In my home town (Oradell NJ) there's a neighborhood that has several residences fed by 240 delta with one side center tapped for 120/240. Built in the late 50's I think, a development of McMansions of the era, with this new feature called "central air". The builder must have used smaller commercial AC units that required 240V delta. There was a garage sale at one of these houses recently, and I saw a big main 3 phase panel, just below the kilowatthour meter, and a 2 phase subpanel, probably for normal household loads.
These houses were fed by 2 transformers, to create a "wild leg" at 208V from ground, and the 240V delta with a missing transformer.
I suppose one could connect a dryer to the "wild leg" and to the appropriate 120V line (so the dryer's motor sees 120V instead of 208V!) and also connect the dryer's 240V heating element to the 2nd transformer, and not bridging the pair of transformers, though is there any way to tell which of the 120V lines the 2nd transformer is connected to? Does the power company have a convention, maybe the 120/240 transformer always on the phase that leads the 2nd transformer? Like 120/240 on phase A, 2nd on B, and other places B then C and others C than A?
I think today's code says that any voltage higher than 120V to ground is not allowed in residences.
