what are the balls in power lines for
Balisor High voltage power cables, particularly those close to airports, need to be visible day and night. During the day, brightly coloured balls positioned along the length of the cables are sufficient, but during the night, lighting is necessary. These beacons provide this lighting by glowing red, the standard colour used in aviation for warning beacons.
Multiway switching In the traveler system, also called the "common" system, the power line (hot, shown in red) is fed into the common terminal of one of the switches; the switches are then connected to each other by a pair of wires called "travelers" (or "strappers" in the UK), and the lamp is connected to the common line of the second switch, as shown.