300kva transformer

[kingelectric]

On the job today there was a 300kva 480v - 120/208v transformer ,they had 2- 2'' conduits feeding the 480v primary side with 3- 3/0 copper wires in each conduit with a ground in each. I would think you would need 4/0 copper to feed this . The 480v has a 360amp rating. any thoughts on this and will the 4/0 still fit in the 2'' conduit? the distance is about 325'

 

[kwired]

What is transformer supplying? What is calculated load? 2 parallel 3/0 is good for 400 amps before any derating if needed. Without knowing more about the load this question is a little hard to answer.

If you intend to get full capacity of transformer your conductors could be a little small. If you do not intend to use full capacity of transformer you possibly could use smaller conductors if correct overcurrent protection is applied. Conductors are sized according to load and/or overcurrent protection and not necessarily to the capacity of the transformer.

 

[iwire]

Assuming normal conditions (not in a boiler room, not on the roof) two sets of 3/0 copper in two separate raceways provides a capacity of 400 amps. Why would you need 4/0s, or 460 amps of copper for this?

What size breaker is being used on the primary?