Mains Required?

Reading through the Github and this forum, I can’t tell if hooking up to mains is actually required. In other words, would i be ok just buying the base, power supplies, and 14 50a split CTs? Thanks, Jonathan

I depends what you want to monitor. If you have specific circuits in mind, you can only monitor those (and not the mains). I think the mains are a good overall picture and sanity check.

You can also use the mains values to calculate unknown circuits. I have 22 circuits. If I monitor the mains + 12 circuits (14 total), I can subtract the 12 known circuits from the mains to get the usage of the 10 unknown circuits.

If I were to only monitor 14 (of 22) circuits, I could never know my total usage (without the mains).

OTOH, if you only have 14 circuits, you can just monitor those, forget the mains, and still have an overall picture of your usage.


Thank you for the response. That is helpful. I should have stated that I have another device for the mains themselves. I more or less just wanted to make sure that software-wise it wasn’t going to be upset if I did not specify two inputs as my mains.

Thanks again,

ehmar is correct. You don’t need to monitor the mains. In fact, you could not connect any CTs and just monitor voltage. Folks in single phase countries have just one main. Three-phase users can have three mains. It’s possible to monitor more than one electric service with a single IoTaWatt and have two or more sets of mains.

If you would like to modify your order to get the IoTaWatt without the 200A CTs and 14 50A CTs, I can do that, just PM me before tomorrow morning. It works out to $2.70 credit.


Thanks for the response and what you do. I’m glad I found this site and product. I had a sense for a few weeks and had to send it back because it doesn’t detect anything. I also thought about the curb energy monitor but don’t trust that they will always be around and they are proprietary and expensive anyhow. Let’s stick with the mains in the order I just placed. I went to look at the panel and I can get away with 12 50A’s. It’s a newer home and a lot of things I don’t care about are on their own circuit by code like a garbage disposal that runs for a few seconds a few times a week. The other device I had on the mains was an efergy and it doesn’t have nearly as good of data analysis anyhow.


I’m backed up on documentation, but be advised that it’s possible to combine circuits into one input using a variety of techniques, either using one CT, or combining multiple CTs into a single input.

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@jjf205 I have done exactly what Bob describes above. I took circuits like my Microwave and Garbage Disposal circuits and combined them using 1 CT. These are devices that are used relatively infrequently, and each has a very distinct power usage signature. Just be sure the CT is rated to handle the combined current of both circuits.

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