General Information
Sources of Supply for Quality Wood Poles and Crossarms
Pole Supply
Engineering and Design Information
Case Histories
Environmental and Wildlife
Product Disposal
Pole Life and Life Cycle Economics
Wood Poles Advantages and Alternative Materials
Wood Preservative Systems

FREQUENTLY ASKED QUESTIONS

The intent of this webpage is to provide answers to all your questions about wood utility poles, along with special links to a variety of other applicable sources of information.   Click on the below subject(s) of interest to access a listing of FAQs.  Should you not find an answer to your specific question please click on "Need Help" for further assistance.


The Basics of the Wood Utility Pole

  1. What is a wood utility pole?
    Quite simply it is the stem of a tree which: (1) has the proper natural characteristics to meet the engineering and design standards to support a utility line; and (2)  has been harvested, shaped, treated and certified to meet the need.

  2. How is a wood utility pole different than a plain wood pole or tree?
    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.

  3. How many wood utility poles are there in service?
    While no central database exists, the general view of the utility and wood pole industries is that there are about 130 million wood utility poles in use across North America. (For more information, see: Utility Solid Waste Activities Group - Docket No. OPP-2004-0402).They 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.

  4. What species are used for wood poles?
    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.

  5. Which species are strongest?
    As can be seen in Table 1 of the national wood pole standard, ANSI O5.1, the designated fiber strength values vary somewhat from species to species.  However, the ANSI O5.1 standard takes 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.  The ANSI O5.1 standard contains limitations on growth rate and other physical properties of poles that ensure that poles produced today are just as strong as ever and continue to meet the strength values contained in the standard. Which class of pole is to be used depends upon the load and design considerations. (For more information, see: NWPC Technical Bulletin - The Wood Pole 2005 - Design Considerations, Service Benefits, and Economic Reward.)

  6. How long will a wood utility pole last?
    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.  

    • Ask the bookkeeper and the answer may be 35 years, as that is the depreciation schedule for the pole asset. 

    • In high urban growth areas many wood pole lines are commonly removed to accommodate expanding right of ways as streets and highways are widened. The poles may be removed in such cases, but not because the pole is no longer serviceable. 

    • If a utility company chooses not to t have a maintenance program for its poles, one could encounter a service life of 40-50 years.

    • Contrary to these perceptions, research of lines in service has demonstrated that a properly maintained wood pole line will have a service life of 75 years or more. (For a full discussion, see:NAWPC Technical Bulletin - Wood Poles How Long Do They Last, and NWPC Technical Bulletin - Estimated Service Life of Wood Poles.)

  7. Are we running out of wood poles?
    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.

    • The managed forests  provide all species, sizes and classes of poles and high grade crossarm timber.

  8. How do wood utility poles compare to steel, concrete and alternative materials?
    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.  Research by Engineering Data Management in late 1990s showed that wood is generally 15% to 100% more cost-effective than thin-walled steel, concrete or composite materials (see figures below).  The more rapid increase in steel costs over wood since that research was completed has only increased the advantage of wood. (For a complete discussion, see: WWPI Wood Pole Newsletter - Lifecycle Study Proves Wood is the Best Investment.
     

       


  9. Is there a perfect pole material? 
    No.  No material will last forever and all materials need maintenance to maximize service life.   Utility pole lines are designed to meet specific safety and design standards that reflect the risks anticipated for events such as wind and ice in the region where they are located.  When  conditions exceed the design criteria, failure may occur, regardless of the pole material.   Lines may be built to higher standards to further reduce the risks, but this comes with  increased costs.  The challenge is to balance line design and costs with the probability of future failure. (For further information, see: WWPI Article - In Search of the Perfect Utility Pole.

  10. Why do utilities prefer wood over alternatives?
    Over 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, and 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.” (For further information, see: Utility Solid Waste Activities Group - Jan. 2005 Analysis.

  11. How are utility poles branded, tagged or otherwise marked for identification?
    Most utility poles, during the manufacturing process, are typically marked in accordance with the requirements found in ANSI O5.1, American National Standard for Wood Poles - Specifications and Dimensions, and in American Wood Protection Association Standard M6, as well as referenced in U1, T1 and M1.  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 ANSI O5.1 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 information 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.

