Reference Voltage Theory

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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…

Other point to take in consideration is the Actual Calibration of the System… The system accuracy of the actual Energy calculator depends on the full calibration of all inputs with their respective current CT sensors…Many CT sensors has their own calibration characterization chart and many others has a zaro and span adjustments to properly calibrate the sensor to ensure the sensor is with the accuracy and within specifications… 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… 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. The same applies to each input of the system. The complete calibration by loop, meaning each input channel must be verified by loop or with all its components connected together (Cable, CT, Reference Voltage)…

Usually, this systems developed or customized as DiY, do not follow strict quality standards. They serve their purposes, as a for reference only. If you base your economic decisions in a instrument that does not offer good Quality control standards on its design and installations, then I suggest to always take in consideration that your reading might be biased by incorrect readings.

Established that point, I believe this system serve a purpose and cover the energy measuring needs for the average energy consumer… whose goal is to have an idea or an approximation of their energy consumption…

Nop, I am not a Sense, Schneider, Wibeee, or any other brand representative… I am just an average energy consumer…

I would like to see a furder hardware approach to monitor loads. Perhaps, focus on smart power outlets connected by WiFi, Power Bus, or any other communication ways. The way the system is designed, is not flexible. 14 inputs just monitor 14 circuits, and only there amperage. If you have 10 equipment connected to a circuit, then which one is On consuming energy? If you can use Smart Power outlets, then you might be able to isolate each equipment connected to every outlet… improving the monitoring to the equipment base system instead of circuit base approach… Of course this could means the incursion to new ways of automation bus like, ModBus, DeviceNet, and many other Bus Communication technology used in this days for Industrial Automation, and DAQs, SCADA, PMS, MES… applied to Home Automation…

Many other systems in the market, use Smart algorithms to detect and create a DataBase of the equipments bases on usage and behavior of each equipment. Using the help of the user, but annoying them with excessive messages just to try to acquire the knowledge to Identify the equipment. It is not a good approach… but the cheaper one. One alternative is to incorporate an ID of every equipment based on the out side where it is connected. This is actually very close to be accomplished by the Smart Outlets and Switches… Those tou can assign a description for the equipment it serves to easely ID them in ab App. Why not to adopt this approach and do some changes to ensure your Energy Management system integrates in this Home Automation approach.

The purpose of a value added system in Energy Monitoring, is to create an awareness of the proper energy saving approach for the average energy consumer. Where the consumer can target the specific Equipment in their home that need to take corrective actions with a proper Energy Management strategy… Where in my home is the 20% of the equipment that is Consuming the 80% of the Energy that is draining my pockets…

Start building on this type of hardware will lead you in a wrong path where is not an exit and will require to trough everything to the garbage and start over in the drawing board for a more flexible hardware approach.

However, it is a good starting point for the average consumer. I am not trying to dismiss this system. I am trying to make the click for those working on the development of this project, to start thinking and designing based on a more flexible and accurate approach. Targeting Energy efficiency and Energy cost reduction. This first steps in this project should be the inspiration for something bigger. Please, just done let the system at this level.

By the way, I am truly considering to acquiring the system.

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“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.

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

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.

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.

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Even when the CTs might be rated to 1% or even less. This is the accuracy specified by the manufacturer under total controlled environment. The total deviation need to take in account all the environment in the specific installation. Wire Size matter to ensure, the minimum require core isolation is met, between the primary and secondary,… Size, type of conductor, shield type, load, voltage, all factors affect the magnitud of the electromagnetic field is created around the cable. Yes there is a common basic law that might be applied generally…

When you connect all instruments together the total circuit accuracy depends greatly on the error introduced by each instrument and but also introduced by external factors. The fact that each CT comes in different Sizes and shapes is to ensue it serve the proper transformer sizing for the application. External Temperature, External Electromagnetic Field, Transformer Core, Burden, Core magnetization, physical configuration, and many other factors will affect the CT Accuracy, repetitivity and performance. The characterization of every CT maintains all this conditions under controlled environment… in Order to find the optimal specification for the CT… Under their Lab controlled environment. Not necessarily to the each specific Installation. The practice not necessarily meets the theory.

