Frequently Asked Questions

Wood Pole basics

Quite simply it is the stem of a tree which has the proper natural characteristics to meet the engineering and design standards to support a utility line and has been harvested, shaped, treated and certified to meet the need.

Only the best trees can meet the stiff standards established for use as a utility pole. Strict standards covering criteria such as straightness, taper, knots, defects and growth rates must be met before a log or a pole can be considered a utility pole. The premier product harvested from our forests, potential utility poles undergo constant quality analysis during the harvest, production and treatment process. Only those meeting the national wood utility pole standards survive the process.

While no central database exists, it's estimated by the utility and wood pole industries is that there are about 150 million wood utility poles in use across North America. Wood poles are used by electric utilities, telecommunication companies, the USDA Rural Utilities Service, municipalities and others as a critical economical component in the North American electric and communication infrastructure.

There are a variety of species that are used as utility poles. Some of the more commonly used species include Southern Pine, Douglas Fir, Western Red Cedar, Lodgepole Pine and Red Pine.

According to wood pole standards, ANSI O5.1 in the U.S. and CSA O15-15 in Canada, the designated fiber strength values vary somewhat from species to species. However, the standards take this into account when establishing the required dimensions of poles of each species. Therefore, the strength of all poles in a given class for any species recognized in the standard is approximately equal.

There is a great deal of misperception in the market about how long a wood utility pole, or more importantly a wood pole line, will last in service. Wood poles are depreciated as an asset in 35 years. However, research of lines in service has demonstrated that a properly maintained wood pole line will have a service life of 70 years or more. For more, go to the Service Life section.

No! North America has vast expanses of well-managed forest land that are growing and can produce more than an adequate supply of wood poles in perpetuity. Wood poles are the premier valued forest product, so, as stands of trees approach harvest age, the prudent manager first looks for those trees which may meet the strict criteria for use as a utility pole. Even though the management of many forest lands emphasizes fiber volume on 40- to 80-year rotations, they will still produce trees which meet and exceed the strict standards for utility poles.

The forests of the United States are in good condition and poised to meet future demand, including wood utility poles:

  • Growth exceeds harvest by 49% on our commercial timber lands.
  • Every tree harvested is replaced – 1.7 million trees planted each day, according to the USDA Forest Service.
  • The forest land base is stable with as much land in forest production as there was in 1900.
  • Managed forests provide all species, sizes and classes of poles and high grade crossarm timber.

Where wood poles are appropriate for the design (i.e. distribution systems and lower KV transmission applications) wood poles are the most cost-effective material. In terms of both initial line costs and overall life cycle costs, wood pole lines are significantly more cost effective than alternative materials.

Wood poles are also more environmentally friendly compared to alternative materials. Assessing the environmental benefits of any product requires a more systematic, science-based approach rather than the subjective and sometimes misleading claims that are often promoted.

Peer-reviewed life cycle assessments (LCAs) for utility poles show objectively that wood poles have lower impacts on the environment. Metrics such as greenhouse gasses, fossil fuel use, acid rain, water use, smog, eutrophication and overall ecological impact were analyzed. In almost every measure, wood poles scored very favorably compared to the alternative materials.

For more, go to the Wood Poles and Environment section.

More than 99% of all distribution lines and a significant portion of lower voltage transmission lines are and continue to be built with wood. Available supply, cost, ease of handling and installation are all factors in this. A study by the utility industry concluded: “The bottom line is that treated wood offers the most energy-efficient, functional, cost-effective and practical material for use by electric utilities in providing electrical service to the public.”

Most utility poles, during the manufacturing process, are typically marked in accordance with the requirements found in ANSI O5.1 or CSA O15-15. The typical information contained on the marking includes a supplier trademark or code, the year of treatment, a code for the plant location, the species of wood, the preservative type and the class and length of the pole. Additional information may be included based on a utility's specifications.

The information is either burn-branded on the pole or embossed on a recessed metal tag affixed to the pole. The tag is normally located at 10 feet from the butt on poles shorter than 55 feet, and at 14 feet from the butt on poles 55 feet and longer. Given the typical setting depths of poles, this normally places the information in the zone from 2 to 6 feet from the ground on an installed pole.


