Mitigating High Number of Voltage Dips Likely Caused By A/C

How was your issue detected?: Power Quality Lab

Did you noticed any other signs of this issue around your home?: Occasional dimming of lights; Need to reset Wi-Fi gateway

Screenshots from Sense Lab

power_quality_raw.csv (26.4 KB)

Background: Live in a duplex apartment with shared line connection to the utility pole. Service is then split and metered separately for each side of our apartments. Installed Sense early in July 2020 on the mains for my unit. Have seen excessive voltage dips only over the past two summers, which leads me to believe this is related to A/C usage. I wasn’t overly concerned with this until we experienced on severe enough last week that it knocked out our WiFi (requiring the gateway to be power cycled). I’m now more concerned about the effect this could be having on our more sensitive electronics and want to mitigate this.

I’ve checked the main Power Meter for the times of reported dips to and most of the time they don’t seem to coincide with my A/C compressor or my fridge turning on. To my knowledge the HVAC system in the adjacent unit is the same as mine. Any ideas on why the identical A/C unit in the adjacent apartment may be the culprit? I don’t know enough about A/C starter caps to know whether they tend to fail instantaneously or degrade over time. Maybe the cap on the other unit needs to be replaced?

In addition to checking this, any suggestions on other fixes/improvements? Or read enough of the other posts on this forum to provide a consensus on what some of the more likely culprits are?

Lastly, do we know what the utility companies stance on these typically is? Do they consider this “normal” or is this something they’ll willingly troubleshoot?

I am in no way an electrical engineer, but my neighbor has two condensers. One was replaced in 2020 with the LEAST efficient unit possible (I read the energy star sticker on the box). When either of their units kick on, my lights dim. Even my own older condenser doesn’t cause the lights to dim that badly. I too have an extreme number of dips and spikes. I’m getting solar installed 8/3, so I’m curious how my power quality will improve once I’m able to feed steady voltage into the house.

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I can’t speak on utility stance or exam causes, but since you posted your data, I couldn’t help but plot. Your issue is symmetric (affect both leg0 and leg1 equally), is all on the dip side and seems to have only a few big outliers, but those are the ones that could affect other electronics in your house.


Good luck with the utility company.

Per PG&E’s documentation they consider a sustained 114 to be within limits (see pages 4-5 of the link). They go on to say that if you go above or below the limits, well this is just normal and so long as it’s not sustained, just deal with it.

Let me clarify that I’m paraphrasing their words. I’m not attempting to be rude by saying “just deal with it”.


Unfortunately, in both my experience and understanding, it won’t. Your inverter will match its output AC voltage to what it senses on the line.

Thanks for the analysis @kevin1. I believe the symmetry between Leg0 and Leg1 doesn’t rule-out the issue potentially being related to the starting of a power hungry 220V device like an A/C compressor. But it also means it could be another type of problem that would be common to both legs.

I think cases like this further demonstrate the potential value of my suggestion under the post below. It would be great if Sense could give some insight into what may be causing the dips, especially for the big outliers. Because as of now, I’m still at a loss regarding how to solve this.

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