Transformer--Subpanel Wiring

Hi Chris,

I am going through the same process with my AV power.

I have been able to get a great deal of info from not only A-gon threads but also white papers on the Jensen Transformer site (Bill Whitlock, Jensen President, has published a lot of peer-reviewed papers on grounding issues), the Ultra-K white papers from the Controlled Power site, the white papers from the Middle Atlantic Products site, the white papers from the Equi=tech site, white papers from the Ground1 site, and papers from the publications page of the Audio Systems Group site.

There is a difference between Hospital Grade Outlets (greater contact force among other benefits) and outlets with Isolated Grounds. Isolated ground duplexes separate the ground lead from the mounting strap of the duplex -- so the ground wire can be isolated from the building ground (metal boxes in the wall, other outlet grounds, etc) until the isolated ground meets up with the other grounds at the source (main panel or isolation transformer). If you check the Hubbell-Wiring site, you can check their online catalog (Hubbell Wiring Device-Kellems) and will see in section A "straight blade devices" that they make hosptal grade, industrial grade, and commercial spec grade duplexes (and explain the differences); and in section J show isolated ground versions of basic and hospital grade duplexes (plus a good explanation of isolated ground).

I believe the advice you read about isolated grounds not being needed in a wood house is because if you are already running a dedicated line (dedicated hot, neutral, ground) from the panel to your audio gear without making a stop at any other outlet or junction, then the ground is pretty much already isolated because the outlet box is nailed to a wooden stud, not a metal building frame. But I'm not an electrician, nor have I stayed in a Holiday Inn.

Chris,

The Controlled Power Ultra-K isolation transformers show an audible noise spec in their website brochure of 45-55dBA at 1 meter.

Take a boombox and your Radio Shack sound meter out to the furnace room and play white noise at 60 dBA from three feet back to see what it will sound like (put the tuner between stations for white noise).

My guess is it will be close to the furnace in loudness, but will be making noise all the time.

David

RE twisting:

Last week I read a paper that favored twisting the hot and neutral together and leaving the ground separate. Pull the three wires through conduit. This has been touted as the way to reduce the induction effect of the H and N on the ground, reducing induced ground voltage that causes noise.

Bill Whitlock (Jensen Transformers) and Jamie Fox presented the paper at last November's AES convention that supported this approach with test data. Titled: "Ground Loops: The Rest of the Story", the twisted configuration offered lower ground voltage induction than Romex (where the ground is between the other conductors) and aluminum MC (metal clad with the three wires configured symmetrically inside).

The synopsis from the AES library website: "The mechanisms that enable so-called ground loops to cause well-known hum, buzz, and other audio system noise problems are well known. But what causes power-line related currents to flow in signal cables in the first place? This paper explains how magnetic induction in ordinary premises AC wiring creates the small voltage differences normally found among system ground connections, even if “isolated” or “technical” grounding is used. The theoretical basis is explored, experimental data shown, and an actual case history related. Little has been written about this “elephant in the room” topic in engineering literature and apparently none in the context of audio or video systems. It is shown that simply twisting L-N pairs in the premises wiring can profoundly reduce system noise problems."

Hope that helps. I am taking this approach on my dedicated lines (with isolated grounds) from my sub panel.

David