The purpose of this recommended practice is to a) Define insulation resistance and polarization index testing of the winding of a rotating machine. b) Review the factors that affect or change insulation resistance characteristics. c) Recommend uniform test conditions. d) Recommend uniform methods for measuring insulation resistance with precautions to avoid erroneous results. e) Provide a basis for interpreting insulation resistance test results to estimate winding suitability for service or for an overvoltage test. In particular, this standard describes typical insulation problems detected by the insulation resistance test. f) Present recommended minimum acceptable insulation resistance values and polarization indices for various types of rotating machines.