The possibility of increasing the transmitted energy through cable lines laid in a cable duct by optimizing power distribution is investigated. The thermal field of the cable block is analytically considered. A simple ratio is proposed to determine the current loading profile of the duct, guided by a homogeneous distribution of cable temperature. For cable ducts with a large proportion of disconnected cables or empty pipes, a method for optimizing load distribution in accordance with the theory of the planar potential problem is presented. In addition, the acceptable accuracy of the discrete source model for calculating temperatures in the cable duct in comparison with the FEM calculation is noted. This approach makes it possible to calculate the cable duct of any configuration and filling, including the joint placement of XLPE and PILC cables in the cable duct, which is currently an urgent task.