The American Wood Protection Association (AWPA) approve two types of preservatives for wood poles: oil-type and waterborne systems. Oil-type preservatives include copper naphthenate, creosote, pentachlorophenol and DCOI. Waterborne systems include ammoniacal copper zinc arsenate (ACZA) and chromated copper arsenate (CCA).

Wood preservatives for utility poles are considered pesticide products that must be approved by the U.S. EPA under the provisions of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). The proper application of these pesticides to poles is governed by AWPA standards.

The most common preservative used for utility poles is pentachlorophenol, followed by CCA. Each preservatives has somewhat different properties and the choice of preservative system is up to the utility.

For more, go to the Wood Pole Preservatives section.

Utilities should specify that the treatment of its utility poles must meet the requirements of the American Wood Protection Association (AWPA) or the Canadian Standards Association (CSA) standards. These standards set specific requirements for quality control and quality assurance that will ensure that the product has the proper preservative retention and penetration to provide decades of service.

Utilities can require the supplier to provide copies of treating records and quality control records indicating conformance with the treating standards. There are also third-party inspection agencies that a utility can employ to provide independent verification of pole quality and the results of treatment.

For more, go to the Wood Pole Preservatives section.

All pesticides, including wood preservatives, must be registered and approved for use by the U.S. EPA under the terms of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) and the Canadian Pest Management Regulatory Authority (PMRA). Many of the preservatives used to treat utility poles have been registered for more than 50 years. Periodically, all registered pesticides must undergo a review prior to being reregistered.

The reregistration process includes the development and submission of data meeting all of the EPA and PMRA requirements concerning the potential human health and environmental risk associated with the use of the preservatives and products treated with the preservatives. Typically, the development of all the required studies cost the registrant millions of dollars.

For preservatives used to treat utility poles, the studies include potential human health and environmental risk associated with production of the pole, risk to linemen from working on the poles, and risk to the general public and the environment from the normal use of the poles. EPA and PMRA makes its risk assessments using very conservative exposure scenarios and, if any unacceptable risk is identified, it simply does not reregister the preservative. Once a product is registered, it is required to go back through the registration process on a periodic basis to ensure that current science and new data continue to support use of the product.

This careful scrutiny by EPA and PRMA of the preservatives used to treat utility poles should ensure the general public that the use of treated wood poles is fully protective of human health and the environment.

No. Penta-treated wood poles remain the backbone of the overhead utility system in this country. For more than 80 years, penta-treated poles have established a solid record of service performance.

The EPA, as well as the PMRA in Canada, conducts ongoing toxicological reviews for pentachlorophenol, requiring millions of dollars in testing and research to provide government with sound, scientific data on penta’s potential impact to human health and the environment. The EPA completed a full public review of the use of penta in 2008, and the EPA registration of pentachlorophenol as a wood preservative was re-affirmed.

Over the decades of use, there have been no documented incidents of harm or illness to any individual caused by casual contact with penta-treated utility poles. Had there been any unreasonable risk to human health or the environment, the EPA would not have approved the re-registration of penta. The EPA’s reaffirmation of penta confirms that casual contact with wood poles treated with the preservative does not pose an unreasonable risk to human health or the environment.

Click here for additional information about penta-treated utility poles.

Designing and selecting wood utility poles

Wood poles are sized and classed in accordance with in standard ANSI O5.1. In Canada, wood pole specifications are published in CSA Standard O15-15, Wood Utility Poles and Reinforcing Studs. These standards cover up to 15 classes of wood poles and lengths from 20 feet to 125 feet.

The classes of poles are based on horizontal load capacities of the poles when loaded as simple cantilevers. ANSI O5.1 and CSA O15-15 contain minimum dimensions at 6 feet from the butt that are derived from standard engineering calculations assuming that the cantilever load is applied at 2 feet from the tip and that the maximum stress occurs at the ground line location.

Due to differing strength and overload factors that apply to wood and other materials, it is not possible to produce a pole in other materials that is a true equivalent to a wood pole of a particular class. For an alternative material, it would take three different specs to provide equivalence to a single class of wood pole under the three load cases of Grade B, Grade C, and Extreme Wind.

