After all demand factors have been taken into consideration for a commercial building, the balanced demand load is determined to be 75 kVA; the building has a 208Y/120 volt, 3-phase electrical system. What MINIMUM size copper conductors with THWN insulation are required for the ungrounded (phase) service-entrance conductors? 4/0 AWG First, apply the 3-phase current formula to find the load in amperes: I=kVAx1000 I=75kVAx1000 =75,000 =208.1amperes E x 1.732 208 x 1.732 360.25 Size 4/0 AWG THWN copper conductors with an ampacity of 230 amperes should be selected as shown in Table 310.15(B)(16).