Hello @cr0ntab,
First, understand that the IoTaWatt is just indicating that it senses reverse current in these CTs, but is automatically correcting those values so that you get correct results. The only time it’s important top get it right is when reverse flow is encountered in normal operation, as with the mains in most North American solar setups.
I really need to add a section in the documentation to explain how to setup split-phase systems, and I plan to do that soon, but in the meantime I just went over this in another post that should explain things somewhat:
Hopefully that will put your mind at ease. Whichever of the two mains is showing reversed can be physically reversed (flip over) or logically reversed (check the “reverse” box in the CT setup). Same goes for the 50A CTs that are reversed. If they are all installed as in the picture, with the arrows pointing away from the breakers, then all of the channels showing as reversed should be in either even or odd rows of the load-center. Because the VT has a non-polarized plug, and I don’t know which “leg” it’s circuit is on, it’s not possible to give absolute advice. It’s all relative, and it really doesn’t matter for accurate results. That said, I have adjusted mine to eliminate the reversed indications.
Update:
As long as the circuit-breakers are 15A, that’s good practice. It saves on copper wire, and the one neutral conductor will never need to carry more current than the greater of the red and black. Although not significant, it can also reduce the voltage drop in the two circuits.
If you have a spare 50A CT, clamp it on that neutral for awhile while using the two circuits, then plot the Amps for all three on the same graph.
Now create an Amps output that is the black minus the red. It should be the same as the neutral.