The first part of the final thesis describes the construction of power cables for medium voltage level, or voltage of 0.6 / 1 kV, 10.6 kV, 12/20 kV, 18/30 kV and 20.8 / 36. The construction of medium voltage power cables is determined by the method of laying, the type of load, the voltage level, and the technical requirements that must be met in order to ensure that the distribution of electrical energy is not compromised. Further are described the methods of labeling, and examples are given from which the cable structure can be read clearly, depending on the alphanumeric and numeric symbols on the cable shell. We have also met the conditions of cable laying in different environments and the rules that have to be observed for laying the power cables in case of laying cables along with other installations or crossing of cables with other installations. In the main part of the final thesis, models ad calculations are described for the determination of the permissible current load of power cables using a replacement thermal models of the cable and correction factors for certain laying conditions. At the very end, it is briefly described how to measure the cable temperature in order to increase the efficiency of the cable itself and its durability.