Maximum permitted Insulation Resistance values HV

There isn’t a single minimum IR for HV use the OEM limits and judge by temperature corrected readings and trend. As a rule of thumb, clean or dry new gear at 3.3 kV or 11 kV should be up in the GΩ range; readings down in the low hundreds of MΩ merit a closer look. For motors, follow IEEE 43 modern form wound: ≥100 MΩ at 40 C; random wound: kV + 1 MΩ). If OEM data is missing, the NETA tables are a practical guide.

There isn’t a single minimum IR for HV use the OEM limits and judge by temperature corrected readings and trend. As a rule of thumb, clean or dry new gear at 3.3 kV or 11 kV should be up in the GΩ range; readings down in the low hundreds of MΩ merit a closer look. For motors, follow IEEE 43 modern form wound: ≥100 MΩ at 40 C; random wound: kV + 1 MΩ). If OEM data is missing, the NETA tables are a practical guide.