    For a more detailed explanation of ANSI and AWPA standards, the North American Wood Pole Council offers a seminar entitled Wood Pole Standards. (For seminar schedule and overview, click here.) 

How to Design and Select a Pole

  1. How do I decide what length and size of pole is needed?
    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.

    To learn more about overhead distribution line design, the North American Wood Pole Council offers a three day seminar entitled Wood Pole Structure Design.  (For seminar overview and schedule, please, click here.) 

  2. How are poles sized and classed?
    Wood poles are sized and classed in accordance with ANSI O5.1, American National Standard for Wood Poles - Specification and Dimensions.  This standard covers 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 contains 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.

    For a more detailed explanation of sizing and classing of wood poles, the North American Wood Pole Council offers a seminar entitled Wood Pole Standards. (For seminar overview and schedule, click here.)

  3. How do I engineer a wood pole line?
    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.

    To learn more about overhead distribution line design, the North American Wood Pole Council offers a three day seminar entitled Wood Pole Structure Design.  (For seminar overview and schedule, click here.)

  4. How can I be sure a wood pole in a utility line is strong enough?
    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 versus 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.

  5. Are steel and concrete poles stronger than wood?
    Wood poles have differing strength values, based on the diameter of the pole and other factors considered in standards.  They can be specified with higher or lower values.   Although steel or concrete poles can be designed and built to strengths that may be beyond the strength of readily available natural wood poles sizes, comparable steel or concrete poles are not “stronger” than wood poles.  In fact, due to the larger variability of strength of natural wood poles and the larger overall safety factors applied to wood poles, the average strength of wood poles is higher than the average strength of poles of steel or concrete designed to the same load case under the provisions of the National Electrical Safety Code (NESC).  This higher average strength of wood results in a lower overall probability of failure in an extreme overload condition such as weather events that may impose loads significantly above the normal design loads.

Standards for the Wood Utility Pole

  1. What are the purposes of the standards?
    The purpose of the standards governing the manufacture of wood utility poles is to ensure the consistent satisfactory performance of the product in its intended use.  The standards are formulated  to produce poles meeting the necessary strength requirements and capable of providing decades of service under harsh environmental conditions.

    For a more detailed explanation of  wood pole standards, the North American Wood Pole Council offers a seminar entitled Wood Pole Standards.  (For seminar schedule and overview, click here.) 

  2. What are the basic standards covering the design and use of wood utility poles and who issues the standards?
    Wood utility poles are manufactured in accordance with the requirements of the standards of two national standards bodies.  The specifications, physical dimensions, and expected strength of untreated wood poles are found in American National Standard Institute (ANSI) Specification O5.1, American National Standard for Wood Poles - Specifications and Dimensions.  The ANSI O5.1 standard covers all species of wood typically used as utility poles.  The standard varies the required dimensions of poles of different species to account for the difference in strength of each species.  Therefore, a pole of a particular ANSI O5.1 class will have approximately the same strength regardless of wood species.

    The preservative treatment of wood poles is performed in accordance with standards published by the American Wood Protection Association.  These standards specify the preservatives approved for use in the treatment of utility poles as well as the required preservative retention and penetration.  The retention and penetration requirements are different for different species of wood, and the requirements change based upon the relative decay hazard at the location where the poles are to be installed.

    The use of wood poles in overhead utility construction is governed by the provisions of the National Electrical Safety Code (NESC).  The NESC specifies the load cases that must be considered in the line design and specifies overload and strength factors dependent upon pole material that must be employed in the design.

    For a more detailed explanation of  wood pole standards and their relationship to the NESC, the North American Wood Pole Council offers a seminar entitled Wood Pole Standards.  (For seminar schedule and overview, click here.) 

  3. How can I be sure the standards meet their purpose of protecting the public?
    All of the standards governing the manufacture and use of wood utility poles are the product of nationally and internationally recognized standards organizations and are developed by balanced committees consisting of users, producers, and general interest members.  These committees function as consensus bodies and operate under written rules ensuring that balanced, technically supported standards are produced.  The conduct of these committees is overseen by a national body that ensures the work of the committees is conducted in agreement with recognized procedures.  Governmental entities may then review the standards and incorporate compliance with the standards into various regulatory requirements.

