Wood Pole Class and Groundline Moment

The horizontal load it can take two feet from the top. What a crew actually has is a load at some other height, a groundline circumference off a tape, and a species. A pole is a cantilever fixed at the groundline and it fails in bending there, so its capacity is the designated fiber stress of the species times the section modulus of the circle at the groundline. Because the section modulus goes as the CUBE of the diameter, small differences in circumference are large differences in strength -- a pole an inch under its class circumference has lost roughly eight percent of its capacity, not one -- and that is why the tape reading matters more than the class stamp. A Class 3 Southern Pine measuring 37.5 in at the groundline at 8,000 psi has 111,315 ft-lb of capacity; re-measure it at 36.5 in and it is 102,647, a 7.8% loss from one inch. The applied side is a SUM of moments, not a single load. Conductor tension at the crossarm, wind on the pole itself, wind on the conductors, and a down-guy's horizontal reaction all act at their own heights, and each contributes its force times its height above the groundline. That is also why a guy attached high is worth so much: it subtracts a large moment at the height where the moment arm is longest. Species enters directly through the fiber stress -- Southern Pine and Douglas Fir at 8,000 psi, Western Red Cedar at 6,000 -- so the same stick in cedar is a quarter weaker. This is a groundline bending check on a solid circular section from values the user supplies. It does not apply the overload capacity factors, strength reduction factors, or load cases that NESC Grade B and Grade C construction require, and it is therefore a screen rather than a design. It does not evaluate decay, checks, shell rot, woodpecker damage, or through-boring and preservative treatment, all of which reduce the effective section and none of which a tape reading reveals -- a groundline circumference on a hollow pole is a misleading number. It does not check buckling under vertical load, embedment or soil capacity, the guy and anchor system, or bolt-hole reductions at the attachment. ANSI O5.1, the applicable NESC edition and grade of construction, the utility's construction standards, and a qualified line designer govern.

groundline diameter d = circumference / pi; section modulus S = pi d^3 / 32; moment capacity = designated fiber stress x S; applied moment = the sum of each horizontal load times its height above the groundline; utilization = applied / capacity.

The groundline bending check with ANSI O5.1 designated fiber stresses CITED, NOT MIRRORED -- entered by the user (8,000 psi Southern Pine and Douglas Fir, 6,000 psi Western Red Cedar). A screen, not a design: NESC grade-of-construction overload capacity factors are NOT applied. ANSI O5.1, the applicable NESC edition, the utility's construction standards, and a qualified line designer govern.

Section-modulus arithmetic on a tape reading; no pole class table is reproduced.

Estimate. AHJ and licensed professional govern.

Field names used by the API: groundline_circumference_in, fiber_stress_psi, load_1_lb, height_1_ft, load_2_lb, height_2_ft, load_3_lb, height_3_ft, check_height_ft, groundline_diameter_in, section_modulus_in3, moment_capacity_ftlb, applied_moment_ftlb, utilization_pct, remaining_load_lb

• Overload capacity factors are NOT applied this is a screen, not a grade-of-construction designthe applicable NESC edition
• Decay and hollow sections are not evaluated a tape reading does not reveal thempole inspection practice
• Fiber stress is a species value entered by the user 8,000 psi pine and fir, 6,000 psi cedarANSI O5.1