Electrical Wire & Cable Size Calculator (Copper & Aluminum)

Answer:

Calculating Wire/Cable Size Formula for Single-Phase Circuits

Wire Circular mils = 2 x ρ x I x L / (% Allowable Voltage drop of source voltage)  

Calculating Wire/Cable Size Formula for Three-Phase Circuits

Wire Circular mils = √3 x 2 x ρ x I x L / (% Allowable Voltage drop of source voltage)  

Where;

• ρ = Specific resistance or resistivity of Conductor
• D = Distance in Feet (One way) i.e. ½ the total circuit length
• I = Load Current

Note: The Value of ρ = Specific resistance or resistivity of Conductor is used here for copper and aluminum is 11.2 and 17.4 respectively at 53° C (127° F).