    For a more detailed explanation of  wood pole standards and their relationship to the NESC, the North American Wood Pole Council offers a seminar entitled Wood Pole Standards.  (For seminar schedule and overview, click here

  4. With more second growth and third growth forests, can we depend upon the strength of wood poles?
    Yes.  The standard for strength which is related to minimum ring count and pole quality characteristics has not changed over time.  While second and third growth forests may grow faster on average, only those trees which continue to meet the long standing ANSI wood pole standards for quality and density can be considered for use as a pole. Physical pole breaking research at Oregon State University in 2006 found no validity to the concern about reduced strength from younger forests.  A study by the wood pole industry in 2007 examined over 20,000 poles, comparing the butt dimension and pole class with tip diameters and density across a full range of species, geography and pole classes.  This research found that on average the tip dimensions for poles entering the market today are one half to two classes larger than required by the standards and that density is more than sufficient to meet the standard. This oversize and density only further assure the user that the strengths designated by the standards are being met or exceeded.   

  5. Is it true that the overall safety factor in the design of poles is higher for wood than alternative products?
    The requirements for safety of overhead lines are found in the National Electrical Safety Code (NESC).  The NESC specifies certain load conditions that must be considered in line design and it specifies the overall safety factor to be included in the design computations.  The overall safety factor has two components: an overload factor applied to the theoretical loads and a strength factor applied to the material strength.  The combination of these two factors results in a larger safety factor for wood than for other materials.  Part of the larger safety factor is associated with the possible greater variability of strength in a natural product such as wood when compared to a manufactured product like pre-stressed concrete.  For critical design situations, such as Grade B in the NESC, wood is penalized for this potential variability by requiring a larger factor of safety.

    However, the actual average strength of a population of wood poles will be higher than the average strength of a similar population of alternate material poles designed to the same NESC load.  This results in better performance of wood poles in comparison to other materials under conditions where an unexpected extreme load substantially exceeds the design load.

    To learn more about safety factors in the design of poles, attend a North American Wood Pole Council sponsored seminar entitled Wood Pole Standards.  (For seminar overview and schedule,  click here.) 

Wood Pole Supply and Purchasing

  1. Will there be an adequate supply of wood poles now and in the future?
    Yes!  Utilities can use wood poles with full confidence that the materials they need now and in the future will be available.   Importantly, they can also rest assured that in case of natural disasters the wood pole industry can respond rapidly to provide the poles needed.

    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.

    Unlike alternative materials, the wood pole industry  maintains a large inventory of poles across a range of lengths and classes.  At any point in time there are an estimated 3 million poles in the production cycle from harvest in the woods through the finished product.  This makes it possible for the industry to meet not only ongoing normal demand, but to respond quickly in times of natural disaster (such as ice storms and hurricanes) to provide the poles, from a few hundred to tens of thousands, to facilitate a timely recovery of the power grids.  

  2. How can I locate a supplier of wood poles?
    The North American Wood Pole Council and its member organizations represent over 95% of the  wood pole producing industry in North America and maintain Sources Of Supply documents that will guide you to a listing of the producers and contact information.

  3. How much advance notice do I need to provide to get poles?
    Most common pole sizes (all classes up to 95 feet in length) are available upon demand from almost any supplier. However, due to possible inventory and species constraints, it is always good to give your pole supplier as much notice as possible to ensure your order is delivered on time with the needed poles.

    The inventory of 95 foot poles in the H-3 through H-6 size will be somewhat limited and the on demand supply of poles in the 120 and 125 foot classes will be very restricted.  130 foot poles will generally be a special order item.

    It is always good to keep your suppliers informed of your expected needs to facilitate production and inventory control, especially if you expect a project will require a large number of a given length and class of poles over 115 feet in length.

    Because of their high value and less frequent use,  longer length transmission poles (120 -130 foot H classes) are not stockpiled in significant numbers.  The wood pole producer needs to be informed of upcoming project plans and demand for the material so that it can be located in the woods, harvested, dried and processed in order the meet the project schedules.

  4. How does the wood pole industry respond to natural disasters where large numbers of poles are needed in a short time?
    One of the great time proven advantages of wood poles is the ability of the industry to respond quickly to the need for large numbers of poles when natural disasters strike and take out the power to large areas and populations.

