What instrument is used to determine insulation resistance in windings?

• A. Megohmmeter
• B. Multimeter
• C. Ohmmeter
• D. Clamp meter

Answer: (A)

Insulation resistance testing examines how well the winding insulation resists leakage when a high DC voltage is applied. To measure this accurately, you need an instrument that can push a substantial voltage through the winding and detect the very small leakage current, so you can determine the resistance in the megohm range. That instrument is the megohmmeter. It is designed to apply high test voltages and measure tiny currents, providing a direct readout of insulation health for windings, motors, transformers, and cables.

A standard multimeter isn’t suitable for this job because its insulation resistance range is limited and it isn’t built to deliver the high voltages or to read the tiny leakage currents involved in insulation tests. An ohmmeter focuses on low resistance to check continuity, not the high-resistance insulation scenario. A clamp meter measures current without breaking the circuit and doesn’t measure insulation resistance at all.