Calculations are simple 400 amp x 208 volts x sqrt(3) gives you 144,102 watts of power, at 80% thats 115,281 watts. Our farm the s9's are averaging about 1100 watts each, which would give you 104 s9 miners. The real trick is balancing the load, we have multiple racks of 200 amp services and have yet to balance one perfectly, leg C is always about 15% less then A or B. Also, use larger wire size, when you have a large feed you have to watch for voltage drop, that will cause the miners to draw more power and start popping breakers.