I AM ABOUT TO BEGIN A PROJECT AT A PRO SPORTS FACILITY IN WHICH I AM REQUIRED TO INSTALL A STEP DOWN TRANSFORMERFROM 480/277 TO 120/208 TO OPERATE A LED VIDEO BOARD THE LOAD IS 250AMPS WHAT IS THE PROPER FORMULA THAT I NEED TO USE TO OBTAIN THE CORRECT SIZE CONDUCTOR ON THE LINE SIDE OF THE TRANSFORMER. ALSO WHAT IS THE PROPER WAY TO GROUND THIS SYSTEM. KEEP IN MIND THIS IS A THREE CONDUCTOR TO A FOUR CONDUCTOR SYSTEM
