Stage grounding/ Generator Grounding

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mason.dale

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Saskatoon SK Canada
Hi,

I work for a live production company. We build stages and roofs, we use big Lighting and Audio systems. my question is when should you use a grounding rode. i watched the you-tube videos, but since we work in very flat fields usually in the middle of nowhere where there isn't alot of other buildings. if there is a lighting strike and it strikes one of the towers that holds up our roof should there be a grounding rode in place in case of that? also in that situation should we also ground the generator to the same grounding rode or leave the generator without a grounding rode? if we are working in the city where there is a lot of other buildings should we leave the stage ungrounded in case of a lighting strike elsewhere?

Thank you in advanced
Timothy Mason
 
I believe each of the items mentioned are considered a separate structure under code and each is required to have its own grounding electrode system. Under current and recent Code editions, that means at least two ground rods for each, unless you perform earth resistance testing and confirm 25 ohms or less, or have other electrodes available which negate the use of ground rods (doesn't sound like it).

I didn't check Chapter 5 for exceptions to the preceding, as I'm doubting there are any.
 
Stage grounding

Stage grounding

Alright so that makes sense. Each tower and the stage should have a grounding rode. What is the minimum safe distanded for the grounding rods from one another? Is there a risk of the election charge traveling down one tower then up the grounding rod of the other?
 
Smart $ said:
I believe each of the items mentioned are considered a separate structure under code and each is required to have its own grounding electrode system.
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One stage structure, many feeders.

Typically there would be a feeder for lighting, another feeder for audio, another feeder for video and yet maybe another feeder for winch motors.

Trying to apply the NEC entirely to a portable stage gets messy fast.
 
I have hooked up a fair amount of outdoor shows.

I tie the generator into a grounding electrode but never bother with the stages. The stage will end up grounded via all the EGCs running to the equipment fasted to the stage.

The issue with trying to ground a portable stage is that many of the interconnections between stage sections are fairly loose so to do an effective job you would be placing wire jumpers all other the place.
 
Note that the OP gives his location as Canada, so perhaps the almost, but not quite, similar provisions of the CEC should be considered. (And no, I do not have a copy.)

Regardless of the chances of lightning strikes, some grounding is required by the electrical code, but the grounding of tall metal towers in a field of short people is a matter of lightning safety which is also not covered in the electrical code and probably requires a very much more robust downlead wiring technique even if only connecting to drive ground rods.
 
GoldDigger said:
Note that the OP gives his location as Canada, so perhaps the almost, but not quite, similar provisions of the CEC should be considered. (And no, I do not have a copy.)

Regardless of the chances of lightning strikes, some grounding is required by the electrical code, but the grounding of tall metal towers in a field of short people is a matter of lightning safety which is also not covered in the electrical code and probably requires a very much more robust downlead wiring technique even if only connecting to drive ground rods.
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I am not very knolegable about lightening protection systems. Maybe someone can explain it to me.

Given a structure made almost exclusivly out of metal, that has at least dozens of points of contact to the earth itself what in the world would a down lead run to an electrode do to increase safety?


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stage05e.jpg
 
Whether well "grounded" or not, you really will be hoping nobody is present during a direct lighting strike.

Having everything bonded together and grounded may still minimize some problems if there is a nearby strike.
 
mason.dale said:
Very good point nut the way we build our stages, we put wood pads under each foot or support so the stage won't sink if it rain out.
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Yeah, lightning just traveled a few miles through air, its not going to have any issue getting around that wood if the structure takes a hit.
 
mason.dale said:
Very true so would it make more sense to do a grounding rods for all three generators and then one for the stage?
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Each generator needs its own grounding electrode system. That means two ground rods, driven at least 6' apart. In reality, many of the installs I've been part of were lucky to have a single ground rod at all. I've had several discussions, sometimes "enthusiastic" discussions, with genny rental companies regarding the necessity of a ground rod. They don't like having to drive one in a parking lot or other paved area. I have always won that argument, either by hammer-drilling a hole down to dirt, or running cam-lok feeder to an easier-to-drive-a-ground-rod location. You can always cut the top of the ground rod off with an angle grinder, or pull it out with a forklift when the gig is done.

