In an insulation megger test, what would a very low resistance reading indicate?

• A. Excellent insulation
• B. Normal operation
• C. Potential insulation failure or leakage
• D. The test was not performed correctly

Answer: (C)

In an insulation megger test, you apply a high DC voltage to the insulation and measure how much current leaks through it, which is shown as resistance. Good insulation resists leakage, so the reading should be very high—usually in the megohms range. A very low resistance reading means there’s a clear leakage path, which points to problems with the insulation such as moisture, contamination, damaged or degraded insulation, or a breakdown path. This indicates potential insulation failure or leakage.

It wouldn’t be interpreted as excellent insulation or normal operation because those conditions require high resistance. A poor test setup could cause odd results, but the most direct meaning of a low reading is that leakage is occurring and the insulation may be failing.