Eh? What about 3-phase (for x-ray systems, etc.
I think what you meant to say there, Neil, was that (in some locations) both 110 and 220 VAC may be taken from a supply transformer in star configuration!
But (and perhaps more importantly in such cases) where is the earth connected?I have always thought that "two-phase power supplies" was an "American idea". I have only ever encountered them in buildings built to "domestic standards" in places like Saudi Arabia (village clinics, and the like). Only once did I come across a piece of "medical equipment" that actually required a 220 VAC two-phase supply in a proper hospital, and that was an ancient baby milk-bottles sterilizer (I think it was) made in the USA.