Molly Ayala
Utility poles are an essential component of electrical distribution systems, and most of them are made of wood. To enhance their durability and protect them from rot, fungi, and insects, these wooden utility poles undergo a pressure treatment process. This process involves infusing preservatives deep into the wood fibres, ensuring long-lasting protection. The treatment methods and preservatives used vary, but the goal remains the same: to extend the service life of the poles. This paragraph will explore the process of pressure treating utility poles, the types of preservatives employed, and the benefits they offer.
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What You'll Learn
The process of pressure treatment
Once the wood has been seasoned or conditioned, the preservative solution is pumped from storage tanks into the retort, completely filling it. Pressure is then continuously applied within the retort to force the preservative into the cells of the wood. The time the poles spend in the retort will depend on various factors, including the size and species of the wood, the preservative being used, and the desired level of protection. At the end of the treatment process, the retort is emptied of preservatives, and the excess preservative is captured on a drip pad.
Core samples are taken from the treated poles to analyse and ensure that quality and durability standards are met. Third-party inspection agencies also take samples during regular visits to confirm the plant's quality control practices. The finished preserved wood poles are then moved to a sorting yard, where they can be shipped to utilities for immediate placement into service.
There are several different preservatives that can be used in the pressure treatment process, including CCA (Chromated Copper Arsenate), CuN (Copper Naphthenate), DCOI (4,5-Dichloro-2-N-Octyl-4-Isothiazolin-3-One), Creosote, ACZA (Ammoniacal Copper Zinc Arsenate), and Penta (pentachlorophenol). CCA, for example, chemically bonds with the wood, reducing the chances of the preservative migrating into the soil or groundwater. Oil-based emulsion treatments can also be added to improve climbability for utility linemen. The choice of preservative depends on various factors, including the species of wood, the desired level of protection, and the environmental conditions the pole will be exposed to.
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The types of preservatives used
There are six preservatives used for utility poles and crossarms in North America:
- CCA or Chromated Copper Arsenate: CCA chemically bonds to the wood, reducing the chances of migration into the soil or groundwater. It is a waterborne preservative.
- CuN or Copper Naphthenate: An industrial-strength, oil-type wood preservative with good gaff penetration for climbing. It is widely applied as a field treatment on end cuts or holes bored into pressure-treated wood during construction.
- DCOI or 4,5-Dichloro-2-N-Octyl-4-Isothiazolin-3-One: This is the newest oil-type preservative available for utility poles and crossarms. It has been used as a wood preservative since 1989 and is also used in water treatment, paints, adhesives, and vinyl roofing, among other things.
- Creosote: This preservative has been used since the mid-19th century in America.
- ACZA or Ammoniacal Copper Zinc Arsenate: ACZA is a waterborne preservative.
- Penta or Pentachlorophenol: This preservative is cheap, easy, and effective. However, it is a possible carcinogen and is banned in most countries.
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The materials used for utility poles
The choice of material for utility poles depends on balancing cost, environmental impact, and material performance. Utility poles support the overhead lines and equipment that power daily life. The materials used can significantly impact a utility's longevity, safety, and environmental footprint.
Wooden utility poles have been the standard for supporting overhead power and telecommunications lines. Wood is abundant, lightweight, strong, and, when treated with preservatives, durable. However, changes in legislation affecting wood preservatives have reduced the lifespan of treated wood, particularly in tropical climates. This has prompted utilities to explore other options, including reinforced concrete, galvanized steel, and composites.
Wooden poles are renewable and offer a lower carbon footprint during production. They are also the least expensive upfront, making them a popular choice for budget-constrained projects. However, they may require more frequent replacement, as they are susceptible to decay, termites, and core rot. Woodpecker damage is the most significant cause of pole deterioration in some parts of the US.
Steel and iron poles are more durable and have longer lifespans, but they have higher initial environmental impacts due to energy use and emissions during manufacturing. They are also more prevalent in the United States due to improvements in engineering, corrosion prevention, and lowered production costs. Steel poles are ideal for high-voltage lines, requiring taller poles for enhanced clearances and longer spans.
Concrete poles are commonly used in marine environments and coastal zones due to their excellent corrosion resistance. However, the drilling of installed concrete poles is not feasible, and they often suffer from reinforcing bar corrosion.
Composites, such as fiberglass, are becoming more prevalent and offer a lightweight, weather-resistant structure.
Other factors to consider when choosing a utility pole material include durability, environmental responsibility, local suitability, and the risk associated with pole failure.
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The history of utility poles
Undeterred, Morse persisted, and in 1844, he successfully transmitted the phrase "What Hath God Wrought" from the Capitol to Baltimore and back using Morse code, marking the first documented use of wooden utility poles. This success sparked a rapid spread of wooden utility poles across the nation, as they were simple to build and effectively carried telegraph signals. The California Gold Rush in 1860 further emphasised the need for prompt communication, leading to the creation of the transcontinental telegraph.
As technology evolved, wooden utility poles adapted to new purposes. By the early 20th century, they were not only used for telegraph lines but also for telephone and electrical lines. The development of electricity generation increased the demand for wooden poles to carry wires, insulators, and other necessary equipment to homes and factories. This led to the establishment of standards for round timbers in 1908 and the adoption of specific guidelines for wood utility poles by the American National Standards Institute (ANSI).
Over time, the treatment of wooden utility poles evolved to extend their service life. The American Wood Protection Association (AWPA) developed standards for pressure-treating wood with preservatives, forcing them deep into the wood fibre to protect against insects, bacteria, and fungi. This process, along with ongoing research, testing, and technological advancements, has contributed to the longevity and durability of utility poles, with many poles lasting 70 years or more.
Today, wooden utility poles continue to be an essential part of North America's electrical infrastructure, with an estimated 150 million poles in service. They support overhead power lines, cable services, streetlights, and various public services. Despite some resistance to their appearance and the rise of alternative materials, wooden utility poles remain the top choice for utilities due to their performance, cost-effectiveness, and environmental benefits.
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The standards and regulations for utility poles
Utility poles are an essential part of the electrical grid infrastructure, and as such, they are subject to various standards and regulations that ensure their safety and functionality. In the United States, the National Electrical Safety Code, published by the Institute of Electrical and Electronics Engineers (IEEE), sets the standards for the construction and maintenance of utility poles and their equipment. This code provides guidelines for the height, spacing, and ownership of utility poles, as well as the materials and treatments used in their construction.
The standard utility pole in the US is about 35 ft (10 m) tall, with approximately 6 ft (2 m) buried underground for stability. To meet clearance regulations, these poles can reach heights of at least 120 ft (40 m). In urban areas, they are typically spaced about 125 ft (40 m) apart, while in rural areas, the distance between poles can be up to 300 ft (100 m). Joint-use poles are usually owned by one utility company, which then leases space to other utilities.
Most utility poles are made of wood and are pressure-treated with preservatives to protect against rot, fungi, and insects. Traditionally, creosote was used as a preservative, but due to environmental concerns, alternatives such as pentachlorophenol, copper naphthenate, and borates are becoming more common. The American National Standards Institute (ANSI), ASTM, and the American Wood Protection Association (AWPA) set the standards for wood preservative materials, preservation processes, and test criteria in the US. These standards ensure that utility poles can withstand the harsh elements and environmental conditions they are exposed to.
The AWPA has also standardized the use of DCOI, a newer oil-type preservative, for utility poles since 1989. This preservative has been thoroughly tested and offers high performance and durability. CCA is another preservative that has been used for many decades to treat Southern Pine and Western Red Cedar poles, providing an extensive record of durable performance. Additionally, penta is effective in resisting fungal decay, and poles treated with this preservative have been known to last 70 years or more.
To ensure the safety and longevity of utility poles, regular inspection and remedial preservative treatments are necessary. Despite the use of preservatives, wood poles can decay over time due to factors such as climate, soil conditions, and even woodpecker damage. Therefore, utility companies must follow maintenance procedures and guidelines to identify and prevent decay and ensure the continued safe operation of the electrical grid.
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Frequently asked questions
Pressure treatment forces preservatives deep into the wood fibre, providing long-lasting protection against rot, fungi, insects, and other causes of degradation.
The preservative solution is pumped from storage tanks, completely filling the retort. Pressure is continuously applied within the retort to force the preservative into the cells of the wood. The time the poles are in the retort will depend on the size, species, preservative and other factors.
Preservatives used include CCA or Chromated Copper Arsenate, CuN or Copper Naphthenate, DCOI or 4,5-Dichloro-2-N-Octyl-4-Isothiazolin-3-One, Creosote, ACZA or Ammoniacal Copper Zinc Arsenate, and Penta or Pentachlorophenol.
