WARNING: This design appears to be potentially dangerous. Utmost care should be taken, and ideally professional advice sought, before attempting to construct this item. Moderator (RW)
Related Forum Thread 
Note from maker of "shield": Correct, do not build this if you dont understad the risks. I personally will run the Pi over WLAN, but that still doesn't take all the risks away. If broader interest for this "shield" I will fix a safer version, no problem. For now v1.0 is quick and dirty and focus is on power measurement capabilities of the ADE7878A.
I made this module as a bolt on (shield) to RPI B+
I logged my energy before via an optical sensor to the meter supplied by the power company , but wanted to see this now on a phase level, that's why I developed this. The Optical sensor giving kWh aggregated will be kept for calibration and aggregated power. I log every minute to an mysql server and via another program I can draw curves for any period of time I have collected data for. This includes also a lot of other parameters like temperature etc.
It's using the Analog Devices ADE7878A for Polyphase Multifunction Energy Metering.
The ADE7878A is high accuracy, 3-phase electrical energy measurement IC with serial interfaces and three flexible pulse outputs. The device incorporate second-order Σ-Δ analog-to-digital converters (ADCs), a digital integrator, reference circuitry, and all signal processing required to perform total (fundamental and harmonic) active, reactive and apparent energy measurement and rms calculations.
Board also contains 3 ports for 1-Wire via DS2484 and a RTC using the DS3232M with battery backup. One ID-EEprom according to RPI B+ spec for shield identification.
Schematic. v1.0 File:ADE7878A rpi.pdf