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What’s new in the IEEE 43 insulation resistance testing standard?

Publication date: 
April 2016
Tom Bishop, P.E., EASA Senior Technical Support Specialist
Type of media: 

The Institute of Electrical and Electronics Engineers (IEEE) standard for insulation resistance testing of motor and generator windings that was published in 2002 has been revised. The 2013 edition was published in March 2014. 

The first change in the new document is a slight change in the title. It has changed from “IEEE Recommended Practice for Testing Insulation Resistance of Rotating Machinery” to “Recommended Practice for Testing Insulation Resistance of Electric Machinery.” The reason for the change was to use the more prevalent IEEE term for motors and generators. Significant changes to clauses of the standard that affect service center repairs and testing are described in this article.

Other significant changes include:

  • A major change in clause 5.4, titled “Polarization index readings,” affects random winding tests.
  • Clause 6.3 of this new edition provides two temperature correction factors, one of which has two distinct formulas for the correction. Windings are now differentiated as being either “thermoplastic” or “thermosetting.”
  • Clause 12.3, table labeled “Recommended minimum insulation resistance values at 40° C (all values in MΩ)”: Minimum insulation resistance for armatures has changed from 100 megohms to 5 megohms.
Winding insulation
Field coils
Motor testing