Three Phase LRC = (HP X "NEMA CODE" X 1000) / (E X 1.732)
Single Phase LRC = (HP X "NEMA CODE" X 1000) / E
"E", Voltage, Values from NEC Table 430.250, or 430.248
"HP", Horse Power, Values from NEC Table 430.250, or 430.248
"NEMA CODE", Values from NEC Table 430.7(B)