Got a nearby body of water? I've heard tell of portable gennys being grounded by attaching an old shopping cart to the ground lead, and tossing it into the water. Sounds like a low-impedance path to earth to me!

As for earthing the tower structures themselves, it couldn't hurt. One staging company I worked with built some interesting adapters just for the purpose; an aluminum half-burger (no anodizing) with a cam-lok connector attached to it. They then ran cam-lock feeder to a single ground rod for the whole stage structure. Quite clever, really.

https://www.thelightsource.com/products/mega-coupler-10

http://www.nationalsupplyonline.com/Cam_Lok_1016_Panel.html



SceneryDriver
 
I do not believe the ground rods provide any extra protection from lightning strikes.

I suspect the stages qualify as structures and thus need a grounding electrode system.

I have seen a few of these over the years and it appears to me that at least the ones I have seen consist of a bunch of disconnected parts that set up next to each other but don't appear to have any real connections to each other. It would be like trying to ground a temporary scaffold.
 
petersonra said:
I have seen a few of these over the years and it appears to me that at least the ones I have seen consist of a bunch of disconnected parts that set up next to each other but don't appear to have any real connections to each other. It would be like trying to ground a temporary scaffold.
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I am sure there are many types but that certainly describes the ones I have worked around.
 
SceneryDriver said:
E
As for earthing the tower structures themselves, it couldn't hurt. One staging company I worked with built some interesting adapters just for the purpose; an aluminum half-burger (no anodizing) with a cam-lok connector attached to it. They then ran cam-lock feeder to a single ground rod for the whole stage structure. Quite clever, really.
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What is a ground rod going to do to add to safety?
 
iwire said:
What is a ground rod going to do to add to safety?
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Since it was the truss and leg system that was grounded (as well as the metallic legs of the staging), I believe it was an attempt to ensure that the metal structure couldn't become energized by a damaged cable supplying power to the lighting equipment hanging from the truss. I liked the idea; it may have been overkill, but overdoing it didn't hurt.


SceneryDriver
 
SceneryDriver said:
Since it was the truss and leg system that was grounded (as well as the metallic legs of the staging), I believe it was an attempt to ensure that the metal structure couldn't become energized by a damaged cable supplying power to the lighting equipment hanging from the truss. I liked the idea; it may have been overkill, but overdoing it didn't hurt.


SceneryDriver
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But in that particular case, bonding back to the grounded conductor of the supply, whether that was POCO temp service or a generator, is more important than connecting to a ground rod.

And, of course, connecting everything to a common ground electrode system does the incidental job of bonding truss to neutral (or other grounded conductor).
 
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While all the supposition thus far is noteworthy, let's get to matters of NEC Code (I'll leave CEC to someone else).

First, I believe the scenarios under discussion fall under Article 525, Part IV in particular. In short, the EGC of equipment circuits is permitted to serve as the bonding means. However, nothing in 525 differs with system or structure grounding electrode systems required under Article 250. For the generators, 250.34 applies. In short, if everything is cord-and-plug connected to the generators, no GES is required; if hardwired, a GES is required. FWIW, there is nothing that says several generators cannot share the same GES.

I'll leave the debate on structure GES's being required or not to y'all.

As for lightning issues, I've always believed 'earth' bonding metal structures actually increases the likelihood of being struck by lightning compared to other higher resistance or shorter conductive objects in the immediately surrounding area. I have not researched the issue, and I believe there are two prevalent theories: a shorter, lower resistance path between earth and above 1) increases the potential to be struck, and 2) brings the structure to the same ground potential as surrounding objects, thereby reducing the the potential to be struck. Given the total distance a lightning bolt travels, I can see where theory #2 may have some merit, but given a substantially taller conductive structure over surrounding objects, I believe I'll stick with theory #1. However, I have to wonder whether 'earth' bonding actually makes a difference unless it is designed to handle the surge without damage to the structure and mitigate threat to occupant life...???
 
Earth bonding serves to control (well anyway strongly suggest) the path the current follows on the way to ground. In the hope that it will not make side trips which happen to intersect with people.
High frequencies and enormous currents with correspondingly high magnetic fields can cause the stroke current to take bizarre paths if there is not a deliberate high current low inductance path provided
 
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