A copper cable used for heavy duty applications in electric arc welding has a diameter of 2.44 cm. It has a rated capacity of 600 amperes with a maximum conductor temperature of 90 C and an ambient air temperature of 40 C. The cable is insulated with rubber (k = 0.13 W/m K). (a) If the electrical resistivity, p, of the copper is 1.7 x 108 Ohm-m, calculate the optimum insulation thickness at rated capacity (from thermal considerations) if the heat transfer coefficient for convection from the outer surface of the insulation is heo = 3 W/m2 K. Recall that the electrical resistance of an electrical conductor of resistivity p, length L, and cross- sectional area A is given by L R = P (b) What is the temperature, To, of the outside surface of the insulation at these rated conditions?