IEEE 43 is the standard behind a test procedure most electrical engineers perform without necessarily naming it: measuring insulation resistance (IR) and calculating the polarization index (PI) of a motor or generator winding. It matters most precisely at the moments a machine's condition is uncertain — after moisture exposure, after long storage, after a repair — because it defines how to run the test consistently enough that the result actually means something. This page explains where that test fits into SRT's own engineering practice, most directly in the flagship Handbook article on flood-damaged motor recovery.
IEEE 43 exists to make insulation resistance testing repeatable and comparable — the test voltage, duration, and interpretation approach it recommends mean that a reading taken today and a reading taken next week (or by a different engineer, with a different instrument) can be meaningfully compared. Without that consistency, an IR reading is just a number with no way to judge whether it's trending toward "acceptable" or away from it.
In SRT's practice, this standard's procedure is applied whenever a motor or generator's insulation condition needs to be judged rather than assumed: after flood or moisture exposure, before returning any machine to service following an extended shutdown, as part of routine condition-based maintenance, and as an acceptance test after a rewind or repair.
Reuses the Engineering Context component, extended with Typical Equipment and Industrial Applications.
Applicable Machine Types
Typical Equipment
Any winding-based electric machine is in scope, but in SRT's engagements this is applied most often to induction motors recovering from flood or fire exposure, and occasionally to generators and large transformers during periodic condition assessment.
Industrial Applications
Assessment begins with a baseline IR reading taken as-found, even when it's expected to be low — this is the reference point every later reading is judged against, not a result in itself.
Inspection includes verifying test equipment is appropriate for the machine's voltage class, confirming test leads and connections are sound, and recording ambient temperature — insulation resistance is temperature-sensitive, so a reading without a recorded temperature is missing part of its own context.
This is where IEEE 43's procedure matters most in SRT's work: repeated IR readings taken through a drying period, with the polarization index calculated at each stage, form the trend that the flagship Handbook article's entire recovery-level framework depends on. A single reading — even a "passing" one — is not treated as sufficient; the trend across the drying period is.
The signature feature of this page.
Ask how IEEE 43 applies to your specific motor situation.
SRT's own edit history of this reference page — not IEEE 43's own revision history.
| Rev | Date | Change |
|---|---|---|
| 0 | 2026-09-13 | First issue — Release 1 |
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