How many amps do you need to run a 35 kva 220 to 480 3 phase transformer?

The formula you are looking for is I = KVA x 1000/1.73 x E, I = 35 x 1000 = 35000/1.73 x 220 = 381, 35000/381 = 92 amps on the primary side.

35000/1.73 x 480 = 830, 35000/830 = 42 amps on the secondary.

Transformer conductors need to be rated at 125% so the primary will need an ampacity of 92 x 125% = 115.

A #3 copper conductor with an insulation factor of 90 degrees C is rated at 115 amps.

The secondary conductors will need an ampacity of 42 x 125% = 53 amps

A #8 copper conductor with an insulation factor of 90 degrees C is rated at 55 amps.