Electrical Troubleshooting Quiz — Sept. 15, 2020
One of the plant’s most profitable production lines was upgraded a few months ago. Since then, things have gone sideways with that line. The upgrade involved replacing various controls, a motor, and a variable frequency drive.
A PLC stopped working and had to be replaced. Operators have complained about receiving a shock upon touching this or that cabinet.
The plant doesn’t have an electrician. It has three “multicraft” maintenance technicians. Prior to taking these jobs, one had been an auto mechanic, another an HVAC tech, and the third an instrument tech. The plant manager contacted your electrical services firm, which sent you to figure out what’s wrong.
The first thing you noticed was the rewiring job looks neat. What may be wrong, here?
The biggest clue is the shock issue. Undesired current is using metallic enclosures as a return path. You need to find which non current carrying metallic objects are not bonded to the equipment grounding (bonding) conductor (EGC) and bond them to it.
Also, inspect every inch of the EGC:
- To ensure conformance with the types of EGCs listed in 250.118.
- For electrical continuity and mechanical integrity.
Kudos to these non-electricians for the neat rewiring (as required by 110.12), but why did that jump out at you? If they are used to low-power wiring that can often tolerate those neat-looking bends made with needle nose pliers, is that what they did here? Insulation resistance testing of all power wiring is a good idea, if that is the case.
Then, walk through the upgrade to identify what has changed. If there is still a problem, that’s where you’ll find it.
About the Author
Mark LamendolaMark 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.