The paper presents a technical approach to the problems of safe and economical control and operation of certain power networks. The initial sections are devoted to a quantitative discussion on circuit-breaker duty and short-circuit phenomena at points of supply and at remote points on the network.Some effects of interconnected working are indicated. Means for current limitation and alternative methods of control under fault conditions are described.The design and protection of cable networks are reviewed and the characteristics of transformers briefly discussed. Finally, some comments are offered on the layout of mediumvoltage apparatus and on the problem of voltage variation at consumers' terminals.The discussion is confined to phenomena on urban networks operating at voltages not exceeding 11 kV.