3-phase power consumption measurement

Hi folks,

Wife has asked me to measure the power on every of the 3 phases, to get a quick overview of our power consumption.

The shelly 3EM looks pretty cool and affordable. It has a clamp for every phase wire:

P.S. photo taken from this video by @nygma2004, and added some label to it myself...

I like such clamps, because then I don't need to mess with my existing AC wires.

However the disadvantage is that it uses wifi. Don't have wifi at the locations where I need to install this device. Would like to have something similar using ethernet, which means via a CAT cable.

The Shelly pro 4 has ethernet and 3 phase power measurement, but internally the L1/L2/L3 are interconnected. Which means it can only measure 3 circuits on a single phase. Buying 3 of such devices would be a bit too expensive...

The shelly pro 1 pm/ offers power measurement of a single phase via ethernet. But then I need 3 of those devices, and it doesn't use clamps so I need to change my ac wiring...

Does anybody knows whether the clamps are accurate enough (compared to attaching the wires directly to the power meter)? And does anybody knows a decent/affordable 3-phase power meter with ethernet?

Thanks !!

BTW. I do not have a digital meter with a P3 port to measure this. And yes I would like to have a wired solution :wink:

For residential use, clamps versus hard wired are the same resolution. Disclaimer, it has been a few years now since I did this so buyer beware. The biggest difference was price as clamps were always more than hard wired. Unless you are shooting for laboratory accuracy either one should work just fine.

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I'm running https://www.aliexpress.com/item/4000763433216.html on Modbus.
Should be calibrated and clamps chosen according to max load.

Edit: Although I'm going the other way round. In the process of replacing it by a EASTRON SDM630 Modbus-V2 MID

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Bart i know you hate wireless - but before we get into that - what are you trying to achieve ? Just total whole of house power measurement - seems pretty pointless ?

I use a device called an IOTAWATT - it has 14 channels for monitoring individual circuits as well as your mains draw (so you can know how much power your oven is drawing, or all the lights in your house etc.

I have 3 of them for the various circuits in our house as well as our Solar, Mains, and battery.

Highly recommend them - but they do run on our friend the ESP8266 - in one location i was worried about wireless coverage so i ran a cable to the location and then put a small cheap Wireless access point there - never an issue with it.

and this router

I have 4 of these routers spread around our place for our IOT network as i gave up trying to find reasonably priced sensors and devices that were not wireless.


Hey Craig,
I not really agree with that. In a couple of months we will have to start paying for peak usage. But at this moment I have totally no clue at all about our consumption. So I want an overview of all consumption to start with. Afterwards I am going to start monitoring the highest consumers in our house.

By showing this total energy consumption in our dashboard I would like to achieve:

  1. Awareness of all my familly members about their behaviour and the effect on the total consumption.
  2. Get a grip on a the sleep usage and unexpected consumptions at some times.

Ah that is very interesting indeed. Especially since I have already some ethernet wired esp's running for other purposes. Thanks for the link!!!!

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Hi, i am use the Aeotec https://aeotec.com/products/aeotec-home-energy-meter/ with Z-Wave. And it is accurate enough. The deviation in the sum of the three phases to the current meter are less than 2%.

I would also recommend the Eastron SDM630, but since you mentioned about not changing the current installation, it is not ideal.

Maybe this product could be of interest for you:

This is a 16 channel current meter, with 16 current clamps. This has modbus RTU as well, but you should be able to use it with an ethernet based ESP board.

I have this beast and already made an Arduino sketch for it, although I have not installed it yet. You can find my video on this and the project in YT, and the project on Github.

The obvious advantage is that you can measure 16 different circuits in your house. The drawback that this is a current meter only. It does not measure voltage, so you either just multiple with a theoretical voltage, of you need another device that measures voltage. I am planning to use my Shelly 3EM to get the line voltage for each phase. But to be honest if you need trends and detect peaks, the current is probably sufficient as well.

I designed the sketch to read the 16 channels every 2 seconds and use that reading to calculate the consumption for that 2 seconds in Node-Red. It is an assumption, but I am not planning to use it for accurate measurement, I want some general data analytics.
My initial plan is to dump all the data to influx and start doing all sorts of queries like: is the usage in the last 15 minutes above long time average (fridge door left open), look for weekly, hourly trend, see if the usage in this period higher than average? Just throw all this on the wall and see what sticks.

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...as already recommended by others, I'd go for a real meter. Use the modbus variant and add a modbus/tcp converter, plus use a PoE Splitter for powering the converter (easy to reset from remote when things/comms get stuck).
I am using this openWB EVU Kit v2 MID – openWB in orrder to enable my EV Wallbox to meassuure the excess energy available from my solar panles to charge my EV.. It is super easy to connect and use via NR.

Whoa, OK...interesting.
Maybe you will need a special meter, that is also holding registers for Pmin/max/avrg in 60sec/15mins intervalls, then? That is a totally different kind of equipment and much more expensive, as it normally needs a synchronised time-source, AFAIK.

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Aaah right - that makes sense - i would definitely recommend the IOTAWATT then as it will be able to do all your extra channels when you want to start drilling down into your actual data (i have a seperate circuit to our kids bedrooms and can tell when they turn on their heater in their room (even though we have central heating) and have the system start turning their lights on and off !)

