[Power Quality]: Failing Phase

A few days ago I was at my computer and it suddenly went dead; simultaneously the uninterruptible power supply alarm sounded. Since the lights in the house were still on, I mistakenly thought the UPS had failed, and wasted several days trying to troubleshoot it.

What had happened was that the line voltage had been below the UPS minimum threshold, the UPS had been supplying the power for the computer, and its battery had run down.

I have had a Sense monitor since 2019 Dec 18, so I went to the Sense website and found a topic I hadn’t been aware of before: Sense Labs. The Fault Detection panel had a red flag on Power Quality; when I clicked on it, this came up:

Other days show a similar pattern. Obviously the white phase is bad. Some days in the afternoon, it spends minutes or hours below 105V. The voltage dips due to motor starts are several times larger than those on the orange phase. My conclusion is that there is a poor connection somewhere on the white phase.

I have also concluded that it is not a problem in my house for two reasons:

  1. The running average of the white voltage graph does not match the power use graph for my house, but represents a magnified version of the orange voltage running average.
  2. I believe I can see motor stalls in my neighbor’s house. Whenever a motor starts, the lights dim momentarily. If it is stalled, they dim for a few seconds, then return to brightness when the motor’s thermal protector breaks the circuit. After a protector cools down, it repeats. If the motor stall is in my house, there would be a big power surge at the same time, but not if the stall is in my neighbor’s house. I believe that the following Power Meter graph shows my neighbor’s motor trying four times unsuccessfully to start, and succeeding to start on the fifth try:

Have you contacted your utility and told them about the issue? We’ve seen similar issues in the forum and that’s typically been the best course of action for users with this problem. Your utility provider should send someone out rather quickly - it would be great if you could let us know what their diagnosis is and what’s replaced when they come out!

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