In distribution network low voltage nominal is defined by consumer but medium voltage nominal can be selected at discretion which is different in various countries. If the costs of network is not sensitive to medium voltage nominal, then, obviously, the lower the voltage the better. The studied model showed that costs abruptly diminish with load density and/or sizes of fed zones growing (up to certain limit), cost and voltage losses are little sensitive to voltage nominal at uniform load density, cost only slightly growing with medium voltage. While at non -uniform load density (when thick load alternates with sparsely populated area) the network costs are critical to medium voltage due to voltage loss, the latter strongly diminishing with medium voltage growing, making it possible to increase medium voltage fed zone. MI the above is dominated by equipment prices and other economic indices.