[SOLVED] Magnetic (clamps) EnergyMonitor acccuracy issues and few general questions (Aeotec ZW95)

I hope there is some electrical engineers or folks with good knowledge and understanding of electricity, if not, can you point me to some good electro forum? Even though I would prefer to solve this here “at home” :slight_smile:

I am not so happy with its accuracy, I must say 99% accuracy is marketing BS. If I knew that, I would go for more intrusive solution (inline wired meter)

The main issue is my induction cooking hob, which is confusing the clamps as it has switchmode powersupply, and is not sinusoidal (according to google explanations of various people with same issues). It shows 100W usage in standby, but real usage with plug-in power meter is 5W. OK, I solved this via simple rule that deducts 100W from the load, but thats not the only issue here…

First, specs:
I have 3 phase 4 wire system in my apartment, where load is distributed on red, yellow and blue phases. All load is single phase 220V, there is nothing that is using more than 1 phase.
I’m using HEM with 3 clamps.

Now, first question that I have:
I did not install this device according to manufacturer specification.
The device comes with 3 power supply wires and demands to be wired directly to the live mains (on the input of the main breaker) of all 3 phases. so each clamp should be powered from a different phase lets say.
I did not want to do that, if I wanted to connect something to the live mains, I would go for something more reliable then clamps.
So I wired all 3 power supply wires to the normal power socket plug on phase1 (red)
I realized that HEM is reading power grid voltage through his power supply, even with the clamps disconnected he knows voltage is 237.2V at the moment.
So I am hoping that this is the only reason why they want it to be wired to all 3 phases, to get the accurate voltage reading for each phase? I don’t care if other phases are 236.9V at the moment, I can live with this margin error.
This is the part where someone with real knowledge can say yes you are right or no, totally wrong install.
One more question about clamp direction - clamps have " K -> L " symbol, dunno what is K, but L stands for load I guess and arrow should point to the direction of the Load if I understand correctly. Anyway I have mostly good and positive reading for 90% of the load, so I assume direction is correct…

Other than induction hob, I have found few lights (some KNX dimmer, some KNX 12V spotlights) that do not show any change or go to negative value! like, load reduces 7W when I start the light.
Also, kitchen exhaust hood fan shows minus 50W on one phase when started!
All other load behaves normally, shows normal positive values on their respective phase when started (some are pretty accurate when compared to plug in power meter).

With all these issues I dont trust this meter at all, I am not confident it will give even close results in kwh as the power company.
Is there anything that can be done to solve these issues? Or just live with it?

I understand that it works best with pure resistive loads with power factor 1
So, induction hob, inductive load, not good for HEM. Kitchen exhaust fan, washing machine - electromotors, not good for HEM.KNX dimmer - doing crazy stuff with electricity to reduce light, confuses the clamps, again not good.

looking forward to your thoughts :slight_smile:

I’d never thought of that - but it’s not so different from a thousand other devices these days, from wall-wart power cubes to dimmers.


In three-phase supplies, the AC phases are carefully and deliberately running out of phase - hence the name.
All phases are cycling up and down + to - volts, but at different times.
When one phase is at peak +volts, another might be at one-third -volts and dropping etc.
As a result, the currents are sloshing in and out like water in a long tub - but again at different times.

To calculate power, you need volts x amps.
You’ve got individual amps from all phases via your “clamps” (which I guess are current transformers). They’re cycling up and down.
But if you take only one voltage measurement, only one phase can correctly calculate power.
Calculations for the other phases will be nonsense, because the volts part of volts x amps is all wrong. You’ll be looking at peak current when the volts is off-peak, and vice versa. That’s how you get a negative power reading - you’re not generating power, you’re misreading.

Yes, the meter really is calculating instantaneous power during the cycles.

Root of the misunderstanding - NO!!. The voltage taps are also used to determine phase timing.

It’s pretty arbitrary but sounds like you have it right - the important thing is they’re all three pointing the same way, the secondary thing is getting it the right way round. if the meter think’s you are consuming and not generating, it’s right.

Bottom line - use the product as the maker tells you.


Great man thanks. This is great news :slight_smile: there is hope that my measurements will start having more sense :slight_smile:
One more quick question - is it mandatory to connect the HEM cables to the main circuit breaker (as the manual wants), or I could connect them somewhere else down the line?
The phase timing reading should be OK somewhere AFTER the main house breaker or no?
Do you recommend to connect neutral BEFORE or AFTER connecting live?

The manual is not that clear to me, it says
Insert the HEM’s live AC Wire into the main circuit breaker’s live terminal.
But on their schema, it is connected after their main circuit breaker, I want to be as far as possible from the input mains which are live :slight_smile:
Ideally I would not like to touch the main breaker.

thanks again!

Review what you are trying to achieve.

You want the current taps to be measuring all the current you use. For that purpose, it doesn’t matter if they are at one end of a length of wire or the other, so long as it is ‘upstream’ of all consumers.

You want the voltage taps to be as close to the electric supplier’s meter as possible, if you want to match what they are billing you for. Here, being at one end of a wire or the other (or one side of a breaker or the other) can make a difference, due to voltage drop along the wire.
But in practice that drop is (or should be, with decent wiring) negligible, and you can tap the volts where you like.

Unlike your supplier, you probably also don’t care if your meter drops dead with a breaker turned off.

thanks again, connected properly as advised/designed, everything runs perfect now, even the mysterious induction hob cooker issue is gone.

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