A megohmmeter is typically used to measure insulation resistance.

• A. Resistance of a conductor
• B. Capacitance
• C. Insulation resistance
• D. Reactance

Answer: (C)

A megohmmeter is used to assess insulation resistance. It applies a high DC voltage to a piece of equipment or cable and measures the leakage current through the insulation, then calculates the resistance in megohms. A high insulation-resistance value means the insulation is good and resists leakage; a low value signals deterioration or contamination that could lead to faults or safety hazards. This is why the instrument is described as measuring insulation resistance.

This differs from measuring the resistance of a conductor, which uses a standard ohmmeter at low voltage to evaluate the metal path itself. It also isn’t used for capacitance, which is about how much charge a component can store per volt, or for reactance, which is the AC opposition that depends on frequency.