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June 2021

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Hi Reader,

This month I wanted to share with you one of the more interesting power quality issues I have seen in my career. An automotive light bulb was used in place of the correct beacon lamp, resulting in multiple failures.

Thanks again for reading.

Rob

​Rob@robdelauter.com ​

​Catch up on past newsletter.

Wrong Light Bulb Causes Failure

Last spring, as COVID-19 kept many of us in our homes and pushed our collective anxiety to new levels, I received a call from a local fire station. Their large garage doors would not close electrically, making it difficult for them to enter and exit the station.

Over the previous week, the company responsible for the maintenance of the doors had been called several times to repair the system. Each time they found a control transformer had overheated and failed. Because failures had occurred on different doors, it was believed to be a power quality issue.

We installed a Power Quality Analyzer (PQA) at the building service entrance, hoping to capture an anomaly the next time there was a failure.

The next morning, I received a call there had been another failure. I returned to the site, downloaded and reviewed the data collected. There was no sign of a problem. We moved the PQA to the distribution panel for the garage door openers and set it to record again.

Not even 24 hours had passed when the customer called with another failure.

This time I asked the repair company to wait for me to arrive. I didn’t believe it was a utility power problem, but something inside the firehouse contributing to the failures. I wanted to discuss the actual failure with the door service company.

Upon arrival, the electrician told me he found something interesting but didn’t see how it related to the failures. He noticed several beacon light covers had melted.

There are two beacons for each door. A red indicates the doors are closing so someone doesn’t drive through it while closing. And an amber that indicates the door is fully open, so a driver knows it’s safe to drive through.

The electrician noticed several of the lenses had become hot and melted. Upon examination, he found the wrong light bulb was used in the lamp fixture. A standard 12 volts 27 watts automotive bulb was used instead of the correct 24 volts 10 watts.

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The control transformer that failed powered these lights. It had an output voltage of 24 volts and was rated for 40VA. Because the wrong bulb was being used, the transformer needed to support over 70VA of load. This overloaded the transformer, resulting in its failure.

The excessive heat from the bulb could not be dissipated and melted the lens cover.

After finding the incorrect bulbs, we spoke to several people. We wanted to know what position the doors were in when they failed. They had always failed when the doors with open.

This new information supported our theory. With the spring weather being nice, the doors were left open during the day. This meant the amber beacon was on for several hours, allowing time for the lens to heat and melt. The transformer was also overloaded for longer periods, causing it to fail.

The electrician replaced the bulbs in all the beacons with the correct ones. He also spoke with his management to ensure everyone was made aware of the importance of using the correct bulbs. There has not been an issue with the doors since.

The electrician’s find of the wrong bulbs was critical to solving the problem. It shows how important all details are collected and evaluated, even those that at first glance appear to have nothing to do with the issue.

It’s always satisfying when the cause of a problem is found. Even more so when it’s something out of the ordinary.

As always, your feedback is welcome and encouraged.

​rob@robdelauter.com