On 23/01/2018 17:55, Harry Bloomfield wrote:
on 23/01/2018, Brian Gaff supposed :
Underground cables are the most difficult of course as there is no way
to find where the break is unless there is a tell tale crater in the
ground nearby of course!

Actually there is - They can send a pulse down a cable then measure the
time for the pulse to be reflected. Time = distance to fault.

It is commonly used on telephone cables too.

Early ehernet transceivers had built in TDR circuits so you could find
faults. I don't know when they were phased out.