It is important that the ventilation system operates well. Ventilation screens and shrouds should remain clean and unobstructed. Dirt and grease should be kept off the motor to allow sufficient dissipation of heat into the surrounding air. Dust and dirt should be cleaned or blown from all motors periodically, as heavy accumulations of dust and debris cause overheating. Only low pressure, dry, oil free air should be used to blow out dirt.
Moisture is also a potential cause of insulation failure.
If moisture is suspected in the windings, such as in locations of high humidity, insulation resistance should always be checked before energizing the motor. Space heaters installed in the motor can help to prevent moisture buildup during non-operating hours. The same heating effect may also be achieved through applying low voltage to one phase of the motor while it is not operating. With this method, the correct voltage level varies, since the stator temperature must be maintained at a level above the dew point. And Furthermore . . .