Ever since the invention of the telegraph and telephone, utility poles have been needed to keep overhead cables from interfering with ground traffic and avoid contact with the ground, people, animals and property.
For much of this time, the wooden utility pole has been the standard for utility companies. Wooden utility poles are harvested long, thin trees, normally pine, fir and cedar. Branches are removed, the bark is stripped and the trunk is shaped to a uniform width. The poles are then kiln dried to remove excess moisture. Drying reduces the weight of the pole and allows a greater volume of preservative to be used. Because a portion of the pole is underground, preservatives against rot and insect infestation are applied to that portion.
Though steel and concrete poles are also employed in some areas, wooden poles have benefits. Because wood is flexible in comparison to steel and concrete, the poles will sway in high winds without breaking. Unlike steel poles, wooden poles are an electrical insulator, rather than a conductor. Poles can be erected without special insulators to the pole itself. Due to their light weight, wooden poles are relatively simple to erect, and a larger number can be transported to the job site with a single truck.
Modern wooden treated utility poles have a longer useful life than in the past. According to inspection data performed by a utility consultant service on more than 700,000 existing poles, the mean useful life can exceed 50 years in less harsh climates and over 40 years in more severe areas.
One reason for the longer life is the advance in preservatives. Quality utility poles are pressure treated with Chromated Copper Arsenate (CCA). In this process, the mixture is impregnated into the wood fibers via a vacuum and pressure chamber. The vacuum chamber allows the wood fibers to expand and accept a larger volume of the preservative.
Pressure is then used to inject the CCA material. Copper is used to prevent rotting and fungus. Arsenic is used to repel insect infestation. For some poles, mineral oil is used as a final, outer additive for lubricity and to make the poles easier for utility workers to climb.
When choosing a supplier, utilities will investigate the manufacturing and treating process to ensure their own standards are met. Because it is a capital investment for electric and communication companies, the longest useful life of the product at the most reasonable price is the goal.