Which instrument is used to measure insulation resistance?

• A. Megohmmeter
• B. Multimeter
• C. Ohmmeter
• D. Ammeter

Answer: (A)

Measuring insulation resistance requires a tool that can apply a high DC voltage to the insulation and measure the resulting current to determine resistance. A megohmmeter is designed for this purpose; it injects a substantial test voltage and reads the insulation resistance in megohms. A high insulation-resistance value indicates good insulation, while a low value points to leakage paths from moisture, contamination, or damage. The other instruments aren’t meant for this test: an ohmmeter checks low, continuity-type resistance; a multimeter can measure voltage, current, or basic resistance but not high-range insulation resistance reliably; an ammeter measures current only.