Electrical Testing Reference

Insulation resistance test

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The insulation resistance test is a direct-voltage measurement in which a steady voltage is applied across electrical insulation and the ratio of that voltage to the current it drives is reported as a resistance. [1] The result is normally expressed in megohms, and the reading taken once the voltage has been applied for 1 min serves as the reference value. [2] [3] IEEE 43-2013 describes the method for the windings of rotating machines, while ANSI/NETA ATS-2025 and ANSI/NETA MTS-2023 call for the test on many classes of power equipment at acceptance and in maintenance. [4] [5] [6] [7]

Definition

In IEEE 43-2013, insulation resistance is the quotient of the direct voltage applied across an insulation system and the current that flows through it, read at a stated time after the voltage is applied. [1] Since the ohm is the volt per ampere, the quantity is a resistance in the ordinary SI sense; the large values typical of sound insulation are expressed in megohms, one megohm being 1,000,000 Ω. [8] [9] [2]

The underlying idea of insulation also appears in federal workplace safety rules: 29 CFR 1910.399 describes a conductor as insulated when a dielectric, which may include an air space, separates it from other conducting surfaces and offers a high resistance to current. [10]

Purpose

IEEE 43-2013 states its aims as defining the insulation resistance and polarization index tests, identifying the influences that alter the readings, recommending uniform test conditions and providing a basis for interpretation. [11] Its scope is the armature and field windings of rotating machines, among them synchronous and induction machines, direct-current machines and synchronous condensers; fractional-horsepower machines are excluded. [5]

The test screens the condition of insulation. A steep drop in resistance between successive tests on the same equipment points to contamination, moisture taken up by the insulation, or cracking, and such comparisons are made between tests run under similar conditions. [12] [13] The method has stated limits: insulation resistance is not a measure of dielectric strength, and a test made with a machine at rest may not reveal internal voids or looseness that shows itself only in rotation. [14]

Principle

The test rests on the relation between voltage, current and resistance captured by the ohm, the SI unit equal to one volt per ampere. [8] IEEE 43-2013 describes a constant direct voltage, normally applied with the winding at negative polarity. [15] The current that flows is small, below a microampere in insulation of very high resistance, and it is not steady: part of it, the absorption current, dies away while the voltage is held, so the apparent resistance depends on when the reading is taken. [16] [17] [3]

The measured value depends on the state of the insulation and on the conditions of the test. Winding temperature has a strong effect, so readings taken at different temperatures are referred to one reference temperature by the method in clause 6.3 of IEEE 43-2013. [18] Moisture matters as well: a winding at or below the dew point can carry a surface film that lowers the reading, and contaminated surfaces or moisture-absorbing materials lower it further, while cleaning and drying can raise it again. [19] [20] For dry insulation in good condition the resistance changes little as the test voltage is raised, so a pronounced fall with increasing voltage is read as a sign of a defect. [21]

General procedure

The test is made on deenergized equipment. Under the general industry rules of 29 CFR 1910.333(a)(1), exposed live parts are deenergized before work on or near them unless deenergizing is shown to add hazards or to be infeasible, and 29 CFR 1910.333(b)(2)(iv)(B) has a qualified person confirm the deenergized condition with test equipment. [22] [23]

Before the measurement, IEEE 43-2013 has the winding discharged and has external equipment such as cables, surge arresters, capacitors and voltage transformers disconnected and grounded, with any item left connected noted in the record. [24] [25] Where the construction permits, each phase is tested on its own with the remaining phases grounded to the core; a test of all phases together examines only the insulation between the winding and ground. [26]

The rated voltage of the winding governs the choice of test voltage, as clause 5.3 of IEEE 43-2013 sets out, and it is raised to its full value quickly and then held constant for the duration of the measurement. [27] [28] Each test record notes the winding temperature, the temperature, humidity and dew point of the surrounding air, the time the machine has spent out of service, the applied voltage and the connections used. [29] After the measurement the winding is grounded through a current-limiting resistor for a period that the recommended practice relates to the duration of the voltage application. [24]

Evaluation

Results are judged in two ways. The first compares a reading with recommended minimums: clause 12.3 of IEEE 43-2013 recommends minimum one-minute values for machine windings that vary with the type and construction of the winding and apply to the whole winding after temperature correction. [30] The second follows the readings over the life of the equipment, a comparison that is meaningful only when the tests are made at similar temperature, voltage, duration and humidity. [13]

