Talkback:
"Power and Grounding for a Post Facility"

I've read about the balanced power notions for a year or so, but haven't read any info about a 220-VAC system. My Neumann disc mastering lathe uses 220 - for the drive motor only - and the 117 VAC systems are inseparable from it. Anyone have a clever notion for deriving 220 balanced power? I'd be really grateful for some good ideas!
--David Sifritt, des@on-ramp.net

The other advantage is that you don't have to deal with explaining to anelectrician what you are talking about. Unless they have done this before,or perhaps done extensive work in hospitals, they will not know how itworks or how to install it. You also, potentially, have the inspectionissues to deal with, though the 1996 NEC does cover symmetrical power.

The reasons not to buy a packaged system are cost and flexibility. In themost recent system I did we used industrial transformers, at a significantcost savings (and also had no startup surge problems caused by toroids). In both systems I have done I needed fairly large amounts of power (150-300amps), and I wanted to put in an isolation transformer and technical powersub-panels in the equipment room anyway. It just made sense to considerthe symmetrical aspect as part of the technical power build. But I had toclearly explain what was to be done and watch over the electricians. Also,these were new systems; not adding symmetrical power to an existingfacility or small studio.

Hope this helps!
-- Eric Wenocur

First, for those who want to give the balanced power approach a test drive, there are a couple of alternatives. My first experiments involved a small isolation transformer originally designed as a 220V to 110V step down device. The secondary is center tapped, allowing me to create a true balanced 110VAC power source. This particular transformer had a relatively small current rating, so I was limited to the devices I could test. Still, it proved to me the value of a balanced power source, there was no hum or noise.

OK, I'm still basically skeptical, and this did not address larger devices with lots of motors, namely my ancient 2" tape deck. In order to further test the hypothesis, I changed a single jumper on the tape deck and operated it off balanced 220V. The idea is the same, two conductors operating at equal potential and opposite polarity, and it did not cost me a cent! I've since gone through a lot of my gear, and found that several items would operate from a 220VAC feed. These devices will probably stay this way, since it greatly reduces the capacity I need to balance at 110VAC.

I would be interested in hearing from anyone who has gone through the exercise of build vs. buy. There are at least two companies selling all-in-one solutions, Equi=tech and Furman. If you know where to find surplus transformers you can save a lot of money. My original intention was to follow this path, but after careful consideration, I am not so sure any more...

1) I could not find toroidally wound transformers on the surplus market. Conventional transformers are a potential noise source, though this was not a problem for me since they would be located far enough from the studio gear. Still, they are physically LARGE, and I just did not have the space to put them on the wall.

2) Both manufacturers have taken most of the pain out of installing these devices. The GFCI breakers are already there, as is additional filtering etc. And they come in nice, easy to install boxes!

Also, any thoughts on running some gear on balanced 220VAC and some on balanced 110VAC? I have given this some thought, and can't seem to find a downside. Can anyone??
--Bill Thompson, wst3@bellatlantic.net

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