Weird voltage wave form during rain

Power quality noted a sudden odd pattern in voltage - it seems to have coincide with rain - Any idea whet this is?

Which portion of the waveform do you find to be weird? The white CT trace between ~10:30am 9/17 to ~12-12:30am 9/18? I assume it was raining during this time? What did your power usage look like over the same 24hr time period?

There seems to be a consistent 9 dips per hour on the phase represented by the white waveform. Since this behavior was only seen on one of the mains, it doesn’t seem like it is coming from the utility supply. What do you have for 120V devices that would trigger fairly regularly at 9x per hour only when it’s raining? Looking at the power consumption may help here.

Sump pump?

Filler text to make forum software happy.

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Thank you for the quick reply. It may be that the rain is a correlation without casusation.

I will look at loads.

Here is where I wish the power was more developed. Wouldn’t be cool to be able to overlay a voltage graph on top of a load graph?
Wouldn’t it be cool to be able to select the voltage window to review?

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I think I may have sent us in the wrong direction. We have nothing that is triggered by rain - no sump pump. Logical guess, Thank you.

Something that crossed my mind is rain = solar variation. Whether weather and solar are purely local doesn’t necessary matter, the grid is impacted.

Another option: grounding variations? Water = better grounding. Given it looks to be on one phase for the most part, perhaps you have a slightly floating neutral/ground?

Consider wider regional grid issues (in the rain) … kinda depends where you are and what’s going on your Utility branch.

Can you share a screenshot of what the power meter looked like over this same 24hr period? As well as a zoomed-in view of 1hr during this period of odd behavior? The consistency in the frequency of the dips at ~9 per hour still feels relevant to me.

Is your residence a single home, or multi-unit? In other words, is the wiring connecting your property to the grid used by any other residence?

Can you confirm that you don’t have solar?

I find the divergence of the voltage between the legs surprising.

Single Home

No Solar

This does seem to correlate with a device that Sense hasn’t identified yet. My guess is it may be a dehumidifier…. Although that frequency of compressor switching is not what I perceive and the wattage (500) seems extreme – I need to dig into this. It may be that the compressor is throwing in the towel…

1 hour at 2pm – the dips not completely align: that may be a graphical error.


I had a situation recently where the Sense detected watts on my solar legs as though it were watts on my mains legs. Specifically one solar leg was cloned on one grid leg. Not all day, but enough that it looked like I was having issues with usage going up as generation went up.

The fix was those watertight extension cables that Sense sent out. So some corrosion was happening in my circuit and it resulted in BAZAAR behavior. Since rain can cause electrical issues perhaps you have a similarly bazaar issue.

However it looks awfully regular to be ascribed to something getting wet.