I = Current in Amperes

A = Cross Sectional Area in mm²

p = perimeter of conductor in mm

Assume that the temperature rise of the conductor is 50°C above the ambient temperature of 40°C, and the resistivity of Copper at 20°C is 1.724 micro Ohm cm, then the current ratings are:

For Flat Bars

I = 7.73 x A^0.5p^0.39

For Hollow Round Bars

I = 8.63 x A^0.5p^0.36

For Solid Round Bars

I = 13.6 x A^0.68

Hollow Round Bars (Bustube)

I = 8.63 x A^0.5 x p^0.36