To prolong the life of electrical systems and motors, regular insulation resistance testing is required. Over the years, after many cycles of operation, electric motors are exposed to environmental factors such as dirt, grease, temperature, stress, and vibration. These conditions can lead to insulation failure, resulting in loss of production or even fires.
An effective motor insulation resistance system has high resistance, usually (at an absolute minimum) greater than a few mega ohms (MΩ). A poor insulation system has lower insulation resistance. The optimal insulation resistance for an electric motor is often determined by the manufacturer’s specifications, the criticality of the application where the motor is used, and the environment where it is located.
It is practically impossible to determine rules for the actual minimum insulation resistance value of an electric motor because resistance varies according to method of construction, condition of insulation material used, rated voltage, size and type. A general rule-of-thumb is 10 Megohm or more. The insulation system of an electrical motor is said to be in good condition if:
Measured Insulation resistance is greater than or equal to 10MΩ
Typical Insulation Resistance Level for Electric Motors
There are no rules for determining the minimum insulation resistance value for a motor. Most data available are empirical. The ones listed below are from grundfos, a leading manufacturer of electrical motors:
