L. D. 1 0.87 2 1.10 3 1.26 4 1.39 5 1.50 6 1.59 7 1.67 8 1.75 9 1.82 10 1.88 11 1.95 13 2.06 15 2.17 17 2.25 19 2.34 21 2.42
The two strongest pins in Table II. appear to be those in use on the line between Shawinigan Falls and Montreal and on the line from Niagara Falls to Buffalo. The former have a diameter of 2-3/4 inches at the shank, and the wire is carried 16-1/4 inches above the shoulder of the pin. On the new Niagara line the shank diameter of each pin is only 2-1/4 inches, but the line wire is only 10 inches above the shoulder. It was found by tests that a strain of 2,100 pounds at the top of the insulator and at right angles to the axis of this Niagara pin was necessary to break it at the shank. This strain is about six times as great as the calculated maximum strain that will occur in service on the line.
Some of the pins here noted are much stronger than those proposed in the above specifications for standard pins. The pins on the old Niagara line have a shank diameter of 2 inches, with a stem only 5-1/4 inches long, while the proposed pin of 2 inches diameter at the shank has a stem 11 inches long. On the Colgate and Oakland line a shank diameter of 2-1/8 inches goes with a length of 10-3/8 inches in the stem, but the proposed pin with this size of shank has a stem 13 inches long. For a shank of 2-1/4 inches diameter the proposed pin has a stem 15 inches long, but the pins with this diameter of shank on the Electra line are only 12 inches long in the stem.
The 2-1/4-inch diameter of shank in the pins on the new Niagara line goes with a length of only 7-3/4 inches in the stem. The new Niagara pin is thus almost exactly twice as strong as the proposed pin, since the strength of a pin where the shank joins the stem varies inversely as the length of the stem, all other factors being the same.
Pins on the Shawinigan Falls line have a shank 2-3/4 inches in diameter, with a length of 13-1/2 inches in the stem; but the largest of the proposed pins, that with a stem 19 inches long, has a diameter of only 2-1/2 inches in the shank.
It is hardly too much to say in the interest of good engineering that the wooden pin of about 5 inches length of stem and 1-1/2 inches diameter of shank, as well as all longer pins of no greater strength, should be discarded for long transmission lines of high voltage. These pins have done good service on telegraph and telephone lines, and on local lighting circuits of No. 6 B. & S. gauge wire or smaller, and they may well be left for such work.