Paper discusses the approach that supports the decision-making under need to provide total multi-line electrical energy supply under appointed maximum level. The data available from power meters allows to estimate the boarders of acceptable level for the external power supply and to predict its overshoot. It leads to rapid decision-making and allows to avoid the penalties on behalf of the power distribution utilities. Data approximation in the form of ellipsoid gives clear graphics and concise analytical description of the desired boarder. Introduced in the paper algorithm involves logarithmic functional transformation of the target criterion that allows to convert the meter data approximation via maximum volume ellipsoid problem to the convex nonlinear mathematical programming.