Bear in mind that E x I X 1.732 is using line-to-line (delta) voltage. If you're using line-neutral (wye) voltage, the 1.73 factor as already been applied, and you can treat them like individual 1-phase circuits.
You didn't say what voltage; but for 208/120, ex:
Delta: 208 x 30A x 1.73 = 10.8kVA
Wye: 120 x 30A x 3 = 10.8kVA