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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Mike Karseboom on July 01, 2014, 01:06:41 AM
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I have an annual event where a metal stage is on asphalt and the local utility company ties into some overhead power lines and provides a panel mounted distro for stage and FOH power. The distro has about 8 duplex edison outlets for 120V service with 20A breakers for each duplex.
After all the reading on this fabulous forum about grounding and bonding, I am now wondering whether the metal stage should be bonded to the ground at the distro panel? I know this is not currently being done.
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I have an annual event where a metal stage is on asphalt and the local utility company ties into some overhead power lines and provides a panel mounted distro for stage and FOH power. The distro has about 8 duplex edison outlets for 120V service with 20A breakers for each duplex.
After all the reading on this fabulous forum about grounding and bonding, I am now wondering whether the metal stage should be bonded to the ground at the distro panel? I know this is not currently being done.
If the stage is metal yes, it should be. anything that can be conductive should be. Wood stages of course can't be.
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And as a follow-up question, what guage wire is appropriate for that purpose?
Which leads to the next question: Do I also need to bond the lighting truss/ground support to earth (the distro panel), if the truss is not integrated into the stage structure?
Do all of the segments of a modular stage (e.g., Wegner Versastage) need to be bonded together?
I apologize for any thread-jacking with my questions. Mark C.
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And as a follow-up question, what guage wire is appropriate for that purpose?
Which leads to the next question: Do I also need to bond the lighting truss/ground support to earth (the distro panel), if the truss is not integrated into the stage structure?
Do all of the segments of a modular stage (e.g., Wegner Versastage) need to be bonded together?
I apologize for any thread-jacking with my questions. Mark C.
For wire size it depends on your over all power draw. I would use either 10, 8, 6, 4 depending on what you are using for your feeder and it's amperage, it's normal for the ground to be smaller than the conductors.
The Wegner Versastage will bond to each other already as they interlock.
Yes, lighting trusses should also be grounded as well.
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For wire size it depends on your over all power draw. I would use either 10, 8, 6, 4 depending on what you are using for your feeder and it's amperage, it's normal for the ground to be smaller than the conductors.
The Wegner Versastage will bond to each other already as they interlock.
Yes, lighting trusses should also be grounded as well.
Yes to bonding the stage to the incoming ground (EGC - Equipment Grounding Conductor)
Yes to bonding the lighting truss to the EGC as well.
The size of the ground/bond wire required is a function of both max circuit breaker capacity and lightning protection. So you should match whatever size ground wire is coming in from the POCO if possible, but probably not smaller than 8 gauge for lightning protection. Also, avoid sharp turns with this bonding wire if possible (no right angle bends) since that will promote lightning side flashes. That's in the amateur radio manual, and those guys worry about lightning a lot.
Yeah, we don't like to think about lightning, but by definition these shows are outside in the summer and typically the highest structure in a flat field. Even if you evacuate the band and stage crew when lightning rolls in (you do, don't you), your equipment will stand a much better chance of surviving a nearby lightning strike if the stage and lighting trusses are properly bonded to earth.
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Typically a POCO will bring in 3 wires and an overhead drop (I am assuming since it is temporary) will usually be no smaller than #4 AL. Someone should be installing/connecting to a grounding electrode (ground rod/s) at the service disconnect?
To ground rods, NEC reqires no that #6-and #6 would need to be used for either a 100 A or 200 A temp service.
EGC is determined by NEC 250.122 depending on breaker feeding equipment as Mike said. This should cover most any distro you run across.
15 amp breaker-#14
20 amp breaker-#12
30 amp to 60 amp-#10
70 amp to 100 amp-#8
over 100 amp to 200 amp-#6
Thought about lightning a lot around here yesterday!
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If the stage is metal yes, it should be. anything that can be conductive should be. Wood stages of course can't be.
Is there some particular section of the NEC or OSHA regulations that I can refer to when requesting that the power company ground the stage when they set up the distro panel?
It is surprising how often you get push back when asking for fairly simple things that could be very important safety wise but might involve a little more work on the installer's part. I would like to have some code to support my request.
Or maybe they figure grounding anything that needs grounding to the distro is my job and they want to make a clear cut boundary between their "system" and the rest of the world, perhaps for liability reasons.
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Or maybe they figure grounding anything that needs grounding to the distro is my job and they want to make a clear cut boundary between their "system" and the rest of the world, perhaps for liability reasons.
This. Grounding someone else's stage isn't the power company's job.
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This. Grounding someone else's stage isn't the power company's job.
Correct. And it's not the generator rental company's job to "ground" your stage either. They're just supposed to drive a ground rod for the generator and make sure the genny's Ground and Neutral bus connections are bonded to it. (Or at least they're supposed to)
And remember that you're not "grounding" the stage... you're bonding it to the incoming EGC (Equipment Grounding Conductor) from your power distro, or directly bonding it to the GEC (Grounding Electrode Conductor) which is your genny's ground rod. See below for basic definitions.
