For tall light towers, maintaining stability is essential. There are a handful of ways to achieve this, from using different types of poles to using a heavy foundation. A very common option that businesses use for supporting light masts is guy wires.
A guy wire is a tensioned cable that is attached to the mast for extra stability, with one end deeply anchored into the ground and other attached to the pole. The cables are installed at consistent intervals, helping the mast withstand bad weather (especially strong winds) and rough treatment. Chance are, you’ve seen these structural components on tents, ships, radio towers and utility poles.
ASTM A475 and Light Masts
Guy wiring systems use industrial strength components to ensure long-term reliability. The main component is the wire, which is often galvanized for additional protection. The type of wire used must be lightweight and extremely sturdy. ASTM A475 is a wiring standard that can be applied to guy wire systems. The guideline covers various types of zinc-coated and steel-type wire strands in multi-layer configurations. This standard sets forth four types (weights) of zinc coatings: Class 1, Classes A, B and C (note, not grades). Other guy wire components include the following: end sleeves, shackles, thimbles, turnbuckles, big grip dead ends and drop forged wire rope clips.
For light masts, guy wires are used for units that are approximately 19 feet high (and above). At 19 feet, a guy wire is used at the center of the pole to prevent swinging. Heavy-duty light towers at heights of 33 feet (and above) with a secure, bolted base may only utilize one set of guy wires, at the top of the pole.
However, it is important to consider that best practices call for two sets of guy wires for standard-height towers, located at the center and at the top. These sections of the pole are the least sturdy, since they are furthest from the foundational base of the unit. For tall light masts or for installations in locations with bad weather, as well as light masts that support heavy equipment, it would be possible to install guy wires in 1/3 increments. In this configuration, the last (third) wire should be installed at the top of the light mast. For telescoping light masts that require additional stability, a guy wire should be installed at each section.
Do I Really Need One?
The need for guy wires depends on several factors. As a general rule, it is advisable to use guy wires to support poles, masts or structures that are taller than 12 feet, at a consistent rate of 10-15 feet of space between each section. However, shorter poles that are exposed to strong winds on a regular basis may also benefit from guy wires. Additionally, some poles that use reliable stabilizing or guiding components may not need guy wires for support. If a large section of the pole is securely buried into the ground and the foundation is set properly (for example, with concrete), the pole’s tolerance to obstruction is much higher.
Naturally, if one has equipment on top of the mast, such as lighting systems, security cameras, telecommunication devices, heavy antennas and etc., guy wires could help reduce shaking, while improving operational stability. On the other hand, some equipment, like an anemometer, does not require a stable base when mounted at the top of the pole. Hence, a guy wire may not be needed, even at heights between 15-20 feet (in locations with stable weather conditions). As a precautionary measure, some installations near power lines and commercial buildings call for guy wires to ensure poles that collapse (in the event of failure) do not cause catastrophic accidents.
Calculating for Guy Wire Length (Pythagorean Theorem)
When setting up a guy wire system for a light mast, it is critical to ensure the length of the wires are correct. Fortunately, the variables of guy wires are straightforward. The first thing to note is that guy wires should extend at an angle of 45 degrees. The pole being supported is erected at a straight 90 degrees, while the ground offers a flat, horizontal surface. When the variables are constant, it would be possible to apply the Pythagorean Theorem to find the length of the wire.
Pythagorean Theorem: a2 + b2 = c2
In this equation, which is visualized as a right triangle, ‘a’ refers to the height of the pole and ‘b’ refers to the distance between the pole and the installation point of the wire on the ground. Variable ‘c’ will generate the length of the guy wire at the top position.
One last thing: guy wire systems are installed by trained professionals and should never be attempted by DIY hobbyists. Although guy wires are not energized (the components do not carry power), they should never be tampered with – as it could compromise the foundational properties of the mast or structure.