For acceptance testing, ANSI/NETA ATS-2025 places its insulation resistance test values in tables: Table 100.1 for electrical apparatus and systems other than rotating machinery, Table 100.5 for transformers and Table 100.11 for rotating machinery. [31] [32] [33] Its Table 100.14 supplies conversion factors for referring readings to a standard temperature, and ANSI/NETA MTS-2023 carries corresponding tables for maintenance testing. [34] [35] The numerical criteria are set out in the cited clauses and tables. [30] [31]

Acceptance and maintenance testing

ANSI/NETA ATS-2025 specifies the test at acceptance across many classes of equipment; for liquid-filled transformers, for example, it appears at clause 7.2.2.B.2. [36] ANSI/NETA MTS-2023 specifies it in maintenance testing, for the same class at clause 7.2.2.B.2 and for oil and vacuum automatic circuit reclosers at clause 7.24.1.B.2. [37] [38]

Other documents that address the test include IEEE C57.13.1-2017, a guide to field testing of relaying current transformers, IEEE/IEC C57.15-2017 for step-voltage regulators and IEEE C57.18.10-2021 for transformers that serve semiconductor rectifier loads. [39] [40] [41] [42] [43] [44]

Notes

  1. IEEE 43-2013, clause 9.2. IEEE 43-2013 treats insulation resistance as the quotient of a direct voltage applied across the insulation and the current that the voltage drives through it, read at a stated time after the voltage is applied. Datum tests.insulation-resistance.definition
  2. IEEE 43-2013, clause 9.2. IEEE 43-2013 expresses insulation resistance in megohms. Datum tests.insulation-resistance.megohm-unit
  3. 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
  4. IEEE 43-2013, clause 11.2. Insulation Resistance is addressed in IEEE 43-2013. Datum tests.insulation-resistance.governed-by.ieee-43(provenance pending)
  5. IEEE 43-2013, clause 1.1. IEEE 43-2013 covers the armature and field windings of rotating machines, among them synchronous machines, induction machines, direct-current machines and synchronous condensers, and leaves fractional-horsepower machines out of its scope. Datum tests.insulation-resistance.scope-machines
  6. ANSI/NETA ATS-2025, clause 7.22.3.B.2. Insulation Resistance is addressed in ANSI/NETA ATS-2025. Datum tests.insulation-resistance.governed-by.ansi-neta-ats(provenance pending)
  7. ANSI/NETA MTS-2023, clause 7.22.3.B.2. Insulation Resistance is addressed in ANSI/NETA MTS-2023. Datum tests.insulation-resistance.governed-by.ansi-neta-mts(provenance pending)
  8. NIST SP 811, web page updated 2025-08-18 edition, clause Table 3. In the NIST Guide to the SI, the ohm, symbol Ω, is the SI coherent derived unit of electric resistance and is expressed in other SI units as the volt per ampere.Value: V/A. Datum qty.ohm.definition
  9. NIST SP 811, web page updated 2025-08-18 edition, clause Table 5. Applying the SI prefix mega, symbol M, which denotes the factor one million, to the ohm gives the megohm, equal to one million ohms.Value: 1,000,000 Ω. Datum qty.ohm.megohm
  10. 29 CFR 1910.399, current edition, clause 1910.399. 29 CFR 1910.399 defines insulated as separated from other conducting surfaces by a dielectric, including an air space, that offers a high resistance to the passage of current. Datum tests.insulation-resistance.osha-insulated
  11. IEEE 43-2013, clause 1.2. IEEE 43-2013 states that it sets out to define the insulation resistance and polarization index tests, identify the factors that change the readings, recommend uniform test conditions and give a basis for interpreting the results. Datum tests.insulation-resistance.purpose-ieee43
  12. IEEE 43-2013, clause 11.1. IEEE 43-2013 reads a sharp fall in insulation resistance between successive tests as a sign of contamination, absorbed moisture or cracked insulation. Datum tests.insulation-resistance.trend-indicators
  13. IEEE 43-2013, clause 11.1. IEEE 43-2013 compares readings over time only when the tests were made at similar winding temperature, test voltage, duration and humidity, with the readings brought to a common temperature. Datum tests.insulation-resistance.trending-conditions
