A plan shall be kept at the mine showing the location of all stationary electrical apparatus in connection with the mine electrical system, including permanent cables, conductors, circuit breakers, switches and trolley lines. The plan shall be of sufficient size to show clearly the position of such apparatus, and the scale shall not be less than five hundred feet per inch. There shall be stated on the plan the capacity in horsepower of each motor, and in kilowatts of each generator, rectifier, and K.V.A. of each transformer, and the nature of its duty. Such plans shall be corrected as often as may be necessary to keep them up-to-date, or at intervals not exceeding six months.