PLC is first line?

[K4680]

Here is the complete box. https://imgur.com/a/syEYc

Do you think PLC would be greatly improved on all circuits with the added phase coupler? Or just on the circuits that are added?

Hi hydr, the phase couplers bring here no advantage. Since this is a 1-phase network, all PLCs are on the same phase!

But I wondering why my PLC performance is so terrible? Wish I had decent PLC connection between the rooms.

Hi, try the devices (PLC) directly wall socket. If you operate the PLC via power strips, the throughput drops rapidly, as it is with line filters or isolation transformers !!