Utility poles are divided into ten classes, from 1 to 10. The classes' definition specifies a minimum circumference that depends on the species of tree and the length of the pole. This circumference is measured 6 feet from the butt of the pole. There is also a minimum top circumference that is the same for all species and lengths.
For example, a class 1 pole has a minimum top circumference of 27 inches. If it is 25 feet long and cedar (most utility poles are cedar), the circumference measured 6 feet from the bottom must be at least 43.5 inches.
The higher the class number, the skinnier the pole. Pole lengths start at 16 feet and increase by 2-foot steps to 22 feet, then by fives from 25 feet to 90 feet. A 90-foot class 1 western red cedar pole weighs about 6,600 pounds. A 16-foot pole weighs only about 700.
Standards (from ANSI) severely limit or exclude various types of damage, including bird holes and insect boring, and describe ways of specifying the pole's straightness.
On curves, hillsides, or other locations where there's an unbalanced pull on the pole, standard practice calls for increasing the portion of the pole that is buried. For example, for poles being set along a straight line, 6 feet of a 35-foot pole would be buried, but if the pole were on a curve, 6.5 feet.
A 35-foot pole is a typical length used in cities to carry one or two crossarms. Poles are spaced about 100 feet to 150 feet apart, with 125 feet being typical.
American Standards Assn.
American Standard Specifications and Dimensions for Wood Poles.
Sponsored by ASA Telephone Group.
O 5.1-1963, revision of O 5.1-1948.
New York: American Standards Association, 1963.
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Last revised: 6 June 2014.