Electrical Testing Reference

Polarization index

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The polarization index is the ratio of two insulation resistance readings taken during one application of direct voltage, the later reading divided by the earlier. [1] In IEEE 43-2013 the two readings are taken 10 min and 1 min after the voltage is applied. [2] [3] [4]

Usage

The term appears in IEEE 43-2013, which covers the windings of rotating machines, and in ANSI/NETA ATS-2025 and ANSI/NETA MTS-2023. [5] [6] [7] As a ratio of two resistances the index is dimensionless and is stated without a unit. [8]

See also

Related entries include insulation resistance, the quantity from which the index is formed, and the dielectric absorption ratio, a variant based on shorter reading times. [9] [10]

Notes

  1. Electrical Testing Reference editorial taxonomy, 2026-10 edition. The polarization index is the ratio of two insulation resistance readings taken at two times after a direct voltage is applied, the later reading divided by the earlier one. Datum gloss.polarization-index.definition
  2. IEEE 43-2013, clause 5.4. IEEE 43-2013 defines the polarization index as the insulation resistance read after ten minutes of applied voltage divided by the insulation resistance read after one minute. Datum tests.polarization-index-and-dielectric-absorption.pi-definition
  3. IEEE 43-2013, clause 5.4. The later of the two readings that make up the polarization index under IEEE 43-2013 is taken ten minutes after the test voltage is applied.Value: 10 min. Datum tests.polarization-index-and-dielectric-absorption.ten-minute
  4. IEEE 43-2013, clause 5.3. Under IEEE 43-2013 the reference insulation resistance reading is the one taken when the test voltage has been applied for one minute.Value: 1 min. Datum tests.insulation-resistance.one-minute-reading
  5. IEEE 43-2013. The recommended practice describes direct-voltage procedures for measuring the insulation resistance and polarization index of stator and rotor windings and explains how to interpret the results. Datum std.ieee-43.scope
  6. ANSI/NETA ATS-2025, clause 7.20.3.2.B.2. Polarization Index and Dielectric Absorption is addressed in ANSI/NETA ATS-2025. Datum tests.polarization-index-and-dielectric-absorption.governed-by.ansi-neta-ats(provenance pending)
  7. ANSI/NETA MTS-2023, clause 7.20.3.2.B. Polarization Index and Dielectric Absorption is addressed in ANSI/NETA MTS-2023. Datum tests.polarization-index-and-dielectric-absorption.governed-by.ansi-neta-mts(provenance pending)
  8. NIST SP 811, web page updated 2025-08-18 edition, clause Table 3, note b. The NIST Guide to the SI notes that the symbol for the derived unit one is generally omitted when values of dimensionless quantities are stated. Datum qty.dissipation-factor.unit-one
  9. Electrical Testing Reference editorial taxonomy, 2026-10 edition. The dielectric absorption ratio is the ratio of two insulation resistance readings taken a short time apart early in a direct-voltage test, the later reading divided by the earlier one. Datum gloss.dielectric-absorption-ratio.definition
  10. IEEE 43-2013, clause Annex A. Annex A of IEEE 43-2013 describes variants of the polarization index built on shorter reading times and states that no agreed pass or fail criteria exist for them. Datum tests.polarization-index-and-dielectric-absorption.annex-variants

Data records

  • The polarization index is the ratio of two insulation resistance readings taken at two times after a direct voltage is applied, the later reading divided by the earlier one. Source: Electrical Testing Reference editorial taxonomy, 2026-10 edition. Verified 2026-10-13. Review status: Agent reviewed. Record gloss.polarization-index.definition

Related entries

Sources

  • ANSI/NETA ATS-2025, Acceptance Testing Specifications for Electrical Power Equipment and Systems, 2025 edition, NETA. Cited: clause 7.20.3.2.B.2. Held as: Purchased single-user copy. Publisher page
  • ANSI/NETA MTS-2023, Maintenance Testing Specifications for Electrical Power Equipment and Systems, 2023 edition, NETA. Cited: clause 7.20.3.2.B. Held as: Purchased single-user copy. Publisher page
  • Electrical Testing Reference editorial taxonomy, Electrical Testing Reference editorial taxonomy of test methods, 2026-10 edition, Electrical Testing Reference. Held as: Own observation.
  • IEEE 43-2013, Recommended Practice for Testing Insulation Resistance of Electric Machinery, 2013 edition, IEEE. Cited: clause 5.4; clause 5.3; clause Annex A. Held as: Purchased single-user copy. Publisher page
  • IEEE 43-2013, IEEE Recommended Practice for Testing Insulation Resistance of Electric Machinery, 2013 edition, IEEE. Held as: Public page. Publisher page
  • NIST SP 811, NIST Guide to the SI, Chapter 4: The Two Classes of SI Units and the SI Prefixes, web page updated 2025-08-18 edition, NIST. Cited: clause Table 3, note b. Held as: Government work. Publisher page

Obtaining the documents

Changelog (19 entries)
DateRevisionChangeReasonBy
2026-10-13created (gloss.dielectric-absorption-ratio.definition)editorial definition of general physics (Task 10 exemplars)agent
2026-10-13reviewed (gloss.dielectric-absorption-ratio.definition)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (gloss.polarization-index.definition)editorial definition of general physics (Task 10 exemplars)agent
2026-10-13reviewed (gloss.polarization-index.definition)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-131created hand-written exemplar for the article generator (Task 10)agent
2026-10-13created (qty.dissipation-factor.unit-one)read from the government page (Task 10 exemplars)agent
2026-10-13reviewed (qty.dissipation-factor.unit-one)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (std.ieee-43.scope)extracted from public pageagent
2026-10-13reviewed (std.ieee-43.scope)fresh-context agent review, research-review.mdagent
2026-10-13created (tests.insulation-resistance.one-minute-reading)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.one-minute-reading)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.polarization-index-and-dielectric-absorption.annex-variants)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.polarization-index-and-dielectric-absorption.annex-variants)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.polarization-index-and-dielectric-absorption.governed-by.ansi-neta-ats)seeded from the test taxonomyagent
2026-10-13created (tests.polarization-index-and-dielectric-absorption.governed-by.ansi-neta-mts)seeded from the test taxonomyagent
2026-10-13created (tests.polarization-index-and-dielectric-absorption.pi-definition)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.polarization-index-and-dielectric-absorption.pi-definition)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.polarization-index-and-dielectric-absorption.ten-minute)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.polarization-index-and-dielectric-absorption.ten-minute)fresh-context review task-10-exemplars-review.md + fix round 1agent

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Permanent revision URL: https://www.electricaltestingreference.com/glossary/polarization-index/rev/1/. Current version: https://www.electricaltestingreference.com/glossary/polarization-index/.

Plain

"Polarization index." Electrical Testing Reference. Revision 1, 2026-10-13. https://www.electricaltestingreference.com/glossary/polarization-index/rev/1/.

Legal (Bluebook, internet source)

Electrical Testing Reference, Polarization index (rev. 1, Oct. 13, 2026), https://www.electricaltestingreference.com/glossary/polarization-index/rev/1/.

BibTeX

@misc{etr-glossary-polarization-index-rev1,
  title = {Polarization index},
  howpublished = {\url{https://www.electricaltestingreference.com/glossary/polarization-index/rev/1/}},
  organization = {Electrical Testing Reference},
  publisher = {Electrical Testing Reference},
  year = {2026},
  note = {Revision 1; last substantive change 2026-10-13}
}

Wikipedia

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