Electrical Troubleshooting Quiz — February 3, 2026

You recently hired on as the Plant Electrical Maintenance Supervisor. The job was created because of a list of problems that have remained unsolved despite the best efforts of the eleven maintenance electricians. The Plant Engineer, we’ll call him Jason, came onboard six months earlier and had discovered that only one of these electricians had even so much as a Journeyman’s card.

One of them, we’ll call him Todd, had an Associate’s Degree in a related field but no experience as an electrician. Todd was the self-appointed Variable Frequency Drive (VFD) Guru. Jason at first went along with this, but grew to have doubts. One reason was that, in reviewing the records, he found Todd had replaced a lot of VFDs over the past couple of years.

But there was nothing to indicate a root cause of failure. Could all of those VFDs have been bad? Jason didn’t think so. Jason also noted that the plant has at least six different brands of drive, which hints at brand-chasing in lieu of troubleshooting. “There can’t be five brands that are no good.”

Now Jason wants you to dig into this, even though you have no experience with VFDs yourself. So you would not be troubleshooting any particular VFD. You would, instead, take a systems approach to the high replacement rate.

What would this approach entail?

Answer to Quiz

Jason isn’t requiring you to troubleshoot any particular VFD, but he is implying that Todd isn’t actually doing this part. Perhaps Todd solves installation errors or adjustment errors by relying on the manufacturer’s tech support to get a new unit operating as needed. Thus, the many different brands.

Start by echoing Jason’s assumption that it can’t be true that only one brand, the latest purchase perhaps, is any good. In fact, there is no name brand that you have to worry about. The competition for reliability, performance, and quality among these brands has been fierce for many years now. You might do better with one than another for a particular application, but you can’t go wrong with any of them.

From there, go to the basics of troubleshooting. The first step in troubleshooting is to look at the power supply. This doesn’t mean everything is fine if you measure 480V on the feeder.

Ideally, every industrial motor would have power correction (PF) capacitors to optimize efficiency. It’s typically not done on most motors due to cost and complexity. Ideally, every motor would have harmonics correction, but cost and complexity again prevent this. In this plant, it is possible that some motors have PF correction. And it is likely that any VFDs purchased in the past few years have both PF correction and harmonics correction. If those are installed where PF correction is already installed, you have a problem. Check for this. If the problem exists, you want the PF correction to be only in the VFD, because it is adaptable.

Something else that happens is motors get “grounded” instead of bonded. This creates a slew of power quality and shock potential issues. Look for load side ground rods and “ground wire” run to the building frame. These are not approved “equipment grounding” (bonding) conductors. See Sec. 250.118(A) for what is approved. And note that grounding electrode conductors cannot be used as equipment “grounding” (bonding) conductors [Sec. 250.118(B)].

Check the connections between the local disconnect and the VFD and between the VFD and the motor. Is the grounded conductor being confused with the grounding conductor at any point? Are the connections properly made (terminals correctly crimped, connection bolts torqued to the correct value)? The “torque by feel” method will invariably result in faulty connections.

If all this passes muster, you could have problems such as voltage sags and spikes caused by a large motor such as a fire pump starting across the line. If you can put a power analyzer on the feeder that supplies a VFD or two and leave it for a few days, you should be able to capture such events.

If the power supply, connections, and bonding are correct, that would appear to leave only errors in selection (wrong drive for the job), set-up, and tuning. Look at the last few VFDs that were replaced. Check the specifications to see what protection modes that each one has and if it’s been replaced what the previous model had. Look at the default settings, the history of setting changes, and what the settings are now. Look at the maintenance history and repair logs to see if Todd ever recorded the settings for these. If not, then update the maintenance procedures such that this information must be recorded.

Remember the word “appear” earlier? You still may have problems that fall outside of troubleshooting the drive system. For example, motor soft foot can result in excess vibration. Maybe the motor is misaligned with the load, or the gearbox needs an oil change. But at this point, you can report your findings back to Jason along with the recommendations for corrective actions those findings will lead you to determining. While you might also conclude that Todd has no business touching the VFDs, let Jason conclude that on his own and deal with it as he sees fit.