Work Problem 17.20 for the case of aluminium rather than copper. The resistivity of aluminum is 2.83 × 10^-6 ohm – cm.

Data From Problem 17.20

Copper wire having a diameter of 3/16 in. is insulated with a 4-in. layer of material having a thermal conductivity of 0.14 Btu/h ft °F. The outer surface of the insulation is maintained at 70°F. How much current may pass through the wire if the insulation temperature is limited to a maximum of 120°F? The resistivity of copper is 1.72 × 10^-6 ohm – cm.