Polarization Index (PI) and DAR Calculator

Formulas

PI = IR(10 min) / IR(1 min) · DAR = IR(60 s) / IR(30 s)

How to read the result

• PI: below 1.0 dangerous, 1.0 to 2.0 questionable, 2.0 to 4.0 good, above 4.0 excellent.
• DAR: below 1.0 poor, 1.0 to 1.25 questionable, 1.25 to 1.6 acceptable, above 1.6 excellent.

These are common guide bands, not a substitute for the limit in your machine's standard or maintenance spec. Trend the values over years: a falling PI matters more than a single reading.

When PI is not meaningful

If the 1-minute reading is already very high (IEEE 43 uses about 5,000 MΩ), the insulation is so good that the current is dominated by instrument leakage and PI can come out near 1.0 without any fault. Judge on the absolute value instead.

A 10-minute test needs a tester that holds its voltage steady that long, so it is done with a motor-driven or digital instrument, not a hand-cranked one. See PI vs DAR explained.

Report form: printable insulation resistance test report (PDF) with PI, DAR and IEEE 43 limits built in.