    The wood pole industry is made up of firms spread across the continent. The industry is composed of not only wood preservers (those who operate the plants) but also white wood suppliers who only manufacture unpreserved poles.  Between the wood preserving plants and white wood suppliers there is estimated to be three million poles at any one time in the supply chain. This means that, between poles being marked in the forest for harvesting to the treated inventories at the plants, three million wood poles are in some stage of production. In large natural disasters like hurricanes and ice storms, the wood preserving firms will coordinate with the affected utilities and co-ops to make sure that their pre-storm inventory levels are adequate and that estimated post-storm needs are in the plant inventory, moving through the supply chain or located at another firm.  A century of experience in responding to natural disasters has helped the industry to hone its skills in emergency response.

    For example, when Hurricanes Katrina and Rita hit the southeast in 2006 over 20,000 poles were shipped from all across the US and Canada to the region within 72 hours and over 100,000 poles were supplied within 60 days.  From tornadoes in the heartland; ice storms in eastern Canada; wind and fire events in the west; or hurricanes in the southeast, the wood pole industry has proven time and again that wood is the only option for fast response to  demand.

  5. How do I ensure that the pole I purchase conforms to the quality required by the standards?
    Assurance of quality can be accomplished in several ways.  The manufacturers of wood poles have internal inspectors and trained staff to detect any non-conforming material and verify compliance to specified treatment standards. Since the manufacturer is ultimately responsible for product quality and treatment, some customers choose to specify that the manufacturer will perform quality assurance task with the necessary documents being forwarded to their staff for review.  Other customers prefer to use independent third party inspection.

    Regardless of who is responsible, the following steps are performed to insure compliance with a customer’s specification.

    The first inspection occurs in the forest when the tree is selected (marked) for cutting as a pole.  After the “bark-on” poles from the forest have been peeled, the second inspection occurs when the poles are graded and classed according to the ANSI standard. A third inspection takes place at the framing station where the classed poles are branded or tagged according to ANSI and customer specifications and the poles are framed (i.e. holes are bored) according to the framing print.  Then the poles are inspected a fourth time by either the in-house quality assurance department or the third-party independent inspector.   Upon acceptance, a hammer mark is placed in the top of the pole. Rejected poles will have the brand and framing removed and be reworked into a shorter pole or another product (i.e. piling, ply blocks, etc.).  Now the accepted poles are loaded on trams for pressure treatment.

    After pressure treatment, a fifth inspection takes place. Twenty wood cores will be taken from the material and tested for preservative retention and checked for proper penetration of the preservative. A visual inspection will also be performed to insure that no poles were damaged during treatment. The compliant material, depending on the customer’s specifications, may be rolled out so each pole can be checked for penetration. If the material fails the retention or penetration requirements, the material is pressure treated a second time and the inspection is performed again.

    A sixth inspection (visual) occurs when the material is loaded for shipment by the manufacturer. Any pole that has been damaged during post treatment handling will be removed from the load.

    A minimum of six different inspections occur in the forest and at the manufacturer’s facility to insure that the wood pole meets quality and customer standards.

    For a more detailed explanation of wood pole standards, the North American Wood Pole Council offers a seminar entitled Wood Pole Standards. (For seminar schedule and overview, click here.) 

  6. How are wood poles transported?
    Wood poles are transported from the producer to the utility yard or construction site by truck or rail. Unlike some alternative materials which can be damaged by minor surface scrapes, treated wood is forgiving.  The poles can be bundled together in a load and can be off-loaded with forklifts or tong equipment and dragged short distances over the ground.  Care istaken not to drop the poles from significant heights.  The customer’s representative at the receiving site should check the material for compliance upon receipt of material and before the driver leaves the yard

Service Life and Economics

  1. How long will a wood pole last?
    Individual wood poles will last in service for 45 to 100 or more years.  Shorter expectancies have been based upon accounting procedures, removal for line changes or lack of effective maintenance program factors unrelated to the durability of individual poles.   Contrary to these perceptions, research of lines in service has demonstrated that a properly maintained wood pole line will have a service life of 75 years or more. (For a full discussion see:WWPI Newsletter-Wood Poles How Long Do They Last, NWPC Technical Bulletin - Estimated Service Life of Wood Poles.)

