Try this url for formula in 3 phase:
http://www.angelfire.com/pa/baconbacon/page2.html

 

You need the amperage for which side: 480VAC or 240VAC?

 

15000/(sq root of 3 X 480) for the secondary

15000/(240) for the primary

hope that helps.

 

It's obvious that the geothermal degradable resistance of Ohms Law is got the area of the frequency divided by kW.

So basically just use the amps to propel the circumference of the triangle and you'll find your answer.