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All the standard pre-loaded sketches are single phase, as that is the UK standard for domestic premises.

First, is yours a 3-wire system or 4-wire? i.e. do you measure 230 V line-line and 132 V line-neutral (or line-earth), or do you measure 230 V line-neutral (or line-earth) and 415 V line-line?

Whichever you have, the standard sketch will not give you the correct results. If you have a 4-wire system, you need to get the 3-phase sketch from GitHub (it's under the emonTx V3.4 at https://github.com/openenergymonitor/emonTxFirmware/tree/master/emonTxV3...) and calibrate it according to the notes in the comments. If you have a 3-wire system, I have a sketch but it's not on GitHub.

But a caution: both necessarily use approximations so the accuracy is not as good as the single phase versions. The limitations are noted in the comments in the sketch. However, many users seem satisfied with the result.

I'm working on what will hopefully be an easier to set up and more accurate version, but it's not ready yet.

There's an explanation of 3-phase electricity in Resources > Building Blocks

Ah! Yes, it's a 3-wire (L1/L2/L3) system with 230 line-line and 132 line-earth.

Edit: earth is separate

Here's a couple of pictures of the circuit breaker/distribution (picture #2 is the bottom right corner of picture #1, the main intake).

The underlying principle behind what you need to do is that to measure the power in any supply, you need one less wattmeter than the number of wires. For 'wattmeter', read 'pair of voltage and current measurements'.

What you've got to do is designate one phase as the reference (I've used Phase 3 in the sketch but as long as you get the phase rotation correct, which of the three is number one makes no difference). Measure the voltage of Phase 1 with respect to Phase 3, and measure the current in the Phase 1 and Phase 2 conductors. You're not interested in the current in the reference phase (Phase 3) because we know it must be the vector sum of the currents in the other two phases. (Otherwise, where is the current going - you have an earth fault that needs to be fixed!)

Therefore, you connect your AC adapter between Phase 1 and Phase 3 (and where you can connect that will probably determine how you number the phases from the emonTx's point of view), and then use 2 CT's on Phases 1 & 2.

The sketch is attached.

What it does is calculate the power in Phase 1 directly, and use a delayed voltage reading to calculate the power in Phase 2. Because of the way that the supply works, the individual powers are meaningless, only their sum has a meaning. You must add power1 & power2 in emonCMS. (If you think about it, the current in one wire can return on one or both of the other two wires, depending on how your appliances are connected. And you have no way to know how that current shares from minute to minute.) 

You can use the 3rd and 4th channels for separate circuits, if you wish.

Thanks for the sketch and explaining this and have a merry christmas! I'll try this as soon as I can :-)