The explanation and method of calculation of motor slip and functions connected with it are introduced in this report. These functions are providing consumption of high and maximal electric energy by low-power asynchronous engine including asynchronous engine with squirrel-cage rotor. T equivalent circuit of asynchronous engine is used for investigation. Using electric T equivalent circuit of asynchronous engine implies that changing equivalent impedances, such as inductive reactance and active resistance, have dependence from motor slip (gliding). It promotes a problem of researching of the dependence difference and ratio of this impedance from motor slip when steady operation mode is used. This problem has solution by analytic and calculation methods and allows to define the parameters, such as cos j, useful capacity, input current, in a narrow interval of gliding during the operation mode. The expression for calculating extreme gliding which limits the area with high and maximal coefficient of using electric energy is shown. Study of dependence of actions of difference and ratio parts of equivalent impedances from gliding shows the existing of two glides. The least of them provides a higher coefficient of using electric energy. With increasing of gliding the aforementioned coefficient reaches its maximal value. The solution results confirm correctness of the chosen method.