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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: charles strickland on March 04, 2021, 12:53:21 pm

Title: stage grounding question
Post by: charles strickland on March 04, 2021, 12:53:21 pm
 Doing a show  with temporary power from the city to a 200 amp service, The stage  is a deck type ( metal frame and stairs  plywood top   Do I need to run my ground from the stage back to the service ground or do I run it to a rod in the ground next to the stage ? The city is  grounded at the bottom of the service poll  Thanks for the advice.
Title: Re: stage grounding question
Post by: Keith Broughton on March 04, 2021, 03:25:52 pm
The outdoor festival venue I work at requires the ground from the service to be connected to the stage frame. Ontario, Canada
Title: Re: stage grounding question
Post by: charles strickland on March 04, 2021, 07:22:45 pm
[ Thanks Keith.
Title: Re: stage grounding question
Post by: Brian Jojade on March 04, 2021, 11:25:22 pm
The reality is your local inspector gets to interpret the rules how they see fit.  Ive seen both as accepted or required solutions/
Title: Re: stage grounding question
Post by: Stephen Swaffer on March 05, 2021, 12:27:40 pm
This goes back to the basic question of "grounding" vs "bonding".  If you do not "bond" your stage to the service "ground" and just drive a ground rod, and say an extension cord gets scraped and shorts to the stage you will never trip a breaker leaving the stage energized and a resulting in a shock hazard.

In my area-and from my understanding of code the proper method would be 4 wires from the service pole to the stage, ground and neutral's kept separate after the "service disconnect" located at the pole and then "re-establishing" a ground at the stage with another grounding electrode.  In this case, the "bonding"-separate ground from the pole and the "grounding" serve two distinct but important purposes.  In my mind, the ground rod requirement would depend somewhat on specific conditions-dry/wet, distance from the service, etc.
Title: Re: stage grounding question
Post by: charles strickland on March 05, 2021, 01:03:29 pm
  I am going 70 ft service to stage via 4/4 soow to distro in rack feeding all stage power from the distro.
Title: Re: stage grounding question
Post by: Keith Broughton on March 05, 2021, 01:39:57 pm
  I am going 70 ft service to stage via 4/4 soow to distro in rack feeding all stage power from the distro.
In our application we had a T on the ground at the power distro near the stage and ran a cable to the stage frame from that T.

Before grounding the stage, we had a case where the stage gear truck that was backed up to the stage had pinched the feeder cable and the stage was "live"
It was pure luck that no one got hurt!
Title: Re: stage grounding question
Post by: charles strickland on March 06, 2021, 05:50:57 pm
I will go from the stage back to the service with the ground and if the inspector has me add a ground rod at the stage   I will. I just wonted  to use the best safety practice and not fry the band when the bass player drops a hot cable on the stage.
Title: Re: stage grounding question
Post by: charles strickland on March 07, 2021, 01:41:39 pm
Can I use stranded wire for my ground to the stage or do I need to use solid wire. Thanks.
Title: Re: stage grounding question
Post by: Tim McCulloch on March 07, 2021, 09:07:30 pm
Can I use stranded wire for my ground to the stage or do I need to use solid wire. Thanks.

Charles, how are you getting power to the stage?  Extension cords from outlets "somewhere," or are you using feeder cable from "somewhere else" to a distro panel at the stage?  Or did I miss this detail...

The reason I ask - Keith Broughton's CamLok "T" is a simple and elegant solution IF you've got feeder and distro.  The alternative, running a lot of #6 to the panel that powers the outlets the extension cords are plugged into, isn't really attractive as you'll have to protect that grounding wire over the run.  The wire can be stranded or solid, IIRC.

Your earlier comment about the bass player dropping a hot cable on the stage makes me wonder if there's a back story or two...
Title: Re: stage grounding question
Post by: charles strickland on March 07, 2021, 10:17:22 pm
  Hi  Tim ,   I'm running 4/4 soow cable from the service   L14 50  to my motion labs distro in the amp rack. C S in. not sure how to config Keith's. T adapter but sounded like a good plan. I would be grateful for any help on how to make one. It would use the ground in my 4/4 to ground the stage back to the service just don't understand how to make the connection .  then there's the story.  I  went to a show just to hang out at the river ,power was genny with no grounding ( I looked.) barefoot stage hand steps on hot wire a gets the hell shocked out of him. Burned his foot      Lived to tell the story. was the bass player's rig.
Title: Re: stage grounding question
Post by: charles strickland on March 08, 2021, 12:25:16 am
 Tim , could I run the ground from my distro pass through to the stage ?
Title: Re: stage grounding question
Post by: Keith Broughton on March 08, 2021, 06:44:51 am
Tim , could I run the ground from my distro pass through to the stage ?
By using the term "pass through" I gather you have a distro with Camlocs.
The pass through will work.

One thing to note, this is a safety ground to help protect people.
I would not consider this lightening protection.
 
Title: Re: stage grounding question
Post by: Helge A Bentsen on March 08, 2021, 06:55:10 am
Is it legal to use a spare outlet for this in your region?
I've grounded power distros using a spare outlet, connected a ground wire only to a plug, labelled it ground and inserted it to a spare socket. The wire ran to a earth rod connecting the stage + power ground together.

