Which instrument is used to test insulation resistance in electrical equipment?

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

Answer: (C)

Measuring insulation resistance needs an instrument that can push a high voltage through insulation and read very large resistance values. A megohmmeter is built for this purpose: it applies a DC test voltage to the insulation and measures the leakage current to calculate the resistance in the megohm range. That high-range measurement is essential because good insulation should offer very high resistance, indicating minimal leakage.

Other tools aren’t suited for this job. A multimeter or ohmmeter is designed for low-resistance measurements and typical circuit-level checks, not for testing the high resistance of insulation under high voltage. A clamp meter looks at current by saturating around conductors and doesn’t measure insulation resistance at all. So they can’t reliably reveal the integrity of insulation like a megohmmeter can.

In practice, insulation resistance testing helps verify that insulation is still effective, free from moisture or contamination, and capable of preventing leakage under operating voltages. Readings in the megohm range suggest good insulation, while low readings point to deterioration that may require maintenance. Always follow proper safety procedures when performing these tests.