GEC - Grounding Electrode Conductor. The phrase "grounding electrode" is the ground rod (or other thing that is stuck into the dirt). So the GEC is the wire that goes from the service point to the dirt.
EGC - Equipment Grounding Conductor. This has to do with equipment. This is the green wire you attach to the external metal parts of equipment, and the one that provides a path for fault current to flow back to the source. I have heard it called the "safety ground."
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Correct. And it's not the generator rental company's job to "ground" your stage either. They're just supposed to drive a ground rod for the generator and make sure the genny's Ground and Neutral bus connections are bonded to it. (Or at least they're supposed to)
And remember that you're not "grounding" the stage... you're bonding it to the incoming EGC (Equipment Grounding Conductor) from your power distro, or directly bonding it to the GEC (Grounding Electrode Conductor) which is your genny's ground rod. See below for basic definitions.
GEC - Grounding Electrode Conductor. The phrase "grounding electrode" is the ground rod (or other thing that is stuck into the dirt). So the GEC is the wire that goes from the service point to the dirt.
EGC - Equipment Grounding Conductor. This has to do with equipment. This is the green wire you attach to the external metal parts of equipment, and the one that provides a path for fault current to flow back to the source. I have heard it called the "safety ground."
Thank you. Thank YOU. THANK YOU! And all folks part of this thread for these important instructions and clarifications!
So... Would this be adequate?
Metal quad box with mounting "tabs" attached to aluminumm stage, two edison outlets, both bonded to the box and the EGC of 10/3 SEOOW feeder from 20a GFCI outlet?
That wouldn't satisfy GEC connection. Can I use say stranded 8ga screwed to the stage, and clamped to the ground rod?
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Since you are using a 20 amp GFCI as your supply I am assuming the 10/3 is a hot/neutral/ground. As long as there is a GEC at the genny you do have a GEC connection-bonded through the EGC. However, it has been discussed in other threads that a ground rod is not a bad idea at the stage. #8 to that screwed to stage would be fine-personally, I would prefer it to be connected to the same piece of aluminum as the quad box probably not a huge deal but for various reasons I think it the best practice.
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Since you are using a 20 amp GFCI as your supply I am assuming the 10/3 is a hot/neutral/ground. As long as there is a GEC at the genny you do have a GEC connection-bonded through the EGC. However, it has been discussed in other threads that a ground rod is not a bad idea at the stage. #8 to that screwed to stage would be fine-personally, I would prefer it to be connected to the same piece of aluminum as the quad box probably not a huge deal but for various reasons I think it the best practice.
I agree. I'd use the same bolt and star washer to attach both to the stage at a single point.
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There is no need to bond to metal quad box to ground on the stage as if it is properly wired it would already be bonded inside the metal box to ground that is coming from the genny (the rod, which your stage is also bonded too).
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I agree. I'd use the same bolt and star washer to attach both to the stage at a single point.
+1 - I like a piece of #8 stranded bonded to a single point. That gives you the best lightning protection and a great low-impedance path for any fault currents from the stage.
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It would be nice if there were some standard hardware (made by the stage co's) that one could clamp or attach to the stage, and plug into with a piece of 2AWG with green camlocks...
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So when I have 8 4x8 platforms in a parking lot, metal legs and frames, wood tops - would you ground every platform individually?
We ground our stageline sl100 all the time but for smaller stuff, It's difficult....
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Or maybe they figure grounding anything that needs grounding to the distro is my job and they want to make a clear cut boundary between their "system" and the rest of the world, perhaps for liability reasons.
Grounding the stage ends up being kind of a "not my problem" problem.
- It's not the PoCo's problem; their responsibility ends at the meter (or in this case, the temporary power panel they provide).
- It's not the staging provider's problem (they don't do anything electrical).
- It's not the lighting or sound provider's problem (they didn't provide the stage -- and the distros are basically glorified extension cords).
- It's not the promoter's problem (it never is).
But you, now being made aware of the problem, have a social responsibility to ensure that best practices are observed to create an electrically safe environment. For the best liability protection, you don't address the issue yourself (unless you are a licensed electrician); rather, you hire a licensed electrician to do the work and backcharge the promoter. In the future, you include this in contracts and riders.
P.S. -- If there are multiple stage platforms, there should be an electrical bond of some sort between each frame in addition to the bond from the first platform back to the distro/ground rod. I'd be careful drilling into stage frame members; drilling in the wrong spot could compromise strength. Some kind of clamp would be ideal; the kind of clamp used for grounding to water pipe may be usable -- but you must have a metal-to-metal connection. Paint or other coatings could create a high-resistance or insulating connection.
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So when I have 8 4x8 platforms in a parking lot, metal legs and frames, wood tops - would you ground every platform individually?
We ground our stageline sl100 all the time but for smaller stuff, It's difficult....