This passed local inspection in my region. Not saying it's best practice or legal in your region.
Title: Re: stage grounding question
Post by: Tim McCulloch on March 08, 2021, 09:35:14 am
Tim , could I run the ground from my distro pass through to the stage ?
"It depends" if you're going for Code compliance or because the bass player shouldn't be given electricity... 

It's not Code compliant, but it will provide a measure of protection.
Title: Re: stage grounding question
Post by: charles strickland on March 08, 2021, 11:13:03 am
My first priority is the safety to those on stage. if the best way is to run a separate ground from the stage back to the service than that's what I will do . If there is another way to get the job done correctly, save some wire and or clean up the run back to the service I would prefer to do it that way. my connection at the distro is single wire twist connector. Using the pass through on the distro out ( not the receptacles on the back ) ground only to the the stage for safety ground was my thought for getting this done, Thanks.
Title: Re: stage grounding question
Post by: Stephen Swaffer on March 08, 2021, 12:36:46 pm
I don't see why using the pass through wouldn't work-I would make sure the connection is secure.   In the end, you are looking for a metallic path back to the service from the stage.

The only time I would be concerned is if there is more than one power source.  When using the pass through, the ground will be disconnected only when the power is disconnected which is the hazard from the powers supply.  Lightning, of course, is a different matter-but if lightning is a concern, standing on an outdoor stage is a bad idea period.
Title: Re: stage grounding question
Post by: charles strickland on March 08, 2021, 12:56:58 pm
The pass through is a locking C S plug, I will go  (ground only) out of it . 6 ga wire to the stage. should be clean and safe .  Thanks for your input.
Title: Re: stage grounding question
Post by: Tim McCulloch on March 08, 2021, 02:32:37 pm
I don't see why using the pass through wouldn't work-I would make sure the connection is secure.   In the end, you are looking for a metallic path back to the service from the stage.

The only time I would be concerned is if there is more than one power source.  When using the pass through, the ground will be disconnected only when the power is disconnected which is the hazard from the powers supply.  Lightning, of course, is a different matter-but if lightning is a concern, standing on an outdoor stage is a bad idea period.

My read of Code was that the temporary structure grounding should not be disconnectable.  The reason I like the Cam-Lok T is because ground continuity will be assured until the lines serving the distro are de-energized.  The reason I don't like using the pass through is because the stage grounding can be disconnected while equipment on the stage remains powered.

In the situation where Charles is the only person who can, or will, be doing the connect and disconnect, either will serve the purpose of grounding the temporary stage structure.  I went looking in 2017 NEC 520 and 525 and it appears that previous edition references to temporary entertainment structures have been moved (I'm guessing to Art. 250).

I probably should read all of 250 again.  It's been a few years.
Title: Re: stage grounding question
Post by: charles strickland on March 08, 2021, 03:11:04 pm
  Good point Tim. I see  where the ground could be inadvertently disconnected but not accidently pulled loose due to the twist lock. The guys that work with me know no one touches the power but me  (ever ) End of show stage power goes off first , Then amps and console. Lastly main service. Will the T work with single cable with C S connectors ? where can I find  out info on them. Thank you.
Title: Re: stage grounding question
Post by: Stephen Swaffer on March 08, 2021, 04:20:29 pm
My read of Code was that the temporary structure grounding should not be disconnectable.  The reason I like the Cam-Lok T is because ground continuity will be assured until the lines serving the distro are de-energized.  The reason I don't like using the pass through is because the stage grounding can be disconnected while equipment on the stage remains powered.

In the situation where Charles is the only person who can, or will, be doing the connect and disconnect, either will serve the purpose of grounding the temporary stage structure.  I went looking in 2017 NEC 520 and 525 and it appears that previous edition references to temporary entertainment structures have been moved (I'm guessing to Art. 250).

I probably should read all of 250 again.  It's been a few years.

I would agree-usually grounding splices are "non-reversible" for permanent connections.  When I said secured, I was thinking something like zip ties, etc. something that would require a tool or some effort to disconnect.  Might not meet the letter of the code-but certainly the spirit as long as a responsible person disconnects power before disconnecting grounding.
Title: Re: stage grounding question
Post by: charles strickland on March 08, 2021, 05:03:14 pm
Sounds easy enough to make it two steps to be able to remove it. code enforcement around here is more code and less enforcement. My main goal was to insure the safety of the stage. 
Title: Re: stage grounding question
Post by: Rob Spence on March 08, 2021, 07:37:21 pm
I also use a CS connected feeder to my distro. I modified the distro ( yes, I know it isnít UL but my clients donít care) to add a brass stud where the original internal ground was terminated. I have a #6 with crimp rings on both ends. I put one on the ground stud on the distro and connect the other end to the stage.
Title: Re: stage grounding question
Post by: charles strickland on March 09, 2021, 02:07:19 pm
 Thanks to everyone for the the  help . This is such a great place, full of knowable people kind enough to take the time to share it with us. Charles