secure intranet with power line carrier (PCL) ?

Hi, I would like to know whether there's viable safe options on the market in order to create an LAN intranet without any connection to the Internet for internal IM & communication. I've asked about software elsewhere but I think I'll stick with Retroshare, as it functions on p2p without central server.

I don't want to link the individual post to the local ethernet wiring for fear of hacking, so i wanted to know whether this could be a safe alternative ? Maybe there's special anti-hacking hard-or software available for PCL ?

I guess I'll need some of there right :

https://www.amazon.fr/TP-Link-Ports-Ethernet-Gigabit-Int%C3%A9gr%C3%A9e/dp/B06ZYJSV5M/ref=sr_1_1?ie=UTF8&qid=1537962863&sr=8-1&keywords=courant+porteur+en+ligne