For specifications of the P1 port see: http://files.domoticaforum.eu/uploads/Smartmetering/DSMR%20v4.0%20final%20P1.pdf

See chapter 4.2 Power supply
The power supply for the P1 port shall be able to withstand short circuits. Manipulation of the
power supply lines shall never influence any other ...

I agree wit topic starter, Domoticz is great but lacks developer documentation. At least I can't find it. Would be very nice to add a developer oriented section to the wiki to document the architecture. My experience is that each developer/contributer will get its own view on the architecture ...