This final paper describes overhead and cable lines and the associated diagnostic methods. In the first half of this paper, the functional and operational part of overhead and cable networks are described. The first chapter describes the structure and composition of overhead power lines with all associated elements. The second chapter is dedicated to cables, their construction, and the materials from which they are made. In addition to the constructive part of cable conductors, cables for low-voltage, medium-voltage and high-voltage networks are also described in more detail.The modern types of cables are also listed in the subchapter on cryocables as well as the specificity of submarine cables. In the second half of the paper, diagnostic methods for overhead and cable lines are described. The third chapter describes in more detail the methods by which failures and irregularities of overhead lines are diagnosed. The described methods are thermographic and laser tests, corona, and video examination. The fourth chapter describes cable diagnostic methods and related test procedures in more detail. The last chapter deals with a newer type of diagnostics based on temperature difference, more precisely thermovision.