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Do the legs clamp together? Ours don't. personally I don't bond the wood stages we use at festivals with metal legs, as the stairs are wood as well so it's kinda a bit useless to bond it to ground. there's not point were could could have current on you from a conductive surface on the stage and then step on the ground to get a nice shock, since wood isn't too conductive (read: anything CAN conduct given the right circumstances, it's about how much resistance there is)
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Do the legs clamp together? Ours don't personally I don't bond the wood stages we use at festivals with metal legs, as the stairs are wood as well so it's kinda a bit useless to bond it to ground.
Our legs have plastic brackets so the stage sections are not electrically connected. I feel the same as you - but in the interest of this wider discussion - I thought it an important point to raise....
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It would be nice if there were some standard hardware (made by the stage co's) that one could clamp or attach to the stage, and plug into with a piece of 2AWG with green camlocks...
Noting the silence from just about everywhere on the web, it would be nice if the stage companies (especially the all aluminum) would make some mention that their platform should be grounded...
ah, but there' liability as referenced by Jonathan...
Grounding the stage ends up being kind of a "not my problem" problem.
- It's not the PoCo's problem; their responsibility ends at the meter (or in this case, the temporary power panel they provide).
- It's not the staging provider's problem (they don't do anything electrical).
- It's not the lighting or sound provider's problem (they didn't provide the stage -- and the distros are basically glorified extension cords).
- It's not the promoter's problem (it never is).
But you, now being made aware of the problem, have a social responsibility to ensure that best practices are observed to create an electrically safe environment. For the best liability protection, you don't address the issue yourself (unless you are a licensed electrician); rather, you hire a licensed electrician to do the work and backcharge the promoter. In the future, you include this in contracts and riders.
P.S. -- If there are multiple stage platforms, there should be an electrical bond of some sort between each frame in addition to the bond from the first platform back to the distro/ground rod. I'd be careful drilling into stage frame members; drilling in the wrong spot could compromise strength. Some kind of clamp would be ideal; the kind of clamp used for grounding to water pipe may be usable -- but you must have a metal-to-metal connection. Paint or other coatings could create a high-resistance or insulating connection.
Now you've ruined my good intentions, Jonathan. (just kidding...)
Though getting the stage sections there from the city requires an Act Of God, then the stage sections are not physically attached to each other... let alone an electrician.
Can I, in good conscience, use the stage now without proper grounding, should I just refuse the job, or stand paralyzed Waiting for the Electrician or Someone Like Him.
Would my liability be more acting to avert an electrocution, or ignoring the problem. I know the answer. No one can know someone else's mind.
Good deeds never go unpunished.
frank
p.s. Letter going to the city today. Maybe they just won't supply the platforms any more! Problem solved!
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Can I, in good conscience, use the stage now without proper grounding, should I just refuse the job, or stand paralyzed Waiting for the Electrician or Someone Like Him.
Remember, you can always use a NCVT to do a quick spot check of the stage and backline for voltage. Be sure to check the microphones as well. I often do a stage check with a Fluke VoltAlert which only takes a minute or two and really gives me confidence that I've done everything I can to protect the talent and crew from shock. I have found a few "ungrounded" guitar amps which made the VoltAlert beep close to their guitars, and at least one small PA system tested hot which was plugged into a convention center's duplex outlet that turned out to have an open ground. I found that one while doing a No~Shock~Zone seminar as a guest speaker. So as I walked up front to discuss hot skin conditions I pointed a VoltAlert at the little mixer as a joke, and it beeped. I was able to show that all their mics were "hot" as well as the active speakers. This must have embarrassed the promoter enough that they called an electrician in during the night and the duplex ground was fixed by the morning. Too much fun, eh? ;)
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Grounding the stage ends up being kind of a "not my problem" problem.
- It's not the PoCo's problem; their responsibility ends at the meter (or in this case, the temporary power panel they provide).
- It's not the staging provider's problem (they don't do anything electrical).
- It's not the lighting or sound provider's problem (they didn't provide the stage -- and the distros are basically glorified extension cords).
- It's not the promoter's problem (it never is).
But you, now being made aware of the problem, have a social responsibility to ensure that best practices are observed to create an electrically safe environment. For the best liability protection, you don't address the issue yourself (unless you are a licensed electrician); rather, you hire a licensed electrician to do the work and backcharge the promoter. In the future, you include this in contracts and riders.
P.S. -- If there are multiple stage platforms, there should be an electrical bond of some sort between each frame in addition to the bond from the first platform back to the distro/ground rod. I'd be careful drilling into stage frame members; drilling in the wrong spot could compromise strength. Some kind of clamp would be ideal; the kind of clamp used for grounding to water pipe may be usable -- but you must have a metal-to-metal connection. Paint or other coatings could create a high-resistance or insulating connection.
This is the issue I was trying to raise above, in post #3 (albeit on a subtle basis). The contact between adjacent metal frames is rather sketchy, from an electrical bond standpoint (in my layman's view). I could use a lighting clamp to clamp on a tubular frame with an 8 gauge EGC, but what is the need between sections? Is that (and truss towers) just a lightning protection issue, or an issue for the energized equipment (lights, audio gear)? Mark C.
