What is a megger and what is it used for?

• A. A device that measures magnetic fields.
• B. A device that generates high-frequency signals.
• C. An insulation resistance tester used to assess insulation quality between conductors.
• D. A device that calibrates avionics.

Answer: (C)

A megger is an insulation resistance tester. It applies a high DC voltage between conductors (or between a conductor and earth) and measures the leakage current to determine the insulation resistance, usually reported in megohms. The idea is that good insulation resists leakage, giving a high megohm reading, while deteriorated insulation—due to moisture, cracks, aging, or contamination—lets current leak and lowers the resistance. This test helps ensure electrical safety and reliability, and it’s commonly used on cables, motors, transformers, and other equipment to assess insulation quality.