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Please Don't: What’s the problem? Or rather, what isn’t the problem?

By Richard P. Bingham | Aug 14, 2023
PQ_shutterstock_2048958428 [Converted]
A recent troubleshooting call from the owner of an ice cream shop came just before one of the biggest times of year for them: the spring holiday period of Easter and Passover.

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A recent troubleshooting call from the owner of an ice cream shop came just before one of the biggest times of year for them: the spring holiday period of Easter and Passover. Apparently, ice cream cakes are a big seller then. Also, baseball and softball players get ice cream after their games. 

The main freezer was going offline several times a week. If it happened when the building was unoccupied, it would be damaging to the products stored in there. The electrician noticed the breaker had been tripped. After repeated similar events, the breaker was replaced, but the problem persisted. 

After determining that there were multiple loads on the circuit, the owner approved a rewiring to feed only the freezer from a new breaker and a dedicated circuit. The profits were still melting away as it continued to go out. The cost of a new freezer was very pricey and the delivery time too far out to make it a viable short-term solution. So, it was time to install a PQ monitor to see what was really going on.

The 240V, 30A circuit was monitored for the line-to-line voltage and line currents as well as the 120V portion (L-N and N-G). The monitor could trigger and record on voltage and current RMS variations and transients. However, it was set up to trigger on just voltage variations, which should have occurred when the breaker tripped. With enough pretrigger cycles of voltage and current waveforms, maybe the cause of the breaker trip by the freezer’s operation could be determined.

Unfortunately, this was not the case. From a PQ engineer’s point of view, it was disappointing. From the owner’s perspective, it was just fine as the breaker no longer tripped and no issues with product damage occurred anymore. 

After a month of no interesting data, the electrician went to remove the instrument. The owner pleaded “please don’t,” as he was convinced the instrument was fixing the problem. Another situation needed monitoring (a microwave tripping breaker), so to his chagrin, it was removed.

Though most people would probably guess that the instrument didn’t do any electrical magic to actually fix the problem, there were instances in the early deployment of PQ monitors where problems did go away when the instrument was plugged in and return when it was removed. This resulted in a notice placed in the user’s guide to not plug the PQ monitor’s power supply cord into the same circuit that was being monitored. Most instruments have significant transient absorbing devices on their power supply front ends to keep the instrument from becoming a victim of what it was supposed to monitor and record. 

The Big Brother effect

Though there is no proof—nor does this article insinuate such—there have been cases where the presence of a PQ monitor may have eliminated the problem by causing a change in the occupants’ behaviors (“Big Brother is watching” syndrome). 

In a call center for a large retail supplier in Philadelphia, the PBX shut down frequently in the midafternoon, particularly on Fridays. It took considerable time for the PBX to reboot and the call center to resume full operation, which resulted in some employees being let go early to start their summer weekend. New wiring feeding the PBX was run from the distribution panel without any improvement in the problem. 

After several PQ monitors were placed at various points within the facility, the data showed that there was no increase in current that would be capable of causing the breaker to trip. The facility manager was informed of this. He declined the suggestion that a web camera be installed to monitor the activity of people entering and leaving the utility closet, saying it didn’t demonstrate trust in the employees. He did agree to putting a lock on the door, and the problem was fixed for good. (I explored this situation in more detail in “Disturbances Must Obey the Laws of Physics,” ELECTRICAL CONTRACTOR, September 2021.)

A Florida office had a strange problem with wires found to have burnt insulation in the mornings. It would only be vertical sections of wire. All kinds of theories were put out there, including excessive radar energy from a nearby Air Force base. High-end PQ monitors with RF detection modules found nothing in the conducted or radiated realm that would explain this. As this was before the days of easily accessible internet webcams, it took a while to install visual surveillance. Another problem fixed, as it turned out to be a disgruntled employee with access to the office in the evening and a lighter.

While the instruments in these situations didn’t detect the problem, the lesson isn’t an uncommon part of PQ troubleshooting investigations. Ruling out what isn’t the potential cause is valuable information in determining what is.

shutterstock / Natykach Nataliia/ urfin

About The Author

BINGHAM, a contributing editor for power quality, can be reached at 908.499.5321.

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