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Tip of the Week: Overcoming Chronic Overload Protection Trips

Jan. 25, 2016
Here's a checklist of issues to look for to solve the problem

A common reaction to an overloaded motor that repeatedly trips its protection unit (or burns open its “heaters”) is to “upgrade” the protection. This “solution” is arrived at after performing some cursory checks on the motor and not seeing any problems. “Must be the wrong size heaters; the motor seems fine.”

The motor might “seem” fine but not actually be fine. For example, it may have bearing problems (which are discoverable with ultrasonics).

But the motor itself might not be causing the overload condition. Causes may include a large change in load (e.g., a scrap grinder is fed too much at a time), misalignment, a broken drive gear, or improper motor drive settings. Power problems (e.g., low voltage or low power factor) also may cause an overload condition.

It’s easy enough to determine the correct size overloads. Once you’ve done that, you know that going larger may reduce the life of the motor.

Before you check the problems already mentioned, check the motor supply:

  • Is the supply voltage correct? Chronically low voltage may result in those chronic overload trips.
  • Are all phases present, or are you single-phasing?
  • Are all phases at nearly the same voltage, or do you have voltage imbalance?
  • What is the power factor at the motor?
  • What does the power look like? Excess waveform distortion and harmonics may cause this problem.
About the Author

Mark Lamendola

Mark is an expert in maintenance management, having racked up an impressive track record during his time working in the field. He also has extensive knowledge of, and practical expertise with, the National Electrical Code (NEC). Through his consulting business, he provides articles and training materials on electrical topics, specializing in making difficult subjects easy to understand and focusing on the practical aspects of electrical work.

Prior to starting his own business, Mark served as the Technical Editor on EC&M for six years, worked three years in nuclear maintenance, six years as a contract project engineer/project manager, three years as a systems engineer, and three years in plant maintenance management.

Mark earned an AAS degree from Rock Valley College, a BSEET from Columbia Pacific University, and an MBA from Lake Erie College. He’s also completed several related certifications over the years and even was formerly licensed as a Master Electrician. He is a Senior Member of the IEEE and past Chairman of the Kansas City Chapters of both the IEEE and the IEEE Computer Society. Mark also served as the program director for, a board member of, and webmaster of, the Midwest Chapter of the 7x24 Exchange. He has also held memberships with the following organizations: NETA, NFPA, International Association of Webmasters, and Institute of Certified Professional Managers.

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