Historic Significance

Native Americans have relied on cedar for centuries.

Long before the first explorers arrived, coastal tribes from Oregon to Alaska recognized the strength and durability of Western red cedar.

They trusted cedar for centuries to provide shelter, household furnishings, and canoes. The sacred totems they carved stand as monuments to the natural endurance of Western red cedar.

New uses for cedar continued to emerge. Settlers split cedar into shakes and milled it into lumber, siding and shingles.

At the turn of the century, cedar was used for telephone and telegraph poles along railroad lines.

Cedar continues to be one of the best pole materials available.

Unique Qualities & Benefits

There isn't just one quality that makes Western red cedar ideal for utility poles.

Cedar provides excellent gaff penetration for secure footing.

Unlike other species, cedar's heartwood produces chemical compounds called extractives that naturally resist decay, fungi and insects. Treatment extends cedar's inherent long service life up to 80 years, with little or no maintenance. Cedar's cost-to-life ratio is unmatched.

Its outstanding carrying capacity and flexibility allows poles to withstand extreme weight and severe weather conditions.

Cedar's straight grain and uniform texture mean virtually no twisting after installation. This minimizes pole fracture caused by severe weather or mechanical damage.

Its light weight makes handling and installation easier. Because cedar weighs about 30% less than other species, it's easier to handle and install. This can make a substantial cost difference when setting poles in difficult locations or for helicopter installations.

And, crews prefer it for climbing. Climbing gaffs dig into cedar easily for safe and secure footing.

Future Supply

Unlike other species, cedar grows well in the shade of other trees.

Electrical utilities across North America have used cedar poles for years and will continue to do so. Cedar pole availability and sales reflect a stable and improving supply.

British Columbia grows 60% of the current cedar pole supply, which is only 2.2% of their total cedar harvest. Washington, Idaho and Montana account for 40% of cedar pole harvest.

Today's Harvesting Methods

As good stewards of the forest, pole company harvesting is more sensitive to the environment today than ever before.

High-lead logging is used to prevent damage to the forest floor during harvest. Logs are picked up so only the ends touch the ground.

Four methods of stand tending, harvesting and site preparation are used depending on climate, terrain and natural resources.

Harvesting today is more sensitive to the environment than ever before.

Selective harvesting is increasingly used in commercial forestry. A limited number of trees of various sizes and ages are harvested in 15 or 30 year intervals.

The continuous forest cover protects the area from extreme weather, erosion, and maintains wildlife habitat. The thinning increases the health of the forest, insuring a harvest for years to come.

The seed tree system leaves selected trees standing to provide a natural seed source for regeneration. This method lowers reforestation costs and results in large, high-value timber down the road.

The sheltered system removes trees in a series of harvests. New even-aged stands are sheltered from severe weather by mature trees left standing.

No matter which method is used, all harvester areas must be reforested on private and public lands. About five trees are planted for each one harvested.

Preparing the Poles

Inspectors classify poles.

Once selected for poles, trees are felled, limbed and cut to proper length.

At the peeling yard, the outer bark and protruding knots are peeled with a roughing head. A finishing head smooths it, leaving a good shell of sapwood for treatment.

After the pole is peeled, it is classified for length and class size. An inspector measures the pole's circumference six feet from the butt, and at the tip. All poles most conform to the American National Standards Institute (ANSI) and Canadian Standards Association (CSA) for knots, straightness, spiral grain, and other properties.

The inspected poles are stacked with similar sized poles to season in the storage deck. The climate of the area where the poles are stored determines the length of air seasoning. Air or kiln drying substantially reduces seasoning checks that might occur after being installed and exposes untreated wood.

Poles with acceptable moisture content are selected for treatment. The pole is then incised, or perforated, to proper depth in the groundline area for additional penetration and retention of preservative in this area susceptible to decay.

Preservative Treatment

Several highly effective preservative treatments are used for Western red cedar poles. All are EPA registered preservatives and include pentachlorophenol, chromated copper arsenate (CCA).

Closed cylinder thermal or pressure treated process.

Butt-treated poles are set vertically in a tank and treated with pentachlorophenol to one foot above groundline, to AWPA and CSA standards. Cedar is the only species where this economical method of treatment can be used.

