> What I heard the distance is almost never a problem, but in some
countries
> parts of the same house can be powered from different phases of the
mains.
> That surely is a problem!

The distance in power line communication is ever problem!
It's not the same if your power line communication equipment is connected
at your home or in machine tooling shop where 12kW electric motors running
near by.
Even in your home it's not the same if to the power line is you switched on
only your lighting or your water heaters (down to 4 ohm active resistance),
gourmet (down to 6 ohm), and everything this is in parallel!

> >
> > What is typical the max distance that a TDA5051A home automation modem
> can
> > be use to send data from one point to another...
> >
> > What is the dependencies?
> > - thickness of wire?
> > - complexity of wires?
> >

IMPEDANCE and the NOISE level in your line.

Check Philips datasheets there are given the output levels at given line
impedance, the receiver sensitivity, S/N ration etc.

The same equipment may run well at 100 meters in one conditions and
couldn't establish communication at 10 meters at other conditions of the
power line.

Cheers
Tsvetan
---
PCB prototypes for $26, http://run.to/pcb

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