  14. IEEE 43-2013, clause 11.3. IEEE 43-2013 notes that insulation resistance does not measure dielectric strength and that a test at standstill can miss internal voids and looseness that only rotation reveals. Datum tests.insulation-resistance.limitations
  15. IEEE 43-2013, clause 5.3. IEEE 43-2013 describes the test as normally made at a constant direct voltage of negative polarity, a choice it links to the electroendosmosis effect. Datum tests.insulation-resistance.constant-dc
  16. IEEE 43-2013, clause 12.2.2. IEEE 43-2013 notes that in insulation with a very high resistance the measured current is below a microampere. Datum tests.insulation-resistance.small-current
  17. IEEE 43-2013, clause 5.4. IEEE 43-2013 links the usefulness of the polarization index to the absorption current, the part of the measured current that dies away while the voltage is held, so the index loses its meaning where that current disappears within seconds. Datum tests.polarization-index-and-dielectric-absorption.absorption-current
  18. IEEE 43-2013, clause 6.3. Insulation resistance varies strongly with winding temperature, and IEEE 43-2013 gives a method for referring readings taken at different temperatures to one reference temperature. Datum tests.insulation-resistance.temperature
  19. IEEE 43-2013, clause 6.2, 6.3.1. IEEE 43-2013 notes that when a winding is at or below the dew point a film of moisture can form on it and lower both the insulation resistance and the polarization index. Datum tests.insulation-resistance.dew-point
  20. IEEE 43-2013, clause 6.1, 6.2, 11.2. Surface contamination, and insulating materials that take up moisture, lower the insulation resistance, and IEEE 43-2013 notes that cleaning and drying can bring it back up. Datum tests.insulation-resistance.surface-moisture
  21. IEEE 43-2013, clause 6.4. IEEE 43-2013 observes that dry insulation in good condition shows nearly the same insulation resistance as the test voltage is raised, while a marked fall with rising voltage points to a defect. Datum tests.insulation-resistance.voltage-dependence
  22. 29 CFR 1910.333, current edition, clause 1910.333(a)(1). Under 29 CFR 1910.333(a)(1), live parts to which an employee may be exposed are to be deenergized before the employee works on or near them, unless the employer shows that deenergizing creates added hazards or is infeasible. Datum tests.insulation-resistance.osha-deenergize
  23. 29 CFR 1910.333, current edition, clause 1910.333(b)(2)(iv)(B). Under 29 CFR 1910.333(b)(2)(iv)(B), a qualified person uses test equipment to verify that the circuit elements and electrical parts to be worked on are deenergized before they are treated as such. Datum tests.insulation-resistance.osha-verify
  24. IEEE 43-2013, clause 4, 5.5. IEEE 43-2013 calls for the winding to be discharged before the test and, afterward, grounded through a current-limiting resistor for a period that it relates to how long the voltage was applied. Datum tests.insulation-resistance.discharge-practice
  25. IEEE 43-2013, clause 8. IEEE 43-2013 has cables, surge arresters, capacitors, voltage transformers and similar external equipment disconnected from the winding and grounded before the test, with any item left connected noted in the record. Datum tests.insulation-resistance.external-equipment
  26. IEEE 43-2013, clause 8. Where the winding allows it, IEEE 43-2013 favors testing each phase on its own with the other phases grounded to the core, and notes that a test of all phases together examines only the insulation to ground. Datum tests.insulation-resistance.phase-connection
  27. IEEE 43-2013, clause 5.3, Table 1. IEEE 43-2013 ties the recommended direct test voltage to the rated voltage of the winding being tested. Datum tests.insulation-resistance.test-voltage-selection
  28. IEEE 43-2013, clause 10. IEEE 43-2013 brings the test voltage to its full value as quickly as practical and keeps it constant for the whole measurement. Datum tests.insulation-resistance.voltage-application
