New 3-phase installation

First off, hi everyone, I am a new member from Australia.

I’ve just had a 18kW solar system installed at my house. I have a 3-phase meter, which means I have 3 cables (plus neutral) coming into the main box from the grid, and 3 cables (plus neutral) from the inverter.

I have one simple question:

  1. I presume the USB power port is use to power the IoTaWatt board, and the 9VAC to sync the phase. How that that work on a 3-phase system? Do I need three transformers? If yes, how are they installed. If not, can the 9VAC be on any of the three phases?

And two related questions (a bit more detailed):

  1. I presume I need 3 sensors for the main feed from the grid, and 3 sensors for the cables from the inverter. I presume this will give me current passing through each of the cables, and that allows me to monitor how much power is generated per phase, and how much power I draw from the grid (or feed into the grid) per phase. Is that correct?

  2. If I run all the 3 cables from the inverter through 1 sensor, I can read how much power is generated by the solar system as a whole (not per phase). Is this correct? Would/won’t the phase difference between the 3 cables (120 degrees apart) affect the reading? I presume I can do the same thing on the grid-side cables as well?


You can do it either way. You can use three, which is the “direct reference” method, or you can use one, which is the “derived reference” method. Most people use derived reference.



No, you can only combine cables on the same phase.

This is all covered in the documentation.

Thanks @overeasy; I appreciate your clear response and I especially liked that instead of telling to RTFM, you provided a tactful reference to the documentation (which I did not find in my initial browse of the web site).

Following this positive interaction, I just went ahead and ordered an IoTaWatt box and 12 CTs. Let the fun begin :slight_smile: