What are the colored balls on power lines?

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Whenever I see large power lines here in California, there are almost always brightly colored balls strung along the lines. Are these to warn aircraft or something else?

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They’re called visibility marker balls or marker balls. You’ll often find them near mountain passes, in the deep valley areas, near major freeway crossings and around airports.

They weight about 17 pounds each. The marker balls are placed on power lines to make the conductor crossings visible to aircraft.

For helicopters and aeroplanes to be able to see the line. But also meant to deter birds from sitting on wire and breaking it.

It is very hard to see wires from the air due to them blending in with ground clutter. The best one can hope is to see the pole lines (pilots are taught to cross over the polls and no in between them). Those pole lines don’t exist when power lines cross valleys.

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Wire strikes were such a problem and danger, accounting as the most common cause of aerial accidents in the late 70s for helicopters, that manufactures added wire cutters to helicopters to make such incidents survivable. A [wire strike protection system](https://en.wikipedia.org/wiki/Wire_strike_protection_system) is found on nearly all helicopters in the world now