240 2 phase setup question and how to confirm accuracy

I’m new so please bear with me on some newbie questions.

I have dual phase power (Canada). I put a CT on each main line (both black wires) no neutral. I read somewhere in the forum about balancing the mains? Is it safe to assume that both mains should have a similar watt draw on them?
Mine has a consistent difference between both when i am drawing from the grid and/or sending to the grid. Is that expected? or is there a chance i don’t have a CT properly clamped down? or is the draw different because power is split across the phases depending on where the breakers are? Like i said, I’m new to this.

Secondly, i have solar edge installed with consumption monitoring and i see a significant difference between the two. If its not due to the above assumption, what is my best way to go about confirming or validating the readings I’m seeing. Unfortunately my volt/amp meter is not the clamp style. Would my only option be to try to track one down and use it to compare?


Not a lot of information to venture a guess. The first thing that comes to mind is that you may have 120/208 service. If you have a voltmeter, can you measure the voltage between the two black mains?

Overeasy is the best resource, but to your specific question:

“is the draw different because power is split across the phases depending on where the breakers are?”

the answer is definitely yes, if you have significant 120V loads active at the time and depending on how they happen to be distributed between the two mains. If you happened to have only 240V loads active at a given time (maybe you can force this for a quick test) you’d expect to see approximately equal power on each main leg.

You’re correct. 500W isn’t a big difference and any number of common household 120V loads could cause it. But he is saying that the Solar Edge consumption is different, which would not be the case with a simple imbalance. So I’m starting with the basics to insure it’s split-phase rather than two-phase which is more common in Canada.

Thanks for both of your replies! They are certainly helping me piece this together.

I checked the voltage across both mains and it is 240. There is also a large sticker on the panel saying its a 240 main :slight_smile: but i figured it was worth double checking anyways.

So based upon the feedback from tcheywood, it now makes sense that the readings on each main would be different. There certainly would be different 120 circuits on each one. Therefore total in our out from the grid is done by adding the two together?

Off topic, but i assume if i eventually wanted to save on inputs, i could put both CTs together using a 3.5 mm splitter?

I have long suspected that my solar edge install is not correctly reading my consumption but have not really had a way of verifying it. For example, during the day when no one is home and consumption shouldn’t change, I see increased consumption correlated to production. I think its because it calculations consumption as production - output to the grid. That is really just an assumption looking at trends.

I am however seeing a difference between what solar edge is saying and what iotawatt is saying. So i guess the question here, is how can i verify which one is right? At this point in time all i can say is one of them is off :slight_smile:

Like i said, I’m new to all this so i appreciate your input!

It appears you have already done that with the output GridPower.

Not going to get into that here. It’s covered in the docs.

You have an arbiter - your meter. You can check the accuracy of the IoTaWatt by comparing kWh over the course of a day or two.

  • Read the meter and note the date and time.

  • Wait until you use about 100 kWh.

  • Read the meter again and note the time.

  • Using Graph+, plot GridPower with start and end date/time corresponding to your meter readings. Look at the statistics tab below the graph where kWh will be shown on the far right.

You say you have solar installed, so you should check “allow negative values” in each of the mains inputs setup before starting the meter test.

Thanks for your help here!

I checked the difference after 100 kWh but saw close to a 2% difference so i decided to run it longer (roughly 170 kWh) and see a difference of 1.34% As that is close to the 1% tolerance on the CTs its safe to say the IotaWatt is doing a much better job of measuring. Now i also have the prof to highlight that my solar edge install needs to be looked at.