  29. IEEE 43-2013, clause 7. IEEE 43-2013 lists what is recorded with each test, among them the winding temperature, the temperature, humidity and dew point of the surrounding air, how long the machine has been out of service, the voltage applied and how the winding was connected. Datum tests.insulation-resistance.records
  30. IEEE 43-2013, clause 12.3, Table 4. Clause 12.3 of IEEE 43-2013 recommends minimum one-minute insulation resistance values that depend on the type and construction of the winding and apply to the whole winding after correction to the reference temperature. Datum tests.insulation-resistance.minimum-values-shape
  31. ANSI/NETA ATS-2025, clause Table 100.1. ANSI/NETA ATS-2025 Table 100.1 gives insulation resistance test values for electrical apparatus and systems other than rotating machinery. Datum tests.insulation-resistance.ats-table-general
  32. ANSI/NETA ATS-2025, clause Table 100.5. ANSI/NETA ATS-2025 Table 100.5 addresses transformer insulation resistance in acceptance testing. Datum tests.insulation-resistance.ats-table-transformer
  33. ANSI/NETA ATS-2025, clause Table 100.11. ANSI/NETA ATS-2025 Table 100.11 gives insulation resistance test values for rotating machinery, stated for a one-minute reading at a reference temperature. Datum tests.insulation-resistance.ats-table-rotating
  34. ANSI/NETA ATS-2025, clause Table 100.14. ANSI/NETA ATS-2025 Table 100.14 provides insulation resistance conversion factors for referring readings to a standard temperature. Datum tests.insulation-resistance.ats-conversion
  35. ANSI/NETA MTS-2023, clause Table 100.1, Table 100.5. ANSI/NETA MTS-2023 carries maintenance counterparts of the acceptance tables, including Table 100.1 for apparatus other than rotating machinery and Table 100.5 for transformer insulation resistance in maintenance testing. Datum tests.insulation-resistance.mts-tables
  36. ANSI/NETA ATS-2025, clause 7.2.2.B.2. Insulation Resistance is specified for liquid-filled transformers in acceptance testing at clause 7.2.2.B.2 of ANSI/NETA ATS-2025.Value: liquid-filled transformers. Datum tests.insulation-resistance.equipment.transformer-fluid.acceptance(provenance pending)
  37. ANSI/NETA MTS-2023, clause 7.2.2.B.2. Insulation Resistance is specified for liquid-filled transformers in maintenance testing at clause 7.2.2.B.2 of ANSI/NETA MTS-2023.Value: liquid-filled transformers. Datum tests.insulation-resistance.equipment.transformer-fluid.maintenance(provenance pending)
  38. ANSI/NETA MTS-2023, clause 7.24.1.B.2. Insulation Resistance is specified for oil and vacuum automatic circuit reclosers in maintenance testing at clause 7.24.1.B.2 of ANSI/NETA MTS-2023.Value: oil and vacuum automatic circuit reclosers. Datum tests.insulation-resistance.equipment.breaker.maintenance(provenance pending)
  39. IEEE C57.13.1-2017, clause 10. Insulation Resistance is addressed in IEEE C57.13.1-2017. Datum tests.insulation-resistance.governed-by.ieee-c57-13-1(provenance pending)
  40. IEEE C57.13.1-2017. The guide describes field test methods for confirming that relaying current transformers are wired correctly, carry their marked ratio and polarity, and remain able to perform as designed when new and after time in service. Datum std.ieee-c57-13-1.scope
  41. IEEE/IEC C57.15-2017, clause 9.7.7. Insulation Resistance is addressed in IEEE/IEC C57.15-2017. Datum tests.insulation-resistance.governed-by.ieee-c57-15(provenance pending)
  42. IEEE/IEC C57.15-2017. The standard covers electrical, mechanical and test requirements for liquid-immersed single-phase and three-phase step-voltage regulators for distribution and substation use, including their controls, within stated kVA and voltage ceilings. Datum std.ieee-c57-15.scope
  43. IEEE C57.18.10-2021, clause 7.8. Insulation Resistance is addressed in IEEE C57.18.10-2021. Datum tests.insulation-resistance.governed-by.ieee-c57-18-10(provenance pending)
  44. IEEE C57.18.10-2021. The standard covers practices and requirements for single-phase and three-phase transformers serving dedicated semiconductor rectifier loads at or above the minimum rating stated in the datum value, including service conditions and routine tests.Value: 100 kW. Datum std.ieee-c57-18-10.scope

Data records

  • ANSI/NETA ATS-2025 Table 100.14 provides insulation resistance conversion factors for referring readings to a standard temperature. Source: ANSI/NETA ATS-2025, clause Table 100.14. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.ats-conversion
  • ANSI/NETA ATS-2025 Table 100.1 gives insulation resistance test values for electrical apparatus and systems other than rotating machinery. Source: ANSI/NETA ATS-2025, clause Table 100.1. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.ats-table-general
  • ANSI/NETA ATS-2025 Table 100.11 gives insulation resistance test values for rotating machinery, stated for a one-minute reading at a reference temperature. Source: ANSI/NETA ATS-2025, clause Table 100.11. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.ats-table-rotating
  • ANSI/NETA ATS-2025 Table 100.5 addresses transformer insulation resistance in acceptance testing. Source: ANSI/NETA ATS-2025, clause Table 100.5. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.ats-table-transformer
  • IEEE 43-2013 describes the test as normally made at a constant direct voltage of negative polarity, a choice it links to the electroendosmosis effect. Source: IEEE 43-2013, clause 5.3. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.constant-dc
  • IEEE 43-2013 treats insulation resistance as the quotient of a direct voltage applied across the insulation and the current that the voltage drives through it, read at a stated time after the voltage is applied. Source: IEEE 43-2013, clause 9.2. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.definition
  • IEEE 43-2013 notes that when a winding is at or below the dew point a film of moisture can form on it and lower both the insulation resistance and the polarization index. Source: IEEE 43-2013, clause 6.2, 6.3.1. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.dew-point
  • IEEE 43-2013 calls for the winding to be discharged before the test and, afterward, grounded through a current-limiting resistor for a period that it relates to how long the voltage was applied. Source: IEEE 43-2013, clause 4, 5.5. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.discharge-practice
  • Insulation Resistance is specified for oil and vacuum automatic circuit reclosers in maintenance testing at clause 7.24.1.B.2 of ANSI/NETA MTS-2023. Value: oil and vacuum automatic circuit reclosers. Source: ANSI/NETA MTS-2023, clause 7.24.1.B.2. Verified 2026-10-13. Review status: Unreviewed. Provenance pending. Record tests.insulation-resistance.equipment.breaker.maintenance
  • Insulation Resistance is specified for liquid-filled transformers in acceptance testing at clause 7.2.2.B.2 of ANSI/NETA ATS-2025. Value: liquid-filled transformers. Source: ANSI/NETA ATS-2025, clause 7.2.2.B.2. Verified 2026-10-13. Review status: Unreviewed. Provenance pending. Record tests.insulation-resistance.equipment.transformer-fluid.acceptance
  • Insulation Resistance is specified for liquid-filled transformers in maintenance testing at clause 7.2.2.B.2 of ANSI/NETA MTS-2023. Value: liquid-filled transformers. Source: ANSI/NETA MTS-2023, clause 7.2.2.B.2. Verified 2026-10-13. Review status: Unreviewed. Provenance pending. Record tests.insulation-resistance.equipment.transformer-fluid.maintenance
  • IEEE 43-2013 has cables, surge arresters, capacitors, voltage transformers and similar external equipment disconnected from the winding and grounded before the test, with any item left connected noted in the record. Source: IEEE 43-2013, clause 8. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.external-equipment
  • Insulation Resistance is addressed in ANSI/NETA ATS-2025. Source: ANSI/NETA ATS-2025, clause 7.22.3.B.2. Verified 2026-10-13. Review status: Unreviewed. Provenance pending. Record tests.insulation-resistance.governed-by.ansi-neta-ats
  • Insulation Resistance is addressed in ANSI/NETA MTS-2023. Source: ANSI/NETA MTS-2023, clause 7.22.3.B.2. Verified 2026-10-13. Review status: Unreviewed. Provenance pending. Record tests.insulation-resistance.governed-by.ansi-neta-mts
  • Insulation Resistance is addressed in IEEE 43-2013. Source: IEEE 43-2013, clause 11.2. Verified 2026-10-13. Review status: Unreviewed. Provenance pending. Record tests.insulation-resistance.governed-by.ieee-43
  • Insulation Resistance is addressed in IEEE C57.13.1-2017. Source: IEEE C57.13.1-2017, clause 10. Verified 2026-10-13. Review status: Unreviewed. Provenance pending. Record tests.insulation-resistance.governed-by.ieee-c57-13-1
  • Insulation Resistance is addressed in IEEE/IEC C57.15-2017. Source: IEEE/IEC C57.15-2017, clause 9.7.7. Verified 2026-10-13. Review status: Unreviewed. Provenance pending. Record tests.insulation-resistance.governed-by.ieee-c57-15
  • Insulation Resistance is addressed in IEEE C57.18.10-2021. Source: IEEE C57.18.10-2021, clause 7.8. Verified 2026-10-13. Review status: Unreviewed. Provenance pending. Record tests.insulation-resistance.governed-by.ieee-c57-18-10
  • IEEE 43-2013 notes that insulation resistance does not measure dielectric strength and that a test at standstill can miss internal voids and looseness that only rotation reveals. Source: IEEE 43-2013, clause 11.3. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.limitations
  • IEEE 43-2013 expresses insulation resistance in megohms. Source: IEEE 43-2013, clause 9.2. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.megohm-unit
  • Clause 12.3 of IEEE 43-2013 recommends minimum one-minute insulation resistance values that depend on the type and construction of the winding and apply to the whole winding after correction to the reference temperature. Source: IEEE 43-2013, clause 12.3, Table 4. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.minimum-values-shape
  • ANSI/NETA MTS-2023 carries maintenance counterparts of the acceptance tables, including Table 100.1 for apparatus other than rotating machinery and Table 100.5 for transformer insulation resistance in maintenance testing. Source: ANSI/NETA MTS-2023, clause Table 100.1, Table 100.5. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.mts-tables
  • 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. Source: IEEE 43-2013, clause 5.3. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.one-minute-reading
  • Under 29 CFR 1910.333(a)(1), live parts to which an employee may be exposed are to be deenergized before the employee works on or near them, unless the employer shows that deenergizing creates added hazards or is infeasible. Source: 29 CFR 1910.333, current edition, clause 1910.333(a)(1). Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.osha-deenergize
  • 29 CFR 1910.399 defines insulated as separated from other conducting surfaces by a dielectric, including an air space, that offers a high resistance to the passage of current. Source: 29 CFR 1910.399, current edition, clause 1910.399. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.osha-insulated
  • Under 29 CFR 1910.333(b)(2)(iv)(B), a qualified person uses test equipment to verify that the circuit elements and electrical parts to be worked on are deenergized before they are treated as such. Source: 29 CFR 1910.333, current edition, clause 1910.333(b)(2)(iv)(B). Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.osha-verify
  • Where the winding allows it, IEEE 43-2013 favors testing each phase on its own with the other phases grounded to the core, and notes that a test of all phases together examines only the insulation to ground. Source: IEEE 43-2013, clause 8. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.phase-connection
  • IEEE 43-2013 states that it sets out to define the insulation resistance and polarization index tests, identify the factors that change the readings, recommend uniform test conditions and give a basis for interpreting the results. Source: IEEE 43-2013, clause 1.2. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.purpose-ieee43
  • IEEE 43-2013 lists what is recorded with each test, among them the winding temperature, the temperature, humidity and dew point of the surrounding air, how long the machine has been out of service, the voltage applied and how the winding was connected. Source: IEEE 43-2013, clause 7. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.records
  • IEEE 43-2013 covers the armature and field windings of rotating machines, among them synchronous machines, induction machines, direct-current machines and synchronous condensers, and leaves fractional-horsepower machines out of its scope. Source: IEEE 43-2013, clause 1.1. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.scope-machines
  • IEEE 43-2013 notes that in insulation with a very high resistance the measured current is below a microampere. Source: IEEE 43-2013, clause 12.2.2. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.small-current
  • Surface contamination, and insulating materials that take up moisture, lower the insulation resistance, and IEEE 43-2013 notes that cleaning and drying can bring it back up. Source: IEEE 43-2013, clause 6.1, 6.2, 11.2. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.surface-moisture
  • Insulation resistance varies strongly with winding temperature, and IEEE 43-2013 gives a method for referring readings taken at different temperatures to one reference temperature. Source: IEEE 43-2013, clause 6.3. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.temperature
  • IEEE 43-2013 ties the recommended direct test voltage to the rated voltage of the winding being tested. Source: IEEE 43-2013, clause 5.3, Table 1. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.test-voltage-selection
  • The test method is named Insulation Resistance. Value: Insulation Resistance. Source: Electrical Testing Reference editorial taxonomy, 2026-10 edition. Verified 2026-10-13. Review status: Unreviewed. Provenance pending. Record tests.insulation-resistance.title
  • IEEE 43-2013 reads a sharp fall in insulation resistance between successive tests as a sign of contamination, absorbed moisture or cracked insulation. Source: IEEE 43-2013, clause 11.1. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.trend-indicators
  • IEEE 43-2013 compares readings over time only when the tests were made at similar winding temperature, test voltage, duration and humidity, with the readings brought to a common temperature. Source: IEEE 43-2013, clause 11.1. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.trending-conditions
  • IEEE 43-2013 brings the test voltage to its full value as quickly as practical and keeps it constant for the whole measurement. Source: IEEE 43-2013, clause 10. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.voltage-application
  • IEEE 43-2013 observes that dry insulation in good condition shows nearly the same insulation resistance as the test voltage is raised, while a marked fall with rising voltage points to a defect. Source: IEEE 43-2013, clause 6.4. Verified 2026-10-13. Review status: Agent reviewed. Record tests.insulation-resistance.voltage-dependence

