Single OCP device for Parallel MV transformers with dedicated feeders

T

tlona1

Member
Can two transformers, installed in parallel and fed by dedicated conductors, be protected but a single primary breaker? Client has a 33kv/65A breaker that feeds a 3.75mva 33kv/480v wye transformer. They current 3.75MVA transformer only operates at only about half its rated load and therefore they want to feed a new 1.5MVA transformer, elsewhere in the facility. This new 1.5mva transformer would be fed by a new dedicated feeder that terminates on the load side of the existing 33kv/65A breaker. This is not for life safety equipment and the client is aware the problems caused by this non-isolation scenario. Thank-you
 
As long as the conductors are sufficiently sized to be protected by the 65 Amp breaker, and the 65 Amp breaker is not larger than the maximum primary protection, I do not see a code issue with this.

The rated primary current of a 1.5MVA transformer at 33kv(L-L) is 26.2A

NEC 450.3(A) allows you to size the primary OCPD breaker up to 300% of the rated amps. 65 Amps is within the 300% range.
 
Thank-you. I have herd/read the intent of table 450.3(A) is for individual MV transformer OCP but I see nothing in the NEC or even IEEE that requires "individual' OCP. for MV transformers.
 
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