The standard medium power AC supply in industrial use in Canada is 575 volts (nominally 600). This provides a nominal 347v from a Y branch to ground. There is almost no 440 volt 3 phase service used here. For low voltage 3 phase service we generally have 208v 3ph which provides 120v single phase to ground from any single leg of the Y. The 575 volt service is generally called "600 volt supply" and I expect this is what the S/390 that started this discussion should be connected to. As someone else mentioned, this is quite "hot". Its a bad idea to attempt to plug a wet Hubbell plug into a live receptacle operating with the 600v service or for that matter to fool around with any tools in the vicinity of live parts. Once a flash-over starts, you've got some real fireworks. Recently I've been recovering some equipment from a deceased scrapper's farm and have had to carry various treasures around a large obstacle with a protruding shaft. I checked the plate and found its a 6000 hp electric motor..requiring 13,200 volt supply. I guess you'd need to be careful working on this one! Dan