You Asked:

What are those balls that hang on the power lines? — Peggy, Bethel, Ohio

Marshall Brain Answers:

The balls are called marker balls, and the goal is to try to make the power lines more visible to low-flying planes and helicopters. Wire strikes cause many accidents because a thin power line is very hard to see from the air. The following video demonstrates the problem that power lines create for aircraft:

Why balls? A sphere has the nice feature that it has the same amount of visibility from every angle.

Here are some of the FAA regulations for installing the balls: FAA regulations for markers

The following video shows a helicopter taking off with one of the marker balls – it gives you a sense of their size, and also shows that installation can be a bit of a challenge:

Installing a marker ball on a power line:

Marker balls are not a perfect solution because they are relatively small. A new system called OCAS (Obstacle Collision Avoidance Systems) could provide a more automated solution:

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