Only three of the load cases contained in the National Electrical Safety Code (NESC) govern the safety of overhead lines. Use of an alternate material pole designed for equivalency at NESC Grade B as a substitute for a wood pole in a line designed to NESC Grade C requirements would result in construction not meeting the requirements of the NESC.

The length and class of pole required are determined by a combination of design factors. The key factor in determining the required pole length is the ground clearance requirement contained in the National Electrical Safety Code (NESC).

The clearance requirement is a function of line voltage, distance between poles (span), wire tension and other factors. The size, or class, of a pole is determined by the design loads carried by it. These loads include horizontal wind loads; vertical loads associated with the conductors, transformers and other equipment mounted on the pole; expected ice accumulation; and unbalanced loads due to wire tension on angle structures. The minimum loads required to be considered are specified in the NESC.

Transverse wind loads (horizontal loads perpendicular to the line) on bare or ice-covered conductors typically control wood pole designs. The load on a pole is easily varied by changing the span distance and the most cost-effective design will often be one that does not require the use of the most popular class and length of pole, which commands a price premium.

The basic methods for the design of an overhead utility line are the same for poles of all materials, but there are some significant differences in the details of the designs. All overhead line designs must meet the safety requirements contained in the National Electrical Safety Code (NESC). The NESC specifies several different load cases that must be considered in the line design and the final design must meet the most stringent of the load cases.

The design process employs stipulated loads to which material strength and load factors that may vary by material and load case, are applied. Typically, horizontal transverse loading governs wood pole line designs. Other design limitations such as local buckling may control designs for other materials.

Due to the use of different load and strength factors for the various NESC grades of construction in wood pole design, there can be no such thing as a pole constructed of alternate materials that can be substituted as “wood equivalent” for a particular class of wood.

Many non-wood poles are marketed for equivalence to a wood pole class based on NESC Grade B transverse load criteria. However, most wood pole designs are controlled by NESC Grade C criteria and a non-wood pole stronger than the “Grade B wood equivalent” would be required as a direct substitute in a Grade C design based on wood. Use of a “Grade B wood equivalent” class pole in a line designed for wood under the NESC Grade C requirements will result in construction not in compliance with the safety requirements of the NESC.

The strength evaluation of an in-service pole starts with an inspection and assessment of the pole’s physical condition. This normally takes the form of a hammer sounding and visual inspection of the above ground portion of the pole and excavation for several feet below ground to allow visual inspection and boring of the ground line and below ground areas. Any external or internal decay observed must be measured so that an estimate of the remaining cross section can be obtained.

The determination of the adequacy of the pole strength follows the procedures in the National Electrical Safety Code (NESC). The different NESC load cases are evaluated based on the conductors and other facilities supported by the pole, the spans and the required NESC grade of construction.

The strength of the pole is computed using standard engineering calculations based on the calculated section modulus of the remaining pole cross section. A comparison of the calculated NESC load on the pole vs. the calculated strength will determine the adequacy of the pole.

The NESC requires that a wood pole be replaced when strength deteriorates to 2/3 of its initial required strength for installations controlled by the district load provisions of NESC Rule 250B, or 3/4 of its initial required strength for installations controlled by the extreme wind load provisions of NESC Rule 250C.

Weather and wood poles

Design and construction of overhead lines must usually be accomplished in accordance with the National Electrical Safety Code (NESC). The NESC specifies certain load conditions that must be considered in line design, and these conditions include extreme weather events including wind and combined ice and wind.

If an actual weather event does not impose loads greater than those estimated in the design, only minimal failures would be expected. However, if the actual loads exceed the design load, failures are expected and the failure rate is dependent upon the initial conservatism in the design and the degree to which the design load is exceeded.

Most failures occur in extreme weather events due to loads imposed by secondary damage effects. Secondary damage effects include downing trees in the right-of-way, windblown debris, and similar unplanned loads. It is impossible to quantify what these loads caused by secondary damage effects may be, and it is impossible to design and construct a system, either overhead or underground, that would be totally immune to unplanned loads of natural events like major storms and earthquakes.

Since the average strength of a population of wood poles is typically higher than the average strength of a population of alternate material poles designed to the same NESC criteria, wood poles have a greater ability to withstand actual loads that substantially exceed the NESC design loads.

Extreme weather events can take the form of extreme wind events such as hurricanes and tornados, or combined ice and wind events associated with a typical ice storm. Under the requirements of the National Electrical Safety Code (NESC), overhead lines are designed to withstand the expected loads of a defined weather event in terms of a specified wind velocity or a specified ice thickness and concurrent wind velocity.

Unfortunately, the storm loads can damage trees, buildings, signs and other non-utility equipment. The primary cause of outages in ice storm events is the falling of ice-covered trees or branches on the utility lines. In extreme wind events like hurricanes, the utilities report that most failures are caused by secondary damage effects such as falling trees or wind-blown debris. It is important to understand that other system components typically fail at rates approaching 10 times that of wood poles.

In the wake of natural disasters such as hurricanes, which have caused extensive damage to the electrical transmission and distribution systems, it is common for the public as well as the public service commissions’ of the affected states to question what can be done to strengthen or “harden” the electrical system.

The transverse load capacity of an overhead system can be easily strengthened, through the use of readily available stronger wood poles, or through reducing the span length. However, the wood poles are not the weak link in the overhead electrical system. Failures of other system components occur at rates that may be 10 or more times higher than wood poles.

Most wood pole failures in extreme weather events are associated with secondary damage effects such as falling trees or wind-blown debris. These loads may be very large and cannot be quantified.

It is unlikely that simply changing to a stronger wood pole would significantly change the system outcome. The unquantifiable storm load could still exceed the strength of the stronger pole and the failure of other system components is already much higher than that of the wood pole.

The cost to convert overhead distribution lines to underground may range from approximately $1 million per mile to more than $5 million per mile depending upon the line type, subsurface conditions and underground construction method. Public service commissions in many states have studied the issue and each has concluded it is financially unfeasible to convert all existing overhead distribution lines to underground.

Although the number of routine outages may be reduced by underground construction, the average length of the outages is much longer because of the difficulty in locating the fault. The cost to repair is much higher than overhead. The expected service life of new underground is reportedly only about 60% of that of overhead and the system reliability of underground declines as the system ages.

The results of the state studies indicate the cost to fund the complete replacement of the overhead distribution system with underground would essentially require immediately doubling the power bills for consumers and the task would take approximately 25 years or more to complete.

For more, go to the Wood Poles vs. Undergrounding section.

One of the proven advantages of wood poles is the ability of the industry to respond quickly to the need for large numbers of poles after natural disasters strike.

Wood pole treating facilities are located throughout the country and have the ability to ramp up production to meet the short-term needs following storms and other disasters. Some facilities can produce more than 400 poles a day. A century of experience in responding to natural disasters has helped the industry to hone its skills in emergency response.

For example, after Hurrican Katrina, some 92,000 wood poles and 90,000 wood crossarms were delivered within four weeks of the storm's passing. In the wake of Super Storm Sandy on the east coast, the industry provided a total of 65,100 wood poles and 103,500 crossarms to return power to the region.

Maintaining wood utility poles

In order to assure safety and achieve maximum service life, all pole lines need to be under an inspection and maintenance program regardless of whether the poles are wood or an alternative material. Because of its susceptibility to decay, especially at the ground line, wood poles should be inspected on a regular basis to identify early stages of decay and take the needed preventative measures.

There are a number of professionally field-applied preservatives that can halt and control decay. If a pole is found to be at high risk, it can and should be replaced, thus extending the life of the full line. Good maintenance programs can double the service life of a line.

Industry surveys indicate utilities typically inspect poles every 8-10 years.

These inspections consist of visual inspection, sounding the pole with a hammer in the above-ground areas, excavation around the pole for several feet below the ground line, inspection for external decay in the ground line area and/or boring to check for internal decay in the ground line area.

More than 90 percent of inspections are not done by the utilities but by contractors specializing in remediating wood poles.

Remedial treatments are usually applied to poles during the inspection process. These treatments are intended to halt any decay or deterioration and protect the pole from further damage.

Treatment to repair poles include application of wood fumigants, internal treatments to treat voids, preservative paste with a moisture barrier, bandage or pole wrap or diffusible rods. These are typically done at groundline, where there is more threat from decay and insects.