75kva step-up

[Ricky A]

I will be installing a 75 kva 3 phase s/u xfmr, 240 hi-leg primary to 480/277 secondary. it will supply power for a glycol chiller located 60 feet from xfmr equip. Do I need both pri and sec protection and what size?

 

[don_resqcapt19]

The transformer must be protected per Table 450.3(B) and the secondary conductors per 240.21(C). Often the secondary conductor protection also provides the transformer secondary winding protection.

 

[Elect117]

I would also add that the secondary conductors, the 480/277V conductors, will require OCPD at their ampacity. You can not round up.

Your transformer can be rated for a higher VA than the glycol chiller. You should install conductors, and the OCPD for those conductors, at the VA or ampacity of the load. You do not need to provide the protection at the FLA of the transformer (as long as you are doing better than 450.3).