  2. How does a wood pole line compare to other products in terms of installed cost?
    In standard distribution line designs and many lower level transmission applications, wood pole lines will be significantly more economical that alternative materials.  Research by Engineering Data Management in the late 1990s showed that wood lines are generally 25% to 100% more cost-effective to construct than thin-walled steel, concrete or composite materials. Since that time the cost of alternative materials has increased at a rate significantly greater than wood costs, thus the advantages are even greater today.  (For a complete discussion, see: WWPI Wood Pole Newsletter - Lifecycle Study Proves Wood is the Best Investment)

  3. How does a wood pole line compare to other products in terms of life cycle cost?
    In evaluating project investments, the full spectrum of cost from project inception to ultimate replacement, needs to be considered.  This will include materials purchase and installation costs, service life of the materials, maintenance requirements over the life of the project and disposition of the materials when removed.  To provide meaningful comparative values for making management decisions, future anticipated costs are discounted (the cost of money) to a current value.   Research by Engineering Data Management in the late 1990s used this approach to compare the cost of pole designs of various materials and concluded that wood is 15% to 100% more cost effective on a life cycle basis than thin-walled steel, concrete or composite materials in distribution applications and lower level transmission uses.

    As impressive as the economic advantages of wood appear from the EDM research, the study was actually quite conservative because it assumed all construction using NESC Grade B standards.  In fact, most distribution systems are designed to Grade C standards where wood has an even greater economic advantage over alternative materials.  (For a complete discussion, see: WWPI Wood Pole Newsletter - Lifecycle Study Proves Wood is the Best Investment.)

  4. How does the cost of a wood pole system compare to underground systems?
    The cost of constructing electric utility lines underground far exceeds the cost of constructing comparable overhead lines using wood poles.  The cost differential varies depending upon the type of underground construction employed and the type of circuit being constructed.  The cheapest underground construction under ideal conditions may be about two times as expensive as overhead while the underground construction  in duct bank systems is many times higher than a comparable overhead system.  Typical costs to construct underground systems may run from about $1,000,000 per mile to over $3,000,000 per mile, with costs in difficult, rocky, or swampy terrain being substantially higher.  Underground joint use services such as cable or telephone may add 30% to these costs.  (For additional information on underground vs. overhead utility service, please see: North Carolina Utilities Commission Study - Full Report  and Florida Electric Utilities Research (Phase 1 - Final Report), (Phase 2 Report), (Phase 3 Report).

Wood Pole Storm Performance

  1. How do you quantify the expected performance of a wood pole to withstand an extreme storm?
    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.

  2. What are the major causes of pole failure during an extreme storm event?
    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.

  3. How well do wood poles withstand extreme storm events compared to alternative materials?
    The year 2005 was the worst hurricane season on record for the U.S.  The states of Florida, Alabama, Mississippi, Louisiana, and Texas all experienced substantial damage to the electrical transmission and distribution systems.  The utilities in these states reported comparable failure rates of wood poles and non-wood poles.

    The variability of strength in a population of natural wood poles is somewhat higher than that of most manufactured structural products.  Because of this, the provisions of the National Electrical Safety Code (NESC) penalize wood and require larger overall factors of safety in wood designs.  Under these provisions the average strength of wood poles is higher than the average strength of alternate material poles under comparable design conditions.  This higher average strength results in a better ability to withstand loads that are substantially higher than the design loads, such as those that occur from secondary damage, like falling trees, in extreme weather events.

  4. Is it more cost effective to move overhead lines underground?
    The cost to convert overhead distribution lines to underground may range from approximately one million dollars per mile to more than three million dollars per mile depending upon the line type, subsurface conditions, and underground construction method.  The public service commission’s of many states have studied the issue, and each has concluded that it is financially infeasible 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, and 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 have indicated that the cost to fund the complete replacement of the overhead distribution system with underground would essentially require immediately doubling the power bills of consumers, and the task would take approximately 25 years to complete. Surveys conducted of consumers have concluded that they do not want to pursue this option at this cost, and that the 100% increase in rates needed is about 10 times the increase that they would be willing to pay. (For additional information on underground vs overhead utility lines, please see:  North Carolina Utilities Commission Study - Full Report  and Florida Electric Utilities Research (Phase 1 - Final Report), (Phase 2 Report), (Phase 3 Report).

