9100, I probably didn't communicate proprely which transformer(s) I was speaking of. I was speaking of the power company's transformers on the pole.
I will post a link to a power company PDF showing their connections. Page 5 shows the "open" connections. Note that phase 3 to neutral reads 208v. In the real world this is usually closer to 197v.
It is widely refered to as the "high leg" even in the NEC (National Electrical Code) or sometimes as the "wild leg" (trade slang).
This is not theory or opinion. With 34 years in the electrical trade I assure you this is real.
knn
Link =
http://www.jea.com/about/pub/downloads/contractor/OH-2-Transformers.pdf
P.S. I tried to upload the link but was told it was too large. Just copy and paste into your browser.
I have been at this a while, too. My first paycheck was from a summer job in 1951 at the the P. E. Chapman Electrical Works. I started working full time a few years later and have done a lot of things, especially since becoming an independent, taking whatever came along. In all that time, the only reference to a "wild phase" was from a steam engine mechanic at the Midwest Old Thresher's Reunion in Mount Pleasant, Iowa. He asked about connecting something to the wild phase coming into their shop. I asked for an explanation, but what I got was very nebulous. He was a machinist/mechanic, not an electrician. That is the only time I had heard the term, probably because I have mainly worked in industry where they had larger services. Personally, I think calling it a wild phase is misleading because it is simply elevated above the others by grounding the center of the winding for the other two phases. In an application like a farm that has a house using single phase power and a few three phase motors in farm equipment, it makes sense because if three phase feeders are present, the power company only has to hang another single phase transformer and run an extra wire. Around here, when they want to save money, they go to a 120/208 service, which is fine for someone who is going to buy all new equipment that will run on 208, but I have worked in one shop that had it and consulted for another. Both had a lot of 240 V equipment collected over the years and everything had to run on the reduced voltage or have a transformer.
When I found the term that Google wanted, which is "high leg delta", I got a lot of information about it. It would be a much better solution for small shops or home machinists than phase converters that are either expensive of don't work very well. I had a static converter on my first mill at home and a commercial rotary when I moved into the shop. Neither was more than barely adequate. I finally badgered the power company into giving me a proper 240 V 3 phase line.
I called Ameren, which supplies power around here and wound up talking to an Illinois engineer instead of one for the Missouri side of the Mississippi, but I was only asking general questions, anyway. The service may be available. It depends on the particular power company, the availability of 3 phase feeders and the probable use. It would be worth an inquiry.
I make transformers and other electrical equipment and my travels have taken me from underground in a coal mine to wiring jet planes, so naturally I wondered how I missed this application. I have shelves full of books on transformers and related subjects. I went through the books I use as references for them and found all sorts of exotic connections like Scott, broken star, 6, 9 and 12 phase conversions, which I knew about, but not a word about high leg delta.
Oh well, maybe the mental activity will delay the onset of Altzheimer's.
Bill
