What are the Current Sensors (CTs) Accuracy? What Class CTs are for Sense Main & Solar

Can anyone expert or Sense Technical Support Team provide detailed Specification on the Current Transformers used in the Sense Main and Sense Solar Current sensors?

We can see these are split core current transformers (Sensors) with CAT IV 250V, 200A ratings however it doesn’t specify the current measurements accuracy class.

I would like to know what accuracy class current being measured.

Thanks!

My assumption is that they are class 1, but its possible they are class 3.

You can search for other posts where people have gone into great detail on comparing their Sense reported numbers against the power company stats. Generally speaking, the consensus is that the Sense is within 1-2% of the electric company bills.
That 1-2% can easily be explained by a brief power outage, network connectivity issues, or the difference in time between what Sense considers Start and End of billing period, vs the power company. Or if there is still someone coming to read the meter by hand showing up at 10 am.

I am assuming Class 1 based on my own and other people’s observations of the perceived accuracy, in addition to assuming that Sense wants it to be accurate, but isn’t going to spend the money on a true revenue grade Class 0.x meter to save a little on the build price.

All that said, @kevin1 who has done a lot of digging into all of this may know more, or maybe JustinAtSense is able to give an official answer if possible.

1 Like

Hi @Manny1314. Accuracy for CT’s is within +/- 2%, but we are typically closer to .5% in testing.

3 Likes

That answers my query. That is pretty good.

Usually CT class are shown on the CT’s itself but it is not listed for sense CTs, So I had to ask.
Thanks for the input.

1 Like

Of course, great question.

1 Like

@Manny1314,
Here’s a view on hourly accuracy for my Sense setup with solar, so 2 sets of CTs involved. I’m comparing the % difference between my Sense hourly net usage (Total Usage - Solar Production) and my utility (PG&E) net meter. The color denotes the net usage range. It’s expected that % differences can get much larger when the value being measured becomes smaller. This is 2020 data to date, a little over 8100 hours, with the hours with known connection and Sense monitor issues removed. Pretty darn accurate.

Since the difference is fairly symmetric, measurements might even be more accurate for longer aggregated periods.

2 Likes

Hi there,

When I fist installed my Sense monitor I wanted to ensure the accuracy of the output with the utility meter. So I started a spreadsheet and compared observed meter readings with the Sense data. It was off by 14% or so. Through the communities help (this community) I had identified the source of the error. I questioned the utility and they stood by their meter citing stringent calibration before they install their meter. It was suggested by the community and the Sense folk to ensure the CT clamps were completely closed. I did that and I didn’t noticed any appreciable gap, but I applied a bit more pressure to close the clamps and then put a piece of electrical tape on the CT’s. I then began my observed readings again and over the period of 320 hours of elapsed time the utility meter reading compared to the Sense data was off by 600 watts (.6kWh) on a total usage of 1,103 kWh.

Thanks,
Hayward

2 Likes

I don’t know whether this is an accuracy issue or not… But what I can tell you is that for my November solar production, the Sense total production was 97.7% of what my solar inverter reported.

Likewise, on my consumption, Sense total consumption was 96.9% of what my metered consumption showed.

Again…not saying one is more accurate than the other…but they are off by low single digit percentages from each other…

1 Like