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Without doing to many quotes, yes THANK YOU all for the clarity on how things can be done in as safe a manner as possible. I have new goal to begin thinking more proactively about potential problems and how they might be mitigated. The idea of sweeping the stage gear with a NCVT as a last step sounds like something worth making the time for as well.
Thank you also for broaching the moral dilemma that is often presented in the real world. Do you refuse to serve and bring the event to a crashing halt if everything is not to "code" or at least to your liking? Doing so may ensure no one will get electrocuted on your watch but what will the consequences be for future work? I know for me at this juncture I would have a hard time putting my foot down unless I could demonstrate a "clear and present danger" like an energized mic or railing. A potential threat or something not quite optimum would be much easier to sort of gloss over.
I suppose that is why I was hoping to push the stage grounding onto the utility company. I think I would like to plead ignorance even though I may know better. Subconsciously I think I am worried that as soon as I do something like ground the stage, or drive in a grounding rod for a generator, that now I am the de facto "expert" and if anything does go wrong I will be the first in line for the lawsuits. Much better to act dumb. Of course I could be the one that gets zapped!
I have to say that every time I bring the feeder cable and distro out and other people plug into it I feel a greatly heightened sense of responsibility. Perhaps my liability is no different than when I plug an extension cord into a wall outlet and then let the muso's plug their amps and pedals into my stage stringers. But the distro seems to take it to a whole new level of "I should know what the hell I am doing".
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Without doing to many quotes, yes THANK YOU all for the clarity on how things can be done in as safe a manner as possible. I have new goal to begin thinking more proactively about potential problems and how they might be mitigated. The idea of sweeping the stage gear with a NCVT as a last step sounds like something worth making the time for as well.
Thank you also for broaching the moral dilemma that is often presented in the real world. Do you refuse to serve and bring the event to a crashing halt if everything is not to "code" or at least to your liking? Doing so may ensure no one will get electrocuted on your watch but what will the consequences be for future work? I know for me at this juncture I would have a hard time putting my foot down unless I could demonstrate a "clear and present danger" like an energized mic or railing. A potential threat or something not quite optimum would be much easier to sort of gloss over.
I suppose that is why I was hoping to push the stage grounding onto the utility company. I think I would like to plead ignorance even though I may know better. Subconsciously I think I am worried that as soon as I do something like ground the stage, or drive in a grounding rod for a generator, that now I am the de facto "expert" and if anything does go wrong I will be the first in line for the lawsuits. Much better to act dumb. Of course I could be the one that gets zapped!
I have to say that every time I bring the feeder cable and distro out and other people plug into it I feel a greatly heightened sense of responsibility. Perhaps my liability is no different than when I plug an extension cord into a wall outlet and then let the muso's plug their amps and pedals into my stage stringers. But the distro seems to take it to a whole new level of "I should know what the hell I am doing".
Well, Mike, it is said that with electricity (and rigging, for that matter!), if you have to ask about something, you're not qualified to do it.
On the other hand, it is important to know enough to know when to say "no" to a dangerous situation, so you are doing the right thing here!
(As for liability for electrical mistakes... well, that's what your insurance policy is for...)
Ray
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This is the issue I was trying to raise above, in post #3 (albeit on a subtle basis). The contact between adjacent metal frames is rather sketchy, from an electrical bond standpoint (in my layman's view). I could use a lighting clamp to clamp on a tubular frame with an 8 gauge EGC, but what is the need between sections? Is that (and truss towers) just a lightning protection issue, or an issue for the energized equipment (lights, audio gear)? Mark C.
How often are/were portable metal stages (and other stage structures: truss, etc.) grounded before the topic was brought up in this forum a few weeks ago? Is this a new area of thought -- hence the lack of approved tools and methods?
That is, was the world blissfully unaware of the potential dangers until a few people with too much free time began thinking about the issue?
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That is, was the world blissfully unaware of the potential dangers until a few people with too much free time began thinking about the issue?
IDK... but we were all blissfully unaware of grounding stage amps and PA systems back in the 60's and 70's and all it took were some dead musicians to change our minds. Of course, nowadays all stage amps and PA systems are grounded by the manufacturer which is enforced by the NEC and UL code. Stages, not so much. But code is now changing to include lots more grounding/bonding for things like hot tubs and marinas.
As far as stage grounding, most of the time we're working on inside wooden stages, but every time I work a festival on a portable metal stage and it begins to rain I get a little squeamish around all that electricity. Even though it's more work and responsibility, I feel good about grounding it. And occasionally one of the band's rodies asks me why I'm driving a ground rod, etc...
After I got my BIG shock from a 650-volt power supply back in the late 70's (was knocked unconscious) I began bringing a Ground Loop Impedance Tester (GLIT) to gigs and tested for proper grounding of the wall outlets as well as checking all backline amps for a proper ground plug. So while the other bands in the area complained about getting shocked, guys in my band began to thank me for NOT getting shocked, especially the times we would play on open stages outdoors that were wet.
