What causes this reading to be "pulled"?

I have a 240-volt split phase system in the US with solar generation feeding a subpanel. Solar is 240V and has a single CT (no neutral) while the subpanel (Hangar) has two CTs (and a neutral). The system has an integrator for the two Main CTs.

My question is why does the mostly-constant Hangar usage appear to be “pulled” by the Solar generation as shown in the graph below. The normal Hangar usage appears to increase slightly during solar generation.

For completeness, here are the Inputs, Outputs, and Integrator.


Independence, OR

The first thing I would look at is the accuracy of the Solar CT vs the two Hangar CTs. You have defined them as “generic”. What are they and are you sure the calibration is correct?

The Solar CT is a YHDC SCT013 50A/1V current transformer with the burden resistor removed IAW this thread (thank you craigcurtin). I configured it for a turns ratio of 1860 and it gives a good comparison with the revenue meter.

The Hangar CTs are YHDC SCT013 20A/1V current transformers, again with the burden resistors removed. I set their turns ratio at 2090:1 after “calibrating” against a Kill-a-Watt. Alas, there is no revenue meter for comparison with these.

But after your response and re-reading that entire thread I believe I need to do a better calibration or at least tweak the turns ratio for the Hangar CTs until I flatten out the Hangar curve. I’ll report back when I have some results.


I’d recommend you get at least one AccuCT and use that to calibrate the bastardized YHDC units. IMO the YHDCs are of lesser quality to begin with and worse after mutilation. While I endorse the Kill-a-Watt for voltage calibration, my experience is that they are somewhat less accurate for power, especially at low power. Echun CTs are very good as well.

No argument: it would be best to do a “real” calibration. But working on the panel is somewhat problematic at this point. So I tweaked the turns ratio (at about 1300 in the accompanying graph) until the Hangar curve flattened out during solar generation and the results are good enough for my purposes. This involved a turns ratio change from 2090 to 2203 and now I’m a happy camper.

If that’s good enough for you. My experience with those voltage output units is that they were all around 1860, and I’ve tested quite a few. So while they may balanced now, I suspect your solar generation and usage may be overstated by 13% or so.