In our days users have problems, that short circuit or even in cases of burning out of filament of incandescence in the electric wiring, that is frequent cases, disconnected not only nearest to the place of short circuit circuit-breaker of the lower (IN) stage but also simultaneously with him circuit-breaker of introduction Besides, proper the standards of IEC / EN 60898 “Electrical accessories - Circuit-breakers for over current protection for household and similar installations”, the circuit-breakers of different descriptions and groups, at the not concerted setting in the networks of low tension of users, create the problems of safety the electric wiring, by reason of insufficient selectivity. In the work are represented the limited volume results of low voltage selectivity verifications, compared various manufacturer, group and nominal currents of low voltage circuit-breakers, as also are given practical advices for circuit-breakers selectivity improvement.