Proper Way to Size Electric Conductor

Calculate the cross-sectional area of a conductor. The formula for calculating the cross-sectional area of a wire is: CSA = π (r-squared), in which CSA is the cross sectional area, π is the absolute value 3.14 and r is the radius, or half the diameter.

Wire sizes are relatively small numbers and are expressed in measures of thousandths-of-an-inch, or mils. Let's say the diameter of the wire is 100 mils. The radius is 50 mils because it's half the diameter.

Thus, CSA = 3.14 (50 to the power of 2), which equals 7,850 square mils. (This is approximate because pi is rounded down to 3.14.)

Calculate the circular wire area of a conductor. The formula for calculating the circular wire area is CWA = π (d-squared), in which CWA is the circular wire area, π is the absolute value 3.14 and D is the diameter of the wire.

Let's say the diameter of the wire is 100 mils. CWA = π (100 to the power of 2), which equals 31,400 circular mills.

Calculate the current carrying capacity of a conductor. For household electricians, size of the wire is often a sufficient determinant of current flow. However, electrical engineers and academicians are interested in current carrying capacity or gauge of a conductor more than the size. Once you determine the cross-sectional area or the circular wire area, you can refer to the standardized American wire gauge table, a widely used reference, to estimate the gauge of the conductor.