I want to monitor my mains whole house energy usage and from reading the Shelly 3em pro seems to be the best to work with HA but I am confused as to how to connect the 3 clamps, circuit panel has 2 120v lines in and the center cable, how should the clamps be attached? Thanks
Use only B and C, do not use A at all. Using the A cable will either cause reading from B and C to zero out or double if you reverse the reading.