  5. Can overhead systems be made stronger using 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 can 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. (For additional information on system hardening, please see:  NAWPC Technical Bulletin VII - The Hardening of Utility Lines – Implications for Utility Pole Design and Use.)

Use and Maintenance

  1. What are the structural advantages of the wood pole?
    The strength and resilience of wood, along with protective preservative treatment, enable wood poles to withstand considerable abuse when being stored, hauled, handled and installed. Wood poles are considered safer by linemen due to the materials’ non-conductive nature and they require no special climbing gear when bucket trucks are not available. Maintenance is simple and can be performed by trained personnel with the poles in place. Installation is easy, as are modifications to meet field conditions or later changes.

    Wood poles, on average, are stronger that alternative materials produced in the same class.  Wood poles will continue to meet the designated class strengths even after years of exposure and surface loss.  (For more information, see:  WWPI Wood Pole Newsletter -Wood Poles: Easy to Handle, Install and Safe to Use.”)

  2. Why is pole maintenance important?
    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.

  3. How often does a pole need to be inspected?
    A wood pole line should be inspected initially after 15 to 20 years of service, depending upon the decay hazard where the poles are installed.  Inspection of a wood pole line will normally consist of 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, boring to check for internal decay in the ground line area, removal of any decay on the exterior surface, treatment of any interior decay with a supplemental preservative, and wrapping the pole with a preservative wrap in the ground line area prior to backfilling.  Poles subjected to repeat inspections on an 8 to 12 year basis, again depending upon the decay hazard in the area, can last 75-100 years.  Poles of all materials must be inspected and maintained on a routine basis to ensure adequate service life and performance.  The article Laboratory and Field Corrosion Investigation of Galvanized Utility Poles describes the recommended practices for steel poles, and these recommended practices may be more expensive than wood pole inspection practices. 

Preservative Treatments

  1. What wood preservative systems are available?
    All wood preservatives for utility poles are pesticidal 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 industry standards published by the American Wood Protection Association (AWPA).

    The AWPA-approved preservatives include both oil-type and waterborne systems.  Oil-type preservatives include creosote, pentachlorophenol in a petroleum oil solution, and copper naphthenate in a petroleum oil solution.  Waterborne systems include solutions containing arsenic in combination with other metals such as chromium, copper or zinc, and systems based on copper and an organic termiticide.

    Each of the preservatives has somewhat different properties and the choice of preservative system is up to the utility.

    For a more detailed explanation of  wood pole standards, the North American Wood Pole Council offers a seminar entitled Wood Pole Standards. (For seminar schedule and overview, click here.) 

  2. How can I be sure the preservatives used are safe and appropriate?
    The U.S. EPA regulates wood preservatives through a registration and approval process under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA).  Before EPA will allow the registration of any pesticidal product, the proponents must conduct testing required by EPA and provide data meeting the requirements of EPA concerning the potential human health and environmental effects of the use of the product.  The development of this data is extensive and typically costs millions of dollars.

    If EPA concludes there is an unacceptable risk to human health or the environment, the agency will not approve the product.  Once a product is approved, it must undergo a periodic review and reregistration process.  Most of the preservatives used for the treatment of poles have a history of many decades of safe application and use, and the EPA registration process ensures their use is mindful of human health and the environment.

  3. How do I select a preservative system?
    All preservatives must be approved by the U.S. EPA under the requirements of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA).  The American Wood Protection Association (AWPA) then evaluates the efficacy of the preservatives before it accepts their use on a product such as poles.  The listing of a preservative in the AWPA standards as an acceptable preservative for poles should ensure that poles treated in accordance with the standard perform as expected in utility line service.  The AWPA standards may have different preservative retention and penetration requirements based on the severity of the decay environment.

    AWPA-listed preservatives include both oil-type preservative systems and waterborne preservative systems.  Each preservative has unique properties. 

    The choice of preservative by an individual utility should be based upon an evaluation of the unique properties of each preservative system.

