What is the purpose of insulation resistance testing in electrical equipment and how is it performed?

• A. To detect insulation faults; use a megohmmeter to measure resistance between conductors and earth, ensuring readings meet standards.
• B. To measure conductor cross-section.
• C. To test insulation color coding.
• D. To verify continuity of a circuit.

Answer: (A)

Insulation resistance testing is about checking how well the insulation of electrical equipment prevents leakage current. By applying a high DC voltage with a megohmmeter and measuring the resistance from conductors to earth (and sometimes between conductors), you can detect insulation faults. A healthy insulation path shows a very high resistance, while degraded or damaged insulation allows leakage, lowering the insulation resistance.

To perform it, first ensure the equipment is de-energized and safe to work on, discharge any capacitors, and then connect the megohmmeter leads between the conductors (or between a conductor and earth) as specified. Apply the appropriate test voltage for a set duration, and read the insulation resistance in megohms. Compare the result to the standards or manufacturer guidance; if the reading is too low, there may be moisture, contamination, or damaged insulation that needs repair or replacement, followed by a retest.

This is why the option describing insulation resistance testing with a megohmmeter is the best choice: it directly assesses insulation health by measuring resistance, which is the practical way to detect faults that could lead to leakage, shocks, or fires. The other options don’t relate to insulation health — measuring conductor cross-section relates to current-carrying capacity, color coding is about identification, and continuity testing checks for an uninterrupted electrical path, not insulation integrity.