Monitoring a 3-phase installation

Hi, I'm looking at using the EmonTxV3 to monitor a 3-phase building and just trying to get my head around the details.

The distribution board I am looking to clamp onto has easy access to the 3 phases for clamping and also has a standard power socket so I can use the AC-AC transformer.

I'm new to this area so after reading all the building blocks section and other sites about 3-phase the socket must be one just one of the phases lines so I could meter the 3-phase using icboredman method (, am I on the right track?

Can I use the EmonTxV3 for this? I know icboredman was using the Duo which has more horsepower but what I would be doing is just using 3 CT clamps to measure current on each of the phases and get voltage from the AC-AC on one of the phases.


The other thing I'd like to do perhaps down the line is take the wireless transmitter/receiver out of the equation and just post energy readings from the EmonTxV3 (or a similar setup e.g. using Arduino Ethernet perhaps).

My question is in terms of measurement accuracy do you think there could be an issue with sending data over Ethernet where the process of connection/sending could delay your execution loop especially if I was trying to connect through router to server offsite?

This leads me onto another question I have regarding my basic understanding of energy measurement/calculation.

As I understand Energy (KWh) is the KW * time. In the case of the EmonTxV3 is takes a measurement/calcuiation every 10 seconds. So the energy is being averaged from that sample over the 10 seconds, is this correct? How does this accuracy compare to what the billing company would be measuring? does it make sense to measure as fast as the Arduino can go, i.e. remove the delay between calculations?

Robert Wall's picture

Re: Monitoring a 3-phase installation

You don't say where in the world you are, so I don't know what your supply is like.

Our 3-phase sketches (one exists for the emonTx V3) take the voltage on the first phase and use a delayed recording of that to compute the power on the other two phases. The accuracy is highly dependent on the phase balance. I don't know anything about the 'foreign' project you mention so I can't comment on that.

You can connect the emonTx V3 direct to a Raspberry Pi, that would be the proven way to get the readings onto Ethernet, and given that the Pi is capable of storing the data locally instead or as well, you might want to look at that aspect. Also, it depends on the data you send. If you send power, then a lost sample means the average between the surviving samples is used to accumulate the energy total. If however you send the accumulated energy total, all you lose is the knowledge of the accumulated total at that instant, the next reading is still the accurate accumulated value.

If you use one of the 'continuous' sketches, then the energy transmitted is the true average over the period between transmissions, so (within the accuracy of the measurement and calibration) should be identical to the supplier's meter reading. That is not the case for the 'discrete sample' technique that samples for 100 ms every 10 s and thus relies on the errors averaging over time for accuracy.

So the short answer is, I think everything you want to do is possible.

If you want a ready-to-install solution, Robin Emley (calypso_rae) might be able to help you.

1.21jigawatt's picture

Re: Monitoring a 3-phase installation

Hi Robert, thanks for the great feedback. I'm located in Ireland so similar setup to UK. 


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