The current transformer is one of the types of instrument transformer which is designed in such a manner so as to produce a current in its secondary circuit which in turn proportional to the current flowing through it’s primary circuit. It is one of the components that needs to be installed inside the electrical panel board in order to measure the current flow through each phase of the three phase system inside the panel. Usually these electrical panel boards were designed by electrical based industries. One of such industries which was in need of a 50:5 ratio current transformer had handed over the current transformer design and manufacturing as an industrial work to the authors. In this paper the authors deal with the optimal design and re-engineering and testing of the current transformer that is used in the measurement of current.