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What are those orange balls on some power lines? – Maggie, age 8, West Chester, Pennsylvania
Have you ever looked up while driving on a highway and spotted those big orange balls hanging on power lines? They look a bit like giant toy beads strung along the electric wires.
What in the world are those overgrown basketballs doing up there?
I’m a professor who teaches about and researches power systems, the big networks that move electricity from power plants to our homes, schools and businesses.
Those big orange balls don’t help with electricity flow or improve the efficiency of the power lines, but they do have a very important job. Officially called aviation marker balls or spherical markers, they’re there to help pilots see power lines so airplanes and helicopters don’t crash into them. They’re like bright warning signs in the sky, protecting pilots, passengers and people on the ground below.
Zen Rial/Moment via Getty Images
Big round warning signs in the sky
Power lines can be very hard to see from an airplane or helicopter, especially when pilots are flying low. Thin metal wires can visually blend into the background of nature.
The orange balls help the lines stand out. You can think of them as being like reflective tape on a bike – just a little something simple that helps people notice a danger before it’s too late.
Orange isn’t a random choice. This vibrant color is very visible to the human eye and especially stands out against the more muted colors of nature – blue sky, green trees or gray clouds. Sometimes the balls are red or white, or even striped, but orange is the most common because it works well in most lighting conditions.
Aviation safety rules in many countries explain which colors should be used so pilots can quickly recognize hazards. Organizations like the U.S. Federal Aviation Administration publish guidelines you can check out about marking obstacles near flight paths.
Lisa Meiman/Western Area Power/Flickr, CC BY
These balls may look like slightly oversized ping-pong balls from your perspective on the ground. But most are actually much bigger, about the size of a large beach ball, roughly 2 to 3 feet (0.6 to 1 meter) across. Each one can weigh 10 to 25 pounds (4.5 to 11 kilograms), about as heavy as a large backpack full of books.
They’re usually made from strong plastic or fiberglass, similar to materials used in boats or playground equipment. That way, they can survive years of sun, rain, snow, wind – and even the occasional bird landing on them.
Even though they sit on wires that carry huge amounts of electricity, the balls themselves are not energized. They’re made of insulating materials, so electricity does not flow through them.
Why are there so many wires up there?
High-voltage power lines are like highways for electric power, carrying electricity from the power plants where it is generated to the places where it is used.
The wires are strung between sturdy metal towers or wooden poles that are very tall to keep dangerous high-voltage electric wires high up in the sky, far away from people on the ground. This design makes it safe to walk, play and drive underneath them. Some transmission towers, especially for very high-voltage lines, can be as tall as a 15-story building.
If you look closely at big transmission lines, you’ll often see three thick wires, sometimes with an additional thinner one on top that’s called a shield wire. Because the shield wire sits higher, lightning is more likely to hit it first, protecting the other wires from a strong blast of electricity that can damage equipment or cause power outages. The shield wire is connected to the ground, so a lightning strike’s electricity can flow safely down the tower and into the earth.
The three main wires work together to carry electricity in a steady rhythm. By sharing the job among three wires instead of one, the system can move more energy with less waste, making it more efficient.
Christian Butt/picture alliance via Getty Images
Clamping the balls to the wires
Installing the aviation marker balls is a job for specially trained crews, often working from helicopters. The power line usually stays turned on while the work is being done, so safety rules and careful planning are critical. The ball comes in two halves that clamp around the wire and bolt together tightly.
Once installed, these balls can last 10 to 15 years, depending on weather and conditions. They don’t need much maintenance, but utilities inspect them from time to time to make sure they haven’t cracked or faded too much.
Not every transmission line needs the markers. Usually only places where aircraft are more likely to fly low – such as near rivers, valleys, airports or helicopter routes – will use these brightly colored balls. Most neighborhood power lines are too low to need markers.
Next time you spot those bright orange dots in the sky, you’ll know: They’re not electrical equipment, and their color isn’t random. They’re simple, clever tools helping keep our busy world a little safer.
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