Electrical Troubleshooting Quiz — December 6, 2026
The plant has multiple fiber optic systems that have been added over time. The oldest and biggest of these is part of the Statistical Process Control System, which carries communications between a few PLC cabinets and several production lines while supplying Key Performance Metrics (KPM) to several departments in the admin building.
Problems with this one started appearing a few months ago. Scrap rates increased due to unintended variations in control. The nice Infographics that helped Purchasing stay on top of raw materials would sometimes just not make any sense.
It turns out that about six months ago, work began on integrating these networks. The Plant Engineer is wondering if this is overloading the “main system” (the original one), and has tasked you with troubleshooting the problem. He has to give the Plant Manager a solution, with cost estimates, in three weeks.
What’s a good way to figure out what’s going on?
Answer to Quiz
You are going to need two pieces of test equipment:
- An optical power meter (OPM).
- An optical time domain reflectometer (OTDR).
It’s unlikely that the network is out of bandwidth, though that possibility may need to be explored later. The most likely cause is human error that has occurred during the process of merging the networks. Focusing on the affected nodes is most likely the fastest way to find the problem. The two most likely problems are a damaged cable (the typical cause is the bend radius was exceeded) and a faulty connection (typically, the connector was not properly made to the cable).
Go into the CMMS or other information sources and find this information on your network cards:
- Wavelength
- Expected dBm
Now you know how to set up your OPM and what the reading should look like. What you will need to do is check each fiber run, one at a time:
- Go to the cable terminus (e.g., at the equipment).
- Conduct a visual inspection. Look for cable jacket damage (from, for example, bending it too tightly) and feel for a loose connection. Record what you find.
- Your OPM should allow you to step through various wavelength options; select the correct one for this signal (as per the CMMS). Go through the normal precheck steps (e.g., zero out the meter).
- Disconnect the cable from the equipment and connect it to your OPM.
- Take a measurement. The value should be very close to the expected dBm. If it’s not, make a note of which cable this is. Repeat for all the cables.
- If all of the cables were “off”, then either you did this wrong or you have a bunch of bad cables. Try this same test on a node not related to the system mergers. If that seems off, then maybe the CMMS is wrong; go to an output device, disconnect the cable, and measure directly from the device. Then go reconnect the cable and measure again at the terminus.
What should you do about any bad readings? For any cable where the dBM was off, use the OTDR to spot where the light is undergoing excessive loss. This will also help you prove you actually have a bad cable.
Replace any bad cables:
1. Perform OTDR on the uninstalled cable. Repeat the OTDR test after installation. The readings should be the same.
2. Perform the OPM testing on the installed cable. It should be significantly better from your As Found reading.
Check the connections:
- Ensure that each connector is properly made up to the cable.
- Ensure that the connection points are clean. Verify “clean” based on the installation specs for that system. In the neutron monitoring systems for nuclear power plants, for example, the spec requires cleaning both faces with 100% grain alcohol.
- Ensure the connections are properly tightened, again referring to the system specs. If there are no specs and it’s a knurled connector, then make it finger tight.
Once you have completed this part of the job, you need to summarize the problems for a report. A Pareto analysis is always good, but you can simply prepare a list of failure modes and note the quantity for each one. For example, “cable failure at first bend from connection point, 11 instances”.
What about that bandwidth? If you need to go down the path of answering this question, it’s a lot trickier than testing for physical damage as we just did. It will begin with an assessment of your network traffic patterns. It may be more efficient and cost-effective to outsource this to a fiber network consultant.
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.