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Insulation Resistance - IR Test

Insulation Resistance test (Megger Test)

Megger test or IR (insulation resistance) test is a strategy in which an insulation resistance meter is used to check the condition of the insulation of an electrical device. Invented in 1889, the IR tester gained its popularity in the 1920s, not much of improvements was done to the device other than the design and the accuracy of the readings.

Insulation Resistance

Insulation Resistance test checks a spot’s insulation by applying a DC voltage of either 250, 500, or 1000 volts for the LV equipment and 2,500 or 5,000 for HV equipment to show the insulation resistance value in kΩ, MΩ or GΩ. The measured value indicates the condition of the insulation or dielectric material between two conductive parts, in the megger test higher values shows that the insulation is in good condition. Theoretically, the insulation resistance value could be limitless, but practically no insulation is perfect, leakage currents through the dielectric will always assure that a resistance value is measured.

Insulation Resistance - IR Test

Why Megger Testing is Done? 

The quality of the insulation decreases with time and environment condition such as temperature, humidity, moisture and dust particles. It also gets affected negatively by the electrical and mechanical stress, that’s why it’s necessary to check the IR value of an equipment on a fixed regular interval to avoid any electrical shock.

IR test does not cause any damage to the insulation, making it a good option to check for any problems or issues. The range of the testing device is between 500 and 1,000 volts, which is relatively low. Because of the low voltage, some punctures in insulation becomes undetected. It gives a general information about the leakage current, and if the insulation areas have excessive dirt, moisture, deterioration or winding faults.

Benefits of Megger Testing

  • Proactive instrumentationCondition Analysis
  • Reduced Risk of Emergency installationFailure
  • Insured convenience
  • Prognosticative Repairs
  • Quality Management
  • Prognosticative instrumentation lifespan


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