On 19/07/2019 10:38, Chris Green wrote:

My tests with a fairly basic pair of Tenda (supposedly Gigabit)
powerline devices suggest that they're only 'good' when used on a
single, or at least closely associated, circuits. However if I can
add more of them so that they 'chain' across the system that could
well be a reasonable solution, but I need to know if they can
interconnect like this. Does anyone know?

I don't know of any that chain together. The way I use mine is that the
relatively low traffic stuff goes over powerline ethernet - printers,
internet radio and email/web browsing of seldom used computers.

It works sufficiently well for me that even across different consumer
units for the original house and extension the printer throughput is not
noticeably affected. Speed isn't great like that. I put a new repeater
Wifi node to fill in the worst gap at the furthest end of the house same
password as the master, but with a different SSID and channel.

You have to experiment to find what works best in your circumstances.
Units likely to have big suppression capacitors on like fancy sockets
for hifi, fridge freezers and oil burners tend to rob signal.

--
Regards,
Martin Brown