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.

Any time it's going to an outlet, instead of hard-wired, you have to accommodate the POTENTIAL, not the actual load. Who's to say you won't get 600W, class A, OTL monoblocks and then plug in some 11,000 BTU portable air conditioners and a vacuum cleaner. Also have to consider the electrical service, since you're adding another 20A without taking anything else away.

The "isolated ground system" has two ground wires, one insulated and going all the way back to the bus bar. Mixed results, mixed recommendations, and not official NEC code. Romex and armored are available as 3C ... but talk about confusing... Got any green nail polish? ;) Otherwise, conduit, $$$.

1) Wrong
2) Ok, maybe, sort of. Ask Almarg.
3) Very wrong. Can't count on copper service pipe. Removed or prohibited from code decades ago. Transformer/shield has to be grounded too.
4) When are they necessary? Google.

Off to a good start. The transformer, though unusual for residential, will provide some common mode noise reduction. Multiple transformers allows isolation between components. Naturally, "the best way" is completely impractical.

Where is this transformer going to be located? They can hum.

DMatt,
Thanks for the info regarding the hospital grade recepticles. I have seen a number of favorite ports mentioned in threads, most often Hubbell 5362s.

Based on what I've gleaned from other threads there is still a benefit to using recepticles with an isolated ground and running the dedicated lines in armored cable. I'm undecided on which to use here. #10 BX has been recommended. I've also seen recommendations for the Belden 8300 series. Also for twisting the wires. Do they need to be twisted if they are running through metal? You'd think someone on Audiogon would have created a cookbook for all this by now.

Ngjockey,
Thanks, I get what you mean by potential draw on the circuits. And I'll simply let the electrician worry about grounding things properly.

You brought up another point though regarding the service amperage that'll go to the sub. I'm trying to get a handle on what's possible. I guess I would like a minimum of four circuits off the subpanel: two for the monos, one analog, and one digital. I've seen recommendations for a minimum 60amp breaker at the main panel to protect what is going to the sub. 1)How do I know what amperage is available to lend the sub? 2)If I can use a 60amp breaker does this mean that I can't exceed a total of 60amps in breakers on the sub?

Chris

Sorry I forgot to add that the transformer and subpanel would be in the furnace room, which unfortunately is right behind where I'd be listening. There is a door. It shouldn't be any more audible than the furnace, should it? Anyway, it'll have to do.

Chris

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