Ya. P. Grinberg believes that calculations of the possible productivity of coal mining machines based on their energy characteristics and on the characteristics of the electric motor or on specific energy consumption are inadmissible in practice, because they do not take into account the variable nature of the load and frequent switching of the motor, and recommends calculating by the root-mean-square current of the motor and its characteristics. Despite the novelty and scientific and practical value of this recommendation, the author's conclusion cannot be agreed with for a number of reasons. ...