The fuse is a simple, cheap and efficient device capable of protecting the consumer and supplier from the harmful overcurrents normally produced by a circuit fault. They have been used with success for many years in low-voltage circuits, and in modern practice the range of application now extends up to 33KV. When current flows in a conductor, a certain amount of energy is generated by collisions between the free conduction electrons moving under the influence of the applied field, and the bound metallic atoms which form the intrinsic lattice structure of the material, This energy is manifest in the form of heat, and causes the temperature of the conductor to rise above that of its surroundings, until the rate of heat generation is just equal to the rate at which energy is dissipated. Using the formal concepts of resistance and current, the rate of energy generation is given by. dU/dt = i2r. (1.1). where, U = energy generated, i = instantaneous current flowing in conductor, r = instantaneous resistance of conductor.