Related entries

Sources

  • 29 CFR 1910.333, 1910.333 - Selection and use of work practices, current edition, OSHA. Cited: clause 1910.333(a)(1); clause 1910.333(b)(2)(iv)(B). Held as: Government work. Publisher page
  • 29 CFR 1910.399, 1910.399 - Definitions applicable to this subpart, current edition, OSHA. Cited: clause 1910.399. Held as: Government work. Publisher page
  • ANSI/NETA ATS-2025, Acceptance Testing Specifications for Electrical Power Equipment and Systems, 2025 edition, NETA. Cited: clause 7.22.3.B.2; clause Table 100.1; clause Table 100.5; clause Table 100.11; clause Table 100.14; clause 7.2.2.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 7.22.3.B.2; clause Table 100.1, Table 100.5; clause 7.2.2.B.2; clause 7.24.1.B.2. 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 9.2; clause 5.3; clause 11.2; clause 1.1; clause 1.2; clause 11.1; clause 11.3; clause 12.2.2; clause 5.4; clause 6.3; clause 6.2, 6.3.1; clause 6.1, 6.2, 11.2; clause 6.4; clause 4, 5.5; clause 8; clause 5.3, Table 1; clause 10; clause 7; clause 12.3, Table 4. Held as: Purchased single-user copy. Publisher page
  • IEEE C57.13.1-2017, Guide for Field Testing of Relaying Current Transformers, 2017 edition, IEEE. Cited: clause 10. Held as: Purchased single-user copy. Publisher page
  • IEEE C57.13.1-2017, IEEE Guide for Field Testing of Relaying Current Transformers, 2017 edition, IEEE. Held as: Public page. Publisher page
  • IEEE C57.18.10-2021, Semiconductor Power Rectifier Transformers, 2021 edition, IEEE. Cited: clause 7.8. Held as: Purchased single-user copy. Publisher page
  • IEEE C57.18.10-2021, IEEE Standard Practices and Requirements for Semiconductor Power Rectifier Transformers, 2021 edition, IEEE. Held as: Public page. Publisher page
  • IEEE/IEC C57.15-2017, Requirements, Terminology and Test Code for Step-Voltage Regulators, 2017 edition, IEEE. Cited: clause 9.7.7. Held as: Purchased single-user copy. Publisher page
  • IEEE/IEC C57.15-2017, IEEE/IEC International Standard: Power transformers, Part 21: Standard requirements, terminology, and test code for step-voltage regulators, 2017 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 5; clause Table 3. Held as: Government work. Publisher page

