Everything You Need About Marker Balls on Power Lines

colored balls on power lines

While driving along the highway, you must have noticed those colorful balls on power lines. If you’re like most people, you probably wondered what they are. The theories about the purpose of those colored balls are varied. Some think they’re weights for the power lines. Others speculate that they’re weather sensors or even surveillance equipment. 

Those assumptions are wrong. If you’re curious about why colorful balls hang on power lines, you’ve come to the right place, as we’ll discuss what balls on power lines mean. So how about we start setting the record straight about those brightly colored balls? 

What Are the Balls on Power Lines?

Those balls on power lines are called marker balls. Also known as “Aerial Visibility Marker Balls,” they weigh about 7.7kg (17 Pounds). Meanwhile, their diameter depends on their location.  

The marker balls used on power lines and less extensive catenary wires (wires that cross lakes, rivers, mountain passes, and the like) below 15 meters (50 feet) should not fall below 51 cm (20 inches). For balls that go on extensive catenary wires and power lines, the size should be at least 91 cm (36 Inches).  

The most common color for these balls is “International Danger Orange,” although you can also see yellow, white, or red balls hanging on power lines. 

Purpose of Marker Balls

The aerial visibility markers are placed on power lines to protect electrical infrastructure and for the safety of low-flying aircraft. The bold solid colors of the balls make the skyline wires and conductor crossings visible to aircraft pilots. Thus, the aerial markers can help prevent low-flying planes from hitting or getting entangled in the power lines. Not only does this save lives, but it can also avert electrical wildfires and power outages in the area. 

The installation of visibility markers is also required by the Federal Aviation Administration. 

Aircraft Safety

Power lines are sometimes difficult to see from the air. This is particularly true in areas with mountain ranges, deep valley areas, and dense forests. In those areas, a power line can become almost invisible to aircraft pilots. The bright red, yellow, and orange balls make the power line stand out in contrast with the terrain, thus enhancing the structure’s visibility to helicopters and low-flying aircraft. 

The balls are also placed on electrical wires on major freeway crossings near airports for the same reason. That is, to protect helicopters and other aircraft that fly low from colliding with the power lines. 

Federal Aviation Administration Requirement

This government agency requires the installation of visibility markers in specific colors (aviation orange, yellow and white) on all power lines 200 feet or higher for the safety of aircraft flying at low altitudes.  

You’re likely to see these markers if you live near airports where there are higher chances of collisions between a plane and a power line. That’s because although large commercial aircraft typically fly at high altitudes, they fly low during takeoffs and landings. Meanwhile, small planes and helicopters often fly at lower altitudes, thus the requirement for power line markers. 


As recommended by the International Civil Aviation Organization (ICAO), the aerial spheres’ diameter should not fall below 600 mm. They should come in a single solid color and should be displayed in an alternating color scheme. Two hemispheres form the globes, which are attached to the power lines with aluminum alloy clamps. 

The spheres are made from high-grade Fiberglass Reinforced Plastics (FRP) and polished on both sides. Drain holes in the marker balls prevent water from accumulating inside. 


The marker balls come in two spheres which are clamped or bolted around the wire, making them easy to install. Here are the specific details. 


The aerial spheres should be installed along the electric lines with a gap of 200 feet (61 meters) or a fraction of this length between each other. In critical areas, the space between the balls should be lesser, at about 30 to 50 feet (10 to 15 meters).  

The balls should be placed at the wire farthest from the ground. If there is more than one wire at this height, the balls should be installed alternately on each wire while maintaining the recommended distance. 

Installation pattern

The aerial balls need to be mounted in alternating colors for maximum visibility. The alternating colors draw the eyes to the power line and capture the attention of the pilots, thus preventing a collision. 

If multiple transmission lines exist in one location, and the distance between the outside lines is over 200 feet (61 meters), the markers are set on an adjacent line. However, if the distance between the outer lines is more than 200 feet, there’s no need to install marker balls on the adjacent lines. 

Common Locations of Marker Balls

To comply with FAA regulations, marker balls should be installed on power lines in areas where the lines might be difficult to see and where the chances for collisions with them are high. Having these aerial spheres lets the pilots see the potential hazards. The typical locations of marker balls include the following. 

  • Deep valleys 
  • Dense forests 
  • Mountain ranges 
  • Airports 
  • Across bodies of water 
  • Canyons 

Types of Power Line Ball Markers

Aside from coming in different colors, several types of aerial visibility spheres exist. 

ABS Standard Marker

This is the most common type of visibility marker and has set the standard for ball markers. These balls come with a spiral line that attaches them securely to the power line. They have superb color retention and are easy to install from a bucket, the ground, or a helicopter. ABS Standard Markers are available in several sizes (6″, 20″, 24″, and 36″). 

EHV 115kV+ Marker

Designed for installation on voltage lines of up to 345 kV, this type of power line marker has a special coating and other unique features to reduce corona effects that sometimes lead to melting in other markers. The EHV Marker comes in  24” (for up to 230 kV power lines) and 

36” (for up to 345 kV power lines). 

High-Temperature Marker

Lines with high voltages or temperatures require ball markers that can withstand elevated kilovolts and temps. High-temperature markers are designed for use in high kV, or high-temperature lines (ACSS/ACCR) or electrical lines rated up to 500 kV or 250° C (482° F). They’re made of aluminum to minimize their weight, making them lighter than other marker balls. For example, a 36″ marker weighs only 20 pounds. They come in the following sizes: 12″, 24″, 30″, and 36″. 

Modern Self-Illuminated Marker/Light

These markers are equipped with 2 steady LED lights for 24/7 illumination, thus making the power line more visible day or night. They have solid-state capacitors and regulators that use the electrical fields generated by the transmission lines to power their LED lights. The aerial spheres are made from aluminum and are available in 12, 24, and 36 inches. 

Low-Cost Marker

As the name implies, a low-cost visibility marker comes at a lower price than other ball markers. They’re meant for low-budget projects and are used on small power lines which are below 50 feet. Low-cost markers are made from ABS with rubber strips for mounting. They come in small diameters (9″ and 20″) that meet the FAA advisory for small markers.   


Now, you no longer have to wonder what those colored balls on power lines mean. They’re all about safety. They protect aircraft and electrical wires, thus potentially saving lives and preventing service interruptions. 

So the next time you drive past those balls, you can share your knowledge about their purpose with your companions and debunk the myths surrounding them.

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