The IOTAWATT has a query language that is simple to use from NR - essentially a REST query and i am able to ask (for instance) for the average grid draw for the last 3 seconds (it stores all of its accumulated data on an SD card)


I still had no time to investigate this further.

But there are some other possiblities:

  1. A PZEM-004T board (e.g. here on Ali) which measures Watt & Volt & Amp, again with two types of clamps possible:

    In all setups I like the open-close clamps, because then I don't need to detach any of my 230V AC wires (i.e. non-invasive approach).

  2. An SCT-013 current sensor (e.g. here)::


    But of course then you need an extra board to connect this to e.g. an esp32. Of course you only have a current measurement, not voltage. So you need to estimate and calculate this yourself.

Didn't find yet a solution where you can connect N of such sensors to a single esp32, and then read those N sensors via wifi/ethernet via that single esp32. If any creative brain in this community has ideas about that, I would love to hear it.

Hi! I use SmartPi (https://shop.enerserve.eu/detail/index/sArticle/330/number/100047.6) which has an raspberry pi build in. So it has wifi and ethernet. Included software packages are node-red, influxdb and grafana setup so that it works out of the box.


Hi Bart,
I'm using the PZEM-004T (with the open CT clamp) flashed with Tasmota - it works really well.
Measurement is sent via MQTT to Node-RED and displayed on NR dashboard and logged to Clarify.
At the moment, I only measure the total counsumption of my house.

I was thinking the same Dave, but instead of MQTT using the RS485 interface for Comms.
I've never used the PZEM, as I already measure power from a self- build device.
It's easier to install if you use a split core CT as it saves disconnecting power cables.

The link below gives the specs.

£3.89 37%OFF | PZEM-004T 3.0 Version TTL Modbus-RTU Power Meter Kwh Meter AC Single Phase 100A Electric Volt Amp Frequency Power Factor Tester

Hey David,
Lets pause and rewind a bit :exploding_head:

  1. You say you can flash Tasmota on this device? Have you more info about that please.
  2. I would have never thought you would ever use the word "Tasmota", after you spend evenings teaching me about EspEasy. So I assume EspEasy is not possible on this device? I had hoped to be able to stick to 1 software for all my microcontrollers.
  3. And how does this mqtt client connect to your mqtt broker? I assume wired?

Hey Paul,
Some questions about this:

  1. Is there any reaso why you would prefer RS485 instead of mqtt?
  2. Do you mean an RS485 to TTL converter and then connect to the gpio pins?
  3. Is it possible to chain such devices? Otherwise I would need lots of gpio pins...

Is the device in your link another one as in my link? The price of yours is better than mine...

Hi Bart,
When I tried to use ESPeasy two or three years ago I couldn't get it to work with the PZEM-004T.
The situtaion might be completely different now,

Here's a link to a write-up I did about how I interfaced the PZEM to a Wemos D1 Mini via level shifters.

This is what the home page looks like in Tasmota for the PZEM.

To put your mind to rest, I actually have a number of devices flashed with Tasmota, for example some Sonoff Basic, S20s and S26s - as well as the Wemos I mentioned above.

EDIT: Just upgraded Tasmota to the latest version 12.2.0

Looks like ESPHome also supports these devices directly.


As you have no wifi at that location, I haven't a clue how you would handle MQTT msgs over cable?? If you can do that, yes, MQTT would be better.

No, it's the same. All I can say is :laughing: :laughing: :laughing: :laughing:

My PZEM-004T module (in the nice see-thru plastic encolsure) came with an RS485 cable.
I cut the USB-end off the cable and connected the wires to my level shifter.

When I upgraded Tasmota (just now) I had to change the setting for GPIO4 to get it working again.

If you decide to go down this route, make sure you get the correct version of Tasmota.


If you are performing a brand new flash, then use 'tasmota-sensors.bin.gz'
If you upgrading from a current version, then you need to do a two-step upgrade.
First flash 'tasmota-minimal.bin.gz' then 'tasmota-sensors.bin.gz'.

This is an interesting discussion about using the PZEM's on 3 phase.

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It seems to me that EspEasy should support it, in their energy build (see here).

Although not quite sure yet what the descriptions on this tabsheet mean. From this discussion I assume that it is not possible with this plugin to have multiple pzem's on a single bus. But not sure...

BTW thanks for sharing the Tasmoto screenshots!

Hi Julian,
Yes indeed EspHome offers a lot of nice stuff. However I try to keep the number of technologies as small as possible, and currently I use EspEasy everywhere (where I cannot run Node-RED yet). But good that you mention it!

Ok, you lost me :woozy_face:

  • So I need to wire the pzem to an esp via an RS485-TTL converter. Is that only because the voltage levels of the signals need to be changed, or is there a protocol switch or something else required?
  • Suppose I had wifi in that area. In that case I also had to wire the pzem via rs485 to the esp, and the esp executes mqtt over wifi. Is that what you mean?

I have a couple of wt32-eth01 devices running. So an esp32 with wired ethernet. And I run EspEasy also on that one. So I assume I have to connect the PZEM-004T (via an RS485 to TTL converter) to my wt32-eth01. But that would only make sense if I could attach a series of those pzem devices to a single wt32-eth01. Not sure whether that is possible...