# One CT for two/three wires for A/C - Three phase

Hi,

I’m about to install my new IoTaWatt in my breaker panel where I have all my A/Cs and I want to monitor them individually. Each A/C unit have three-wire loads (no neutral). So, to optimize the connections, I was planning on using one CT for each unit, but I dont know if that is possible. Meaning that I will be using one CT for three wires. I don’t know if the three wires will fit, but maybe I can try one CT for two wires and another CT for the third wire?

PS. I live in Mexico and here we have 120V three phase.

That’s not possible. You can measure a three wire load with two CTs.

You cannot mix wires from different phases in the same CT.

Three-phase 120V is the same as in the US.

I see that you ordered one VT, so you will be using the derived reference method. The first thing I would recommend is that you get the mains installed and measuring accurately. There is a tutorial here.

It is very important that all of the CTs are oriented the same way. They have an arrow on the bottom, install them so that the arrow points toward the circuit breaker. Then follow the tutorial to identify and configure the phases.

Once you identify the phases as A, B or C, where A is the phase with the VT, you should trace those circuits in the panel to identify the phase of each of the wires in the AC circuit breakers.

The procedure for measuring a three-wire circuit with two CTs is not explained in the documentation. What I recommend is that you install a CT on the phase A wire and configure it with “Mains Phase” C-A (-150°) “Reverse”. Install the other on the phase B wire and configure with “Mains Phase” B-C (+90°). Then create an output that adds the two together. That total will be the power for that AC unit.

Ok, and it is possible to measure the three-phase A/C with one CT?

No. That’s explained above.