[Manish Jain]

ELECTRICAL LOAD CARRYING CAPACITY 
OF COPPER WIRES OF DIFFERENT THICKNESS

Below are the important Table which one should follow for determining the proper size of wire for electrical circuits 



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)

If the wire size is greater than all gauges (i.e 0000 is largest one size of wire in), then electrical engineer measure it in CM, kCM or MCM instead of inches, because inch is a small unit of these kinds of  wires. Where;
A circular mil (CM) is a unit of circular area with a diameter of one mil (one thousandth of an inch). It corresponds to 5.067×10-4 mm².
Where:
1000 CM (circular mils) = 1 MCM or 1 kcmil = 0.5067 mm², so 2 kcmil.
It is a unit for referring to the area of a wire with a circular cross section.

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