Two Minute Tips  

Trend Is Your Friend

Noah Bethel
Noah Bethel | Vice President-Product Development, PdMA Corporation

Troubleshooting a motor without historical data to reference for a change in baseline or a gradual trend up or down can be a difficult task. The IEEE 43 standard (Recommended Practice for Testing Insulation Resistance of Rotating Machinery) states that 100 Meg is the minimum acceptable resistance-to-ground value for a form wound AC motor. So, a 110 Meg insulation-to-ground reading on an installed form wound motor would normally create a cause for concern. However, if you had five years of data on the very same motor that showed only a 1 Meg drop over the five years, your ability to quantify the severity of the low resistance-to-ground would be far better. With trend as your friend, no immediate action would be necessary as the condition is above the minimum and stable. With no history you might feel that this was an imminent failure risk and decide to secure production, resulting in an unscheduled outage, to prevent a potential catastrophic failure that in all likelihood would not have happened. So, get your baseline on all assets worthy of your interest and schedule some future tests to establish a trend.

To see a case study on the proper use of trending insulation resistance-to-ground and using that trend to take appropriate action go to the PdMA YouTube Channel 

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About the Author

Noah Bethel
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.