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You would appear to have a three-phase, three-wire supply there, so yes, you need 2 CTs and you need the 3-phase, 3-wire sketch to get the correct readings, assuming you have a single voltage monitor and you want to read real power. The default sketch loaded into your emonTx will not give the correct readings for real power, though it will for apparent power (VA).

Darn. Ok. I have an emonpi. Does that mean I have to load a new sketch on the arduino in the housing via a usb programmer? Is there any info on this you can link me to, please?

And what is the reading I get from the one clip I have now? A part of the usage, or just gibberish? It seems to be a valid reading, though too low.

I think you need to tell us a little more about your system.

What voltage is your mains supply? Would I be right in guessing that it is 230 V line-line and 132 V line-earth?

Are you using an ac adapter to measure voltage, and it's 230 V and connected across 230 V?

That is the "shop standard" YHDC SCT-013-000 CT in the photo and it is on a line conductor that the ac adapter is on?

If that is what you have, you will be measuring the power correctly only if all your loads are only connected to the same pair of wires as the ac adapter. Otherwise, the second phase and third phase conductors, neither of which have a CT, can be carrying current that is not measured, hence you are missing some of the power.

Note that a CT and ac adapter are equivalent to a wattmeter, and classical electrical theory dictates that you need one fewer wattmeter than the number of wires in order to measure the total power. That is why you need one more CT, not two.

There is one exceptional case where that is wrong and you do only need one CT, and that is when the load on all three phases is accurately balanced. That is unlikely to be true for you.

I don't know whether the instructions for re-loading the AVR with a new sketch have been written yet.

I think you need to tell us a little more about your system.

What voltage is your mains supply? Would I be right in guessing that it is 230 V line-line and 132 V line-earth?

230 V, yes. (Emonpi says 253 V, but I think that's alright as the voltage can be +/-10% of 230 or something.)

Are you using an ac adapter to measure voltage, and it's 230 V and connected across 230 V?

I'm using the AC adapter, yes.

That is the "shop standard" YHDC SCT-013-000 CT in the photo and it is on a line conductor that the ac adapter is on?

Yes, it's the CT from openenergymonitor shop. But I do not know if it's on the same line as the AC adaptor.

If that is what you have, you will be measuring the power correctly only if all your loads are only connected to the same pair of wires as the ac adapter. Otherwise, the second phase and third phase conductors, neither of which have a CT, can be carrying current that is not measured, hence you are missing some of the power.

I understand.

Note that a CT and ac adapter are equivalent to a wattmeter, and classical electrical theory dictates that you need one fewer wattmeter than the number of wires in order to measure the total power. That is why you need one more CT, not two.

Alright, have ordered another CT now.

There is one exceptional case where that is wrong and you do only need one CT, and that is when the load on all three phases is accurately balanced. That is unlikely to be true for you.

Agree.

I don't know whether the instructions for re-loading the AVR with a new sketch have been written yet.

Ok. But the sketch is here available for download?

Thanks for all your answers. I dropped out of Electrical Engineering and went to Computer Science/Engineering. So all the raspberry pi things are easy, but the fusebox is a scary place. =)

Here is the sketch. I don't think it's made it into Github. It is for the emonTx V3.4, so it will need some work to convert it for the emonPi. Clearly, everything involving CT3 & CT4 can go. Then it should be reasonably easy to take the remaining parts of this and merge into the emonPi sketch.

Most of what you need to know is in the comments at the top of the sketch, but ask if anything is not clear.

I can't find the arduino sketch that came on my emonpi on github. Probably need that to convert this, or to revert if I mess up the arduino.

Found: https://github.com/openenergymonitor/emonpi/tree/master/Atmega328/emonPi...

Now to see if I can make sense of these two...

Hm. Getting even more complicated:

A single AC-AC adapter is required and must be connected between L1 and L3.

How do I know that the socket I've got my AC-AC in is on L1 and L3?