Which calibration is right?

Guys, 3 phase down here in Australia.

I have done a basic iotwatt setup - voltage derived for phase 2 and 3

The system is running fine and producing what seems to be sensible data when compared to my electricity company.

I have setup a new pool pump and swimming pool environmental management system (like a Salt Water Chlorinator).

I am planning on automating this through my home automation system which uses Node-Red and Tasmota devices.

I have connected the pool pump and chlorinator to a Sonoff POWr2 running Tasmota.

I have calibrated it using a Power Meter and a halogen bulb.

However when i monitor the power useage from the WebUI on the device i see the following

The figures it presents are reasoanbly around what i would expect as the pump is 750w and then whatever the ioniser/chlorinator etc is drawing

However in the IOTAWatt screen i get this

(There are other loads on the blue phase at the moment which is where the pump is connected)

And this is the emoncms printout for the blue phase

During 12:00 to 1:30 the pump was running and nearly the only load on that phase.

So IOTAWatt seems to think that the unit is running around 500w with a very low PF of around 0.5 (on average), but this does not line up with what i am seeing at Tasmota

Any ideas how i go about finding out what is going on ?


Probably not configured correctly. How does it compare to your meter?

Yeah well that is the funy thing. You go through a calibration process when you set one up - using a known source - which i did - using a 50w halogen bulb - this was through an old iron transformer so total draw according to my meter was 62w and voltage was 249.1 - so i dialed those in through the Web interface on tasmota and then confirmed that the current draw was correct.

My meter does not report PF

So then i unplugged the bulb and transformer and plugged the pump and chlorinator into the meter (and through that into the Sonoff) and then checked the readings and the voltage, amps and Watts all looked about right.

So then i came up and looked at IOTA and thats when i saw the discrepancy. (The reason is stood out so much is that for the last month i have been running the setup through another Sonoff (that does not do power measurements) but does let me do remote switch on and off and monitor for run time.)

IOTAwatt was pretty consistently reporting around 250 to 300w only for the pump and i thought it was the most efficient pump i had ever seen. !!

Then i plugged it into the new Sonoff today and thats when it stood out to me so vividly.

I can chuck a CT onto the circuit that the pump uses (there are a few other things on that circuit) and then not down some run times etc and report further if you like ?


Have you checked the kWh of the three phases against your revenue meter for any length of time?

Yep - and they pretty much match up to the totals

Thats why i think IOTA is right but can not understand such a big difference between the two.

And also why IOTA thinks it is so low - which seems too fanciful when looking at th enameplate ratings


It is a little hard to get an exact against the power company bill though as we have 11.5kw of solar and try to only run the pump when we have excess solar - so IOTA sees the draw - but nothing goes out to the power company

I am about to commission my 2nd IOTA later this week when i get a replacement meterboard in - it will then monitor solar output as well as total grid draw/feed - not just my consumption


I think it’s important to reconcile your installation against a standard like a utility meter as I have my doubts about the integrity of your mains installation.

I’ve said this before, but maybe bears repeating, there are 24 combinations of CT orientation and phase assignment, but only one of them is correct.

I’m seeing negative power on two of your mains and a power factor of .40 on the other. Maybe the large negative is solar export, and maybe you have a 1,400 Watt load that has a .40 power factor, but that is uncommon.

I’m reasonably confident the other measurement you showed is accurate, and confident IoTaWatt can be equally accurate, so there is a discrepancy there.

You do not have IotaWatt configured correctly. Take a look at what Tasmota is saying. It says the power factor is 0.88. That is believable for a motor. Now look at phase Blue on IotaWatt. It say 0.42 for power factor which is less than half of what it should be.

I don’t have have 3phase at home, so I don’t know what you need to do to make sure you have it right. But, I would look at PF to see if they are where they should when using a pure resistance load.


OK thanks guys - sort of think you are right.

WIll investigate and go through the doco further and see what i can find - i have triple checked the orientation of the CT clamps so i can only assume the only real problem left is a misidentification of the phases.

Will play around today and see what i get

Thanks for your time


Posted this today.

Yep as per the post you linked to - i have gone through and followed the steps and turns out my first batch of CTs from China was labelled incorrectly in terms of current flow.

I will test the pool pump shortly and advise back on that

Great support once again Bob - thanks