For in-service AC induction motors made before 1970, what is the minimum insulation resistance value for PI and DAR according to NETA standards?

For in-service AC induction motors made before 1970, the National Electrical Testing Association (NETA) standards specify a minimum insulation resistance value that is crucial for ensuring the safety and reliability of electrical equipment. According to NETA standards, the minimum insulation resistance value for both Polarization Index (PI) and Dielectric Absorption Ratio (DAR) is set at 1.0 megohms. This means that for motors manufactured prior to 1970, achieving these values is critical, as they indicate the motor's insulation condition.

An insulation resistance measurement of 1.0 megohm suggests that the motor's insulation is adequate, providing a level of confidence regarding its safety and operational efficiency. The Polarization Index is a ratio derived from taking separate measurements of insulation resistance at different time intervals, while the Dielectric Absorption Ratio measures how well an insulation system can absorb and hold electrical energy. Both values being at least 1.0 reflect good insulation health and help inform maintenance decisions.

By ensuring that the insulation resistance meets these standards, organizations can mitigate the risk of electrical failures, enhance equipment lifespan, and promote workplace safety.