Circuit All Equipment in this Room to the Same Electrical Phase?

[hdp]

I am working on the electrical design for a fairly technical office building with Video - Teleconferencing Rooms. The boiler plate information on the client rough-in and circuitry requirements indicates that all this audio-video equipment should be connected to the same electrical phase "to minimize interference". I know of wiring errors (multiple neutral-ground bonds, for example) that have caused great consternation to users of these types of equipment. I have also had requests (I think legitimate) to provide dedicated neutral conductors. However, I have not had a request to connect all interconnected equipment to the same phase. Has anyone had a similar design request? Is there a gap in my experience that prevents me from immediately thinking, "that's a great idea"?

Thanks for your valuable time.

 

[hdp]

P.S. Project is in the U.S. Service voltage is 208Y120V 3 Phase, 4 Wire.

Thanks...

 

[dpc]

I've never heard of this requirement. But it isn't going to hurt anything to make them happy. I'd do what they ask unless it is creating a major headache. But I can't see any real logic to it. Reminds me of the requirements for "isolated quiet grounding systems" - except those were an NEC violation.



David Castor

http://www.cvoes.com

 

[hdp]

Thanks for the reply, David. I've also had the occasional request for "clean grounds", "isolated ground rods" and the like. This particular wrinkle is new to me, and I'm not really very new! As you said, it's not a big deal to meet their requirement. I was just curious as to whether others in the industry had seen such a design parameter.

 

[PHovnanian]

This could be a leftover requirement from the "old days" of ungrounded public address amplifiers and other such audio equipment. Some of these had problems with AC hum, were equipped with 'ground switches' and could be lethal if one piece of equipment had a hot chassis. Having more than one phase powering things could just confuse things.

 

[waross]

That brings back memories of a mis-spent youth.
I did a lot of stage lighting and special effects when I was in high school, both for school productions and for the local adult drama group. Our high school principal was active in the adult drama group and would from time to time visit me back stage as I was setting up for some production or other. He would often stand near the vertical 2" pipe that was used to mount spot lights at the edge of the stage and lean with one hand on the pipe. Once or twice a year I would innocently hand him the mike connected to the "hot" amplifier. The mike was always at about 55 Volts to ground and it would get a satisfying reaction.
I liked the principal. The teacher that I didn't like was talked into zapping himself with an old model T ignition coil. Those things would throw an arc of almost an inch.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[DanEE]

Had a tour of a 1800 seat auditorium on our local college campus used primarily for performing arts. It just recently went thorough a major renovation..

All sound system equipment is feed from one dedicated distribution panel with isolated grounds i.e. the grounding scheme required in Health care Facilities i.e. NEC Article 517. (USA)

 

[hdp]

Thanks for all replies. If I am able to determine the basis of this request, I will post the information. The client is a pseudo-governmental agency. Details of their requirements are few and far between.

 

[alehman]

This is still a requirement of some closed-circuit television equipment manufacturers.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[WoodrowJWeen]

I've also heard of this requirement from audio/visual consultants. Used to be so that if you switched from a source on one phase to one on another phase, the sync would be off by 120 degrees and you'd get that slight picture roll as the the TV monitor adjusted. Keeping them on one phase eliminated the roll. Can't see as how that is necessary these days, especially with digital sources. Probably just one of those "we've always done it that way" things without knowing why. Sort of like the magic ground rod triangle.

 

[EEJaime]

Hello,
At one time in healthcare work we were required to insure that all devices at a critical care patient bed location be connected to the same phase of power. This was in a licensing document that the state published-California Title 8 or something like that. I have not seen it anywhere else officially, and I don't know if that document is still around. Never actually explained the reasoning, but we assumed it had to do with patient monitoring instrumentation issues.
Good luck in your research, and it would be good to find out the reasoning behind this.
Regards,
EEJaime