House with Delta mains connection


I’ve been looking for a means to monitor my house energy usage for a while. I discovered this site thanks to Google.

The electricity supply into my house uses three wires, with 230V between all three. One of the three wires is used as neutral, and the other two are used as live. I think that this means that the electricity coming into the house uses a Delta topology, as distinct to a Wye-topology

Does your monitor measure energy usage for this scenario?

Many thanks,

Yes, we can do that. There’s a sketch for the emonTx (only the emonTx, not the emonPi) for “approximate” measurement of a 3-phase supply, and it can be set up as in your case to treat one phase as the neutral, so that the second phase is shifted 60° in relation to the first.

By “approximate”, I mean the emonTx has only one voltage input, therefore it is accurate so long as the voltages of the two phases you are using are the same (or the same within a error band that you find acceptable).

To do the measurement, you’d need an emonTx, a.c. adapter and two c.t’s, then if you want to log and record the data using emonCMS, you need in addition an emonBase and power supply. You can buy emonCMS on an SD card, or you can download it free of charge.

If you think (or know) the two voltages you use vary too much from each other, then you can treat your supply as two single-phase supplies. In that case, I’d suggest an emonPi to measure one phase and run emonCMS, and an emonTx to measure the second phase and send the data to the emonPi. If you do that, you need 2 × a.c. adapter, 2 × c.t, 1 × Raspberry Pi 5 V d.c. power supply, 1 × emonTx, 1 × emonPi, emonCMS.

Which of those two schemes you choose might depend of exactly what you want to measure in total, and what you foresee you might want to measure in the future. The emonTx has four current inputs, the emonPi has two. If you want to measure more than the total house consumption, then all the other things you want to add will affect your decision.

Many thanks Robert for your detailed reply.

I have some further questions.

What do you mean by “sketch”?

The emonPi has two CT inputs, can I use that, or do I have to use the emonTX? You mention both in your reply. Is it that the emonPi takes the measurement with two CTs connected as two single-phase sources, whereas the emonTx is a true 3-phase measurement system?

In the meantime I’ve browsed further through the site, and came across this post from Belgium. I also live in Belgium, but in my case, only L1 and L2 are used as live circuits and L3 is used as N. In that post, there is a reference to a special 3-phase version of the firmware. Is that the version I would have to use?

I checked the voltage cross the two phases using a cheap voltmeter, and they are identical, but this is probably not an accurate indication.


A sketch is a Arduino word for program or code. It is the firmware that runs on the EmonTX.

No, only the EmonTX due to the internal design. If/when you order from the shop, I think they will load the right firmware if you ask.

Indeed you would. If the shop does load it for you, you must also specify all the options inside the sketch - which c.t. inputs are allocated to which phase, etc. There is a list and a description of each in the file emonTx 3-phase PLL User Doc.pdf, which comes as part of the download of the sketch, from Github or Update to 3-Phase PLL sketch

(Done any other way, it would be unrealistic to have one download for each possible permutation.)