Which unit is typically used to express insulation resistance in preventive maintenance tests?

Which unit is typically used to express insulation resistance in preventive maintenance tests?

• A. Ohms
• B. Kiloohms
• C. Megohms
• D. Milliohms

Answer: (C)

Insulation resistance in preventive maintenance tests is a high-impedance measurement. To capture the small leakage currents that occur through insulation, technicians express the reading in megohms. A megohm meter applies a DC test voltage and measures the resistance; healthy insulation yields very large values, typically in the millions of ohms. Using units such as ohms or milliohms would produce impractically small numbers or imply a near-short, which isn’t how insulation is described. Kilohms would still be much smaller than typical insulation resistances and can obscure whether leakage is acceptable. Therefore, expressing insulation resistance in megohms best reflects the actual electrical isolation quality and aligns with the measurement tool (megger) used in preventive maintenance.

Insulation resistance in preventive maintenance tests is a high-impedance measurement. To capture the small leakage currents that occur through insulation, technicians express the reading in megohms. A megohm meter applies a DC test voltage and measures the resistance; healthy insulation yields very large values, typically in the millions of ohms. Using units such as ohms or milliohms would produce impractically small numbers or imply a near-short, which isn’t how insulation is described. Kilohms would still be much smaller than typical insulation resistances and can obscure whether leakage is acceptable. Therefore, expressing insulation resistance in megohms best reflects the actual electrical isolation quality and aligns with the measurement tool (megger) used in preventive maintenance.