Yup: there’s a current transformer on each circuit leaving the breaker panel (up to 14 different circuits), one on each of the main feed lines, and then a small plug-in voltage transformer to measure voltage, phase angle, and frequency.
It takes all that data, polling each sensor a few dozen times a second, calculates power usage, stores, and presents it all with the above graphs in a simple little web interface. It can also export that data to more powerful graphing/data analysis solutions, but I’ve been pretty happy with what’s onboard.
(2 phases of a 3 phase apartment supply. Outputs are math output of multiple inputs. Ex: Main_A+Main_C=Total_Power)
The setup inside the breaker panel is something you should hire an electrician for if you aren’t extremely confident and knowledgeable about what you’re looking at. There is a lot of potential to injure yourself or burn your house down, even with all the breakers off.