Two Minute Tips  

You Have Water Where?

Noah Bethel | Vice President-Product Development, PdMA Corporation

For many of us it’s the rainy season and with that comes elevated concerns about the insulation integrity of our electric motors and generators. It never ceases to amaze us how water finds a way into places that it’s not supposed to be in. As a gentle reminder, the IEEE-43 standard tells us that low voltage random wound motors should have an insulation resistance-to-ground (RTG) reading of >5MΩ for continued operation. For a DC or medium voltage form wound motor the insulation RTG should be >100MΩ for continued operations. If your motor was manufactured before 1970 the guidelines suggest 1MΩ per 1000V + 1MΩ. As an example, a low voltage (460v) motor manufactured in 1965 should have a minimum RTG value of 1.46MΩ.

For the latest in IEEE Standards visit their website at To see a case study on water and insulation systems visit the PdMA YouTube channel at

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About the Author

Noah Bethel Vice President-Product Development, PdMA Corporation

Noah has over twenty-five years of broad operations and electrical systems maintenance experience in industrial, commercial, and military settings ranging from nuclear submarines to world class amusement parks. His experience includes high and low voltage, AC and DC, power generation, power distribution, motors, and motor controllers. Noah is currently in charge of product development for new and existing PdM technology at PdMA Corporation.

Noah is a graduate of the University of the State of New York and the Naval Nuclear Power School and Training Unit. He is a Certified Maintenance Reliability Professional, with field experience in motor circuit analysis, current signature, power analysis, thermography, vibration analysis, oil analysis and ultrasonic testing.