Buck-Boost Transformer with Three Phase Wiring

Question

I live in a residence with 120v / 208v electrical service. (Measured as leg1: 124v, leg2: 125v, 215v across legs) I am nearly certain that the service is the result of two legs of three phase power. I live in a city near apartment buildings and other commercial structures. Can a single phase buck-boost transformer be used to raise the voltage? I’m concerned because the transformer wiring diagram connects the two legs across the two primary windings (leg1-h1-primarywinding1-h2-h3-primarywinding2-h4-leg2) and I know it’s not advisable to short between out of phase legs.

I have found a couple sources that say this should work, but nothing that tells me why it will work and I’m unsure as to the quality of the sources. Many thanks for your help! Matt

Answer 1

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.