Which instrument is used to check insulation resistance on cables?

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

Answer: (D)

Insulation resistance testing checks how well the insulation on a cable resists leakage by applying a high DC voltage and measuring the tiny leakage current; the resulting resistance (in megohms) tells you how healthy the insulation is. The instrument designed for this is a megger, which provides a controlled high voltage and measures the leakage current to give a clear insulation resistance reading. Other tools aren’t built for this purpose: a multimeter or an ohmmeter measures low resistance and continuity with low voltages, not the high-voltage leakage through insulation; a clamp meter measures current in a live conductor without opening the circuit, not insulation integrity. Using a megger helps reveal degraded insulation, moisture, or contamination that would reduce insulation resistance.