Buck-Boost Transformer with Three Phase Wiring
The fact that the 208 V legs come from two phases of a three-phase system does not affect the use of the transformer. Those two legs constitute a single-phase source. However for the high side legs of the boost transformer, one leg is the connected to a 208 V leg and the other is connected to a boosted leg that adds 32 volts. With respect to common, one leg will still be 120 volts and the other will be higher, somewhere between 120 and 150 volts. The boosted 240 volt source can only be used for 240 volt loads that do not require a neutral connection. Some internal parts of such loads likely require 120 volts. An example would be a stove or clothes dryer that has a 120 volt timer inside. If all internal 120 V components are connected between common and the lower of the two legs there would be no problem, but making sure that is as it needs to be may be difficult.