NEIEP Mechanics Practice Exam

When using a megger to check insulation resistance to ground, what is an acceptable minimum resistance?

1. 0.1 M ohm

2. 0.5 M ohm

3. 1 M ohm

4. 5 M ohm

The correct answer is: 1 M ohm

In evaluating insulation resistance with a megger, achieving a minimum resistance of 1 M ohm is generally considered acceptable because it indicates good insulation quality. Insulation resistance is a critical measure for electrical safety; a resistance above this threshold suggests that minimal leakage current will occur, which is essential for preventing electrical shocks, equipment damage, and ensuring overall system reliability. Resistance values below 1 M ohm may signal potential issues within the insulation, such as degradation, moisture ingress, or other forms of damage, which could compromise safety and performance. Therefore, a standard threshold of 1 M ohm is widely endorsed across various electrical codes and standards as a minimum requirement for ensuring adequate insulation integrity, making it the appropriate choice in this context.