We have a 3-phase installation in our house, so in a normal way I think I'll need 3 OEM's to measure the complete power usage.
BUT, we have 3 live-wires coming in and only one neutral-wire going out.
So would it be enough to only put a CT-sensor on the neutral wire to measure the complete power usage?
Re: 3-phase question
No. Read the article on 3-phase in Building Blocks. That will tell you why.
If you want an accurate measure, you need 3 emonTx's. If you are content with an approximation that might be good enough for you, then you can use one emonTx and the 3-phase sketch. The comments in the sketch explain the limitations.