Table 10019 from ANSINETA MTS2011 provides recommended test voltages for proof testing and field testing mediumvoltage power circuit breakers and switchgear

Test & Measurement

Tip of the Week: Medium-Voltage Circuit Breaker Testing

May 15, 2017

3 tests that should be part of a preventive maintenance program for medium-voltage circuit breakers.

These three tests should be in your preventive maintenance program for medium-voltage circuit breakers:

1. Contact resistance test. Use a digital low-resistance ohmmeter (DLRO), not a digital multimeter (DMM), so that you can measure the resistance at a relevant test voltage instead of at 9VDC. Test the line to load terminals for each phase; the readings should not vary by more than 50 percent.

2. Insulation resistance testing. Some instruments have both the megohmmeter and insulation resistance testing functions. Test phase to phase and phase to ground with the contacts open. Use the manufacturer’s recommended testing voltages and acceptance values, if available.

3. Dielectric withstand voltage. Perform this test with a high-potential meter (hi-pot) from the line side of each phase with the breaker open. Also perform it on the load side of one phase, with the line and load sides of the other phases tied together to ground. As with insulation resistance testing, Use the manufacturer’s recommended testing voltages and acceptance values if available.

Other tests will be appropriate depending upon the application and the circumstances. In addition, you should use thermography as a predictive maintenance tool for all of your circuit breakers.

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.