3 Phase Aus Setup - Determine B or C phase when only AirCon uses other phases

Thanks for a fantastic product and community!

I’ve recently got my IoTaWatt up and going. I have a derived 3 phase config. Finding Phase A was pretty simple, as for whatever reason, my place is entirely rigged with lighting and its 3 power circuits and oven all off of “Phase A” - confirmed via power readings and whats wired on the box.

It would appear - which seems odd to me, but hey, I’m not a sparky - that only my Slab Heating (not in use and effectively decomm’ed) and my AC Compressor are using any other phases. My AC is actually a 3 phase unit and also has CT’s on all 3 phases.

My question is - how can I go about determining which is B and which is C and then correlate that to the AC CT’s (3 x CT’s)? If the compressor is on, I’m drawing power on all 3 phases of the Mains, and indeed show that to the AC unit… but just randomly guessing which phase is which seems a complete fools journey.

So how am I best to work out which phase is which. I’m guessing, even if I physically correlated it - I still wouldn’t know which was B and which was C relative to the VT’s “A” phase… or can I somehow ? There’s no colour coding to go by either…

Any help/suggestions would be great :slight_smile:


I think you can make a good guess as it is likely the electrician has wired up the phases in order. So since you already know your Grid Phase A is the Iotawatt Phase A I would then just make the next breaker along B and then C. I just setup mine and I knew that my VT was on Grid Phase B so that became IotaWatt phase A. Thus Grid phase C became IotaWatt phase B and Grid Phase A became IotaWatt phase C. I then checked it as per the docs and it was correct. If you have got nothing else then this is better than nothing.

An AC compressor should draw similar load from each phase, so setting all three of the AC CTs to phase A should show one that is about twice the Watts of the other two. That’s phase A. Now set the other two to phase B. Whichever is very close to phase A is the real phase B. The other, of course, is phase C and if you set that it too should come into line with phase A power.

It goes without saying that the compressor needs to be running while doing this.

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Thanks overeasy - that helped a lot. I seem to now have reasonably close Main’s and AC reading. Crappy power factors though, about .7 , but I guess that is because its a 20 year old AC unit.


Yep and you will probably also find the standby power draw is quite substantial for no reason also. Our 20 year old Daikin was pulling 85 watts 24x7.

We have just replaced it with a new Inverter Dakin and it is chalk and cheese difference