Essentially a AC current meter without taking voltage and power factor into account - What could possibly go wrong? 
Maybe just skip installing the current transformer at all and just guesstimate in software - might be even more precise 
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What I still don’t understand from most of your posts is that CT Clamp energy measurement is propagated throughout the smart home community, guides and youtube channels… hence how I came to try it out.
But every post you have is saying that they’re (worse than) useless?
Honest question; are you just the only person out there that understands this? Or are you just being extremely ‘to the letter of the law’ on this?
Is there any scenario where a CT clamp can be useful in your mind, or should all the guides people have written be taken down?
My planned intended use case was to compare my immersion heater on my hot water tank to my gas boiler in months when i’m not using the heating (i.e. the only thing using Gas in my house is the hot water so i can get that from my supplier)
It would be for “one off” comparison, not long term actionability…
What would you say to be the correct way to do this if not with a CT clamp?
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CT (current transformers) are also part of non-contact power meters - but alone they are not more than current meters (the name implies).
I have the intrinsic goal that people educate themselfs. For that I mostly give hints/links which should give the reader enough clue to learn the basics and come to their own conclusion. 
Sadly most users don’t take this extra 3 minutes, or did you @vaderag open the link in my previous post which might have your post made obsolete at best?
No, at least @Jpsy knows about it and was so kind to even explain it. 
Some times I think we are not only living in a post-factual society but maybe also reached peak of education already 
Definitely. Most obviously as part of (real) power meters. 
I emphasis that you first understand why you will not be able to get real/active power readings with a current meter (start with link provided in my previous post and also don’t be shy reading some wikipedia articles) and after that, do your conclusion! Feel free to share it with us 
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In fact I opened and read it twice… but I still don’t feel it made my post obsolete, in fact it prompted my post
I actually feel this is entirely missing the point - people asking questions are generally trying to learn… in fact it is in not asking question that people imply a “peak of education” where people run forward with assumptions
I (like many others given your previous post) watched a number of videos and read a number of articles before embarking on building the CT clamp… they were all implying the use case of energy monitoring - that is not a fault of the learner if the teachers are incorrect.
I was asking why they are incorrect and you are correct
I was taught in school that P=IV… the clamp measures I and the V is defined by the grid (230-240v here)
Power factor was not taught and I still do not understand the relevance - if the current is being drawn then it’s being used and therefore paid for - what relevance does efficiency have to my consumption measurements?
Perhaps instead of getting irate with people trying to learn you could put your efforts towards a guide educating on how to solve the problem people here are trying to solve?
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My post lists plenty of threads in this very forum that (by hard labor) came all to the conclusion that current meters don’t replace power meters in real world AC scenarios 
But your energy provider will not bill reactive power/energy
And just because your teacher told you (with the assumption PF=1) their is no need anymore to do a research when challenged with facts?
Or is it:
So you are good? 
Well, not for private households usually. I emphasis a again starting with some basic articles on wikipedia about (re)active power. Otherwise we both just wasting our time here… 
I came to the conclusion I was wasting my time after your previous posts, but the above post seemed to imply success in this method (as the original guides I read did)
In any case, I guess this can stay on the shelf since the hardware I have is apparently useless according to you
It is funny how I can’t find a single UK source mentioning energy monitoring that mentions this phi number
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That only works for DC power, or AC power that’s purely real (real/active used here is as opposed to reactive, a specific term in power engineering). The moment you have AC, the power factor is critical. I’ve explained this in my posts too.
Can you share just one of those sources?
It was simplified, I’d say. You’re generally not going to teach wave theory and electromagnetics to school children. My school curriculum didn’t cover AC in any detail, so all electrical theory was DC.
It’s useful as current meter or even power meter for electric boiler for example.
Unfortunately not for general energy monitoring since power factor of normal house loads varies (~0.5-1.0)
On images below there is voltage and current, for example 230V/10A RMS. On first one pf=1 and voltage and current peaks at the same moment, so power is IV. On next image power factor is 0, so when voltage peaks, current is zero and when current peaks voltage is zero. If you use voltage meter you get 230V and current meter reads 10A, but your power is zero.
In real life it’s something between of these extremes.
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Sure - was sitting in the doctors reading about this so have a bunch of links in my history…
Energy monitors - Centre for Sustainable Energy
A sensor which clips onto the power cable of your electricity meter and measures
the amount of electricity passing through it.
How to Monitor Your Home’s Electricity Usage
Convert volts/amps to watts: If your appliance’s power requirements are in volts or amps, you can calculate an appliance’s running watts with this equation:
Volts (V) x Amps (A) = Watts (W)
How to calculate power consumption of a device - Energy Initiative
Once you have the voltage and current values, you can simply multiply them together to get the power consumption of the device in watts.
Kilowatt-Hour (kWh) | Formula & How to Calculate Power Consumption
Another way to calculate power consumption is to use the formula P=IV, where P is power, I is current, and V is voltage. This method can find the power consumption of an appliance if you know the current and voltage.
And where I can find Power Factor mentioned, it seems that [ in any case no less than 0.95 power factor.] which would make an assumption of 1 not too far from reality?
(Document Library - Connections quotation (ukpowernetworks.co.uk)) ?
