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I installed a TED 5000 in 2012.  This particular unit is no longer available.  This thing would measure voltage and current on both phases and send that information over power line communications to a gateway that was then hardwired Ethernet into a router.  The gateway would record usage data and show a nice web interface (example screenshot above).

The main issue with this setup was the power line communications.  PLC is extremely susceptible to noise so I had to install an X.10 filter similar to this one.

There are now much better devices on the market but TED 5000 was a first of its kind.