Wood Utility Pole Dimensions

Utility poles are ubiquitous. They are everywhere carrying electricity to homes and business along with also carrying telephone, cable news and even music before MTV stopped that,  telegraph at one time and who knows what else. We modelers could and simply select a wooden dowel that looks about right, stick on some cross-arms and go about our business. That is a bit hard for me .. my Persnickety kicks in. To that end here is some research for those with my condition.

WoodPoles.corg has a bunch of downloadable files including an Excel file – ANSI Dimensions for Wood Poles. They also have a nice calculator for Pole Dimensions.

“The load-carrying capacity of wood poles is determined by its dimensions, length and amount of taper from top to bottom. ANSI national standards, developed by the ASC O5 Committee, define poles in classes based on these dimensions and the species.”

To determine the required circumferences the calculator uses pull-down menus to select the Species, Pole Class and Length. The minimum top and bottom circumferences, as defined under ANSI standards, will then be shown.

  • Class Loads: The Horizontal Load in Lbs two foot down from the top of the pole determines the Class. NAWPC Wood Pole Code Overview – Class Loads
  • Class examples: 10 is 370 lbs, Class 7 is 1,200 lbs, Class 1 is 4,500 lbs, while Class H6 is 11,500 lbs.  There are 15 Classes in total across that range.
  • General Class Applications are
  • Class 10,9,7,6 Telecom Only Poles,
  • Class 5,4,3 for Distribution (or “feeders” which carry power from local substations to customers. They generally carry voltages from 4.6 to 33 kilovolts (kV) for distances up to 30 miles, and include transformers to step the voltage down from the primary voltage to the lower secondary voltage used by the customer. A service drop carries this lower voltage to the customer’s premises.
  • 3,2,1,H1,H2,H3,H5,H5,H6 for Transmission. Subtransmission lines carry higher voltage power from regional substations to local substations. They usually carry 46 kV, 69 kV, or 115 kV for distances up to 60 miles. 230 kV lines are often supported on H-shaped towers made with two or three poles. Transmission lines carrying voltages of above 230 kV are usually not supported by poles, but by metal pylons (known as transmission towers in the US).

For we modelers this means that modeling Distribution poles is most common meaning Class 5,4 and 3. Example of use .. plugging in a Class 3, Southern Yellow Pine with a 40ft length into the calculator gives us a pole with a 23″ circumference of 23″ at the top and 36″ circumference 6′ from the butt. Changing the Class to 5 gives a 19″ and 31″ circumference respectively

In O scale then the Class 3 pole would be 7.3″ and `11.5″ – or 0.15″ and 0.24″.  This gives a guide as we can then simply take a 1/4″ dowel and taper it to approximately that 0.15″ dimension at the top.