If the electric motor has capacitors, they must be properly discharged. The insulation resistance needs to be measured by means of a mega-meter and when the motor rests, when it is cold and completely disconnected from the mains. It is indicated that each phase is rigorously isolated and tested separately, making possible a comparison between the insulation resistance in each phase. In order to test one of the phases, the other phases must be grounded. The test that evaluates all phases simultaneously checks only the insulation resistance against the earth, and the insulation resistance between the phases is not evaluated.
It is indicated that the insulation resistance of the motors is measured periodically so that the storage conditions can be evaluated from the electrical point of view mrosupply electric motors. Taking into account the drop in insulation resistance values, the storage conditions need to be analyzed, evaluated and corrected, when necessary. The insulation resistance measurement must be carried out in a safe environment. To avoid the risk of electric shock, it is extremely important to discharge the terminals immediately before and after each measurement.