Obtaining the documents

Changelog (87 entries)
DateRevisionChangeReasonBy
2026-10-131created hand-written exemplar for the article generator (Task 10)agent
2026-10-13created (qty.ohm.definition)read from the government page (Task 10 exemplars)agent
2026-10-13reviewed (qty.ohm.definition)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (qty.ohm.megohm)read from the government page (Task 10 exemplars)agent
2026-10-13reviewed (qty.ohm.megohm)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (std.ieee-c57-13-1.scope)extracted from public pageagent
2026-10-13reviewed (std.ieee-c57-13-1.scope)fresh-context agent review, research-review.mdagent
2026-10-13created (std.ieee-c57-15.scope)extracted from public pageagent
2026-10-13reviewed (std.ieee-c57-15.scope)fresh-context agent review, research-review.mdagent
2026-10-13created (std.ieee-c57-18-10.scope)extracted from public pageagent
2026-10-13reviewed (std.ieee-c57-18-10.scope)fresh-context agent review, research-review.mdagent
2026-10-13edited (std.ieee-c57-18-10.scope)statement reworded; figure moved to value (prose rule 7)agent
2026-10-13created (tests.insulation-resistance.ats-conversion)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13provenance noted (tests.insulation-resistance.ats-conversion)locator from the NETA index table of contents (section and table numbers, titles and tables_referenced only); no body text usedagent
2026-10-13reviewed (tests.insulation-resistance.ats-conversion)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.ats-table-general)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13provenance noted (tests.insulation-resistance.ats-table-general)locator from the NETA index table of contents (section and table numbers, titles and tables_referenced only); no body text usedagent
2026-10-13reviewed (tests.insulation-resistance.ats-table-general)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.ats-table-rotating)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13provenance noted (tests.insulation-resistance.ats-table-rotating)locator from the NETA index table of contents (section and table numbers, titles and tables_referenced only); no body text usedagent
2026-10-13reviewed (tests.insulation-resistance.ats-table-rotating)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.ats-table-transformer)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13provenance noted (tests.insulation-resistance.ats-table-transformer)locator from the NETA index table of contents (section and table numbers, titles and tables_referenced only); no body text usedagent
2026-10-13reviewed (tests.insulation-resistance.ats-table-transformer)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.constant-dc)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.constant-dc)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.definition)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.definition)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.dew-point)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.dew-point)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.discharge-practice)corrects tests.insulation-resistance.discharge: IEEE 43-2013 is a recommended practice, so 'calls for' replaces 'requires' (review fix 10)agent
2026-10-13reviewed (tests.insulation-resistance.discharge-practice)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.equipment.breaker.maintenance)seeded from the test taxonomyagent
2026-10-13created (tests.insulation-resistance.equipment.transformer-fluid.acceptance)seeded from the test taxonomyagent
2026-10-13created (tests.insulation-resistance.equipment.transformer-fluid.maintenance)seeded from the test taxonomyagent
2026-10-13created (tests.insulation-resistance.external-equipment)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.external-equipment)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.governed-by.ansi-neta-ats)seeded from the test taxonomyagent
2026-10-13created (tests.insulation-resistance.governed-by.ansi-neta-mts)seeded from the test taxonomyagent
2026-10-13created (tests.insulation-resistance.governed-by.ieee-43)seeded from the test taxonomyagent
2026-10-13created (tests.insulation-resistance.governed-by.ieee-c57-13-1)seeded from the test taxonomyagent
2026-10-13created (tests.insulation-resistance.governed-by.ieee-c57-15)seeded from the test taxonomyagent
2026-10-13created (tests.insulation-resistance.governed-by.ieee-c57-18-10)seeded from the test taxonomyagent
2026-10-13created (tests.insulation-resistance.limitations)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.limitations)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.megohm-unit)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.megohm-unit)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.minimum-values-shape)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.minimum-values-shape)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.mts-tables)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13provenance noted (tests.insulation-resistance.mts-tables)locator from the NETA index table of contents (section and table numbers, titles and tables_referenced only); no body text usedagent
2026-10-13reviewed (tests.insulation-resistance.mts-tables)fresh-context review task-10-exemplars-review.md + fix round 1agent
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.insulation-resistance.osha-deenergize)read from the regulation page (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.osha-deenergize)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.osha-insulated)read from the regulation page (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.osha-insulated)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.osha-verify)read from the regulation page (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.osha-verify)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.phase-connection)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.phase-connection)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.purpose-ieee43)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.purpose-ieee43)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.records)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.records)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.scope-machines)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.scope-machines)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.small-current)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.small-current)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.surface-moisture)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.surface-moisture)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.temperature)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.temperature)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.test-voltage-selection)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.test-voltage-selection)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.title)seeded from the test taxonomyagent
2026-10-13created (tests.insulation-resistance.trend-indicators)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.trend-indicators)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.trending-conditions)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.trending-conditions)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.voltage-application)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.voltage-application)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.insulation-resistance.voltage-dependence)method fact restated from the licensed-copy digest (Task 10 exemplars)agent
2026-10-13reviewed (tests.insulation-resistance.voltage-dependence)fresh-context review task-10-exemplars-review.md + fix round 1agent
2026-10-13created (tests.polarization-index-and-dielectric-absorption.absorption-current)restated from the IEEE 43-2013 digest, which gives the clause (5.4) but not the full description of the current components (Task 10 fix round 1)agent
2026-10-13reviewed (tests.polarization-index-and-dielectric-absorption.absorption-current)fresh-context review task-10-exemplars-review.md + fix round 1agent

Cite this page

Cite the governing standard for the fact itself; cite this page as the finding aid.

Permanent revision URL: https://www.electricaltestingreference.com/tests/insulation-resistance/rev/1/. Current version: https://www.electricaltestingreference.com/tests/insulation-resistance/.

Plain

"Insulation resistance test." Electrical Testing Reference. Revision 1, 2026-10-13. https://www.electricaltestingreference.com/tests/insulation-resistance/rev/1/.

Legal (Bluebook, internet source)

Electrical Testing Reference, Insulation resistance test (rev. 1, Oct. 13, 2026), https://www.electricaltestingreference.com/tests/insulation-resistance/rev/1/.

BibTeX

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

Wikipedia

{{cite web |title=Insulation resistance test |website=Electrical Testing Reference |publisher=Electrical Testing Reference |url=https://www.electricaltestingreference.com/tests/insulation-resistance/rev/1/ |date=2026-10-13 |access-date= |version=1}}