If the measured insulation resistance of the motor is less than 1 MΩ / kV with a minimum of 1MΩ, when the machine is cold it is to be dried out before full voltage is applied to the terminals of the motors and the drying out is to be continued as long as the insulation resistance rises or until a sufficiently high value that is not less than 1 MΩ / kV with minimum of I MΩ at 75°C is reached.
While proceeding for point as above said, following factors are to be kept in mind which affect the insulation resistance measurement. They are,
a. Surface condition.
b. Moisture.
c. Temperature.
d. Magnitude of test voltage.
e. Duration of application of test voltage.
f. Residual charge in the winding.
g. Ageing of the insulation.
h. Mechanical stresses.