    For a more detailed explanation of  wood pole standards, the North American Wood Pole Council offers a seminar entitled Wood Pole Standards. (For seminar schedule and overview, click here.

  4. How do I assure the quality of the wood preservative treatments?
    Utilities should specify that the treatment of its utility poles must meet the requirements of the American Wood Protection Association (AWPA) standards.  The AWPA standards have 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.  The utility can require the supplier to provide copies of treating records and quality control records indicating conformance with the AWPA 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 a more detailed explanation of  wood pole standards, the North American Wood Pole Council offers a seminar entitled Wood Pole Standards. (For seminar schedule and overview, click here.) 

  5. How do I assure that we handle and install the poles appropriately for the system?
    Poles should be produced in accordance with the standards of the American Wood Protection Association (AWPA).  AWPA Standard M4, Standard for the Use of Preservative - Treated Wood Products, provides valuable guidance on the proper handling and use of treated products such as poles.

    From a structural and safety perspective, the installation of poles should be in accordance with the National Electrical Safety Code (NESC), which has been adopted by most jurisdictions for the safety of overhead lines.

    For a more detailed explanation of  wood pole standards and their relationship to NESC, the North American Wood Pole Council offers a seminar entitled Wood Pole Standards. For seminar schedule and overview, click here.)

  6. How can I address customer environmental and safety concerns about wood utility poles?
    Concerns regarding the environmental or safety aspects of the use of treated wood utility poles should be relieved by the rigorous regulatory process that must be followed in order to get the preservatives used to treat utility poles approved by the U.S. EPA.  All pesticidal products, 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).  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’s 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 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 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.

  7. What is a Consumer Information Sheet?
    A Consumer Information Sheet (CIS) is a preservative-specific document intended to inform the public and users of treated wood products regarding the safe handling, use, and disposal of treated wood.  There is a separate CIS for creosote-treated wood, pentachlorophenol-treated wood, and wood treated with inorganic arsenical preservatives.  Each CIS contains U.S. EPA accepted language that was developed as part of the prior preservative reregistration process that concluded in 1986. [The most recent reregistration was completed in 2009.]

    Due to their age, the CIS documents, in particular those concerning inorganic arsenical treated wood, may not reflect some changes in allowable uses, but they continue to provide good general guidance on the safe handling, use, and disposal of treated wood.

  8. What is a Material Safety Data Sheet?
    A Material Safety Data Sheet (MSDS) is a document that provides the information necessary to ensure the safe handling and use of a product in a place of employment.  The regulations implementing the Occupational Safety and Health Act (OSHA) are the source of the MSDS requirements.  OSHA regulations require manufacturers to prepare an MSDS on any product that presents any potential hazard to a downstream user.  The manufacturer must provide the MSDS to other employers that purchase his product.

    Wood products require the preparation of an MSDS because of the potential exposure of employees to wood dust from sawing or other woodworking activities.  For treated wood products, in addition to the potential wood dust exposure, the MSDS provides additional information on the safe handling, use, and disposal of the treated wood product.

Environmental Considerations

  1. How do wood poles fit into the public concern about sustainability and being “green?
    Wood poles are far and away the most environmentally appropriate and sustainable pole material. In terms of sustainable supply, renewability, carbon sequestration, energy consumption and air and water pollution – the wood pole is the green alternative. Preservative treatment increases the benefits by extending the service life of wood.

  2. How do wood poles relate to global warming and CO2 emissions?
    There are two principal ways that wood poles contribute to the efforts to minimize CO2 emissions and global warming: Carbon storage and low energy consumption.

    The growth of a tree is a natural process which takes carbon out of the atmosphere and when harvested moves this carbon to storage in wood products while at the same time displacing fossil intensive products like steel and concrete..  The harvested wood pole represents stored carbon while the forest from which it was removed is replanted and grows another crop of trees, renewing the taking of  carbon out of the atmosphere. According to the Consortium for Research on Renewable Industrial Materials (CORRIM)   “The most (carbon) storage comes from intensive short rotations harvesting before the forest growth begins to slow, storing carbon in products and substituting as early as possible for fossil intensive products. “ (For more information see: CORRIM, March 2009 Fact Sheet #5 - Maximizing Forest Contributions to Carbon Mitigation: The Science of Life Cycle Analysis – a summary of CORRIM’s research findings.)

