In article ,
tony sayer writes:
BT use an instrument which is basically an oscilloscope and a
pulse generator. The pulse goes down the cable and bounces back
from where the break is. The initial pulse followed by the
'echo' are displayed on the 'scope, from which can be determined
the time between the two and thus the distance to the fault.

Suggest a metal detector would help you plot the cable route.

What Harry described is a Time-Domain Reflectometer (aka TDR). Not
a lot of people know that.

Not a lot know how expensive they are either. We use one for finding
faults on co-ax cables up transmission towers.....

I used to run about 3km of thick and thin Ethernet in ceiling voids, and
there was never a TDR on the market cheap enough for `them' to let me get one.
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SAm. all sweeping generalisations are false