Question

A copper wire of radius 0.5mm is insulated with a sheathing of thickness 1 mm having a thermal conductivity of 0.5 w/mk. The outside surface convective heat transfer coefficient is 10 w/m2k. If the thickness of insulation sheathing is raised by 10mm, then the electrical current-carrying capacity of the wire will: (a) increase, (b) decrease, (c) remain the same (d) vary

Answer 1

(C) Remain the same.  

The electrical current carrying capacity of a copper wire does not vary because of the insulation sheath surrounding it. The current carrying capacity of any conductor is purely dependent on the material being used, namely its resistivity, length and area of cross-section.  

However, the only perceivable difference will be in the temperature of the outside surface of the sheathing. More insulation material suggests that there will be more heat dissipation and lesser temperature on the outside.