Which instrument is commonly used to test insulation integrity in electrical equipment?

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

Answer: (A)

Insulation integrity is determined by how much leakage current the insulation allows when a test voltage is applied. To gauge this, you measure insulation resistance, which requires applying a known, high DC voltage and seeing how much current leaks through the insulation. The megohmmeter is perfect for this task because it is purpose-built to apply a high DC test voltage and accurately measure the resulting leakage current to compute the resistance in megohms. This high-resistance, high-voltage test is essential to verify that the insulation will perform safely under operating conditions. Other instruments aren’t suited for this purpose: a multimeter handles basic voltage, current, and low-resistance measurements at typical operating levels; an oscilloscope shows waveform shapes, not insulation resistance; a clamp meter measures current without breaking the circuit and doesn’t provide insulation-resistance data. So, for testing insulation integrity, the megohmmeter is the appropriate tool.