The cost of a two-core feeder cable, including installation is Rs(90a + 20) per meter and the interest and depreciation charges are 10 %, The cable is 2 km in length and cost of energy is (4p) per unit. The maximum current in the feeder is 250 A and demand is such that copper loss is equivalent to what would be produced by the full current flowing for 6 months. If the resistance of conductor of 1 cm² and 1 km length is 0.173 12. Apply kelvin's law to calculate the most economic cross-sectional area.