Graphs of Utility Voltage for detecting issues


Did anything ever come of this? I am curious for an update from Sense on any voltage or other power quality features. Sampling at 1 MHz offers a lot of potential.

I have had LED lamps going out prematurely and it would be helpful to know if I just happened to get a high rate of lemons–across two different manufacturers–or whether I have another problem :frowning:


@eric2 since your friend is at the end of his utilities grid line and you suspect an issue with the transformer size feeding that line, have you considered a whole house surge protector? it would at least save his electronics…


Funny you should mention that… :wink:

I am headed down there in a few weeks to install one (or several). Right now the debate is how many to install. There is one 400a panel with three subpanels. Debating whether we should install them in just the main panel, or in all the panels.

Having them in all panels gives more paths to dissipate current and some level of redundancy…


I’ve tapped into the voltage and overall watts to create these - updated every 30 seconds and stuffed into an RRD. The data is in the API for sure… Just not historical.

Haven’t trended enough to know if it’s useful or not. :slight_smile:


@Dave Hey that’s sweet. Would you be interested in sharing your code and configuration? This sounds like a perfect job for one of my 20 raspberry pis.


I agree that this would be a useful feature. Perhaps to be enabled in settings by more advanced users, since the basic users may find it confusing / not useful.


I would love to see two lines at the bottom of the main graph indicating line voltage for each leg of the 220. Give users the ability to turn that off/on.


Yes agree voltage graph would be helpful… reading the website it implies voltage is recorded but it is not available in any historic format. I’m having a issue where electric car charging is interrupted by ac compressor due to voltage drop and as others have said utility doesn’t have the granular data to support the drop. I’m using nowhere close to my 400 amp service and this isn’t an issue on my side of the meter.


I had an issue and where we live in Kentucky, the utility was required to investigate at no cost to us. They brought out a different meter for one week and this meter recorded what was happening. While our meter was taken off, it was tested. At the end of the week they removed the recording device and replaced our meter. A couple weeks later we were provided with the results.
I’m wondering if this may apply everywhere


@scott.f, that is an excellent real life example that explains the usefulness of the historical voltage graph (plus a data export). Hopefully this feature is on the development roadmap.


The only time I’ve monitored the Utility incoming voltage was using an enterprise-grade APC UPS (as mentioned by others). I had it hooked it up with a serial cable and logging onto a computer which was part of a homebrew server farm. This was Lower Manhattan on the morning of August 13, 2003.

I stared at the graphs, as you do. Feel the power!

Sometime in the afternoon the APC relays starting clicking and the thing was going crazy beeping and generally letting me know I’d probably screwed something up. Oh boy.

Then boom, BLACKOUT.

I still feel some responsibility for what was supposedly the second most widespread blackout in history.

That said, yes indeed input voltage logging and graphing would be a very handy feature but at minimum (as discussed elsewhere on the forum) I’m still hoping for a pro-active max load watts ( = panel current overload) and min/max input voltage alert. This wouldn’t involve, I assume, any particularly complex GUI rebuild or backend complications. The hardware is already sufficient. At minimum it could simply be a universal non-adjustable alert that the input voltage is lower than a particular threshold or the load is approaching the 200A Sense CT max. For all we know this could already be a feature?

Related to that is my understanding that Utilities will often drop supply voltages at peak load (generally in a heat wave). It would be nice to be aware of when that happens … if nothing else it could be used as an alert to tweak the AC thermostat to avoid the guilt of causing the next blackout!

And a final thought: there are increased postings from eCar owners (congratulations!) and those with PowerWalls and other wonders … max current seems like a real possibility as does the Utility tweaking the supply voltage down more frequently that in times past.


The problem with this is there are many users successfully using Sense for 400 amp service. They could suffer alerts or whatever was out in place that would degrade their experience. The overall idea is great but the 209 amp preset cutoff wouldn’t work well.


May want to tread carefully here: “electrician required”

As far as I understand a 200A-rated CT like the Sense ones is not going to give you meaningful output beyond its max 200A rating. It could tolerate, perhaps, slight overload current for a short period but would certainly not meet code requirements if installed in a panel (forget the actual panel rating) if the actual wire current is ever over 200A. Most panels are going to be loaded with significantly less than their rating so, sure, you could put 200A CTs in a 400A panel but you would still benefit from an alert at <200A. Derating is usually 80% (I believe) so an alert at 160A would be “safe”. Yes, the alerts would be annoying if you have a 400A-capable wire but they would also be telling you that you are wrecking your CTs. Could be wrong. I guess this has been discussed somewhere.

There’s nothing to stop you using alternate CTs on the Sense but physics dictates the higher the max current the lower current resolution is going to be.

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I’m curious what the NEC has for codes when it comes to Sense or other monitors . They are not actually part of the electric service and current passes “by” rather than “through” them.


Strictly speaking the Sense itself, as a device, is a hybrid because it’s fed by direct 208/240 @ low current and, via the CTs, “current passing by”. I think the NEC has been pretty clear on CTs and cabling within a panel but there’s probably argument about what line powered devices (line powered) can go inside a panel.

Sense is Intertek certified so it’s all been thought through I guess.

My main point above was suggesting that you might want to be careful putting a 200A CT on a 400A wire. Maybe there’s an electrician out there who can weigh in on those calculations: what happens to 200A CT hit by say 300A for a few hours? I assume it won’t melt but it must start to get warm?


I know if at least one user that has been using the CT’s on 400 amp service without problems. I think he experiences some clipping.
Somewhere here, there is discussion on this subject but I don’t remember where it’s at.


Not an electrician, but an EE.
I’m guessing that Sense chose the CT to get close to, but stay out of flux saturation at 200A, to avoid clipping due to saturation. But even at that point, the CT is going to be losing energy to heat due to hysteresis. Pumping the current by another 50% might only increase the lost energy by 80% or so. I think it might get a bit warmer, but not hot. Biggest issue is that both the CT and the A/D will saturate and clip, so power waveforms will be flattened.


I looked for a chart or calculator for that … not wanting to really work it out!
This is reassuring to hear from an EE. Thanks.

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