Trivia

Subject:
Answer : Wood pole

Gary Smyth
>Answer: Taken from the Lineman’s and Cableman’s Handbook, Fifth edition. A rule often followed for determining the setting depth in soil is to take 10% of the pole length and add 2 ft., with a minimum of 5 ft. Therefore the setting depth of a 40 foot pole would thus be 10% of 40 = 4 ft + 2 ft. = 6 ft.

It will be noted that the setting depth of 5 ft. for a 20 ft. pole the increase in depth averages 4 inches for each 5 ft. increase in pole length.

There are 10 grades of wood poles. A #1 pole will support the most weight, a #10 the least. The test for a #5 pole is that it must support 1900 lbs. applied two feet from the top and pulled at a horizontal angle. If it does it passes the test--but when installed in the field it is only permitted to support 475 lbs. when new. This is a required safety factor of four. The National Electrical code recognizes that over the twenty five to thirty year life of a pole it will deteriorate and loose its weight supporting capacity. The inherent strength factor will allow the pole to deteriorate up to 2/3 during its lifetime. This would still leave an adequate safety margin if the pole was properly treated and continuously maintained.

Poles are also identified by their length. A 35 foot #5 pole would be identified by 35-5 burned into the pole. Poles are different lengths because of required clearances between supported service lines. A standard pole (35-5) can carry a 7200 volt line, transformer, drop line, telephone line, and one or two cable lines. There are required distances between each of the lines, and there are required minimum distances that the lines must be supported above the ground. Different classes of roadways, drive ways and business/residential environments require different minimum clearances. Higher voltage carrier lines require greater clearance distances. All of these factors go into determining the minimum length of a pole for a specific installation

Pole wood codes:

WC = western red cedar
WP = ponderosa pine
JP = jack pine
LP = lodgepole pine
NP = red pine
DF = douglas fir
SP = southern pine
WL = western larch

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