Insulation Resistance PI/DAR

Polarization index and dielectric absorption ratio.

Before you calculate

Polarization index and dielectric absorption ratio

Ratios of timed insulation-resistance readings from one test. There is no universal PASS; isolate and discharge the item safely.

Learn more — complete guide →

Step 1

Timed readings of one test

Enter only readings actually taken at these times, at the same applied DC voltage. A missing reading is never estimated.

Resistance unit

Reading at 30 s (MΩ)

Reading at 60 s = 1 min (MΩ)

Reading at 10 min (MΩ)

Advanced: DAR time basis and test voltage (optional)

DAR time basis

The item is a rotating machine (enables the IEEE 43 caution)

Applied DC test voltage (V)Used only for an indicative leakage current V/R at 1 minute.

Step 2

Results

PI = R10min / R1min4.00Calculated (dimensionless)

DAR (60 s / 30 s)1.67Calculated (dimensionless)

Insulation resistance at 1 min150.0 MΩ

No PASS or FAIL. What a PI or DAR value means depends on the equipment, its insulation system, the test voltage, temperature and humidity, and the procedure you follow. Trends of the raw readings over time are often worth as much as the ratio.

Safety: isolate the item, prove it dead, follow the equipment's test-voltage requirements and protect connected electronics. After a DC test the item can hold a dangerous stored charge: discharge it with the approved method and confirm the discharge. Qualified personnel only.

1. Polarization index

Ten-minute reading divided by the one-minute reading of the same test. The units cancel.

PI=\frac{R_{10\,min}}{R_{1\,min}}

PI=\frac{600}{150}=4

2. DAR (60 s / 30 s)

Sixty-second reading divided by the earlier reading; the time basis is part of the result.

DAR_{30}=\frac{R_{60\,s}}{R_{30\,s}}

DAR=\frac{150}{90}=1.667

Calculations use full precision internally; the displayed numbers are rounded for readability.