When you close a switch to initiate an electrical current down some long wires it takes a measurable time before you know what's at the far end of the wire. Th

When you close a switch to initiate an electrical current down some long wires it takes a measurable time before you know what's at the far end of the wire. Therefore if the wire is either intact or broken at the far end, over a 500m distance the first 1.6us of measurement looks exactly the same.