I have seen several discussions about having powerlin devices on separate domestic circuits. Our house (UK) has one circuit for upstairs power sockets and another circuit for downstairs sockets. When I put 2 devices on the same circuit they worked fine..then I tried with the "master" adapter upstairs and the "slave" on the downstairs circuit. Hey presto they connected fine with probably only a 15% drop in transmission speed.  So the reports that suggest this setup won't work are probably incorrect... although it may depend on individual wiring systems.