What Wood Are Utility Poles Made Of?
- The first utility poles were put up in 1844 when Samuel Morse created a telegraph line between Washington DC and Baltimore. He first tried burying the line, but encountered problems and switched to lines on poles. His call for pole suppliers specified chestnut poles. Chestnut is plentiful in the eastern USA and has good rot-resistant properties, so originally it became the most common utility pole wood.
By the 1890s utility poles were carrying electric power and, later, telephone and cable too. As lines moved further west, other tree species came into use. Also, in the 1920s, chestnut trees were afflicted by chestnut blight disease and so alternatives had to be found to chestnut in the eastern states. Utility poles need to be tall, straight, strong and rot-resistant; southern yellow pine, western red cedar, Douglas fir and lodgepole pine are preferred species. Western red cedar has high natural resistance to rot and insect boring but is expensive. Southern yellow pine and Douglas fir are perhaps the most common woods used today.
Many utility poles have a plate or engraved set of codes which gives information about the pole such as the manufacturer. It also can include a code for the wood used -- for example, SP for southern pine. - The earliest wood poles were untreated and tended to rot fairly quickly. The first pole treatment was creosote: the butt (bottom) of the pole was dipped in creosote before being buried in the ground. Later the poles were completely covered with creosote. From the 1940s onward, other types of treatment were developed, including CCA (chromated copper arsenic) and Pentachlorophenal, often known as Penta.
- Utility poles last about 20 to 25 years. Approximately 3 percent of poles are replaced each year -- over 4 million poles. Even though those poles may not be safe as utility poles any more much of the wood may still be usable. Rather than being burned or shredded, there is today an environmentally driven movement to recycle them; sometimes they are available for consumer use.
- Although wood remains the most common material for utility poles, it is not the only one. There are also concrete, metal and composite poles. Metal poles were not considered desirable for electrical lines because of the danger of electrocution, but modern companies have worked to overcome that. There is current interest in composite poles, both for sustainability reasons and because they last longer in areas that are hard on wood, such as coastal locations where wood is subjected to constant salt and damp. For this reason, places like Hawaii and the Caribbean islands have experimented with composite poles.
