12.1 General

Though there is no unique method of commissioning induction motors for general industrial drives, it will be in the interest of the user to follow the relevant recommendations made in this as well as the foregoing sections. In any case, the recommendations of IS:900 previously mentioned, would also be found much helpful


12.2.1 Check that the frame is earthed by two separate connections made at two separate places, and the earthing is done as per IS:3043. Earth connections shall be checked for tightness and resistance. Check the continuity of the main and the looped earthed wires.

12.2.2 Check the insulation resistance of all windings by 500V megger. If the insulation resistance is less than that stated in section 2.1, dry out the windings as detailed in section 2.1.1. Megger also space heaters, if provided, separately. DO NOT megger other electrical fitments such as thermistors, etc., where provided.

12.2.3 Check that the connections are made strictly in accordance with the diagrams of connection provided for the motor and for the switchgear.

12.2.4 Before the motor is switched on ensure that the rotor can rotate freely without any obstruction or noise.

12.2.5 Check that the bearings are charged with grease of the correct grade and that it is not caked or contaminated. Over-greasing and under-greasing should both be avoided.

12.2.6 Check the mechanical operation of the control gear, including that of the protective devices. Check that the packing material used for preventing damage to critical components are removed.

12.2.7 Check the operation of the entire control circuit by simulation, without switching on the motor supply interlocks used to prevent unsafe operation shall be checked by a competent person by making a deliberate attempt to per form operations which the interlocks are designed to prevent.

12.2.8 Ensure that the motor and the load are not coupled initially.

12.2.9 Ensure that all the pre-commissioning checks are made on the driven machine according to the instructions given in its operating manual.


12.3.1 A transient kick start may be given to ascertain, the direction of rotation. If it is incorrect, stop the motor, and inter change the connections to any two phases in the starter. Re-start the motor, and examine carefully for any evidence of unusual sound, vibration, electrical or mechanical fault conditions and undue temperature rise of the bearings, even through EVERY motor is subjected to stage-by-stage inspection followed by rigorous electrical tests and final inspection. Run the motor in uncoupled condition and check the vibration level. Vibration measured on no load must be within 25 microns (peak to peak) or as accepted in the order. Then run the motor in uncoupled condition with half-coupling pulley mounted on the motor shaft extension and check the vibration level. This vibration shall also be within 25 microns (peak to peak) or as accepted in the order.

12.3.2 Couple the motor with the driven machine. Check that the driven machine is not loaded, start the motor, and examine carefully for any evidence to unusual sound, vibration, electrical or mechanical fault. If no abnormality is observed, run the motor for a few hours. Check the bearing and the body temperatures.

12.3.3 Load the driven machine as indicated in the manual for the driven machine. As far as possible increase the loading gradually. Allow the motor to run under full load conditions for few hours, provided there is not indication of fault any where. During this period, note the current drawn by the motor, the input power and the speed, and check that the current does not exceed the rated value as stated on the motor, and determine the cause. It could be that the voltage is lower than that specified or the motor may have been overload. The motor should not be restarted until the cause of this problem has been eliminated. Check the vibration level on load over that measured on no-load(in coupled direction) should not exceed the value given in the following table.

Allowable increase in vibration amplitude (peak to peak in mm) when the motor is coupled to the load and tested, over the vibration amplitude of motor tested in uncoupled condition.

Synchronour speed rev/min. Increase in vibration amplitude(peak to peak)In Microns


To obtain the required direction of rotation of the motor, whether horizontal or vertical and whether uni-directional or not select the proper phase sequence of supply to the motor.

12.5 REVERSAL OF ROTATION If the direction of rotation is found to be opposite to the direction required, effect reversal by interchanging ANY two of the three supply leads connected to the stator switch (breaker of starter). DO NOT interchange any leads either inside the motor or in its terminal box after the cable joining is completed.