Development of market relations in the power sector tightens the requirements for uninterrupted and qualitative power supply of customers. In the proposed work there is highlighted issue on determining the influence of the number of connected to the urban medium voltage distribution network elements (transmission lines, switchgear, transformer substations) and its impact on power supply reliability. Additionally, it is suggested the approach to the methodology of power supply company’s potential damage calculation due to network equipment failure and electricity not supplied to consumers.