I have a bad Ethernet cables through unused chimney from my apartament to the basement. The workers I asked to pull it just did it brute force and 2 of pairs are broken. When I was chatting with Claude to see if I can use it somehow to send Ethernet packets one of the Claude responses was to use broken cables as a pilot to pull fiber channel!
You can run 100mbps with only two pair, if you have something on at least one end which you can tell to only negotiate to 100.
Nice one :)
I tried this in my house that has ancient copper telephone lines. I was trying to get some level of walled ethernet. I wanted to use the existing wires to pull new ethernet as is discussed here, sadly the builders had stapled them to the interior studs when they ran the telephone lines back in the 70's.