The general formulas for computing actual shielding factors of high-conductivity overhead ground wires hung on power and tele-communication lines are given. These formulas are derived from a system of finite difference equations representing the relation between the currents in successive sections of the multiply-grounded shielding conductors

and the subsequent substitution of terminal conditions corresponding to the particular circuit arrangement under consideration. It is found that the actual shielding factor can be written as the sum of the intrinsic shielding factor t0 and a correction term evaluating the effect of finite conductance of the ground connections. It is also shown that the shielding factor formulas given in Engineering Report No. 26 of the joint subcommitte on development and research of the Edison electric institute and the Bell telephone system are only special cases of the general formulas given in this article.