This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
Poles should be of selected quality of chestnut or cedar, and should be sound and free from cracks, knots, or other flaws. Experience has proven that chestnut and cedar poles are the most durable and best fitted for linework. If neither chestnut nor cedar poles can be obtained, northern pine may be used, and even other timber in localities where these poles cannot be obtained; but it is found that the other woods do not last so long as those mentioned.
Fig. 63. Cut-out Panel with Push-Button Switches.
The proper height of pole to be used depends upon conditions. In country and suburban districts, a pole of 25 to 30 feet is usually of sufficient height, unless there are more than two or three cross-arms required. In more densely populated districts and in cities where a great number of cross-arms are required, the poles may have to be 40to 60 feet, or even longer. Of course, the longer the pole, the greater the possibility of its breaking or bending; and as the length increases, the diameter of the butt end of pole should also increase.
Table XI gives the average diameters required for various heights of poles, and the depth the poles should be placed in the ground. These data have been compiled from a number of standard specifications.
Length of Pole
6 in. from
Diameter at Top
Depth Pole should be Placed in
9 to 10 in.
6 to 8 in.
5 1/2 "
5 1/2 "
6 1/2 "
16 to 17 "
7 1/2 "
7 1/2 "
8 1/2 "
As it is somewhat difficult, because of irregularities in size, to measure the diameter of some poles, the circumference may be measured instead: then, by multiplying the diameters given in the above table by 3.1416, the measurements may be reduced to the circumference in inches.
The minimum diameters of the pole at the top, which should be allowed, will depend largely on the size of the conductors used, and on the potential carried by the circuits; the larger the conductors and the higher the potentials, the greater should be the diameter at the top of the pole.
Poles should usually be painted, not only for the sake of appearance, but also in order to preserve them from the weather. It is particularly important that they should be protected at their butt end, not only where they are surrounded by the ground, but for a foot or two above the ground, as it is at this point that poles usually deteriorate most rapidly. Painting is not so satisfactory at this point as the use of tar, pitch, or creosote. The life of the pole can be increased considerably by treating it with one or another of these preservatives.
Before any poles are erected, they should be closely inspected for flaws and for crookedness or too great departure from a straight line. Where appearance is of considerable importance, octagonal poles may be used, although these cost considerably more than round poles. Gains or notches for the cross-arms should be cut in the poles before they are erected, and should be cut square with the axis of the pole, and so that the cross-arms will fit snugly and tightly within the space thus provided. These gains should be not less than 4 1/2 inches wide, nor less than 1/2 inch deep. Gains should not be placed closer than 24 inches between centers, and the top gains should be at least 9 inches from the apex of the pole.
Fig. 64. Cut-Out Panel with Push-Button Switches. With Cover.
Where poles are subject to peculiar strains due to unusual stress of the wires, such as at corners, etc., guys should be employed to counteract the strain and to prevent the pole from being bent and finally broken, or from being pulled from its proper position.