Which test equipment can be used to test the condition of insulation in electrical apparatus?

• A. Multimeter
• B. Oscilloscope
• C. Voltage tester
• D. Megohmmeter

Answer: (D)

Testing insulation resistance is about seeing how well the insulating material holds up to leakage currents. The instrument designed for this is a megohmmeter, an insulation resistance tester. It applies a high DC voltage to the insulation and measures the leakage current, giving a resistance value in megohms. A high resistance means the insulation is in good shape; a low resistance indicates leakage paths due to moisture, cracks, aging, or damage.

Regular multimeters measure resistance at low voltages and aren’t meant to stress insulation to reveal leakage paths, so they can miss problems that only appear under higher voltage. An oscilloscope looks at signal waveforms, not the integrity of insulation. A voltage tester checks whether voltage is present, but it doesn’t assess insulation quality or leakage. So the megohmmeter is the appropriate tool for assessing insulation condition.