your right i have not had to ever before had to select the primary side of the transformers size conductors. they have always been in place prior to the install so pardon my ignorance to understanding how this conductors minumum size shall be. there is a formula so the question at hand is do i take 250amps multiply that by 125% which gives me around 314 and divide that number 0.0057 which are the windings listed amounts of seperation to derive the answer of 175 amps and if i were going to use a thhn conductor that a 1/0 would be of proper size. the temperature inside this room is around 100 degrees at its peak