Full-length treated poles are pressure or thermal treated, to AWPA, CSA or ASTM standards.

During pressure treatment, preservatives are forced into wood cells in a closed cylinder, or retort, under pressure. Although not required, many utilities request groundline incising for treated poles.

Full-length thermal treatment is a two-step process. The hot cycle expands the air in the out layers of wood and expels some of the air and water vapor. The cold cycle causes the air and water vapor to contract, creating a partial vacuum that draws preservatives into the wood cells.

Total Quality Management

Tag shows location, maker and date.

Western red cedar poles are inspected several times from harvest to final shipment.

After treatment, poles are inspected for proper penetration and retention of the preservatives. Tests are in accordance with AWPA or CSA standards. Inspection certificates are furnished upon request by treating companies or independent agencies.

To assure long pole life, WRCPA members have developed extensive quality management programs to assure white wood requirements are met or exceeded before treatment and to check treatment results. Independent inspection agencies are also used for this purpose at the buyers option. When inspected by an independent agency, the agency marks the pole, usually a hammer mark, on the butt, tip, or both.

Western red cedar poles serve utilities in all climates. They withstand extreme desert temperatures, mountain snowfall, high winds and northwest rain.

Washington Water Power, in Eastern Washington, experiences a broad range of climates. There's snow in the north, dry but fertile plains in the south, lush mountains to the east and arid foothills in the west. The utility has used cedar since 1903. Crews prefer cedar for climbing and management likes its superior life cycle.

Cedar has the best cost-to-life ratio.

Nevada Power prefers cedar in its severely dry climate. The utility notes, "With cedar poles you don't get twisting when the moisture content drops." They have been using cedar since the 1930s and one line from 1937 is still in operation.

Hydro-Quebec's 300,000 cedar poles endure severe wind, snow and thunderstorms to bring power to seven million customers. They began using cedar exclusively for their wood poles over 50 years ago and believe no other material will do the job.

West Penn Power in Pittsburgh has been using cedar since about 1938. With a line installed in 1955, they've experienced less than 10% change-put. They haven't replaced poles often enough to get a suitable size sample to calculate cedar's life-cycle cost.

West Penn engineers say, "Cedar lasts longer than other species and doesn't check as much." They also appreciate cedar's lightness for ease of handling and climbing.

Tacoma Public Utilities in Tacoma, Washington has relied on this native species for almost a century. The utility continues to choose cedar for its longevity and ease of climbing. Secure footing is especially important in Tacoma's wet climate.

More and more utilities are recognizing cedar's advantages, and integrating it into their existing and new lines.

Pole Capacity

Transmission poles have line capacities of 33 kV or higher. The lengths generally range from 60 to 125 feet, and are usually class 1,2,3 or H series poles (see technical data).

Distribution poles are single pole structures, and usually range from 25 to 55 feet long. Class 1 through 7 poles are generally used.

Cedar poles have a high strength-to-weight ratio. The pole classes specified in American National Standards ANSI 05.1 are based on resistance to specific lateral loads.

Standards

Western red cedar poles are manufactured and treated under one of the following standards.

Physical Properties: ANSI 05.1 or CSA 015

Butt Treatment: American Wood Preservers Association AWPA C-7 or Canadian Standard CSA 080.7.

Full length thermal: AWPA C-8 and ASTM D4064 or CSA 080.8.

Full length pressure: AWPA C-4 or CSA 080.4.

Structural Tests

Lateral stress testing, courtesy BPA

Tests conducted at the University of Colorado under the direction of EPRI show the mean effective modulus of elasticity (EMOE) for distribution poles to be 1,120 ksi.

Static strength tests conducted in 1985 by the Bonneville Power Administration (BPA) concluded cedar experiences little loss of strength over time. Ten 38 year old Western red cedar transmission poles retained over 80% of the strength of new poles at the time of failure.

The modulus of rupture, or stress level at failure, has been slightly reduced by weathering, checking or splitting. The older poles sustained an average of 85% of the expected lateral load capacity as listed in ANSI specifications for new poles.

Installation

ANSI specifications indicate setting depth is 10% of the pole length plus two feet, a point commonly known as the "groundline." A properly set cedar pole will have at least one foot of the incised groundline area above and two feet below the surface of the soil.