Siemens SIMOTICS M-1PH3 Manual page 108

Commissioning
8.3 Checking the insulation resistance
Note the following:
• Dry, new windings have an insulation resistance of between 100 MΩ and 2000 MΩ
(sometimes higher).
If the insulation resistance is close to the minimum value, this could be due to humidity
and/or an accumulation of dirt.
• The insulation resistance of the motor winding can drop during the course of its service
life can drop due to ambient and operational influences. The critical insulation resistance
for a temperature of 25 °C on the winding can be calculated by multiplying the rated
voltage (kV) by the specific critical resistance value (0.5 MΩ/kV)
Example: Critical resistance for a rated voltage (V
0.6 kV × 0.5 MΩ/kV = 0.3 MΩ
Note
Cleaning and/or drying the windings when reaching critical insulation resistance
If the critical insulation resistance is less than or equal to this value, the windings must be
dried or, if the fan is removed, cleaned thoroughly and dried.
Note that the insulation resistance of dried, clean windings is lower than that of warm
windings. The insulation resistance can only be evaluated accurately when measured on a
winding that has been cooled down to room temperature (approximately 20 °C to 30 °C).
Note
Measured value close to critical value
If the measured value is close to the critical value, the insulation resistance should be
subsequently checked at suitably regular intervals.
Values apply for measurement at a winding temperature of 25 °C.
106
) of 0.6 kV
N
Equipment Manual, 01/2021, A5E43087278-004
1PH3 main motors