This example shows how to size the primary-only protection overcurrent device and conductor for a fully loaded 45kVA, three-phase, 480V transformer. (a) 70A breaker, 6 AWG conductor (b) 100A breaker, ...

If the primary phase voltage in a typical delta/wye system is 480V, the secondary phase voltage is 120V. Delta and wye transformers also differ with regard to their phase voltage versus line voltage ...