Aircraft electrical installations are sized according to the American Wire Gauge Standard. Wire size is indicated by a unit called circular mil.
One circular mil = cross sectional area of 1 ml (0.001 inch) diameter wire
To determine the size, square the wire’s diameter measured in thousands of an inch.
If a wire size is 0.025 inch diameter
0.025 in = 25 thousands of an inch
(25) * (25) = 625 circular mils
Square mil is the unit of measure for rectangular conductors, such as bus bars or terminal in length.
1 circular mil = 0.7854 square mil
Basic guidelines of AWG standards
– Only even numbers are used
– Small wires have higher numbers
– Large wires have small numbers
– A 20 gauge wire is =0.032 inch diameter
– And 0 gauge is = 0.325 inch diameter