Reference Voltage Theory

[overeasy]

“The proof of the pudding is in the eating.”
–Confucius.

Seriously, this post is not the basis for a discussion, but I do want to debunk some of the misinformation.

@Guaitiao

Since most of the USA user will use a Split Phase system (120v) with a single phase system (220v), How IOTaWatt is calculating all parameters if it only uses one split phase of the 220Vac supply? It is wier that this system does not monitor both split phase voltage references or at least the main phase circuit voltage with the L1, L2 and Neutral… Reference voltage is crucial for energy calculation and can not be taken as a given constant… It is actually a variable as well as the actual current variables consumed in both split phases… In Split phase circuits, estimating the voltage from L1 to Neutral, based on the Voltage reading in L2 to neutral, is not a good approach for accuracy in the estimation or calculation. Be careful to trust something that don follow the very basic laws in electrical circuits…

I point the reader to this post from a couple of years ago:

120V/240V split phase voltage reference

I’ve been monitoring my US split-phase service for two years now using a single 120V reference on one “leg” of the service. The results have been excellent, with overall and individual results within 1% of the utility meter and several revenue grade EKM meters on individual circuits. I long ago became comfortable with the notion of the single 120V reference, even though that voltage typically varies between 119V and 121V throughout the day with excursions even further off the mean from time to…

@Guaitiao

This means that when it says it is passing 1 Amp through the wire it is actually passing 1.0 Amps and not 1.25, or 0 Amps…

To suggest that CTs may be +25%/-100% accurate is completely wrong for even the most low quality units. Reputable manufacturers typically produce CTs that are +/- 1% or as in the case of the AcuCTs +/- .5%. You would be hard pressed outside of a lab to find equipment capable of finer calibration. As a practical matter, field calibration is not possible, or for that matter, desirable or necessary.

@Guaitiao

This readings greatly depend on the Wire Size, the tension or Voltage and the induction noise around the CT Pick Up sensor affecting the CT reading or accuracy.

Wire Size and Voltage have nothing to do with the current reading of the CT. If a #8 wire is carrying 10 amps in a 240V circuit, it will read the same as a #14 wire in a 120V circuit carrying 10 amps. Induction noise, except maybe when reading milliamps, is a second order factor at best.