Electrical Troubleshooting Quiz — September 2, 2025
A local manufacturing plant closed down in 2022 and re-opened early this year. The previous maintenance staff have all moved on, and the plant hired replacements with only a year or two of experience. When it became obvious that someone more experienced was needed to handle the trickier problems, they hired you.
One of those problems you were hired to address is the drive motor for Line 3. It was replaced due to a high vibration alert. The responding electrician tightened up the mounting bolts, and yet a few hours later the alarm went off again. Next, another electrician replaced the motor. A few days later, the alarm went off again. Another electrician tightened the mounting bolts. As before, this appeared to be the solution, but it was only a matter of hours until the alarm went off again.
How would you solve this problem?
Answer to Quiz
Before doing anything else, determine if there is actually a problem. Use a handheld vibration tester. If the readings align with what the vibration monitoring system is seeing, then proceed to troubleshoot the motor system. If there is a discrepancy, check the vibration sensors, wiring (if applicable), and the monitor. You can skip this crosscheck step if you can visually see the vibration or you can readily feel strong vibration via a hand on the motor.
Tightening motor mounting bolts that are correctly torqued almost always causes “soft foot.” This is a bending of the motor mounting flanges that is nigh impossible to repair. So to fix this problem, you will need to ascertain the condition of the motor feet. First, record the actual torque of the mounting bolts. Then remove the bolts and remove the motor. Use a straightedge to determine if the motor feet are bowed or straight. If the latter, replace the motor.
When you have excess motor vibration, the cause is almost never loose mounting bolts. If the motor was installed correctly, the only thing that would cause those bolts to loosen is excess vibration. So your next step is to identify the cause of that vibration.
Begin by examining the driven load for uneven variations. For example, are operators slamming parts onto the conveyor, are there jams in the system, is the load varying sharply, and so forth. Address these issues and also determine if perhaps the motor vibration alert setpoint is too low. Maybe you need to allow for the variances in the load.
AFter that, check the motor itself for axial runout. The standard method uses a machinists dial indicator or similar (e.g., a caliper with a digital readout).
Unless it’s a c-face mount (bolts directly to the driven equipment), the motor is attached to a base that sits on a pedestal. Typically, the base is made of steel, and the pedestal is poured concrete. If either one is undersized for the application, you will get vibration. Quite often, the same force that causes the vibration also twists the base out of true or cracks the pedestal. Normally, when either one is undersized you can see the deflection with the unaided eye while the motor is driving the load.
But you might not see that in this instance, so measure the angular deflection. One method is to use a dial indicator to precisely measure the deflection. If you set the dial to zero when the motor is not running, then run the motor for a minute, the dial will read the deflection that occurred.
If there’s any deflection in the pedestal, you have to replace the pedestal with one that is more substantial and ensure it’s adequately secured to the floor or other structural surface. If the deflection is only in the base and it’s minor, you might be able to fix that by adding a brace or two; this job is best left to a qualified mechanic (bolted on brace) or welder. If deflection is significant, a qualified person will need to design a base that is stiff enough for the application.
If support for the motor all checks out (no deflection), then the problem is in the coupling to the load or the load itself. A laser alignment is in order, at this point. Once the alignment is determined to be correct, check for vibration. If you still have vibration, check the gearbox for axial runout the same way you checked the motor. If it checks OK, you may still get vibration due to lubrication issues, so check the gear oil. It should appear light-colored and stink of sulfur, and there should be enough of it to show full. If any of these conditions isn’t true, replace the oil. Don’t add oil to a low gearbox, unless only a little is needed, because if it’s been running with low oil then the oil that’s in there is probably damaged from overheating.
Then perform the same base and pedestal checks on the gearbox that you did on the motor. At this point, you will have examined the entire motor system. And that brings us to another point, a lesson you must convey to those young electricians. A motor is always part of a system. You don’t just jump into a system and randomly address some part of that system as if it’s the problem. Doing so will usually create other problems. Instead, you proceed methodically. You use measurements instead of guesswork. This applies to other systems, such as your power distribution system, as well.
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.