Settle a debate.......orange balls.

[frog]

they are a kind of abacus from an ancient dutch football civilisation

[peteroldracer]

The balls are for inspection purposes: it helps an inspection vehicle driving along the motorway to see the wire, note if it is starting to droop and needs retensioning, and for the same sort of inspection by a helicopter. In both cases it makes a difficult-to-see wire more visible.

[keddyboy]

In the UK they used to put discs on the wires. These were there to stop rodents spreading via the electricity lines, perhaps this is another way as ronnie rodent would be hard pushed to cross a ball like structure.

[Travelogic]

All this doesn't explain why the balls are orange.
When I stumbled upon this 'orange balls' thread, I thought it was a debate about Ian Paisley.

[JAKE M]

The orange balls are put there as a conversation piece. Someone always asks what they are for. It's even on forums now Leave them alone . It's now part of spains heritage.

[peteroldracer]

FAA Regulations
AC 70/7460-1K
Obstruction Marking and Lighting

Markers are used to highlight structures when it is impractical to make them conspicuous by painting. Markers may also be used in addition to aviation orange and white paint when additional conspicuity is necessary for aviation safety. They should be displayed in conspicuous positions on or adjacent to the structures so as to retain the general definition of the structure.
They should be recognizable in clear air from a distance of at least 4,000 feet (1219m) and in all directions from which aircraft are likely to approach. Markers should be distinctively shaped, i.e., spherical or cylindrical, so they are not mistaken for items that are used to convey other information. They should be replaced when faded or otherwise deteriorated.
a. Spherical Markers. Spherical markers are used to identify overhead wires. Markers may be of another shape, i.e., cylindrical, provided the projected area of such markers will not be less than that presented by a spherical marker.
1. Size and Color.
The diameter of the markers used on extensive Catenary wires across canyons, lakes, rivers, etc., should be not less than 36 inches (91cm). Smaller 20-inch (51cm) spheres are permitted on less extensive power lines or on power lines below 50 feet (15m) above the ground and within 1,500 feet (458m) of an airport runway end. Each marker should be a solid color such as aviation orange, white, or yellow.