This project is second iteration of DIY Life. Previously he has built a single phase power meter using similar technique. He wanted to keep things very simple, os he used only non-contact current measurement only by using Talema AC1030 current sensors on each phase line. They are capable of capturing 30A nominal and 75A maximum current. In order to measure power accurately a voltage measurements should be taken. But for sake of simplicity, voltage is only taken as 220V.
The only focus is to measure current correctly which depends on burden resistor selection and measurement drop voltage through Arduino analog input. Input current then must be calibrated with known load. Rough estimate can be made with 100W light bulb. If you are considering building this three phase power meter, be sure to simulate project on provided Autodesk Circuits simulator. Here you can tweak your circuit and test sketch code.