I Got A Friend Excited About Purchasing and Installing Sense... However

I was in a meeting with a co-worker and started doing some screen sharing with him on my Sense web dashboard… He was EXTREMELY excited about installing Sense…

And then I found out that his setup might not be compatible with Sense… I need your help to let me know if hey can implement Sense, and if so, how… And perhaps the answer isn’t “YES”… Maybe the answer is a “YES, BUT…”

He has a 400A service with a 30 panel solar system and a 100A sub-panel feeding another residence (his in-laws live in the unit serviced by the sub-panel).

He wants it all… He wants visibility to all of his consumption, as well as solar production…

Is this doable at all?

I have a 400A main service with solar, all using a single Sense. Even with 2 EVs charging and 2 AC units on, I never exceed the 200A limit of Sense’s calibration, so I was able to put Sense onto my 400A mains and use the second port for solar. To do this, I needed to put my main CTs into the electric meter box ahead of the meter because the mains immediately branch out into a busbar that feeds the two subpanel when they exit the meter. I can share more including a picture if you are interested.

ps: I do have a second Sense, but I use that for DCM measurements for a couple of my 240V devices.

Ah… So the 200A limit is not a hardware limit… He can’t the CT clamps around his 400A service, as long as the power consumption does not go above 200A, is that right?

What happens when the consumption goes over 200A?

At some point/place on this forum @RyanAtSense answered that question. The CTs are calibrated together with the Monitor to work up to 200A. Above that current level you might see clipping of the current waveform (flattening). Not a hazard, but an accuracy issue.

What happens when clipping happens? Will the data look strange for the short amount of time that consumption goes over 200A, and quickly returns to normal and accurate after usage returns to under 200A?

And does it happen immediately at 201A? Is it a binary condition? Or does it survive a small breach into the 200A+ range, and gets worse as it approaches 300A and 400A?

Is there a possible graceful solution if he is willing to purchase two Sense devices to avoid this clipping issue?


Now we are into educated guess land… There are two reasons CTs will clip.

  1. Saturation of the CT core - transformers have a linear range where AC current through the CT induces AC current in the sensor coil of the CT, in a nearly linear fashion. At some point the current hits a “knee” and the sensor coil current begins to flatten even as the CT current increases, causing clipping of the sensor current. This is a graceful effect that slowly causes the sensor current to fall off. Sense may have already calibrated for this effect.
  2. Exceeding the range of the A/D converter - inside the monitor is a device that converts the voltage across a reference resistor that is fed by the sensor coil in each CT. That A/D converter is set to a maximum range that is somewhat above the voltage that would be produced by 100A going through that one CT (200A for both CTs.). I’m not sure what the margin is, but if you exceed that current, the measurement will flatline - a hard clip.

I’m not sure there is an easy 2 Sense approach for them unless there is a clean branching of the main panel from the sub-panel that allows one to put CTs on pair of mains that feeds each and treat them separately. That would be what some people call parallel sub-panels.

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You beat me to it, @kevin1. Can add a little bit more on each of these after speaking to hardware.

To add a bit more detail, at 200A data should be fine. As the current increases, the CT will start to saturate and it will become increasingly inaccurate, but it will return to normal as the current drops.

The only thing that here is it’s actually per sensor, so each leg can go over 200A and be fine. So they could get to 400A total in the panel and still be okay.

At a certain input level, the current will blow the input to the ADC. This shouldn’t happen until around 275A (or higher.)