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Author Topic: Unusual Grounding Issue  (Read 3111 times)

Jonathan Kok

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Unusual Grounding Issue
« on: December 03, 2010, 10:20:42 pm »

So...ran into a new one for me.

Just finished an install, and something quite unusual popped up.  But before I begin, I should preface this by saying the system is NOT ground-isolated (client couldn't afford it).

The (analog) install is clean as a whistle.  No hum, no buzz, just beautiful, clean sound from stage to speaker.  HOWEVER...

Static electricity is the death of it.  It's a church, however the seating is on upholstered chairs.  If someone sitting within a few rows of FOH shuffles around...SNAP! CRACKLE! POP! goes the PA.  I kid you not.  It's not exactly subtle, either.

None of the chairs are in contact with FOH.  All chairs have rubber feet.  In fact, the chairs within FOH, oddly enough, don't cause this problem (despite being the exact same type of chair).  It occurs only with the chairs that rest on the carpeted floor (FOH is on a 1' wooden riser).

The board is an A&H ZED-428.  With all of the inputs muted, and the master faders down, the system still pops.  In every speaker.  Main Left, Right, Centre, and Monitors.  Even in the headphones. Disconnect the outputs from the console, and the popping stops.  Connect an input directly into an output (thus bypassing the board), and it's clean.

I need to crack open the inputs into the console; they got tugged a little, and one of the grounds may have popped, and is now touching the shell.  Even then...I hesitate to blame the popping on something like that.
The carpet comes into direct contact with conduit, though that occurs ~50' from FOH.  And that particular conduit is electrical (though all the conduits in the building, including AVL, undoubtedly intersect).

Anyone ever had to ground a carpet before?
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Dick Rees

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Re: Unusual Grounding Issue
« Reply #1 on: December 03, 2010, 10:57:01 pm »

At a church install I tweaked they had a similar static discharge problem.  I wired the chassis of every piece of gear at FOH and drained it off to the ground connection of the power outlet.  Problem went away......except when the Pastor wore synthetic materials under his robes.  Then a spritz of Static-Guard on his trouser legs got rid of the pops from his wireless rig.

Try grounding the chassis of the Zed and see what happens.
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Charlie Zureki

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Re: Unusual Grounding Issue
« Reply #2 on: December 04, 2010, 11:04:29 am »

  Hello,

 The carpet is  grounded.  I believe the problem is the upholstery on the chairs, and static build-up creates a voltage differential to the earth (carpeted floor).

 You wrote that the chairs have rubber feet?  If the chairs are metal remove their rubber feet, the problem should go away.

 If the chairs are wood...you'll need to some how run a conductor from the chair back to the seat and then to the chair arms (if upholstered) to the floor. (carpet)  

 Cheers,

 Hammer

 btw...is the surface that holds the console a rubber or plastic topped table? And, are you sharing the same surface with a lighting or video system?  
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Jonathan Kok

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Re: Unusual Grounding Issue
« Reply #3 on: December 06, 2010, 12:36:43 pm »

Thanks for the tips!  Not sure when I'm going to get back there, but I'll be sure to try them out.  I had thought that the chassis of the console would be grounded via the ground pin on the IEC plug...is that not the case?

Charlie, the FOH desk is a standard laminated countertop.  A/V/L are all controlled from the same desk.  Video controls are in a wooden knock-down rack (which also contains audio and lighting tie-lines); lighting is via a PC.
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Charlie Zureki

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Re: Unusual Grounding Issue
« Reply #4 on: December 06, 2010, 06:30:03 pm »

  The Console case is grounded. I believe it is the static charge from the nearby seats that cannot find it's way to ground....so discharge the seats to ground.

 Hammer

 ps. static charges can build up to thousands of volts, they'll arc to the easiest path to ground.  Static charges can ruin IC chips.
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Andy Peters

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Re: Unusual Grounding Issue
« Reply #5 on: December 08, 2010, 01:18:31 am »

Jonathan Kok wrote on Fri, 03 December 2010 20:20

So...ran into a new one for me.

Just finished an install, and something quite unusual popped up.  But before I begin, I should preface this by saying the system is NOT ground-isolated (client couldn't afford it).

The (analog) install is clean as a whistle.  No hum, no buzz, just beautiful, clean sound from stage to speaker.  HOWEVER...

Static electricity is the death of it.  It's a church, however the seating is on upholstered chairs.  If someone sitting within a few rows of FOH shuffles around...SNAP! CRACKLE! POP! goes the PA.  I kid you not.  It's not exactly subtle, either.

None of the chairs are in contact with FOH.  All chairs have rubber feet.  In fact, the chairs within FOH, oddly enough, don't cause this problem (despite being the exact same type of chair).  It occurs only with the chairs that rest on the carpeted floor (FOH is on a 1' wooden riser).

The board is an A&H ZED-428.  With all of the inputs muted, and the master faders down, the system still pops.  In every speaker.  Main Left, Right, Centre, and Monitors.  Even in the headphones. Disconnect the outputs from the console, and the popping stops.  Connect an input directly into an output (thus bypassing the board), and it's clean.

I need to crack open the inputs into the console; they got tugged a little, and one of the grounds may have popped, and is now touching the shell.  Even then...I hesitate to blame the popping on something like that.
The carpet comes into direct contact with conduit, though that occurs ~50' from FOH.  And that particular conduit is electrical (though all the conduits in the building, including AVL, undoubtedly intersect).

Anyone ever had to ground a carpet before?


It's very simple. The carpet is a nice static generator. While it "comes into direct contact with the conduit," that's irrelevant if the carpet itself is non-conductive.

So when someone shuffles along the carpet, he generates static electricity which builds up on his body. When that person touches something that's conductive, that static is discharged. Somehow it is getting discharged onto the chassis of the console or some other piece of kit in your rack.

A couple of things you can do, in order from least expensive (and thus least effective) to most:

0) Figure out how to raise the humidity in the room. Lots of air conditioning tends to drop the relative humidity to desert levels, and the lower the humidity, the greater the chance of static buildup.

1) spray the carpeted area near the FOH gear with a product called Staticide. This stuff prevents static buildup. If you're really cheap, spray the area with a solution of dishwashing soap and water. The advantage of the Staticide is that it lasts a lot longer. The soap solution will have to be re-applied every day.

2) Rip up the carpet and replace it with something that's conductive, which will prevent static build-up.

-a
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Jordan Wolf

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Re: Unusual Grounding Issue
« Reply #6 on: December 08, 2010, 01:50:56 am »

Andy Peters wrote on Wed, 08 December 2010 01:18

...Rip up the carpet and replace it with something that's conductive, which will prevent static build-up.

I vote for diamond plate.

http://www.guardhousesonline.com/design_options/images/Aluminum%20Diamond%20Plate%20Floor.jpg
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Scott Helmke (Scodiddly)

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Re: Unusual Grounding Issue
« Reply #7 on: December 15, 2010, 10:51:50 am »

Jonathan Kok wrote on Mon, 06 December 2010 11:36

Thanks for the tips!  Not sure when I'm going to get back there, but I'll be sure to try them out.  I had thought that the chassis of the console would be grounded via the ground pin on the IEC plug...is that not the case?


I've found that about 1% of all molded IEC cables are miswired.  You might want to check the cables in that install.
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