Polarization Ratio Calculator

Enter Test Data

Use one-minute and ten-minute insulation resistance values to estimate polarization behavior, compare against a target, and document the test outcome.

Equipment Type

Resistance Unit

Test Voltage (V)

Resistance at 1 Minute

Resistance at 10 Minutes

Resistance at 30 Seconds

Ambient Temperature (°C)

Reference Polarization Ratio

Inspection Notes

Example Data Table

These sample values show how the ratio changes with insulation response over time.

Equipment	1-Min Resistance	10-Min Resistance	PR	Condition
Motor A	120 MΩ	300 MΩ	2.50	Good
Transformer B	80 MΩ	100 MΩ	1.25	Fair
Cable C	65 MΩ	58 MΩ	0.89	Poor

Formula Used

Polarization Ratio = Resistance at 10 minutes ÷ Resistance at 1 minute

Resistance Increase = Resistance at 10 minutes − Resistance at 1 minute

Increase Percentage = ((Resistance at 10 minutes − Resistance at 1 minute) ÷ Resistance at 1 minute) × 100

The polarization ratio compares the insulation resistance measured after ten minutes with the value measured after one minute during a DC insulation test. Higher values usually show stronger absorption and polarization effects, while lower values can point to contamination, moisture, leakage, or insulation aging.

How to Use This Calculator

Select the equipment type and the resistance unit used in your test record.
Enter the measured resistance at one minute and ten minutes.
Add the optional thirty-second resistance to estimate DAR as a supporting metric.
Enter test voltage, temperature, and a reference ratio if you want a comparison check.
Submit the form to show the result section above the calculator.
Review the ratio, condition label, change values, and notes before exporting the result.

Frequently Asked Questions

1. What does polarization ratio measure?

It measures how insulation resistance changes between one minute and ten minutes during a DC test. The ratio helps indicate dryness, cleanliness, and polarization behavior.

2. Why is a higher ratio usually better?

A higher ratio often means resistance continues rising as polarization develops. That pattern usually suggests healthier insulation than a flat or falling response.

3. Can I compare results from different temperatures?

Direct comparison can be misleading because insulation resistance changes with temperature. Trend results only after using a consistent method or applying accepted temperature correction practices.

4. What if the ratio is below one?

A value below one means the ten-minute resistance is lower than the one-minute value. That can indicate moisture, contamination, surface leakage, or unstable testing conditions.

5. Is polarization ratio enough by itself?

No. It should be reviewed with equipment history, temperature, test voltage, cleaning condition, and other insulation tests for a stronger engineering judgment.

6. What is the difference between PR and DAR?

PR uses ten-minute and one-minute resistance values. DAR uses an earlier short-time reading, often sixty seconds divided by thirty seconds, to assess early absorption behavior.

7. Which equipment commonly uses this test?

It is commonly used for motors, generators, transformers, switchgear, and cable systems where insulation condition trending supports preventive maintenance programs.

8. When should I export the result?

Export after checking the entered values, units, and interpretation notes. Saved records are useful for maintenance reports, asset histories, and trend reviews.