Wiring a Transformer

Your wiring size must be rated for carrying at least the rating of the protective device protecting it (in this case a 100A circuit breaker).

I am assuming that you know what wiring size you need that will be able to handle 100A in your particular application, if not see previous threads on wiring size selection.

The minimum ampacity of the secondary conductors is a product of the primary side over current device.

The ratio of the secondary to the primary on this transformer is 480/208 or 2.30:1. So to limit the secondary current to 100 amps, the primary needs to be fused at, using the equation of 100/2.30, 43 amps. I would use a 40 amp breaker to protect the primary and #8 AWG wire. Or you could use a 50 amp breaker, with #6 feeding the transformer, and still be within the ampacity limit of your #2 on the secondary.

If you wanted to use the full 112kVA... you would need the following...

Primary max amps = 134.9 A

Secondary max amps = 311.2 A

Max Standard Primary Overcurrent device = 175 A

Minimum Primary Conductor Ampacity = 168.6 A

Minimum Secondary Conductor Ampacity = 389 A