Harry Bloomfield wrote:
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.

Time domain reflectometer, I think. AIUI it has to be calibrated by
cable type.

Probably does not help with where the cable is located - though you
could do the same for both ends, add the two lengths together and it
would give the limits of where it could be.

Even better, if you have the distances from two points, draw the arcs of
the circles and where those arcs intersect is the point of break.
Assuming the cable runs in reasonably straight lines of course.

Owain