Electrical Troubleshooting Quiz — August 5, 2025
A plant that’s a couple hours from your electrical service firm has twelve small production lines, and they are nearly clones of each other. The problem is they don’t stay running. At any given time, only four or five are making product because the rest are down and waiting for spare parts. Those parts are typically circuit boards.
Each line is on its own 480V distribution transformer and panel, mounted on the wall near the line it is supplying. The plant has a thin expertise level, but the maintenance staff is capable of taking voltage measurements and performing basic maintenance tasks and simple repair tasks (such as swapping out all those cards). Identifying the cause of this excessive component failure rate is beyond their capabilities, thus the call to your firm. How might you troubleshoot this?
Answer to Quiz
If only one machine were toasting circuit boards, you would start with the DC power supply in that machine. And you would probably find that power supply is defective. It is unlikely that all twelve power supplies are defective. What is likely is the same human error was made at each of the twelve machines.
The most likely human error is one that involves bonding and grounding. Some confusion may arise where distribution transformers are involved. Though they are on the load side of the service, they are considered separately derived sources. So the grounding and bonding rules for sources apply to transformers. They have a supply side and a load side. There is no direct electrical connection between these sides, unless one is introduced via grounding and bonding errors.
We ground on the supply side, and bond on the load side. The primary of a distribution transformer is the supply side, so it needs to be grounded. The secondary, however, is not grounded.
If you connect both sides to ground, you provide an electrical connection between the primary and secondary. This can look correct, and an installer would likely do all of them the same way. Or perhaps someone in maintenance “fixed” a non-existent grounding error by disconnecting the ground connection on the primary. It’s also possible that someone disconnected (or failed to install) proper bonding jumpers on the load side. Many kinds of errors could be made here. Then there are issues inside the equipment itself for example using the equipment chassis as the negative DC return. A thorough visual inspection is in order. Start by tracing the return path for the power supply.
You also want to measure the voltage between the transformer case and the Equipment Grounding Conductor (EGC), which is really a bonding conductor. That case should be bonded and thus at zero potential. If you get anything else, something is wrong. Maybe the transformer case bonding strap isn’t connected, there’s a break in the EGC, or the EGC is connected to the neutral.
It would be surprising if the aforementioned process did not disclose the error that is causing so much circuit board failure. But there could be other causes, such as these:
- Bond between the neutral and the EGC or between the neutral and equipment “ground” terminals. The neutral is the grounded conductor, but it is not a bonding jumper. The neutral conducts unbalanced current back to the source. If, instead, it is conducting unbalanced current to the “ground” terminals of the card slots then you’re putting 277V on one side of a 5V power supply.
- Large motor starts across the line. Is there a fire pump or plant air compressor motor that is throwing big transients into the system? Use a power analyzer to see what the power looks like at each feeder. Also try to determine how often the fire pump gets started.
- Excess heat in the cabinet. What is the temperature in the spots where these cards are inserted? Is there an air supply with a filter? Is that filter clogged?
If all else fails, then you have to broach a “blame the customer” issue. That would be careless handling of circuit boards while installing them. Any error here could explain all of the failures.
- Find out from the supplier exactly how these are supposed to be installed. What are the cautions, is there a special tool or technique beyond standard circuit board handling?
- Can these be hot-swapped, or must the power be removed first? If the latter, is this stated in the maintenance procedure? Is there even a procedure?
- Look up the repair records to see who has replaced any circuit board that has subsequently been replaced again. Ask this person to show you how to change out the board. You may spot errors of execution here, but if you do not then ask that person to describe or demonstrate some wrong ways. These would include not handling by only the edges, touching the contacts, twisting it, and even setting it on a metal surface with the circuit tracks down.
- If you find errors, write up a procedure and make a video showing proper technique. Then tell your client contact it isn’t any one person, there was just a training gap. Provide the procedure and the video, while saying these will allow the plant to satisfy the “qualified person” rule of the NEC and also end the circuit board failure 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.