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.
Paul