The ANSI 051 standard lists 25 native tree species that exhibit the physical and mechanical properties that allow approval for utility pole use. Six of these species account for 90 percent of the poles used in the United States.
Four of these are in the Southern Pine group and include loblolly, longleaf, shortleaf and slash. The other two species are Douglas-fir and western red cedar that are predominantly used as the large Class H transmission poles.
ANSI specifications list criteria for pole acceptance in the four categories of shape, growth characteristics, naturally occurring defects and processing defects. Shape is the circumference taper of a pole.
The largest percentage of Class 5 poles are made from Southern Pine that has an ANSi spec of no more than 025 inch circumference taper per foot of pole length. Growth characteristics include knots, rate of growth and compression.
Processing defects include splits, checks and mechanical damage.
Southern Pine logs used for utilitly poles are debarked, steam cured and then treated with a wood preservative. The final manufacture step is to evaluate the poles to see if they meet ANSI specifications.
To be accepted, Class 5 poles must withstand fiber stress of 8,000 pounds per square inch.
Length and Class
ANSI standards require that Class 5 poles have a minimum 19-inch pole-top circumference. At six feet from the pole butt the minimum circumference has to be 23 inches for 20-foot poles, 255 inches for 25-foot, 275 for 30-foot, 29 inches for 35-foot, 31 inches for 40-foot, 325 inches for 55-foot and 34 inches for 50-foot.
The ANSI standard requires that all pole classes bear markings that include the supplier's code or trademark, the plant where the pole was treated with preservative, year of treatment, pole species, preservative used and circumference class and length.