What instrument is used to test insulation resistance between heating cable conductors and metallic grounding?

• A. Megohmmeter
• B. Multimeter
• C. Ohmmeter
• D. Continuity tester

Answer: (A)

Insulation resistance testing relies on measuring how well the insulation between conductors and earth resists leakage. A megohmmeter is designed for this purpose because it can apply a high DC voltage and measure the resulting leakage current, giving a reading in the megaohm range. That high resistance indicates healthy insulation; a low megaohm (or kiloohm) reading signals leakage paths or insulation breakdown. When testing heating cables, you typically check between each conductor and metallic grounding to ensure there’s no unwanted current path to earth.

Other instruments aren’t suitable for this job. A multimeter can measure resistance, but its ranges are for low to moderate values and it uses low test voltage, which isn’t adequate to reveal insulation faults. An ohmmeter is intended for measuring small, known-resistance values in circuits or components, not for assessing insulation health. A continuity tester checks whether a circuit is open or closed and also uses low voltage, providing no meaningful insulation-resistance information.

Safety note: ensure the system is de-energized and any capacitors are discharged before performing insulation resistance testing.