Thanks - that image is very helpful in trying to understand this - but… (and i appreciate this situation isn’t going to occur in real life) I struggle to believe that my electricity supplier is just going to charge me zero in the extreme example - surely they’re just going to charge the v x i even though they’re offset?
At least in Europe residential consumers are billed only for real power, nothing for reactive power.
Did you (yet) read the Wikipedia article about power like suggested couple of times already? 
The first (
.) chapter teaches you about
Active, reactive, apparent, and complex power
But wait! More to come 
Chapter three (
.) does really talk about
Power factor
But actually only briefly 
Still it does link the whole article with the title Power factor directly for you 
Awesome! Isn’t it?
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If you scroll back this very thread about a month you can read following
But sometimes a picture can says more than thousand words… 
(
clickable!)
Those articles all omit very important information. As already mentioned, with AC the PF is vital. They mostly assume resistive loads.
You can calculate the error exactly. Would you be happy to pay 5% more on your electricity bill?
Residential homes generally don’t need power factor correction, which is why if you could manage to have a purely capacitive or inductive load, you’ll be using no real (active) power. Your kWh consumption would be zero. If your provider tracks reactive power, they will of course notice, or they will just think it’s fishy that you have a power connection, yet use nothing. Your provider is safe in their assumption though, as it would be very hard and pointless to make a purely capacitive or inductive load at scale.
I can’t imagine any real life application for this, to have a device that does some work without active power.
Yeah, of course. This was theoretical, but I think you knew that.
Thanks for sharing this - spent some time setting it up today and getting some good data on my power usage (without power factor) on devices that I previously had zero data…
A CT clamp is seemingly no worse than this once dialed in, and with over 10k downloads it seems like everyone must be barking mad to want to do this?!
IMHO the problem here is your validation of the term “meaningful”… If I want to compare usage throughout my house, or to know what is using the most energy in my house, assuming a power factor of 1 gives plenty of data to go on and will allow me to better understand the big draws… no?
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May I suggest you, if you want energy monitor go with Shelly EM.
If you have any single resistive loads to monitor, CT alone is good. You don’t need even to measure voltage to get power, because current draw is defined by voltage.
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You’ve basically nailed it, right there. It all hinges on what a person means by ‘meaningful’, and what their goal is.
In my case, I wanted something simple and quick to give me a general idea of input watts to the separate spur that drives my heat-pump. Something I could look at via HA and know ‘it’s running’, or ‘it’s running harder’, or ‘it’s off’ without having to go outside in the cold. If it could also give me a reasonably accurate steer on rough kWh usage over time, within a reasonable degree of comparison to the figures I’m being charged on my electricity bills (not that they are separate down to that device, alas, but hey, if the totals I see roughly match, and most importantly, my billing cash figures roughly match, then to hell with it; I’m happy!)
It’s all about your objectives.
Certainly, if I have the time (and I certainly have the inclination, and the theoretical knowledge; I just don’t have the time or the tools perhaps), I’d love to know exactly what my real vs reactive power is, and know precisely how many carbon atoms I’ve saved the planet from suffocating on this week, and launching NASA’s new 'Pedant 13 Trollsat" into geostationary orbit above my house. But at this point in time, it’s not my most-important project. I’m fully aware of this method not being precisely accurate, but to say that it’s worse than useless or entirely meaningless is, well, quite frankly, just another guy’s opinion, and he’s welcome to it.
It’s good enough for government work, as we say round these parts. It matches my electricity supplier billing well enough, in its context, to give me an idea of what to expect next time they ask for money, and it’s not let me down yet. Maybe I just got lucky with the calibration? Or maybe the systems I was using to calibrate it with were just ‘good enough’.
My longterm plan is to stick a Waveshare RS485 on the inside of my heat-pump’s main unit, and suck the ‘official’ data straight out of it, and have the heat-pump tell me exactly what it’s consuming, and what it’s doing with it, and its own assessments of things like COP and SCOP and exact flow/return temps, demand inputs, etc, down to the nearest millisecond. I’m ready to rock with that, but I’m still waiting for my heating engineer’s firm to come back and promise me that adding this won’t invalidate the warranty and yearly service contract I have with them. Life sometimes just has to work its way around the hurdles we get given, and sometimes NASA-level precision just isn’t vital, for ‘eyeballing stuff’.
The physicians among us are quite correct, of course. But they’re working to a different goal, I think. Or at least, the goal we’re working to at this moment is not as lofty as theirs is, perhaps. Maybe it’ll come in time, but first steps are just that - first steps. They’re never worthless, even if they’re inaccurate, just so long as you’re aware of your margins of error, and if you can still make use of those numbers, over time, and achieve your current goal before upping the ante, then great. We’re all learning, and one day this planet won’t look like Fallout 4. Or maybe it will anyway, in which case, have fun, don’t electrocute yourself, and fill your boots with enjoyment while you may.
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Sometimes a picture tells more than a thousand words:
- W is what you really use and what you pay for.
- VAr only swings back and forth through the wires between you and the power plant. It does not deliver any real work (but unfortunately heats the wires).
- VA is what you measure with simple methods that do not take Cos Phi into account. The difference between VA and W can be tremendous.
Enjoy your beverages.
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That’s why I drink straight from the bottle, stays cool and power factor is good.
So far I haven’t found a way in HA to reduce the consumption.
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