An insulation resistance test measures insulation quality and is performed when?

• A. Measures electrical wiring color codes.
• B. Measures track gauge.
• C. Measures fuel efficiency.
• D. Measures insulation quality to detect deterioration; performed during PM or when a fault is suspected.

Answer: (D)

Insulation resistance testing checks the quality of electrical insulation by measuring its resistance. When insulation is in good condition, resistance is very high; if insulation has deteriorated, moisture, contamination, or damage create leakage paths and resistance drops. This test is most useful during preventive maintenance or when a fault is suspected because it helps detect insulation problems before they lead to outages, shocks, or fires. It isn’t about color codes, track gauge, or fuel efficiency, which are unrelated to insulation quality. In practice, the test is performed with power off, using a megohmmeter to apply a voltage across the insulation and measure resistance, then comparing the reading to acceptable values to determine if action is needed.