 sections of staging on approximately 2' legs with vinyl/rubber caps.

The sections do not bolt or clamp together - there is some motion among the sections.
While this reply has nothing to do with electricity, it is important none-the-less.  This condition is unsafe.  Have the city install C-Clamps between the sections.  It's a cheap way to insure that nobody gets injured, and is common practice in staging.
Title: Re: Grounding stage sections?
Post by: Stephen Swaffer on March 04, 2014, 08:22:58 pm
Tom.

GFI circuits do not need a ground to function.  They measure the current on the hot and neutral wires and compare them-if they are not within the trip threshhold  of each other-ie current has gone anywhere else than back to the source, be that a gen set or a service-they trip.  GFI receptacles do not need a ground to function, and I have installed enough GFI breakers to know they they have no connection to ground-just to the neutral.  If they did sense a true ground, they could guard against the RPBG that is so dangerous.

OPCDs absolutely MUST have a low impedance ground path to function correctly in all situations.  OPCDs should take care of hot-neutral faults-if sized properly, and if the equipment grounding conductor exists as it should, it will trip on a hot-ground fault, although a GFCI will often react quicker than a  circuit breaker,if there is one in the circuit.
Title: Re: Grounding stage sections?
Post by: TJ (Tom) Cornish on March 04, 2014, 09:42:02 pm
Tom.

GFI circuits do not need a ground to function.  They measure the current on the hot and neutral wires and compare them-if they are not within the trip threshhold  of each other-ie current has gone anywhere else than back to the source, be that a gen set or a service-they trip.  GFI receptacles do not need a ground to function, and I have installed enough GFI breakers to know they they have no connection to ground-just to the neutral.  If they did sense a true ground, they could guard against the RPBG that is so dangerous.

You are incorrect - they do need a ground to function - however, it's not the ground at the screw of the GFCI, but rather the bond at the service panel connects the literal ground - the concrete slab, the dirt, etc., to the neutral wire.  Without this, there is no way for any current to leak out and go anywhere - there is no circuit.  Think about it - where would the fault current go?  There's no current unless there's a completed circuit.

This is a common misconception, as you are indeed correct that the ground screw of the GFCI doesn't need to be connected, but that's not the whole story.
Title: Re: Grounding stage sections?
Post by: Mike Sokol on March 04, 2014, 10:21:39 pm
You are incorrect - they do need a ground to function - however, it's not the ground at the screw of the GFCI, but rather the bond at the service panel connects the literal ground - the concrete slab, the dirt, etc., to the neutral wire.  Without this, there is no way for any current to leak out and go anywhere - there is no circuit.  Think about it - where would the fault current go?  There's no current unless there's a completed circuit.

This is a common misconception, as you are indeed correct that the ground screw of the GFCI doesn't need to be connected, but that's not the whole story.

First of all, here's a primer I wrote on GFCI theory to get everyone on the same page: http://www.noshockzone.org/rv-electrical-safety-part-viii-gfci/ (http://www.noshockzone.org/rv-electrical-safety-part-viii-gfci/)

As you note, a GFCI doesn't need a ground wire connected to the green ground screw to operate. But to be 100% accurate, a GFCI really doesn't need a ground path at all to trip. It's looking for an unbalanced current between the hot and neutral lines. So having some or all the neutral return current go through another neutral path outside of the GFCI's path will unbalance the GFCI sensing circuit and cause it to trip. 

It's all a bit crazy until you draw it out on paper and look at the current paths. But I will agree that anything conductive you can stand on or touch should be bonded/grounded somehow. Just exactly how to do this so it's safe and code compliant under all circumstances will require a bit of thinking. For instance, portable generators...
Title: Re: Grounding stage sections?
Post by: frank kayser on March 04, 2014, 11:10:16 pm
While this reply has nothing to do with electricity, it is important none-the-less.  This condition is unsafe.  Have the city install C-Clamps between the sections.  It's a cheap way to insure that nobody gets injured, and is common practice in staging.

Indeed, if nothing else, the "floating" stage sections are, at best, a real PITA.  At worst, edge sections waiting to snag and cut a cable, energizing the platform.  The floating platform also makes for unsure footing, pinch points that could take a finger, or worse.
Safety is safety - call 'em as you see 'em.  Yeah, another good point to put on my list to talk to the city about.


good call, Scott.
Title: Re: Grounding stage sections?
Post by: Lyle Williams on March 05, 2014, 02:02:22 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.
Title: Re: Grounding stage sections?
Post by: Stephen Swaffer on March 05, 2014, 08:55:08 am
You are incorrect - they do need a ground to function - however, it's not the ground at the screw of the GFCI, but rather the bond at the service panel connects the literal ground - the concrete slab, the dirt, etc., to the neutral wire.  Without this, there is no way for any current to leak out and go anywhere - there is no circuit.  Think about it - where would the fault current go?  There's no current unless there's a completed circuit.


Technically, you are correct.  However, if there is truly no ground connection and NO current can flow, then there is no hazard , so no current can flow through me, correct?  That is the basic principal of "hot bare hand" work.  (I am NOT advocating doing that kind of work, however unless you are paid and trained to do it!)

If a GFI is in place, with no ground thus no hazard you are safe,  If a ground exists-intentionally or not-you still have the safety net in place.
Title: Re: Grounding stage sections?
Post by: TJ (Tom) Cornish on March 05, 2014, 09:06:25 am
Technically, you are correct.  However, if there is truly no ground connection and NO current can flow, then there is no hazard , so no current can flow through me, correct?  That is the basic principal of "hot bare hand" work.  (I am NOT advocating doing that kind of work, however unless you are paid and trained to do it!)

If a GFI is in place, with no ground thus no hazard you are safe,  If a ground exists-intentionally or not-you still have the safety net in place.
My point in these posts has been to draw attention to the fault current path(s) and get people to start thinking about the ground/stage/guitar strings/whatever as a possible current path.  If there is truly no other path - such as the Honda EU2000* which is a completely floating system - then a single fault is not a hazard, and a GFCI would never trip, as there isn't a current path for the fault current to go to.

That said, there is almost always a fault current path, and the mechanism that GFCIs usually trip is due to leakage to ground - bathtub water pipes, wet concrete floor, touching the faucet handle, etc.  This tripping action happens because of the G->N bond at the panel, which is necessary for other parts of the electrical system.

*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.
Title: Re: Grounding stage sections?
Post by: TJ (Tom) Cornish 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.
Title: Re: Grounding stage sections?
Post by: Tim McCulloch 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.
Title: Re: Grounding stage sections?
Post by: Mike Sokol 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/ (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... ;)
Title: Re: Grounding stage sections?
Post by: Ray Aberle 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/ (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
Title: Re: Grounding stage sections?
Post by: Mike Sokol 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.
Title: Re: Grounding stage sections?
Post by: Mike Sokol 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.   
Title: Re: Grounding stage sections?
Post by: Stephen Swaffer 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.
Title: Re: Grounding stage sections?
Post by: Lyle Williams 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.
Title: Re: Grounding stage sections?
Post by: Lyle Williams 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.