In this paper an approach to choosing the optimum cross-section for cable lines in conditions of incomplete and uncertain information is considered. The existing methods of such choice are considered: method of economic current density and economic intervals’ method. In the work the correction of the economic intervals' method is offered under market conditions of costs. As example, 110 kV cable lines with copper vein are selected. Economic nomograms with different standard cross section are calculated and constructed. The choice of cross- sections by economic considerations is actual and for modern market conditions of economy. The graphics using MathCAD software are offered.