What does insulation resistance testing measure, and what indicates good insulation?

What does insulation resistance testing measure, and what indicates good insulation?

• A. It measures resistance between conductors or to ground using a megohmmeter; a high resistance indicates good insulation.
• B. It measures voltage drop across insulation; high drop indicates good insulation.
• C. It measures capacitance of insulation; high capacitance indicates good insulation.
• D. It measures insulation thickness; greater thickness indicates good insulation.

Answer: (C)

Insulation resistance testing checks how well the insulation blocks current by measuring the leakage resistance between conductors or to ground with a megohmmeter. A high resistance value means little leakage current at the test voltage, which indicates good insulation. If the resistance is low, leakage paths exist due to moisture, contamination, or damage, signaling degraded insulation. This test isn’t about how much voltage drops across insulation, nor about the insulation’s capacitance or thickness—it specifically uses DC to assess the resistance to leakage, and high resistance is the sign of sound insulation.

Insulation resistance testing checks how well the insulation blocks current by measuring the leakage resistance between conductors or to ground with a megohmmeter. A high resistance value means little leakage current at the test voltage, which indicates good insulation. If the resistance is low, leakage paths exist due to moisture, contamination, or damage, signaling degraded insulation. This test isn’t about how much voltage drops across insulation, nor about the insulation’s capacitance or thickness—it specifically uses DC to assess the resistance to leakage, and high resistance is the sign of sound insulation.