Megger use and safety precautions - Solutions - Huaqiang Electronic Network

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When using a megohmmeter, it's important to be aware that some models have a scale that starts at 1 MΩ or 2 MΩ instead of zero. This can lead to inaccurate readings when measuring the insulation resistance of low-voltage electrical equipment in wet conditions, as the actual insulation resistance may be below 1 MΩ. Here are some key points to consider when using a megohmmeter:

  1. Place the megohmmeter on a flat and stable surface to avoid any shaking that might affect the reading. If the device is level-adjusted, make sure it is properly positioned before starting.
  2. Use dedicated measuring leads or high-insulation-strength single-core multi-strand flexible cables. Avoid using stranded insulated cords, as they may not provide accurate results.
  3. Before measurement, perform an open-circuit and short-circuit test. When the "L" and "E" terminals are open, the pointer should read "∞". When shorted, it should read "0".
  4. Ensure the equipment under test is disconnected from the power source. Never touch the device during the measurement process.
  5. Before measuring, fully discharge the equipment, especially capacitive devices like cables, motors, transformers, and capacitors. Failure to do so could result in electric shock.
  6. Connect the "E" terminal to the equipment’s casing or ground, and the "L" terminal to the conductor being tested. For cable measurements, connect the insulation to the "G" terminal. In wet conditions, use the shield terminal to reduce surface leakage current effects.
  7. Record the ambient temperature and humidity before testing, as these factors can influence the insulation resistance readings.
  8. Keep the megohmmeter away from areas with strong electromagnetic fields or large currents to ensure accurate results.
  9. Turn the handle clockwise at a steady speed of around 120 RPM. If the device has high capacitance, increase the speed slightly to prevent pointer oscillation.
  10. For capacitors, cables, large transformers, and motors, allow sufficient charging time. The longer the capacitance, the more time is needed. Typically, the reading after one minute is considered valid.
  11. After testing, discharge the equipment to eliminate any risk of electric shock.
  12. Do not measure double-circuit overhead lines or busbars if the induced voltage exceeds 12 V, or during lightning storms or when connected to overhead lines.
  13. Clean the surface of the device before testing to prevent leakage currents from affecting the results.
  14. Do not touch the measuring parts or the megohmmeter terminals until the device has fully discharged and the instrument has stopped rotating to avoid electric shock.

By following these guidelines, you can ensure safe and accurate measurements when using a megohmmeter. Always prioritize safety and proper procedure to protect both yourself and the equipment.

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