My value of 176 for the voltage calibration assumed your original transformer, divider and a guess at the transformer regulation; which is why I wrote “about”. You can never calculate the exact calibration value because you do not know the exact value of every component. The way you measured - mains voltage and Arduino pin voltage - is actually what all the maths about transformer ratio, regulation and divider ratio is all about and if I’m not wrong, the last line of the explanation says exactly that. The only way that you are wrong is that this number does not take account of the ADC reference voltage not being exactly 5 V. The accurate way to calibrate is to look at the voltage that your Arduino is reporting in software, and compare that with the mains voltage that you measure.

The real reason for calculating the calibration constant is to show whether there is a gross error somewhere - which usually means a wrong or faulty component. If the value you calculate from knowing the component values and transformer ratio is close to the value you get by trial and error, then you can be confident that everything is probably correct. (This is how we found that your input circuit was wrong - proving the method works!)

So to your motor.

You have a 3-phase auto-transformer, which I presume is star connected and you are measuring line-neutral voltage and line current. I also assume your motor is a balanced load (there is something seriously wrong if it is not - but a few percent of imbalance can be expected.

I’m a bit surprised that the current wave is a sinusoid but the voltage is not - I think that might be the transformer is being used outside its rated capacity - or is it just a bit of “flat-topping” that you’re seeing?

But “This distortion would change the rms value” is quite incorrect. The rms value is the direct current that would give the same heating effect in a pure resistor. The *relationships* between rms, average and peak values all change when harmonics are present, but if your meter measures true rms current, or voltage, then that is what you measure whether there are harmonics present or not. EmonLib also calculates the true rms values of voltage and current, and the true average power (note there’s no such thing as “rms” power - that’s a nonsense). You can look at the maths to see that.

You might like to read @dBC’s post: Measuring reactive power to build NILM system - #7 by dBC