Electrical Troubleshooting Quiz — Feb. 18, 2020
Since April, operators in Building C have been complaining about receiving shocks from their machines. On a given machine, it happens intermittently, and the incidents may be days or even weeks apart. Installing ground rods hasn't stopped these shocks.
Since last August, motor failures in Building C have increased 64%. In the other buildings, however, the rate has remained about the same.
Because a new process control system was installed in Building C last March, attention focused on that for a long time, but it all checks out. It’s installed per the manufacturer's site installation manual, including the separate ground using a 25-ft electrode. Discussions with the manufacturer have ruled out their system. Where should you look next?
Installing ground rods on the load side accomplishes nothing, because a connection to the earth is not a low-impedance return path to the source. To eliminate differences of potential, and thus shock, you must provide a low-impedance path to the source, which is done with bonding; see Art. 250, Part V in the 2020 Edition of the National Electrical Code (NEC).
These facts are how we know what is causing both the shock problem and the motor failures. That control system is not properly installed. Confusion over grounding and bonding and insufficient knowledge of the principles discussed in IEEE-142 Recommended Practice for Grounding of Industrial and Commercial Power Systems have long plagued these systems.
To solve those problems, replace the “separate ground” with bonding that complies with NEC Art. 250, Part V. A problem with doing this is the typical installation manual requires full compliance for the warranty to be valid. That condition is not legally enforceable if the installation manual requires violating the NEC, so document the discrepancies.
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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.