During insulation resistance testing, which reading indicates healthy insulation?

• A. Reading should be more than 10 MΩ
• B. Reading should be more than 1 MΩ
• C. Reading should be more than 100 kΩ
• D. Reading should be less than 1 MΩ

Answer: (B)

When we perform insulation resistance testing, we’re measuring how well the insulation resists leakage current between conductors or to earth. The higher that insulation resistance value, the less leakage there is, and the healthier the insulation. A reading above 1 MΩ is typically considered acceptable for many low‑voltage installations, indicating good insulation. Values below this suggest increased leakage due to moisture, contamination, damage, or aging. So, a result of more than 1 MΩ is the indicator of healthy insulation. Readings well above that (for example, >10 MΩ) are also good, but the minimum benchmark most commonly used is 1 MΩ. A reading less than 1 MΩ points to potential insulation problems.