One of the requirements for the HaD Prize entry is a system design document, so here it is. Basically tldr of what I wrote in my detail description.

You have small and cheap sensor board that connects to your machines via CT sensors and the current values from these sensors are turned into a voltage signal that an MCU (ATtiny) picks up and sends it wireless to the server.

I put the RPi in dotted lines as I may replace it later on with an small MIPS board with Wifi and Ethernet built-in that sits on the sensor Board and receives sensor data over serial/i2C/SPI. That would make the whole thing most cost effective and smaller and everything is one neat package.