I personally think it's important to take the high road and try to do the right thing as much as we can. This business is hard enough as it is without having to worry about getting electrocuted.
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IDK... but we were all blissfully unaware of grounding stage amps and PA systems back in the 60's and 70's and all it took were some dead musicians to change our minds. Of course, nowadays all stage amps and PA systems are grounded by the manufacturer which is enforced by the NEC and UL code. Stages, not so much. But code is now changing to include lots more grounding/bonding for things like hot tubs and marinas.
As far as stage grounding, most of the time we're working on inside wooden stages, but every time I work a festival on a portable metal stage and it begins to rain I get a little squeamish around all that electricity. Even though it's more work and responsibility, I feel good about grounding it. And occasionally one of the band's rodies asks me why I'm driving a ground rod, etc...
After I got my BIG shock from a 650-volt power supply back in the late 70's (was knocked unconscious) I began bringing a Ground Loop Impedance Tester (GLIT) to gigs and tested for proper grounding of the wall outlets as well as checking all backline amps for a proper ground plug. So while the other bands in the area complained about getting shocked, guys in my band began to thank me for NOT getting shocked, especially the times we would play on open stages outdoors that were wet.
I personally think it's important to take the high road and try to do the right thing as much as we can. This business is hard enough as it is without having to worry about getting electrocuted.
While we are on topic, is anyone grounding their roofs? Or are we lumping roofs into the term "stage"?
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While we are on topic, is anyone grounding their roofs? Or are we lumping roofs into the term "stage"?
I have a study somewhere where an electrician who was checking out a lighting fixture on a roof was shocked by an ungrounded roof section which was electrified by a wire with the insulation worn through (I think that was why the lighting fixture was dead). He was startled enough to fall from the ladder he was on and shattered the bones in both of his legs. A big lawsuit was filed but I don't think he was awarded any money since he was "supposed" to take proper precautions and know better. I'll try to dig out the link today.
So yes, metal roofs are supposed to be bonded to building steel (and ground) according to code, as is your furnace and duct work in your house. I'll see if I can find a synopsis of the new 2014 NEC grounding requirements and post them on their own thread.
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Yes to bonding the stage to the incoming ground (EGC - Equipment Grounding Conductor)
Yes to bonding the lighting truss to the EGC as well.
The size of the ground/bond wire required is a function of both max circuit breaker capacity and lightning protection. So you should match whatever size ground wire is coming in from the POCO if possible, but probably not smaller than 8 gauge for lightning protection. Also, avoid sharp turns with this bonding wire if possible (no right angle bends) since that will promote lightning side flashes. That's in the amateur radio manual, and those guys worry about lightning a lot.
Yeah, we don't like to think about lightning, but by definition these shows are outside in the summer and typically the highest structure in a flat field. Even if you evacuate the band and stage crew when lightning rolls in (you do, don't you), your equipment will stand a much better chance of surviving a nearby lightning strike if the stage and lighting trusses are properly bonded to earth.
Mr. Sokol Sir!
While reading this thread as it progresses, car battery booster cables keep crossing my mind.
No they're not purpose designed and approved for bonding metal stage sections together.
No they're not designed to make a fabulous electrical connection through rust and/or paint.
On the plus side;
They're readily available.
They're produced in sufficient quantities to be affordable.
Many clamps, with a little persuassion, could chew through paint and corrosion.
They'd be quick and easy to apply / strike AND without tools.
They're manufactured in a choice of guages, most adequate for bonding metal stage sections together.
They may only be rated for 12 - 24 VDC but perhaps they'd be up to this sort of challenge.
One more negative point; they'd probably walk like crazy during strikes and load-outs.
Yes, I understand they're not the 'right' answer but they keep crossing my mind as something appreciably better than nothing.
While we're chatting, I'm VERY pleased to see you and your forum here at Prosound.
Thank you so much and your notion of inviting manufacturer's engineers as guests is excellent.
In return for their participation, I don't have a problem with them mining your readers for any knowledge and application info they can glean even though this is leaning towards a violation of forum policy for manufacturers and their reps. In this sense we're inviting the manufacturers to participate and I think it would be in everyone's interest to provide any feedback requested.
Toodleoo!
Ron Hebbard
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Mr. Sokol Sir!
While reading this thread as it progresses, car battery booster cables keep crossing my mind.
No they're not purpose designed and approved for bonding metal stage sections together.
No they're not designed to make a fabulous electrical connection through rust and/or paint.
On the plus side;
They're readily available.
They're produced in sufficient quantities to be affordable.
Many clamps, with a little persuassion, could chew through paint and corrosion.
They'd be quick and easy to apply / strike AND without tools.
They're manufactured in a choice of guages, most adequate for bonding metal stage sections together.
