[Solved] Only one IoTaWatt input for mains split phase?

Hello there!

I do not have an IoTaWatt yet, but I plan to get one when they’re back in stock. That said, I had a question:

In the “CT Basics” documentation (CT Basics — IoTaWatt 02_03_20 documentation), at the very bottom, it says “Two individual CTs can also be combined with a common headphone splitter and fed into a single IotaWatt input. When combining this way, both CTs must be the same model with an individual capacity sufficient to measure the combined capacity of the two circuit breakers.”

Would that also work with the mains split phase? I have a 200A split phase 120/240v panel and it surely would be nice to be able to monitor almost all circuits, I attached some pictures below for reference.


You can do that with 200A mains CTs as long as the combined total doesn’t exceed 200A. If it does, then you would need 2 x 400A CTs.

Thank you, that’s what I thought. I’ll get two 400A CTs and use the 200A ones for my 20 kW electric furnace.

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I don’t see a neutral wire going to the furnace. If that’s the case, you could use a single 100A CT on only one of the wires and “double” it, then with the saved input there you could use the 200A CTs on the main into two inputs.

Thanks for the advice but there is a neutral, it’s the big blue wire coming from the bottom left of the box, so I need 2 CT clamps anyways, and I’ll still use the headphone splitter trick for those two as well :slight_smile: