High-powered flood lights and area lights are typical fixtures used to illuminate outdoor areas like streets, sports fields, athletic courts, and parking lots. These projects require tall poles to mount the fixtures up high. These poles and their attachments need to be able to withstand windy conditions to ensure that they are safe and reliable. But how can you determine if they can handle these conditions? That’s where EPA ratings come in.
EPA ratings are used to determine if poles and their fixtures can meet the requirements of a given geographical area. One of the first things that you’ll need to consider about the sturdiness of your pole and fixture assembly is the local conditions of where it will be installed. Some areas, such as along the coast, around the Great Lakes, or in the mountains experience stronger wind conditions than other parts of the country.
What is EPA?
EPA stands for Effective Projected Area. A fixture’s EPA measures the cross-sectional area of a fixture. It is then diagrammed onto a two-dimensional plane. In other words, it is the measurement of a three-dimensional object on a two-dimensional area.
EPA represents the visible area of a three-dimensional shape by the wind at a particular angle. Let’s use a three-dimensional shape of a cone as an example. From one angle, the cone appears as a triangle. From another angle, the cone appears as a circle.
All components involved (the pole, the fixture(s), and the tenon) will each have an EPA. The overall EPA and the weight of the components mounted on the pole must not surpass the pole’s maximum rating for the wind zone where it is located.
The EPA of any pole assembly will vary depending on its shapes, angles, and sizes. As an example, the shape of a pole can alter its EPA. For instance, square poles have a larger EPA than round poles.
The structural requirements of a light pole are affected by the following:
The type of luminaire used
The number of luminaires mounted to the pole
The height of the pole
The type of mounting bracket used to attach the luminaire(s)
The type of luminaire that is used makes a huge difference. Each luminaire housing has a distinctive effective projected area. You can calculate an EPA manually by multiplying the exposed surface area of a fixture by the shape factor. However, it is simpler to consult the luminaire specifications that are given by the manufacturer.
What is an EPA wind rating?
An EPA wind rating is the calculated maximum wind speed that a pole-mounted fixture is able to handle in a specific area. This rating will directly affect the type of pole that will be used to mount the fixture(s).
Depending on where the pole and fixture assembly are installed, it is required to withstand worst-case wind conditions. Worst-case wind conditions are defined by the geographic region the pole/fixture is located in. In general, most areas in the United States have worst-case wind scenarios of 70-90 MPH (miles per hour).
Areas that encounter wind gusts between 110 to 130 MPH are considered to be high wind zones. For example, cities along the coast, like Miami and Houston, are in 110 MPH wind zones. In this case, a fixture mounted on a light pole must be able to manage 110 MPH winds without failure.
How is an EPA wind rating calculated?
Wind pressure values, fixture weight, and fixture EPA are combined to evaluate a fixture’s wind rating.
- Worst-case wind pressure values determine a fixture’s wind rating and drag profile. These values have been accumulated over multiple decades. These factors determine the amount of force applied to the fixture (including its mounting hardware) at any one time. To make it easier to determine the wind speed in your specific location, the American Society of Civil Engineers has created a wind speed map of the United States.
- A heavier fixture will apply more force on its pole and mounting hardware. Its weight will influence its wind rating.
- The EPA is the projected area combined with the appropriate drag coefficient. The drag coefficient can be defined as the resistance created by the object or shape in a fluid environment. In this case, the fluid environment is air. The drag coefficient will vary. This will depend on the shape of the object. A lower drag coefficient will coincide with lower resistance created by the object.
Consulting with your local authorities about building codes is the safest way to make sure that you are obtaining equipment that can withstand these windy areas. The best way to establish the requirements of your project is to:
Determine the site location.
Determine the EPA and overall weight of the pole assembly.
Verify the wind load requirement.
Consult with the pole manufacturer to ensure that it can withstand the local conditions.
About the Author
Dwayne Kula is President of LED Lighting Supply. On any given day, Dwayne is writing content for the site and helps manage the marketing initiatives that are on-going. He has a Software Engineering degree and still dabbles in writing software for the company as needed. When not working, he enjoys spending time with his family, working out, playing the occasional game of golf and exploring New England.