In paper a choice of 0.4 kV cables’ cross-sections by economic and technical criteria under market price conditions is examined. Nowadays reliable and unambiguous information about the cost of the equipment for transmission lines, building and construction works, financing terms, etc., is absent because the prices are free and market. For 0.4 kV lines it is necessary to consider not only economic criterion, but also technical requirements, as they can be prevailing with considerable lengths. The modified method of economic intervals with checking by permissible heating current and voltage losses is used for reasonable choice of cross-sections. The boundary lengths by voltage losses are determined and dependences are constructed. The graphical realization for method of economic intervals using MathCAD software is offered. The modified method provides reasonable technical and economic choice of 0.4 kV cable lines’ cross-sections.