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Isolated grounds for installs


Jamin Lynch:
I've heard various views on permanent installs that the audio, video and lighting systems should each have their own isolated grounds. What is best? Can you explain the pros and cons, problems and pitfalls?


Kevin Graf:
The major problem is that in any commercial building, church or school, sooner or later the 'IG' will be corrupted. Installer's (like HVAC) will connect their equipment to any handy ground.

Another problem is that many electrician's and audio guy's don't understand the correct way to wire an 'IG' system.  I read descriptions on audio pages of really strange set-ups.

Frank DeWitt:
Here is a good paper on the subject.

If you have some control on new construction wiring, one of the best things you can do is have the hot and neutral twisted and pulled in conduit with a non twisted ground.  The ground can be a isolated (at the outlet) star ground system but the twisting is just as important.

My work is in an existing building so I rely on a lot of Jensen isolation transformers and Jensen equipped DI boxes to keep the system free of hum.

Kevin Graf:
For more on the twisted pair plus ground idea, see:

"Ground Loops: The Rest of the Story"
Bill Whitlock, AES Fellow and Jamie Fox, P.E.

This paper was presented at the AES 129th Convention, 4-7 November 2010, San Francisco, CA, USA

There is also a patent application, but tiring to read it will turn your brain to mashed potatoes.

Kevin Graf:
For a much easier to read Bill Whitlock power point on the subject, see:

"An Overview of Audio System Grounding and Interfacing"
Bill Whitlock, President
Jensen Transformers, Inc.
Life Fellow, Audio Engineering Society
Life Senior Member, Institute of Electrical & Electronic Engineers

slides 31 to 44


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