I can remember years back we had the remains of the Rhodesian Puma crash in out hangar where he was doing ultra low level down a road when the phone lines crossed over to the other side, none unfortunately survived and the phone cables where found wrapped around the rotor mast.
They also trialed a system for detecting cables with current flowing through them, it consisted of a circle of lights that lit up to show the position of the power cables in relation to the aircraft, they I believe had probs as the frequency was similar to that given off by the rotors. but after a succesful trial flying towards power lines they were returning to base and the good old electricity board had turned off the juice for repairs, they cleaned the aerials off the bottom of that one if memory serves me right.