Power Quality - 1000+ Spikes or Dips in Last 30 Days

How was your issue detected?:
Pretty much entirely through the Sense Labs feature. I honestly had no idea how bad the power quality actually was before this feature was available.

Did you noticed any other signs of this issue around your home?:

  • Occasional subtle flickering of lights
  • Not unusual for my UPSs to trigger a couple times a month (without an actual outage)

Screenshots from Sense Lab
Voltage Graph screenshot

Event Timestamp Screenshot

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Does anyone have any thoughts on how to track down the root cause here? The fact that this is consistently an issue on L1 but rarely an issue on L2 makes me think that there’s an issue inside the house.

Here’s another example:

So far I’m not noticing any clear correlation with specific devices.

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Do you have any device that presents a very heavy 120V load and is intermittently on an off. This big down spikes look like the possible startup of a motor. Assuming you have already checked Sense Labs for a floating neutral ?


Or you could have a 240 VAC device (like an A/C compressor) and one of the legs (L1) has a loose connection which requires a higher starting amperage. You would need to check all the electrical terminations. Re-tighten the lugs. Do you have any areas where there might be a possibility of Al (Aluminum) and Cu (Copper) wires being connected (spliced) together? You shouldn’t have Al/Cu splices, but people have done this in the past. Maybe the wires were improperly connected. Just thoughts…

Hey @kelchm. Do you have multiple panels/is Sense monitoring only one of them?

I see some signs of a poor neutral connection in that voltage chart. What does the “floating neutral detection” section of Sense Labs say?

Having thought about it some more, it could be from the dehumidifier that I run year round in my basement. I’ll try turning it off for the next few days and see what things look like.

My first thought was that it could be the 4-ton Mitsubishi Mini Split system I had installed last year, but I’ve confirmed that Sense continues to detect these issues even when that system is completely turned off.

As far as I’m aware there’s no aluminum wire in the house other than (maybe?) the main service lines. The house was built in 1978, which I understand should be after the usage of aluminum wire was phased out.

I do have two sub-panels, but only only a single 200A service. Sense is installed in the main panel with the CTs on the service mains immediately before the main disconnect.

No floating neutral detected by Sense to date:

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Hey @kelchm. We took a deeper look at this for you, and it looks like there’s a few things potentially going on. Grabbed a few screenshots for you, courtesy of Data Science.

Overall, we noticed some typical symptoms of a Power Supply issue - a potential neutral issue and some external interference. It’s also worth noting that right now, the Floating Neutral detector is a semi-manual process. The issues you’re seeing here that are indicative of a neutral issue would be flagged by the next update to the Floating Neutral detector, which you would be able to see in Sense Labs.

In the highlighted region in this image, you’ll see a 1000W load appears to be causing an inverse 3V dip, which could cause flickering of lights (and other symptoms you might have noticed). This is indicative of a neutral issue.

Above, you’ll notice a fluctuating voltage supply. Typically, this could be due to several reasons including:

  • An in-house appliance which is not monitored by Sense is causing the issue (which you ruled out with the answer to my original question).

  • Since there is no in-house load corresponding to the voltage fluctuations here, it leads us to believe there is an external issue (neighbor, lines feeding into the house) that could be causing irregularities here.

If you do have someone out to inspect this, or manage to resolve the issue it would be great if you could share that with us here or via Private Message :slight_smile:


Thanks Justin (and the Data Science Team!), this is immensely helpful.

If I’m reading the first screenshot correctly it looks like the load is actually 1182W, is that correct? It’s kind of an odd looking power curve, I’m honestly not sure what device that would be from. Do you happen to have a date stamp for this particular screenshot?

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Interesting result after turning off the dehumidifier late yesterday afternoon:

This obviously isn’t the only issue present, but it does seem to have made a pretty dramatic difference.

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Nice investigatory skills, @kelchm. Looks like you’ve found one of the devices causing the Voltage dips.

Still investigating this at this point. The data from last night seems to show pretty clear evidence of a neutral issue:

Here’s my power meter zoomed in to 6:30PM-9:30PM:

The two big consumers that were running at this time would be my water heater and well pump as somewhere in this range someone was taking a bath (thus the long run time on the water heater). Any ideas?

@kelchm Based on our original assessment from Data Science, I’d recommend contacting an electrician to ensure there’s nothing wrong here. We’re limited in our ability to diagnose beyond some of the tell-tale signs of a neutral issue, so the best next step here is to get someone to verify those findings in-person. Always better safe than sorry with neutrals :slight_smile:.

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I certainly understand Sense’s stance on this, but without actually having a way to reproduce the issue I’m highly skeptical that an average electrician is going to be able to find anything meaningful. Living in a rural area it’s often difficult for me to find qualified tradespeople at all.

I have checked the basics at this point and haven’t identified anything interesting of note beyond an (unrelated) miswired outlet in the garage. My hope in sharing details here is that someone might spot something I’ve overlooked or that ultimately my experience can help someone pinpoint the root cause of their own issues :slight_smile:

That said, I’ve identified an interesting pattern over the last week or so that has me completely baffled. While the timing isn’t exactly the same, there’s clearly some event happening on a daily basis in the range of 7PM-11PM.

Looks like a 240V (dual leg) device turning on with a weak/loose neutral somewhere as you suspect.