What is insulation resistance testing and a common acceptance criterion?

What is insulation resistance testing and a common acceptance criterion?

• A. Megger insulation resistance test; high resistance indicates good insulation; common criterion: IR > 1 MΩ per kV of system voltage
• B. Continuity test with a multimeter; target IR > 100 Ω
• C. Capacitance test of insulation; target IR > 10 nF
• D. Voltage withstand test at rated voltage for 1 second; criterion IR > 0.1 MΩ

Answer: (A)

Insulation resistance testing measures how well electrical insulation resists leakage currents. A megohmmeter applies DC voltage across the insulation and measures the leakage current, giving an insulation resistance in megohms. A higher resistance means the insulation is preventing leakage effectively, which indicates better insulation condition for equipment like motors, cables, and transformers. A common acceptance criterion is that insulation resistance should be greater than 1 megohm per kilovolt of system voltage, because higher voltage stresses require more insulation integrity to keep leakage low. The other described tests aren’t about long-term leakage resistance: a continuity test checks for a direct conductor path and isn’t about insulation quality; a capacitance test measures a stored charge property rather than leakage resistance; a dielectric withstand (hi-pot) test applies a high voltage to test dielectric strength and is typically evaluated by leakage current or breakdown, not by insulation resistance in megohms.

Insulation resistance testing measures how well electrical insulation resists leakage currents. A megohmmeter applies DC voltage across the insulation and measures the leakage current, giving an insulation resistance in megohms. A higher resistance means the insulation is preventing leakage effectively, which indicates better insulation condition for equipment like motors, cables, and transformers. A common acceptance criterion is that insulation resistance should be greater than 1 megohm per kilovolt of system voltage, because higher voltage stresses require more insulation integrity to keep leakage low.

The other described tests aren’t about long-term leakage resistance: a continuity test checks for a direct conductor path and isn’t about insulation quality; a capacitance test measures a stored charge property rather than leakage resistance; a dielectric withstand (hi-pot) test applies a high voltage to test dielectric strength and is typically evaluated by leakage current or breakdown, not by insulation resistance in megohms.