I mean, the simplest answer is to lay a new cable, and that is definitely what I am going to do - that’s not my question.
But this is a long run, and it would be neat if I could salvage some of that cable. How can I discover where the cable is damaged?
One stupid solution would be to halve the cable and crimp each end, and then test each new cable. Repeat iteratively. I would end up with a few broken cables and a bunch of tested cables, but they might be short.
How do the pro’s do this? (Short of throwing the whole thing away!)
This one here does time domain reflectiometry which will tell you exactly where the break is:
https://www.amazon.com/Ethernet-NF-8209-Distance-Location-Measurement/dp/B08M3SRB2Q/
I was curious if that would work on ethernet cable! I’ve seen it done on coax, wasn’t sure if it would work well enough on UTP to be useful outside a lab setting. Cheap too. Cool!
Some of the reviews say it didn’t work for them to find a break, but I have that exact one and have had good luck with it. So YMMV. Obviously the ten times the price Fluke will do better.
TDR isn’t exactly rocket science and the speeds needed to do it are surprisingly reasonable. You can build your own for a few bucks if you have an oscilloscope as well.