Nowadays the insulation of power cables is generally made of plastic, at low voltage the most widely used polimer is PVC. Built-in cable lines must meet the requirement of operating reliably, therefore it’s necessary to examine the condition of the cables periodically. In my thesis, I present the examination of the long-term ageing of a PVC insulated cable, which aged during operation. For the interpretation of measurements performed during examination, insulation technical knowledge is required, therefore first I give theoretical summary, then I detail the measurements, and finally I evaluate the condition of the cable based on the results of the measurements. I examined the dielectric properties and the hardness of three segments of the PVC cable, that was taken out of operation. According to the results of the measurement of dielectric parameters, the electrical parameters have deteriorated greatly during operation, their values don’t meet the required standards. The adverse change of electrical and mechanical properties refers to the ageing processes in the insulations. So the examined, PVC insulated cable has aged significantly, during the ageing, the plasticizer and active stabilizer concentration of the core insulation reduced.