They may only be rated for 12 - 24 VDC but perhaps they'd be up to this sort of challenge.
the cables you refer to are offten CCA (Copper-Clad Aluminum) cables which aren't suitable for this purpose. Also for temporary power sitituations where your grounding rod will likely be distant and near a gennie you really want a go insulator to protect it, those cables aren't rated for the voltage or amperage which may make it melt.
CCA is generally only good for high frequency or low power stuff. DC and AC power just aren't the same. also I believe the cables would be less than 20feet.
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the cables you refer to are offten CCA (Copper-Clad Aluminum) cables which aren't suitable for this purpose. Also for temporary power sitituations where your grounding rod will likely be distant and near a gennie you really want a go insulator to protect it, those cables aren't rated for the voltage or amperage which may make it melt.
CCA is generally only good for high frequency or low power stuff. DC and AC power just aren't the same. also I believe the cables would be less than 20feet.
Hello again Jason!
Understood; I did write they aren't purpose designed for this application.
Clipped between sections of metal staging I suspect they'd handle a few hundred amps long enough to trip a breaker in a better than nothing situation. In my neighbourhood they'll survive enough 12 VDC current to crank an icy cold car engine for a couple of minutes.
Quoting you: "CCA is generally only good for high frequency or low power stuff."
High frequency such as 12 VDC and low power such as 150 amps.
Let's not get too serious, or too silly, about this; I did begin with their not being purpose designed for the application.
Toodleoo!
Ron Hebbard
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Hello again Jason!
Understood; I did write they aren't purpose designed for this application.
Clipped between sections of metal staging I suspect they'd handle a few hundred amps long enough to trip a breaker in a better than nothing situation. In my neighbourhood they'll survive enough 12 VDC current to crank an icy cold car engine for a couple of minutes.
Quoting you: "CCA is generally only good for high frequency or low power stuff."
High frequency such as 12 VDC and low power such as 150 amps.
Let's not get too serious, or too silly, about this; I did begin with their not being purpose designed for the application.
Toodleoo!
Ron Hebbard
Using something like that or even suggesting people us that on a public forum is a liability issue.
Again DC and AC are very different. 12vdc is low power even if high amps.
If you get inspected your show might be called until it is fixed. as even though bonding isn't 100% require (though you could debate it is by the newer NEC codes) if they see something like that in use it will def get their attention.
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If there is a wooden deck that makes electrification of the legs unlikely (and conduction of hazardous voltages limited to a section of legs) I wouldn't bother grounding the stage legs.
Double pole GFCI/RCD appears to be a simpler safety solution.
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Let's not get too serious, or too silly, about this; I did begin with their not being purpose designed for the application.
Toodleoo!
Ron Hebbard
Yes, let's not get too paranoid. The OP did note this is not an approved connector for this application, nor would it pass any inspection. However, I did know one band in the 70's who used car jumper cables to tie their power distro into the bar's service panel. I'm only noting it here to show that just because something DOES work, DOESN'T mean we should do it.
However, as I've noted before, I'm currently in communication with at least one person on the NEC grounding committee that's working on the 2017 code cycle. So if there's grounding/bonding ideas we think should be run by the committee for consideration, I can do that. However, I'm fairly certain that car jumper cables wouldn't make the cut. But I do plan to show them the data for my "bed-o-nails" grounding system for temporary stage and generator grounding.
But let's be careful about posting too much info on non-code ideas on this forum. There's way too much of that crap on the web as it is, and we're trying to be a source of correct info.
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Not advocating the use of automotive jumper cables for this purpose, but just want to correct a couple of points that I believe are common misconceptions:
They may only be rated for 12 - 24 VDC but perhaps they'd be up to this sort of challenge.
Voltage ratings of wire and cable are not for the conductor, but for the insulation around it. Current ratings are for the conductors, not the insulation. Since grounding conductors are often provided uninsulated, I would think that the voltage rating of automotive jumper cables should be irrelevant in a grounding application. You just don't see voltage ratings on bare wire.
CCA is generally only good for high frequency or low power stuff. DC and AC power just aren't the same.
And copper-clad aluminum has been used for 120/240/etc.V//60/50Hz wiring in the past, and may still be permissible under NEC in certain applications with listed connectors. Why would someone use CCA? 1) because aluminum is less expensive than copper, and 2) because corroded copper has better electrical properties than corroded aluminum. Uncorroded aluminum is a decent enough conductor; the bad press that aluminum wiring has received in the past is due to its properties when it corrodes and also its softness that contributes to loose connections.
As far as I know**, the NEC hasn't approved any spring-clamp devices for temporary grounding. And if they did, I'd suspect that a welding ground clamp might be a better choice than an automotive jumper cable. I believe any inspector would approve stage grounding using the same fixed "pipe grounding" clamps required for permanent installs. Installing and removing those clamps really doesn't take a lot of time; just a little more than installing and removing a lighting fixture clamp from an overhead truss. And getting a spool of #4 AWG copper wire isn't THAT difficult or expensive in the grand scheme of things.
If you are renting a stage, do you really think the stage provider is going to appreciate you scratching through the paint to get a good ground? Better talk the issue over with them first.
