Who many amps are needed to feed a 600 v to 480 v 3 phase 70 KVA transformer?

The equation for amperage when the kilowatts are known is Amps = kVA x 1000/1.73 x Volts.

The electrical code states that a feeder for a transformer has to be rated at 125% for the primary and secondary load amperages.

The amperage on the primary needed to supply a 70 KVA three phase transformer to its full capacity at 600 will be 68 amps. 68 x 125% = 85 amps. A #4 copper conductor with an insulation factor of 90 degrees C is rated at 95 amps.

The amperage on the secondary needed to supply a 70 KVA three phase transformer to its full capacity at 480 will be 84 amps. 84 x 125% = 105 amps. A # 3 copper conductor with an insulation factor of 90 degrees C is rated at 115 amps.