480/208-Volt Transformer

[Campbellsfrontier]

With a 480-volt 3-phase Primary feed connected to a 1,200-amp, 208/120-volt, 3-phase Secondary, What size Transformer do I need to feed the 1200-amp switchboard? According to the Electrician Bible app on my phone, it states it would require a 250kva transformer. However, the Square D pocket guide says it would need to be 500kva. Which one is right?

 

[Dsg319]

Voltage x sqrt of 3 x amperes=VA

208 x 1.732=360
1200a x 360=432,000va.

So next standard size would probably be 500kva.

The above calculation is for the full capacity of the switchboard. Not the calculated load.

 

[Campbellsfrontier]

That's what I thought, just wanted to make sure.
Thanks