Measurement of 3 phase power as in most of Europe


Measurement of 3 phase power as in most of Europe


In large parts of Europe, 3-phase power supply is used in ordinary households.

Unfortunately, OpenEnergyMonitor does not have a device that can handle this by default.

It is recommended to use 3 x emonTx that will be installed with 3 Phase sketches.

It could be very desirable if there was an emonTx 3 phase device, with 3 x CT inputs and 3 x AC measure inputs.

Possibly with AC transformers built-in on the board so that only 3 phases could be connected from a group switch with small fuses. (2-6 Amp) to measure the AC voltages.

I would think that a great many would demand such a product.

Have you on OpenEnergyMonitor made you think about developing such a device?

I seem to have seen someone be developing such a board?

I understand your problem, and the suggestion has been made. But as yet, there has been no indication that this is under active consideration.

A few minor corrections to, and comments on, your synopsis:

There are in fact two systems, 3-wire and 4-wire, that may be sufficiently different to require different solutions, at least in the firmware. I believe that Norway uses a 3-wire system with no neutral, with 230 V line-line, the rest of Europe uses a 4-wire system with 230 V line-neutral and 400 V between lines. It is not necessary to measure all 3 voltages in the 3-wire case, because the third voltage is not necessary to measure total power, and power per phase has no meaning as all loads are delta-connected, but it may be desirable to measure all three currents.
In fact, the UK is unusual in that 3-phase is almost unknown in private houses and most small commercial and business premises.

Unfortunately, you have misread this. We suggest an emonTx per phase where monitoring of several circuits per phase is required, or one emonTx using the 3-phase sketch where whole-house monitoring is sufficient.

I agree, and that would be within the capabilities of the Atmel328P.

Though I can appreciate the ease of installation and use of such a device, bringing mains voltages inside the case means that it would need regulatory approval and be CE marked before it could be put on sale. That would inevitably be a costly exercise. And how would you suggest making connection to the 3-phase supply? You obviously know European practice better than I do. Would you expect a 5-pole connector on a trailing lead? When we use a CE-marked adapter, we do not need such regulatory approval.

I agree that I think there would be a potential for such a unit. Would you be able to give an estimate of the actual potential sales of such a unit? If you could, I am sure that @glyn.hudson & @TrystanLea, the owners of Megni, the firm that makes the emonTx and emonPi, would be interested.

I believe @calypso_rae was considering developing a three-phase energy diverter, but I do not know what progress has been made.

If you bite the bullet on all the regulatory hoops and run mains voltages into your box, you might also consider a DIN-rail enclosure and then just use screw terminals to terminate the three phases. That’s a very convenient solution assuming they have enough spare space on the rail. (I’m assuming Europe is very similar to Aus/NZ with DIN rail breakers).

You’re obviously thinking of something that you expect to be installed professionally. I hadn’t and won’t think about details along those lines unless or until I’m asked.

After I wrote all the above (my reply to Sune), it did occur to me that G&T might be considering moving to a higher-powered processor/ADC, and were holding back on a three-phase unit until that had received further consideration.

Well from the end user’s point of view, they’re almost certainly going to have to get a sparkie out either way. It’s very rare for a 3-phase residential setup to have any 3-phase outlets and extremely unlikely they’d have one near where the energy monitor has to go. So then it comes down to which is the cheapest to install… the 3-phase outlet or the energy monitor. They’ll each need a 3-phase breaker. The former needs the outlet and a plug and some drilling while the latter needs some DIN-rail and wires (assuming space in the cabinet).

There are of course other considerations:

. if the end user is expected to tinker with the monitor on an on-going basis, then putting it on a plug obviously makes sense.

. if there is spare DIN rail space (and no tinkering required) then everything is neatly located where it needs to be and both the voltage signals and CT cables all get tucked nicely behind the DIN-rail covers. If there isn’t, then expanding the cabinet may cost more than putting in an outlet.

. the closer you get to the main breakers and meters, potentially the higher the isolation requirements, but you may want to design for that in any case, to give you the flexibility

Hello Robert


Measurement of 3 phase power as in most of Europe


Sorry for my late reply, but I just had to think about your comprehensive writing and some possible solutions.

Yes, I have an electrician background so my insight into Danish conditions is great.

I’ve been thinking a lot about how it can be best to handle a 3-phase installation with existing equipment, or maybe existing equipment with small adjustments.

DIN Rail
In Denmark, we have used “DIN rail” since approx. 1970, so it is very common here. Therefore, it makes sense to use DIN mounted components in both private households and in industry. When looking at European trade pages, it seems that “DIN rail” is used in most of Europe today, as the standard of safety equipment is based on “DIN rail”

Have looked at 3 phase systems in Europe and, as I see it, 4 Wire solutions are used throughout Europe. Also in Norway. The main reason for this is that the 4th Wire is neutral, and most often connected to Earth from the EL supplier. It is the basis for being able to use an HPFI relay, as personal protection.

See my link here:

As I see it, there are 3 phases + neutral + earth, the predominant standard in the largest part of Europe, but you are right in that in France, Belgium and Norway are some older 3 Wire systems yet. But new installations are 3 phases + N + Earth in star clutch.

Households in Norway have 230V single phase (IT-N), 230V three-phase (IT-N) or 400V three-phase (TN-S) wiring, the latter only used in new areas.

Proposal for a solution
AC adapter for “DIN rail”

With the shown AC adapter for DIN mounting, it makes sense if the emonTx V3 had 3 AC input so that 3 phase systems could be handled in this way and calculate REAL POWER. Thus, approval issues are also resolved.

There is no need for a USB plug when it is in a power panel, so it will be easier with a 3x voltage input terminal and it will also fill less. I think there should be a solution that can be used both single-phase and 3-phase privately, and 3-phase for “DIN Rail” assembly. (Housholds and Industry)

If you want a cheap 3-phase installation in your home, you can solve this by allowing an electrician to install 3 single 230V sockets, at each phase, from a 3-phase circuit breaker. Here you can then install 3 x 9V AC adapters that are also used today.

The UK is special in this area, as many older installations are based on 1 phase solutions.
But in most of Europe today, there are 3 phase solutions that prevail. Therefore, I think there will be a big market for this particular solution.
The current solutions with 3 x emonTx3 + emonPi will be unnecessarily complex to install, and I think I’m dissuasive. Also myself.

Could Glyn be persuaded to take it into consideration in emonTx V4?

Danish house installation anno 1976
Here is my house installation done in 1976 where everything is made as “DIN rail” assembly.
In 1976, it was normal to use a 3-phase group switch for 3 light groups. However, it is a dangerous solution if the Neutral cord fails, as some devices will be exposed to 400 V. I plan to change this soon.

That is a very attractive suggestion.

I agree.[quote=“Bielefeldt, post:6, topic:3781”]
Could @glyn.hudson be persuaded to take it into consideration in emonTx V4?

You need to ask him.
In that respect, the emonTx V2 could easily be extended to have 3 voltage inputs, simply by adding 2 more voltage input circuits externally and connecting to header pins on the pcb.

Very true. That is why I always tell people that the neutral wire must always be considered a “live” wire, because when the neutral fails upstream, on the downstream side of the break, the neutral can be at 230 - 240 V.

I have sent Glyn a link to this thread, so we have to wait for what he has to say.

Thank you for your support :slight_smile: