A perfect example of Thumping.
"A cable thumper is basically a portable high voltage surge generator. It is used to inject a high voltage DC surge (about 25 kV) into the faulty cable. If you supply a sufficiently high voltage to the faulty cable, the open-circuit fault will break down creating a high-current arc. This high current arc makes a characteristic thumping sound at the exact location of the fault.
To find the location of cable fault using the thumping method, a thumper is set to thump repeatedly and then walking along the cable route to hear the thumping sound. The higher the dc voltage applied, the louder will be the resulting thump. This method is useful for relatively shorter cables. For longer cables, the thumping method becomes impracticable (imagine walking along a cable that runs several kilometers to hear the thump)."
Info Source : Electrical Easy