**I haven't studied a recent copy of the NEC.
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**I haven't studied a recent copy of the NEC.
That's a separate issue since many of us don't feel like dropping money on a book we infrequently use. But I have a contact at the main NFPA office (the agency in charge of NEC content and publication) who has hinted there were online resources available which included parts of (or maybe even all of) the latest NFPA 70E document. If that's the case I'll ask if I can post those links here in the interest of educating sound professionals who aren't exactly electricians, but who perform many electrical tasks including stage and generator distro and grounding, etc...
I'll shoot him an email this afternoon and see if he responds. Could be next week before he gets back to me since we're soon into the July 4th Independence Day holiday. For our non-USA readers, that's a really big federal holiday with lots of fireworks and family BBQs. Yum! ;D
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That's a separate issue since many of us don't feel like dropping money on a book we infrequently use. But I have a contact at the main NFPA office (the agency in charge of NEC content and publication) who has hinted there were online resources available which included parts of (or maybe even all of) the latest NFPA 70E document. If that's the case I'll ask if I can post those links here in the interest of educating sound professionals who aren't exactly electricians, but who perform many electrical tasks including stage and generator distro and grounding, etc...
I'll shoot him an email this afternoon and see if he responds. Could be next week before he gets back to me since we're soon into the July 4th Independence Day holiday. For our non-USA readers, that's a really big federal holiday with lots of fireworks and family BBQs. Yum! ;D
There is a link on the NFPA website for "Free Codes." You can't print or download, and I've not found a way to browse within chapters - you have to flip pages sequentially (though that could be due to the javascript blocker I use with Firefox). You have to register with an email address (NFPA will send you a nice letter suggesting you make an eventual purchase) to use the free service.
http://www.nfpa.org/codes-and-standards/free-access
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But let's be careful about posting too much info on non-code ideas on this forum. There's way too much of that crap on the web as it is, and we're trying to be a source of correct info.
Exactly
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As far as I know**, the NEC hasn't approved any spring-clamp devices for temporary grounding.
I should've googled this before. A search for "temporary grounding clamp" reveals a bunch of options (try an image search for the same). They seem to be mostly marketed toward utilities for use when they're working on the lines. However, the few that I found prices for (I didn't research extensively) show that they are hideously expensive, between $100-200 each and up to $600 for a prefab jumper with a clamp on each end. If you're going to bond several stage sections together with them, that gets awfully expensive in a hurry.
A spring clamp might be fine for a jumper cable (where it is used very temporarily and in full view of the user) or a welding clamp (where if it comes off it's obvious because things don't work), but for a safety ground I doubt it would be approved since it could easily be dislodged accidentally. For a safety ground, I would expect a screw clamp of some sort would be required to prevent inadvertent disconnection.
An ideal clamp for our application (bonding metal stages to ground) would have a single-sided clamping mechanism (to allow it to clamp onto the edge of a large plate) and be capable of clamping flat or curved surfaces from 1/4" to 3" in thickness. It would accept either bare wire into a lug, or a cam-lock connector. Clamping would be by means of handscrews, requiring no extra tools.
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Maybe we need a vise grip like thing with a lug on it to connect a cable? It could clamp pretty securely to flat and round objects.
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Maybe we need a vise grip like thing with a lug on it to connect a cable? It could clamp pretty securely to flat and round objects.
I did exactly that about 40 years ago. I kept a pair of Vice-Grips with a wire lug screwed to the side in my band roadcase with a roll of #8 green stranded wire. After clamping it to a known ground (big metal water pipe in the basement) I would put a wrap of e-tape around the latching handle. I was pretty confident that it wasn't going to come loose. Hey, I've accidentally left a pair of Vice-Grips clamped under my trailer for a year and heaven knows how many miles. Found them a year later still clamped onto the frame. ;D
I don't think Vice-Grips would pass inspection nowadays and I've never seen it mentioned in code for use a temporary ground, but I'll bring it up as a possible solution with my contact on the NEC 2017 committee when I present my bed-o-nails temporary ground solution. In the meantime, we can't recommend Vice-Grips as a safe or code compliant solution except in a post zombie apocalypse scenario. :o
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http://www.scottgrossstore.com/servlet/the-5447/Tweco-Welding-Ground-Clamp/Detail
(http://www.scottgrossstore.com/catalog/Tweco92101150.jpg)
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http://www.scottgrossstore.com/servlet/the-5447/Tweco-Welding-Ground-Clamp/Detail
(http://www.scottgrossstore.com/catalog/Tweco92101150.jpg)
Frank - Good find. If this is UL approved for grounding a welder, there's a chance it could also be approved for temporary AC grounding. I'll run this by the grounding and bonding forum on Mike Holt's website. Perhaps they know or can quote code about this sort of application.
