Transformer Size

[ed downey]

I am looking at a one line diagram that shows a 300KVA 480V Delta to 480/277V Y transformer. The primary side of the transformer is being fed from a 600A circuit breaker in the Main Switchboard. The secondary side of the transformer is feeding a 600A main circuit breaker distribution panel.
My question is this: Is the transformer sized correctly? (if I calculate 125% of The 300KVA I come up with 451A)

 

[hbendillo]

Re: Transformer Size

The 600-amp circuit breaker on the primary is alright because we are allowed to "oversize" the breaker on the primary up to a certain limit for inrush. However, the secondary breaker in that case should be rated no more than 500-amps. Does the panelboard connected to the secondary have a main breaker? Although the panelboard is rated 600 amps it could have a main breaker rated 500-amps.

 

[ed downey]

Re: Transformer Size

The Panelboard On The Secondary Has A 600A Main Circuit Breaker. Also It Seems To Me To Be A Waste Of Money To Run A 600A Feeder To The Primary Side Of The Transformer Since You Can Only Have A Maximum 500A On The Secondary.