Electrical Troubleshooting Quiz — March 3, 2026

The plant engineer came back from a tour of the plant and stopped by your office (electrical maintenance manager) with a question. She had walked past a motor control center and noticed a cover was open and a floor fan was blowing air into the open enclosure. She had several concerns with this and said:

• “People are exposed due to the open cover.”
• “If whatever is in there is too hot, this can’t be a correct answer.”
• “Being a chemical engineer, I don’t know your electrical code. But it sure looks like a code violation to me. Isn’t that violating the listing or something?
• “I don’t like floor fans in general. In this particular case, we now have a cord running along the floor in front of this set of 480V panels.”

An inquiry revealed that the fan was placed by an operator “to stop nuisance tripping” of the motor. But the only work request for a trip in the past six months was three weeks ago. The responding electrician replaced the heater strips in the motor starter and recorded the motor had not tripped when he checked back an hour later. Apparently, it did trip again and someone replaced the heater strips and then set a floor fan in front of the open enclosure (no record of this in the CMMS). What should you do to solve this problem?

Answer to Quiz

Not bad for a Chem E, even though these issues would be obvious to any electrician or electrical engineer. It’s bad that the plant engineer was the one to discover this, but maintenance people don’t have the time to walk around looking for these kinds of self-inflicted wounds.

Let’s go to the order of priorities:

1. Safety
2. Environment
3. Production

The operator had put production above safety. That is the first thing to fix, you’ll need to remove the fan and close the enclosure door. Before you do that:

1. Verify that the heater strips are the correct size. There is often a chart right on the motor starter telling you what size to use.
2. Set up some instrumentation so you can monitor what happens as a result. Monitoring the temperature of the motor windings or the heater strips might seem like a good idea, but temperature is a slowly changing variable and this won’t give you actionable information. Instead, use a DMM with a current clamp and recording features.

Because making this DMM connection is working hot and the equipment is known to not be in working order, you will need the electrician performing the work to fill out a Hot Work Permit per NFPA 70E Sec. 130. In the interim, red tape off the area to protect other workers.

Once the DMM is connected and securely hanging or sitting in the enclosure, close the cover and remove the fan. Let the DMM monitor current for a couple of days. If there’s no record of excess current and the heater strips don’t open, continue to monitor for a week if possible.

If the heater strips open during the monitoring phase, you will likely find that the motor heater strips are working correctly and opening in response to excess current. Now you must determine why there is excess current. Most likely, it is not an issue with power factor, voltage imbalance, or harmonics, because it’s just this one motor with the problem. But check all of these anyhow. And if you find they are all within spec, consider that the combination of “almost too high” voltage imbalance, “almost too low” power factor, and “almost too much” harmonic distortion could combine to cause too much current draw. Also look at motor vibration and alignment.

The most likely culprit is the load. If there’s a gearbox, have the mechanics check the oil quality and oil level. Now look at what’s on the other side of that gearbox (or where one would be, if there isn’t one). Is there anything obvious, such as an overloaded hopper? Discuss the overload problem with the system engineer and ask if there’s something on the load end that might be causing it.

Also look at where the motor physically sits. Is it hot enough that ventilation would make a significant difference? Is the motor sitting under excess dust or fibers? If it’s not a totally enclosed motor, are its vents clear?

While all of this is going on, the heaters may still be blowing. If the open cover and fan thing happens again, the plant engineer will need to meet with the production superintendant and the plant manager. Both are incentivized toward higher production, but in a typical manufacturing concern the plant manager is also held to that safety-environment-production priority plus the plant manager is responsible for maintenance costs. If the motor is unprotected and burns up, that’s another cost plus an unscheduled and possibly extended interruption in production.

If there is no identifiable load problem, then determine if this motor is correct for the load it is connected to. If the specs all work out, the motor may have winding or bearing issues. Replace it with a new one, then send it to a motor shop for analysis. Why send it for analysis? If it checks out to have no problems, then replacing it wasn’t the answer and you need to keep looking. If it has a problem that makes it run less efficiently, then you can be fairly confident the entire debacle originated with this particular problem in this particular motor.