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http://www.scottgrossstore.com/servlet/the-5447/Tweco-Welding-Ground-Clamp/Detail
(http://www.scottgrossstore.com/catalog/Tweco92101150.jpg)
Lighting folks use a similar clamp to attach lighting fixtures to round pipe. The "Altman" C-clamps are a standard item that lampies should be familiar with, and which they often have an extra one or two of with their gear. I offer no judgement as to the suitability of those clamps for electrical purposes. Mark C.
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Lighting folks use a similar clamp to attach lighting fixtures to round pipe. The "Altman" C-clamps are a standard item that lampies should be familiar with, and which they often have an extra one or two of with their gear. I offer no judgement as to the suitability of those clamps for electrical purposes. Mark C.
Good info. I'll toss that into my inquiry to Mike Holt's forum.
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The "code speak" term is "listed for the purpose"-for that you'd have to check manufacturers data sheets, i am guessing-if you can find them.
The other term used is "solidly connected". I think common sense would lead to the conclusion that vice grips with a permanent welded lug, or a mechanical connection like a C clamp with a screw would be a solid connection, vs a spring type clamp like jumper cables-how many times have you had one slip off in the 2 minutes it takes to get a car started?
Practically, I am happy with something that gives a solid connection. On the liability side, the UL listing would help the lawyers, since I often wonder about their common sense. One works and keeps everybody else safe-the listing protects your finances IMO.
BTW-code still recognizes copper clad Al. Also, FWI, ground rods are usually copper clad iron (steel). They all conduct electricity a lot better than earth.
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I wrote to the stage manufacturer requesting assembly instructions and whether their engineers have an approved methodology to accomplish connecting their staging to EGC and to earth ground. To my dismay (but not to my surprise) I received the answer:
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Hello Mr. Kayser,
Attached are stage assembly instructions. We do not have an approved methodology for accomplishing grounding for the stages.
Please let me know if you have any questions.
Thank you.
Sincerely,
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Believing this would be the reply, I was looking at grounding lugs - I found two that look like possible candidates - UL Listed. Of course, the uses of these are different from bonding an outdoor stage. These are lay in lugs which would allow a single large-gauge wire to be a continuous bonding conductor - the first easily applied/removed from the stage sections and cable laid in.
Mike, think you could run these up the flagpole over at Mike Holt's forum?
http://unitedstructuralproducts.com/product/us-tray/components/bonding-and-grounding/ground-wire-clamp/
Datasheet indicates "cable tray"... (I'd post a picture, but my past attempts have ended in failure...)
http://www.elecdirect.com/catalog/df208983-6f76-455f-b7b7-91bc983c6c39.aspx
Talks about use on roof solar panels - also have seen identical parts cable trays and direct burial.
Both come made from different materials...
Some products mention UL Pub 467, so I thought I'd take a peek.
http://www.techstreet.com/products/1854110
UL Pub 467 Grounding and Bonding Equipment - 50 pages - $631.00
Ouch! I know someone has to pay for the work. I'm wondering how many electricians have a copy or access to a copy.
I really like the musicians I work with - just trying to be safe.
frank
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I'm not sure what this means or if it's relevant to the topic, but it sure is funny. Let's see... don't pee from an ungrounded stage?
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I'm not sure what this means or if it's relevant to the topic, but it sure is funny. Let's see... don't pee from an ungrounded stage?
If you're far enough away from the electrified surface you are urinating on, due to the surface tension of water, the stream will become broken droplets and you won't be shocked. That doesn't mean I'm going to test the theory.
Back in my younger days (most of you would probably say I'm still in my younger days) I worked as a laborer on a Christmas tree farm. One of the farmhands on the shearing crew needed to relieve himself and picked the electric fence to do so... my brother (the landowner and boss) and I both watched amusedly waiting for it -- why warn a young punk when you're about to see the best entertainment in years? -- but that lucky city-slicker didn't even experience the slightest discomfort.
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but that lucky city-slicker didn't even experience the slightest discomfort.
One time I accidentally rode my bicycle through an electric fence when I was a kid. Nothing intermittent about that and it hurt like heck.
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When I was little, at camp a group of us would hold hands, one guy would hold a metal rod and the guy at the opposite end would grab the electric fence. I did that only once.... It was dumb.
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Amazingly quick learner!
I was at a major venue this weekend. With little to do while waiting for the event to start I was killing time by inspecting their wiring. Most of it appeared to me messenger supported with the bare supporting strand used as the neutral, so no EGC run with the feeders (A disconnect was labeled clearly defining each conductor). However, the disconnect was mounted to the steel structure-which in this particular case also clearly served as a grounding electrode do to foundation bolts-it was attached through beam clamps as in this picture. If this passed an inspection,one would assume that these beam clamps would be acceptable for grounding. Much cheaper than weld clamps and the ones I like have two 1/4-20 tapped holes-perfect for attaching lugs to connect #12-# however big you need to go (within reason-I have used 500 mcm grounds before-but that is not common and would be a fairly large sound system). In any case, they would clamp securely to any angle or structural members on a stage-I get them for about a buck a piece.