Isolation transformer and with branch breaker

[aNerdyEngineer]

I have a branch circuit breaker for a motor but between the breaker and motor is an isolation transformer. I only have the one breaker (primary side). Do I need to size the breaker per the isolation transformer primary current times 125% from NEC 450.4 or can I size the breaker for the motor load using 430.52 which gives me 250%?

 

[ActionDave]

I think you need secondary protection.

Single or three phase?

 

[aNerdyEngineer]

The line is 480 3phase, load is 480 3phase that goes to our AC/DC drive for a DC motor. I'm sizing the transformer per sqrt(2/3)*ADC to give me AAC to work with.