Free Engineering Tool
Insulation testing
Motor Minimum Insulation Resistance Check
Pick the winding type and rated voltage, enter your reading and temperature, and see whether it clears the IEEE 43 recommended minimum.
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- Runs in your browser
- Your numbers never leave your device
Inputs
kV
MΩ
°C
Readout
MIN-MΩ at 40°C
Your reading at 40°CWhite line: minimum
The IEEE 43 minimums (at 40°C, 1 minute)
- Older windings, field windings, others: rated kV + 1 MΩ.
- Form-wound AC and DC armature windings built after about 1970: 100 MΩ.
- Random-wound stator coils, and form-wound coils rated below 1 kV: 5 MΩ.
Your reading is first corrected to 40°C with the halving rule (see the temperature correction calculator), then compared with the minimum.
Important
- This is a recommended minimum for an in-service machine, not a guarantee of health. A pass with a falling trend still deserves attention.
- Your plant or customer specification may set a higher limit. Always use the stricter one.
- The suggested test voltage shown is a general guide for the rated voltage. Check the machine's own instructions.
Related: how to test motor windings and the motor insulation testing schedule.
Report form: printable insulation resistance test report (PDF) with the minimums, PI and DAR built in.
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