Balanced 120VAC or 60VAC to ground?

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chuckwheat

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Does anyone have experience with two-phase 120 volt wiring? It was suggested as a solution for a ground noise problem in a recording studio. After a little research, it seems as though it may be the fix we are looking for, if installed correctly. Feedback? Anyone?
Thanks for your time.
 
dereckbc

dereckbc

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Re: Balanced 120VAC or 60VAC to ground?

I have designed a few systems using 120/60 in data centers. Basically using a 480 UPS feeding a PDU with 6-phase output. Same principle recording studios use. It takes special wound transformers to develop 120/60 output. Very similar to a 240/120 transformer except there is no neutral (grounded circuit conductor) involved, which is the biggest culprit of all ground noise experienced in both digital and analog environments.

Most equipment will work fine with balanced power, however now and then some will require some modifications. In particular RFI filters and MOV's installed on the AC line side.

There are restrictions where it can be used, special circuit design considerations and requirements, all outlined in NEC 647.

It was originally designed in the 80's out in LA by the recording industry, and is now starting to be used by the telecom industry. However it may be short lived in both industries because improved signal transmission techniques like balanced and optical mediums which require no ground reference.

What is it you are looking for???
 
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hurk27

Senior Member
Location
Portage, Indiana NEC: 2008
Re: Balanced 120VAC or 60VAC to ground?

The first thing I would do is to understand what causes grounding noises or ground loop problems also known as the ever annoying 60hz hum, pops Etc...
This area is very misunderstood by many electricians and most sound men. Most properly installed equipment that is connected as per the NEC will not have these problems other than the RFI ones. and the pops that are produced when something is switched off or on. isolation and filtering are the only way to eliminate these noises. But the ground loop problem is almost always caused when the grounded conductor (neutral) is bonded at more that one location and audio equipment has line voltage supplied to it from more than one location. This causes a parallel path of neutral current (that will take all paths to source) to be placed on the shielding of common audio cables between equipment fed from different sources. This is the primary cause of a ground loop. With this understanding checking for theses multiple grounded neutrals is a must. as applying a balance power supply to an existing wiring system that has these problems will cause other problems.

Also using a single point grounding scheme with any grounding to any equipment that will have other common connecting shielding will also help eliminate ground loops. If conduit is used then use isolated grounding that is brought back to one point in the system usually the main service panel, otherwise you will have to try to keep your conduit runs isolated from incidental contact of other grounding to maintain a single grounding path back to the main service, which can be very hard to do.

[ August 15, 2004, 11:24 PM: Message edited by: hurk27 ]
 
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chuckwheat

Member
Re: Balanced 120VAC or 60VAC to ground?

Thanks for the input,
The situation goes like this...
A fella asked me to rough out some lighting, sounded simple enough...The lighting is in his brand new recording studio. Another electrician had already roughed in the power. He seems to have done a very good job, but the the thought did cross my mind that a typical residential power layout might not be exactly what this guy was looking for. So I did a little research, and asked him if his previous electrician had given any consideration to potential ground noise problems. The answer was no. So to date there is no problem, as the studio is not operational yet.
However, if it becomes a problem, I was exploring options on this guy's behalf. I appreciate the link, it was actually a tech release from an engineer from equi-tech that led me to post the question. Basically i was just curious how field proven the method was/is. Also, this guy seems a little bit old-school, and I want to discourage him from simply 'lifting' the ground.
 
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luke warmwater

Senior Member
Re: Balanced 120VAC or 60VAC to ground?

I have my own home recording studio.
I have a portable recording studio.
I've been in and out of the music business since before I could drive.
I also have a sound company.
They are seperate from my Electrical business.

Wayne and Dereck have given you some good info.

Now let me ask you some questions:

Is there any fluorescent lighting?
Are there any lighting dimmers?
Do all of the dedicated circuts go back to a sub-panel, or all the way to the Main loadcenter?
Does your client have any rack-mounted power conditioners that he is planning on using?

It's hard for me to say that you should definately have him purchase an Equitech unit (or equivelant) because I don't use one.
In my home setup, I have no noticible noise from ground issues.
I have a bigger problem with mic isolation.(a phantom powered AudioTechnica 40series can pick up a pin dropping on carpet if it isn't isolated good)

Now if he is using cheap outboard gear, It's not gonna matter what isolation he uses for ground noise, because alot of the cheaper equipment is going to be noisy no matter what.
ie. In my live rig, I tried a dual channel Behringer compressor. It's cheap. It's noisy. Even plugging into a power conditioner. Still noisy.

I just took my portable system to my buddy's house. I had no problems with ground noise.
 
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chuckwheat

Member
Re: Balanced 120VAC or 60VAC to ground?

To answer your questions...
1)There is no flourescent lighting. Having done a little home recording myself, and knowing vaguely of its' ills, I suggested all incandescant recessed lighting.
2)He would like to be able to use dimming switches, and I did tell him this may not be the best idea. He is willing to try anyhow, and jump off that bridge when he comes to it. I actually roughed the lighting in such a way that he could control the lighting mood from his console, if he chose. It's also not to late to suggest low voltage lighting with a theater-style control board if he wants to get real fancy. What I suggested so far was an old fashioned floor or table lamp in each of his isolation booths for ambience if the musician is really that picky.
3)The lighting is independant of the studio power and originates in the main panel. The AC for the console and wall outlets originates in a standard sub-panel.
4)He does plan on using a power conditioner, though I am unsure of the brand and model. He is actually on a trip to Nashville as I write this to tour studios and weigh his options.
 
dereckbc

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: Balanced 120VAC or 60VAC to ground?

FWIW here is an idea. You said he is going to use power conditioning. So why not run dedicated 240 circuits to the control room and studio, and then use plug-n-cord rack mounted balanced power systems with power condtioner built right in and kill two birds with one stone. If you use the plug-n-cord units you by-pass all the NEC restrictions.
 
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luke warmwater

Senior Member
Re: Balanced 120VAC or 60VAC to ground?

I agree with Dereck.

I just recently returned from Nashville. Great trip from what I can remember. Here is a picture.
 
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