Second Iotawatt and 3phases sharing


In case I would like to have more measurements, means to acquire a second Iotawatt, my question is the following:
Is it possible to share the CT for the 3 main phases between 2 devices? Or do I have to connect 3 additional?



Not possible. Sorry, but you might also try using derived reference (one mains CT/IoTaWatt) and see if the results are satisfactory. You may be surprised.


there I’m a bit confused, when you speak about derived reference like in the wiki (
you have anyway 1 CT per phase, this means 3xCT… and on this post you speak about 1 mains CT per IoTaWatt…


It’s me that was confused. Sorry. You’re right, both methods require 3 CTs. It’s one VT vs three with derived reference.

You can’t share the CTs. You will need three more for the mains on the second IoTaWatt if you want to measure the mains on both. If you are uploading the data to influxDB or EmonCMS, then you probably don’t need to measure the mains again with the second IoTaWatt.


But if I do not connect the mains on the second device, how do I declare for the CTs what is the reference phase?


You should be able to share the voltage reference (VT) between the two Iotawatt whether you use one or three VT. Will need a cable adapter.

Each input on both Iotawatt needs its own CT.


The phase reference comes from the VT(s). If you were to delete the mains CTs on your first IoTaWatt, you would see that it will keep logging power for all of the other inputs.

In the interest of being specific about how to do this exactly, it would be helpful if I knew whether you are using Direct (3 VTs) or Derived (1 VT) reference.

If you are using Direct reference, the phase of any particulat CT is implied by the voltage reference that you select for it. For Derived reference, you will select phase A, B or C for any particular CT, with phase A being the phase of the VT.


Hi, I’m using derived reference