Sanity check: Three phase Wye but with some delta consumers

I’m ready to buy a IotaWatt meter (as soon as it will be available again) but I have a doubt regarding the setup. I’m going to install the meter in Italy, on a Three phase + Neutral system:

  • Difference between each phase and neutral wire: 230 V
  • Difference between each phase: 400 V

For now, I would like to monitor the global consumption and maybe in the next few months I’ll buy more Current clamps to monitor 3 three-phase sub circuits.

I’m not sure if there will be problems in computing the energy consumption and the power utilization given that in the system there are some three-phase asynchronous engines that are connected only to the three phases (i.e. in a delta configuration).
Would that requires any additional precautions to correctly install the IotaWatt?

Let me know if you need further details.

Thanks a lot for your help

Nothing additional required. You would be able to measure the three-wire load by either of two methods. One method uses three CTs, the other uses two CTs.

Thank you for your fast response. I think that the method you mentioned is the one described in this post, right?
(the post contains also a link to this article

What I’m not yet able to grasp after reading thoroughly the post is how to handle the situation in which you have mixed loads in the same circuit, i.e.:

  • Loads connected from phase to neutral wire at 230volts like heating or lights
  • Loads connected between phases at 400 volts like engines.

If I want to measure the power used by this circuit, where do I have to connect the VT? Do I need a voltage reference of 230 volts or one of 400 volts? I’m still feeling that there’s something missing in order to correctly compute the power used. (I could simply check as soon as I will have a Iotawatt unit but I would prefer to order everything I need on the same order).


Yes, that article explains how to measure a three-wire load with two CTs. You can also measure it with three CTs.

Those loads are on the same service, but they are not in the same circuit.

I’m assuming that you intend to use “derived reference” where the IoTaWatt has a direct reference (230V) for phase A and derives a reference for phases B and C by numerically shifting phase A. It also derives a reference for the phase-to-phase voltages by shifting phase A appropriately and adjusting the voltage by \sqrt{3}, ( 230 \times \sqrt{3} \approx 400)

When derived reference is enabled, you will select the reference to use when you configure each CT.


For your three-wire load, you might put a CT on the phase B wire and use B-C for a reference, and a CT on the phase A wire and use C-A for a reference. (Because phase A is the C_A voltage, you would need to also reverse the CT orientation physically or virtually with the reverse checkbox.)


Really appreciate your explanation, everything is clearer now.

Cannot wait to have a IotaWatt unit to play with! :slight_smile: