Computes the Polarization Index (PI = IR at 10 minutes รท IR at 1 minute) and assesses it against IEEE 43's published condition bands and recommended minimum PI by insulation class.
Standards followed
IEEE 43-2013 (recommended practice for testing insulation resistance of rotating machinery)
What it can do
- PI value from the two timed IR readings.
- Condition band: <1.0 dangerous, 1.0โ2.0 questionable, 2.0โ4.0 good, >4.0 excellent.
- Pass/fail against IEEE 43's recommended minimum PI (1.5 for Class A insulation, 2.0 for Class B/F/H).
Example problem
IR(1min) = 15 megohms, IR(10min) = 33 megohms, Class B/F/H insulation.
- PI = 33/15 = 2.2.
- Band: 2.0โ4.0 โ Good.
- Minimum recommended for Class B/F/H = 2.0 โ 2.2 โฅ 2.0, meets minimum.
PI 2.2 โ Good, meets IEEE 43's minimum recommendation.
Want the full step-by-step version?
PI is most meaningful when the winding is dry and clean; a low PI can also result from surface contamination rather than genuine insulation degradation.