— Wire/Cable Sizing & Voltage Drop
Copper conductor ampacity from NFPA 70 (National Electrical Code) Table 310.16 (75°C column), and voltage drop from the standard NEC/IEEE design formula VD = 2·K·I·L / CM (K = 12.9 Ω·cmil/ft for copper, CM = circular mils, L = one-way run length, the factor of 2 accounting for the round-trip conductor). Either check a chosen gauge, or find the smallest gauge that satisfies both ampacity and a maximum voltage-drop percentage.