I believe they use devices that act like some kind of radar. They send a signal across the wire and measure how long it takes to bounce back. They can get a rea

I believe they use devices that act like some kind of radar. They send a signal across the wire and measure how long it takes to bounce back. They can get a really good estimation of the distance between the ping and the cut. But maybe others can explain how this works. Edit: this website explains other methods very well https://www.electricaltechnology.org/2015/06/cable-faults-how-to-locate-faults-in-cables.html https://www.electricaltechnology.org/2015/06/cable-faults-ho...