The topic of this thesis is related to medium voltage power cables, and their impact on the operation of the power grid. The paper describes the medium voltage network, as well as the shares of cable and overhead lines, and at the end of the paper, problems are given due to the cabling of 35 and 20 kV network. The topology and description of each network are presented in detail, as well as the elements of these networks. Medium voltage substations, cables and overhead lines are described, which includes conductors, insulators, poles, and other parts such as couplings and suspension accessories. Data on the shares of the overhead and cable network in Croatia, but also in the European environment are given, shown in the tables and graphs. Long cables have significant capacitive property to a large extent, and can be replaced by a real capacitor, which is explained in the paper. The problem occurs when the cable is idling or when it is very lightly loaded, which leads to an increase in voltage at its ends. We call this effect the Ferranti effect, which is described in detail in the last chapter of the thesis. In addition to a theoretical explanation of the effect, an little example was made in PC program NEPLAN. The aim of this thesis is to describe the medium voltage network, and to present the issue of cabling that has negative effects on the operation of the entire network. These effects can be minimized through the analysis, so that the electricity grid can continue to function smoothly.