What are those colourful Aerial marker balls on power lines?

Have you ever noticed that some colourful balls are hanging on the High voltage transmission lines or power lines? You might have a question in your mind that what are these colourful balls and why they are hanging on these power lines? You will get all your answers in this article.

What if I tell you that these balls are placed on those wires Just to enhance the decoration of the city, I know that you won’t agree with me and this is also not the actual reason. But yes, they look beautiful on those wires.

These colourful balls are called “Aerial Marker balls” or “visibility marker balls” or simply “marker balls”. They are also famous with one more name which is “span guard balls”

When some helicopter or an aircraft fly at low altitudes then it is very difficult to see the transmission wires clearly. So, to identify the wires these balls are placed on power lines.

Aerial marker balls hanging on power lines
High voltage power line with big ball for warning pilots, low flying aircraft and helecopter.


Aerial marker balls or Visibility marker balls are used for the safety purpose only. They save lives and infrastructure by making transmission lines and communication lines visible to Helicopters and Low flying Aircrafts.

Generally helicopters and aircrafts fly at high altitudes But they tend to fly at low altitudes at some locations like, River, Hilly areas, Deep valleys, Highways and Runways. To protect them, these aerial marker balls are used on these power lines.

Features of aerial marker balls

  • Weight of aerial marker balls is around 5 to 8 kg.
  • The visibility marker balls are made up of Hard Plastic which can withstand High temperature also.
  • Generally the diameter of these balls is around 36 inch. But, for less extensive catenary wires like on River, lake (50 feet height) 15m, the diameter of these balls is around 20 inch.
  • Generally, Aerial marker balls are installed in Orange colour when there are less than four marker balls on a given wire. Red, Yellow and White are some more colours which are available when there is more no. of marker balls are used.
Aerial marker balls
Aerial Marker Balls hanging on power lines

How they get installed on such heights and difficult locations?

If this question arises in your mind, then you might also think about cranes and lifts. But here I remind you once again that these Span guard balls or aerial marker balls are not used on every transmission line, they are used on the locations where helicopters and aircrafts tend to fly at low altitudes like River, runways and valleys, and cranes cannot reach everywhere.

So, my answer to the above question is that they are installed on the transmission wires and communication wires with the help of the Helicopters and skilled person.

These balls are hollow from inside and made up of hard plastic from outside. They are screwed tightly from both sides. You can clearly see it in below picture.

Installation of aerial marker ball

Now, this is the situation when a aircraft is flying in the day time, but what will happen if the aircraft is flying during night when there is very low visibility, it is really hard to see these markers balls clearly. Read this post to know this answer. How do pilot see transmission lines at night?

You can also see our Video below to understand it in a better way.

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