Two Minute Tips  

Leading and Lagging Indicators

Noah Bethel | Vice President-Product Development, PdMA Corporation

Leading indicators are those that occur early in the P-F curve while lagging indicators occur later in the failure cycle. Both are key indicators, but it is important to know which one you are dealing with to better diagnose the severity of the situation.

Phase resistance, like infrared thermography, is a leading indicator of power circuit anomalies. Performed at proper intervals you would expect the resistance imbalance to identify early stages of a power circuit high resistance connection. At early stages, the effect of a high resistance connection on the motor is minimal and only localized heating occurs. At later stages the current through the affected phase changes resulting in circulating currents in the motor. These circulating currents cause elevated temperatures that may reduce the life expectancy of the insulation system.

Finally, both indicators being on the P-F curve doesn’t mean you have to wait to get to the lagging indicators to make a decision. The general rule of thumb is that the earlier you can correct these issues, without affecting production, the less expensive the repair.

To see a video on the Power Circuit Fault Zone visit our website 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.