### Strange results with 3-phase 400V input

Hello,

I'm trying to monitor the power input of my house in Switzerland. I have a emontx v3 with 3 CTs powered by a AC-AC power (everything bought from OpenEnergyMonitor shop). The input is 3-phased 400V and there is 5 wires: 3 phases (black, brown, grey), 1 neutral (blue) and 1 earth (green-yellow). I plugged the 3 CTs to the 3 phase wires like I used to do with my OWL power meter. The total power never exceeds 10kW based on the electrical company meter installed.

To calculate the total power, I sum all the inputs and multiply by SQRT(3) because the AC power measured is 240V (Vrms) and I have 400V input. Is it ok?

By comparing to the OWL meter and the electrical company meter which give approximatively the same results, I saw that the power calculated in emoncms is not correct:

• One phase alternates between negative and positive values. Is it possible?
• The total power calculated is sometimes approximatively correct and sometimes it is more than 1kW greater for example.

It looks like I did something wrong...

### Re: Strange results with 3-phase 400V input

No, that is not OK!

The default sketch in the emonTx V3 is SINGLE PHASE. It calculates real power for 4 wires all fed from the same phase. If two of the three c.t's are on different phases, those values will be wrong - by factor of approximately 1/√3. You will get a result much closer to the true value, but still an approximation that assumes the voltage amplitude of the three phases is identical, if you download and use the three-phase sketch from GitHub. You must have the ac adapter on the phase that CT1 is on, measuring L-N. Usually brown is phase 1, black is phase 2 (CT2), grey is phase 3 (CT3). You keep the sequence the same even if you measure the voltage of phase 2 (say). Then you can sum the three (or 4) real powers.

### Re: Strange results with 3-phase 400V input

Thanks Robert, I will try the 3-phase sketch hosted on Github.

### Re: Strange results with 3-phase 400V input

Ok, I used the 3-phase sketch, added the support for DS18B20 and everything is working well. Thanks again Robert.

### Re: Strange results with 3-phase 400V input

Hi,

I got the same issues but with other electrical  schema: 3 phases without neutral (240V between phases). I use emontx3 with AC adapter. I saw somewhere in this forum that only 2 CTs were necessary. If I plug these CTs on L1 L2 phases, does it mean that I have to measure voltage between the same phases ? Do I have to update something in the three-phase sketch ?

I also want to measure power provided by PVs that are connected to 2 SMA convertors. Their output are bipolar ('Phase'/'Neutral'). 'Neutrals' are connected together to L2. 'Phases' are connected respectively to L1 & L3. I guess that only one CT is needed (on the common wire 'neutral') ?

Jean-Luc

### Re: Strange results with 3-phase 400V input

That is a very interesting system. I suggest you should regard Line 2 (Black) as your "neutral" (but ONLY as far as the emonTx is concerned).  The reference voltage that you measure will be L3 (Grey) - L2 (Black) and the "L1" c.t. (CT1) will be on the Grey phase, "L2" c.t. (CT2) will be on the Brown phase. Unfortunately, you will also need two c.t's on the PV, on Brown and Grey phases, because that too is a 3-wire system.

You will of course need to use the 240 V ac-ac adapter.

Depending on the rating of your converters, you might need to put an additional burden resistor in parallel with R18 to increase the maximum current that channel 4 can read.

You will need to use the three-phase sketch, but you must modify it because the angle between the phases is only 60°. I suggest you put CT3 onto the Grey PV phase and CT4 onto the Brown PV phase. You change "#define PHASE2 8" probably to "#define PHASE2 4" - but you will need to find out by trial and error  the number you need when you commission it, and with it the value for Phasecal2, and "#define PHASE3 ..." and Phasecal3 will be the same. The sketch assumes CT4 is on the same phase as CT1, and uses the same phase shifted voltage so no separate adjustment of Phasecal is possible for CT4 (without altering the sketch).

### Re: Strange results with 3-phase 400V input

Many thanks Robert,  I'll test your solution.

Jean-Luc