Why is the megger DC voltage chosen to reveal weaknesses more clearly?

• A. To reveal moisture content
• B. To reveal weaknesses more clearly
• C. To trigger protective devices
• D. To increase insulation resistance measurement speed

Answer: (B)

Applying a high DC bias stresses the insulation so any leakage paths become apparent. A megger sends a steady direct current through the insulation, and any weak spots—such as moisture ingress, contamination, or microcracks—offer a conductive path. That causes more current to flow and lowers the measured insulation resistance, making faults visible under stress. The DC bias emphasizes resistive leakage rather than the capacitive/impedance behavior you’d see with alternating current, so weaknesses don’t get masked by reactive effects. It isn’t primarily about measuring moisture content, triggering protective devices, or speeding up the test; it’s about revealing actual leakage paths by holding the insulation under sustained voltage.