Which device is used to measure insulation resistance?

• A. Ohmmeter
• B. Magnetometer
• C. Megahertz meter
• D. Megger

Answer: (D)

Measuring insulation resistance hinges on seeing how well insulation resists leakage current when a high voltage is applied. The instrument designed for this is a megger, short for megohm meter. It applies a high DC voltage to the insulation and measures the tiny leakage current, converting it into a resistance value in megohms. A high megohm reading means the insulation is in good condition; a low reading signals possible deterioration, moisture, or contamination that could lead to leakage or faults.

The other tools aren’t suited for this purpose. An ohmmeter checks low-resistance continuity in a circuit, not the insulation’s resistance at high voltage. A magnetometer measures magnetic fields, not electrical insulation. A device described as a megahertz meter focuses on high-frequency RF signals, not insulation resistance.