Precautions when measuring megger insulation for megohmmeters - Solutions - Huaqiang Electronic Network

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Precautions for measuring electrical insulation using a megohmmeter:

1. Always place the megohmmeter on a flat and stable surface before use.

2. The standard speed for testing is 120 revolutions per minute (rpm). Maintain this speed during measurement for accurate results.

3. Perform a self-test: - Open circuit test: When the generator reaches 120 rpm, the pointer should point to “∞”. - Short circuit test: Slowly rotate the meter; the pointer should move to “0”.

4. The insulation resistance between motor windings, phase-to-phase, and phase-to-case should be at least 0.5 MΩ. For portable power tools, it should be ≥ 2 MΩ.

5. When measuring line insulation: - Phase-to-phase resistance should be ≥ 0.38 MΩ. - Phase-to-neutral (zero) resistance should be ≥ 0.22 MΩ.

6. For medium and small motors, a 500–1000 V megohmmeter is typically used.

7. If the phase resistance reads zero, it indicates a short circuit in that phase.

8. If the resistance is 0.1 or 0.2 MΩ, it suggests that the insulation performance has significantly deteriorated.

9. The higher the insulation resistance of electrical equipment, the better its safety and reliability.

10. Conclusion: If the insulation resistance of the motor or circuit is found to be degraded or shows signs of a short circuit, immediate repair is necessary. Do not use the equipment until it is properly fixed and tested safe.

Proper use of a megohmmeter ensures accurate assessment of electrical insulation, helping prevent potential failures and ensuring the safety of both personnel and equipment. Always follow manufacturer guidelines and safety protocols when performing these tests.