Derived Three-phase questions


Hi, I have a question regarding derived three-phase: Should I always pick the phase that gives the highest power reading? One example: Right now my heat pump reads 1300W on phase B, 880W on phase A and 440W on phase C. If I use phase A or C, I get reverse polarity symbol in IotaWatt’s status screen.

Now, it has been on phase B the past week or so. I have compared kW/d readings with the heat pump’s own reported daily power consumption (on the unit’s screen), and the Iotawatt consequently reads higher consumption than reported by the HP. Typical values are
Tu: 20 kWh vs 14 (HP disp), IotaWatt 43% higher
Wed: 25.4kWh vs 20 (HP disp), IotaWatt 27% higher
Thu: 13.2kWh vs 9.3 (HP disp), IotaWatt 42% higher

So the factor is not entirely constant, but sort of. AFAIK, there are no other users on that connection. If the IotaWatt had been set to phase A, it would have given slighly lower (but closer) readings than the HP, while phase C would obviously be wrong.

What is the correct setup? Is my heat pump under-reporting??

02_03_20 to be MINOR auto update Jan 2

I can’t speak for the heat-pump, all I can do is help you insure that the IoTaWatt is correctly setup. As a first step, I usually try to get the mains reporting so that they are in close agreement with the utility meter. With derived reference, you should be able to get within a few percent of that.

So if you want to do that, you should start by reading the derived reference configuration documentation at

Then you might post a picture of your mains and a screenshot of your inputs display. My online time overlaps with Norway in your afternoon/evening, so if you get me in your afternoon and are prepared to go back and forth, we might be able to resolve the initial setup in a few days.


Really appreciate any help, so I will post photos and screen shots soon.
For now, I have one question: I got all the polarities wrong on the CT sensors. On the three mains, I switched them around (easy) but on the rest of them (the 0013’s) some are a bit difficult to reach. For now, I switched polarity in the config. Will that be a 100% solution or should I take the effort to turn them all around?

BTW , I found using a 1.6kW hairdryer an excellent tool to figure out polarity and phase.


B[quote=“OlavKristiansen, post:8, topic:591”]
For now, I switched polarity in the config. Will that be a 100% solution or should I take the effort to turn them all around?

That is a100% solution.

Great. When using that exclusively on a circuit, the PF should be 1.00. If on the wrong phase, it will be close to .50. On the correct phase but backwards, the power should be ok but it will show the reversed sign. Wrong phase and backward is where it gets crazy.