It is recommended to test the system against certified equipment (NIST or other certification institute, or at least ensure the manufacturer of the reference instrument is certified) in situ. To ensure our installation is correct and it is not affected by the operation of our loads, and to mitigate and correct every CT installation to ensure it is not being affected by the sorrounding magnetism created every time a heavy load starts…

My Industrial expirience with CT is that most people asume their spec as a given…But in the practice the accuracy of the Total Loop might be biased by all connections, circuits and instruments affecting the performance of the loop.

I have being involved in many fields, design, implementation, calibration, certification, and validation, investigation related to Pharmaceutical Products manufacturing equipment and processes which the quality of the product depends on a current measurement as a critical parameter in the process. I used to be a Machine development and process Development Scientist.

I have found improper design implementation from Japanese, British, USA, German, French and Italian pharmaceutical equipment manufacturers that fail to comply with very basics calibration, installation, and application of the CTs. Causing millions $ in losses in Pharmaceutical Product rejects. Mainly caused by improper readings from a CT and there respective application, installation and Calibration in their entire zero to span range.

Of course I am no trying to apply all requirements to a none critical application like measuring a house energy consumption. But the user should ensure at least that the current and voltage readings are accurate enough to be trusted. At least a Heavy Load test shall be performed to ensure the readings are not affected by at least by external electromagnetic fields caused by improper installation. To accept a reading as acceptable you must compare it with a (certified) equipment in at least three points of the entire Span… 0%, 50% and 90%. This might vary.

For example if you turn off all your breakers for your loads…Your should be reading a Zero Values. If you turn on a heavy load, perhaps an electric stove, The reading should conform the reference voltmeter reading, with the IoTaWatt reading and should compare to the expected calculated reading… If you turn one heating element of the stove, the reading you are measuring should be reflected only in that input… While you are increasing the load, by turning every heating element and increasing the heat, you should only get the expected reading. All other loads that are turned off, should not give you any reading… If any does read, for example every time you turn on your stove, then you get and external magnetic field influencing in the CT for the load that is reading something, but it should not since it is off…

Those external magnetic influence shall be found and corrected to ensure proper and trustable reading…

It might no be the CT it self, but it might be the input or an improper connection, it might be improper CT Size… Improper CT Phase or direction, all those little things that can alter your readings and hence you total loop accuracy.

All inductive, Resistive and Switching loads might present different challanges in the voltage and curren reading using CT… The user must keep an eye. Every tome a motor is activated, or a heavy Resistive load like the Stove…

What I have see in some installation pictures for the CTs used for a IoTaWatt is that many people do not have enough space in thier distribution panels, and they indiscriminately pack these CTs in whatever place and in whatever direction they could be fitted.

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Hmmm… So, from my personal experience, I have found the IoTaWatt to be very accurate when installed per @overeasy’s instructions found in the documentation. There is no need for microAmp accuracy when monitoring a home electrical panel’s circuits, thus no installed calibration is required nor would it be a wise use of one’s time and money, IMHO. I have compared my power company’s energy tracking to the IoTaWatt’s energy tracking and have found them to be within <1% of one another. I am an Electrical Engineer with over 30 years of professional experience, and I have not found the IoTaWatt to ever not perform up to its advertised specifications. It works extremely well for such a low cost solution, and has helped me to easily identify branch circuits with inefficient devices, as well as a faulty Nest thermostat that was continuously calling for my HVAC systems auxiliary heat strips to run continuously (fun when the AC and Heat Strips fight each other for half the night! :wink: ) I also use it to help with home automations, such as sending notifications whenever my washer or dryer complete a laundry cycle via the Hubitat integration that I wrote some time ago.

I can fully appreciate that medical devices may require tighter tolerances and specifications, as we are possibly talking about devices that influence whether or not a patient lives or dies. But in the field of residential home energy monitoring, the IoTaWatt performs amazingly well, and provides the homeowner with amazing insight into energy usage throughout the entire house.

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