The insulation resistance value has been measured, but how much is considered "qualified"? This is the issue that many users are most concerned about during actual testing.
The qualification of insulation resistance is not a fixed value, but depends on the type of equipment, voltage level, age of the equipment and on-site environmental requirements. This article takes the ETCR3500 series high-voltage insulation resistance tester as an example, based on GB 50150, DL/T 596 and other standards, to sort out the qualified reference values of insulation resistance of common electrical equipment to help you quickly judge whether the test results are qualified.
Insulation resistance qualification standards for different equipment
Insulation resistance "pass" is not a fixed value, but depends on the type of equipment, voltage level and site requirements. The following are common reference standards (based on GB 50150, DL/T 596, etc.):
Equipment Type | Test Voltage | Insulation Resistance Qualification Requirements (Reference Standard) | Source Basis |
Low-voltage Lines, Distribution Boxes | 500V | ≥0.5MΩ (damp locations); ≥1MΩ (general locations) | GB 50150 |
10kV Power Cables (Main Insulation) | 2.5kV or 5kV | No unified absolute qualification value. Empirical standard: ≥1000MΩ per kilometer for new cables; ≥400MΩ per kilometer at 20℃ for in-service cables can be used as the minimum qualification line | DL/T 596 |
6kV High-voltage Motors | 2.5kV | Not less than 6MΩ (calculated as 1MΩ/kV) | Industry General Standard / DL/T 596 |
10kV High-voltage Motors | 2.5kV or 5kV | Not less than 10MΩ (calculated as 1MΩ/kV) | Industry General Standard / DL/T 596 |
Oil-immersed Transformers (10kV Side) | 2.5kV | Insulation resistance value shall not be less than 70% of the product factory test value; Dielectric Absorption Ratio ≥1.3 (applicable when capacity ≥4000kVA) | GB 50150 |
Transformers (110kV and above) | 5kV or 10kV | Insulation resistance value shall not be less than 70% of the factory test value; Dielectric Absorption Ratio ≥1.3; Polarization Index ≥1.5 | GB 50150 / DL/T 596 |
Zinc Oxide Surge Arresters (35kV and below) | 2.5kV | Insulation resistance ≥1000MΩ | GB 50150 |
Zinc Oxide Surge Arresters (above 35kV) | 5kV | Insulation resistance ≥2500MΩ | GB 50150 / DL/T 596
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Special instructions:
The above values are based on experience. Different industries and regions may have more stringent requirements.
For large-capacity equipment such as transformers and cables, single insulation resistance (IR) is not the only criterion, and Dielectric Absorption Ratio (DAR) and Polarization Index (PI) must also be considered.
Differences between old and new equipment: For new equipment or equipment that has just been repaired, the insulation resistance should be close to the factory value; for equipment that has been running for many years, a certain drop is allowed, but if it suddenly drops significantly, you should be vigilant.
Iridium Electric specializes in the R&D and production of high-voltage insulation resistance testers, including the EM3500, EM3520, 5 kV high-voltage insulation resistance testers, EM3500B, EM3520B, 10 kV high-voltage insulation resistance testers, EM3520C, 15 kV high-voltage insulation resistance testers, and the EM3580 online insulation resistance tester.
ETCRMETER is a high-end brand of ETCR. All products are manufactured by ETCR, which also provides technical support and after-sales service.
For more information, please visit the Yidian Measurement & Control official website: www.etcrmeter.com
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