Never ever try to connect the neutral of a single buck boost transformer fed by a 208Y/120 system. the problem is much worse than a simple un-balance.
Very simplistically, assume you are bucking the 208V up to 236V. The low voltage side line to neutral is 208V/1.73 = 120V, and the high voltage side is then 236/1.73 = 136V. As you can see 120V does not equal 136V therefore the two neutral points are not the same and cannot be tied together without creating a short circuit.
Okay you say, you won't tie them together, well how will your 120V equipment like being connected to 136V?
