A/V Branch Circuit EGC's

[infinity]

I've been given the task of installing an IG system for A/V receptacles in an existing Theater. Currently the A/V receptacles are grounded like a normal duplex device. All of the A/V receptacles are on the same phase of the 3 phase 208/120 volt panel as per the advice of the A/V consultant. The receptacles are existing and the new spec calls for all IG devices and the IG EGC's are to be two trade sizes larger than the phase conductors. Also the IG system is to terminate at the XO of a 75 KVA transformer which feeding an A/V distribution panel. Can someone please explain this design? Why does the EGC need to be two sizes larger than the phase conductors? What's so different about A/V equipment that this should even matter?

 

[LarryFine]

Rob, it's about 90% BS, but simple enough to do as they wish and get paid profitably.

 

[infinity]

Well I agree, but they do seem to have a legitimate noise problem that is likely the result of ground loops (their theory). I have no problem fixing as per their request I was just wondering why an over-sized EGC is needed and what's so special about this equipment.

 

[gar]

100125-2334 EST

inifinity:

Maybe they need even larger EGCs. They are trying to lower the impedance of the common (ground) path between different pieces of equipment.

In the old days when audio transformers were more common it was easy to provide ground isolation. Today it seems these systems should use differential line drivers and receivers, or digitize and transfer signals over fiber optic cable.

What is their noise problem? 60 Hz, 120 Hz, hiss (white noise), or some other kind of noise source?

.

 

[zbang]

Rob, it's about 90% BS, but simple enough to do as they wish and get paid profitably.

99 and 44/100ths percent? But, as you say, if they've got the $$$....

but they do seem to have a legitimate noise problem that is likely the result of ground loops (their theory).

And IMHO this won't make any better. (And, I still can't understand why some audio people are so afraid of signal transformers. They're a useful tool for solving problems and the good ones don't hurt the sound at all. 'course they also cost $50+ each, but that's still cheaper than lots of other solutions.)

 

[cadpoint]

I found this search engine the other day.

www.nssn.org

I used "audio visual" in the advance, I forgot how I found it but UL based their wiring method was NFPA 70, some where in this search engine...

If there throwing some odd spec at you you can search it here. The advance search is extensive, UL is listed twice. But there mostly papers for sale.

Another like page has some extensive listing of national, federal, and it seems every U.S. department HERE

Or try this search engine, http://www.pdf-search-engine.com which seems more commerical.

Enjoy

 

[cadpoint]

Granted your talking AV equipment but computers usually are controlling that now, here goes, round two:

On 2.21.07, MHE put out a newsletter on, "Guidelines for Grounding Information Technology Equipment (ITE)" 2/15/97

I’m not going to call for a release:
Copyright ? Mike Holt Enterprises, Inc. All rights reserved.
This article is protected by United States copyright and other intellectual property laws and may not be
displayed or published on the internet without the prior written permission of Mike Holt Enterprises, Inc.

If you can find this newsletter great, if not you cannot find it using his site,
Try a pdf search engine and look for this: ite_grnd.pdf

This is an 11 page pdf of how a computer society sees their bonding and grounding requirements all based on
1996 nfpa-70, other good references are listed on the last page it also covers other articles of equipment in addition to 250.

I hope everyone looks it up. It well worth it, OK JMO