    Wood poles will continue to store carbon during their service life, during reuse and in disposal for a total period easily in excess of a century – an accepted goal for carbon storage strategies. There is an added environmental benefit if wood poles were combusted for energy in lieu of landfill disposal. (See the following report for more information: End-of-Life Management of Preserved Wood-The Case For Reuse For Energy)

    Research into pole alternatives worldwide indicates that, without exception, the total energy requirements associated with wood materials are considerably lower than those of commonly substituted materials such as steel and concrete. The use of low-energy-consumption wood materials rather than substitution of energy-intensive alternative materials will contribute substantially to an overall decrease in carbon dioxide emissions, the principal green house gas of concern. (For a full discussion, see: NAWPC Technical Bulletin - “Wood Materials Used as a Means to Reduce Greenhouse Gases (GHG): An Examination of Wooden Utility Poles.”)

  3. How much power is needed to produce a wood pole?
    A central focus of the discussions over global warming is the production of energy using nonrenewable carbon based sources such as oil and coal.  Mother Nature produces wood by combining sun, water, minerals in the soil and time in contrast to the alternative materials which require extensive mining, refining and complex industrial processes. The only energy requirements for wood are in the conversion process from a standing tree to a serviceable pole. On average the wood product, like poles, will require less than 10% of the energy to produce compared to steel or concrete: 3.32 million BTU oil equivalent per ton of wood product compared to 41.75 for alternatives. Similarly, the processes for wood products produce proportionally less water and air pollutants. (For more information, see: NAWPC Technical Bulletin- Wood Materials Used as a Means to Reduce Greenhouse Gases (GHG): An Examination of Wooden Utility Poles”)

  4. Won’t we run out of poles if we continue to cut our forests?
    A common, but declining misperception is that we are running out of forest lands and wood supply.  In fact our forests are in great condition, and  managed forests  can provide all species, sizes and classes of poles and high grade crossarm timber in perpetuity. The land base is stable with as much forest growing today as there was in 1900.  Growth on our commercial timber lands exceeds harvest by 49%.  Every tree harvested is replaced – 1.7 million trees are planted each day.  Wood poles are the premium value forest product and are thus a focus for the prudent forest manager.  Today’s silvicultural practices allow new trees to grow strong and straight in a time efficient process ensuring a sustainable supply of wood poles.

  5. How do I construct my wood pole line to protect birds of prey?
    The design, construction and maintenance of pole lines to minimize the electrocution threat to birds of prey has become an important issue in recent years.  The non-conductive nature of wood poles and crossarms is a major advantage over alternative materials, plus wood poles can be more easily adapted to meet the safe spacing requirement to protect the birds. (For a full discussion and design guide, see:  NAWPC Technical Bulletin- Raptor Electrocutions and Distribution Pole Types.”)

    If you would like more information on line design, the North American Wood Pole Council is sponsoring a series of Wood Pole Structure Design Seminars.  Click here for seminar information.

  6. Are there special steps I should take if wood poles are used in highly sensitive or aquatic environments?
    In the vast majority of uses treated poles will not lose enough preservative to cause a significant environmental impact.  Where there is concern guidance is available to help evaluate specific cases and to apply the Best Management Practices developed by industry for treated wood used in such environments. (For more information on best management practices and environmental guidance, see: “WWPI Best Management Practices in Aquatic and Other Sensitive Environments”, and “Treated Wood in Aquatic Environments”.   Also, see NAWPC Technical Bulleting - "Pressure-Treated Wooden Utility Poles and Our Environment.")

  7. How do I dispose of my wood poles when they are removed from service?
    When a wood pole is removed from service there are various options for disposal.  Reuse of the pole is the most common and preferred option, ether as a pole, if suited, or as alternative use (such as posts) with appropriate ownership transfer practices.  If full disposal is needed, the material may be used in cogeneration in some cases or more commonly it will go to an approved landfill.  Treated wood passes the Federal EPA screening rules and is classed as a non-hazardous waste for disposal.  Some states have more stringent rules requiring disposal in lined municipal landfills.  (Additional information and guidance can be found in the Product Disposal section of www.Woodpoles.org.)

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