tranformer supply circuit breaker size in the sourece , the minimum

[Toros]

What is minimum size breaker in the source (A panel board) for 45 kva-3ph.-tranformer .
the subject, the load is lights/ receptacles through a sub panel ( total 20,000 VA).

Also, what minimum size fuses in primary side, adjusnt mounted manual disconnect switch

 

[don_resqcapt19]

The NEC does not set a minimum size for the primay OCPD. We need to know the voltages to make any OCPD sizing calculation. You can't go too small or the OCPD will open on the transformer inrush current.

 

[Toros]

thank you