Some of the important factors affecting the strains on insulator pins vary much on different transmission lines, as may be seen from the following table of lines on which wooden pins are used. On the older line between Niagara Falls and Buffalo, the regular length of span is 70 feet, and each copper conductor of 350,000 circular mils is attached to its insulator 7.5 inches above the cross-arm. On the new line the length of span is 140 feet, and each aluminum conductor of 500,000 circular mils is attached to its insulator 10 inches above the cross-arm.

Table I.—Data of Lines on Wooden Pins.

Location of the Lines.Circular
Mils
of Each
Conductor.		Feet
Length
of Span
Between
Poles.		Inches
from Wire
to Shank
of Pin.
Colgate to Oakland[[B]]133,100...13
Electra to San Francisco[[A]]471,03413015
Cañon Ferry to Butte[[B]]105,600110131⁄2
Shawinigan Falls to Montreal[[A]]183,750100161⁄4
Niagara Falls to Buffalo[[B]]350,0007071⁄2
Niagara Falls to Buffalo[[A]]500,00014010
Chambly to Montreal[[B]]133,1009081⁄2
Colgate to Oakland[[A]]211,600...13
[A] Aluminum conductors.
[B] Copper conductors.

Table II.—Dimensions of Wooden Pins in Inches.

Location of Lines.Length
of
Stem.		Length
of
Shank.		Diameter
of
Shank.		Diameter
of
Shoulder.		Diameter
of
Threaded
End.		Length
of
Threaded
Part.
Colgate to Oakland103⁄853⁄821⁄821⁄213⁄82
Electra to San Francisco12 47⁄821⁄423⁄413⁄82
Cañon Ferry to Butte121⁄251⁄82 21⁄211⁄83
Shawinigan Falls to Montreal131⁄25 23⁄43 1 ..
Niagara Falls to Buffalo[[A]]51⁄46 2 23⁄4 7⁄811⁄2
Niagara Falls to Buffalo[[B]]73⁄46 21⁄423⁄411⁄221⁄2
Chambly to Montreal[[C]]7 5 11⁄217⁄8....
Cañon Ferry to Butte[[D]]123⁄877⁄821⁄821⁄211⁄83
[A] Pins on old line.
[B] Pins on new line.
[C] Approximate dimensions.
[D] Pole top pins.

To compensate for the greater strains introduced by doubling the length of span and using pins of longer stem, the diameter of the shank of the new pins was increased to two inches. One line between Colgate and Oakland is of copper, and the other is of aluminum conductors, but the same pins appear to be used for each. On the line between Cañon Ferry and Butte, Mont., the pin used in pole tops has a shank 23⁄4 inches longer and 1⁄8-inch greater in diameter than the pin used in cross-arms. The weakest pin included in the table seems to be that in use on the line between Chambly and Montreal, which is of hickory wood, about 11⁄2 inches in diameter at the shank, and carries its No. 00 copper wire 81⁄2 inches above the cross-arm.

The following dimensions for standard wooden insulator pins to be used on all transmission lines are proposed in vol. xxi., page 235, of the Transactions of the American Institute of Electrical Engineers. These pins are designed to resist a uniform pull at the smaller end and at right angles to the axis in each case. The length of each pin, in inches between the shoulder and the threaded end, is represented by L, and the diameter of each pin at its shank by D.

L.D.
10.87
21.10
31.26
41.39
51.50
61.59
71.67
81.75
91.82
101.88
111.95
132.06
152.17
172.25
192.34
212.42

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 23⁄4 inches at the shank, and the wire is carried 161⁄4 inches above the shoulder of the pin. On the new Niagara line the shank diameter of each pin is only 21⁄4 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 51⁄4 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 21⁄8 inches goes with a length of 103⁄8 inches in the stem, but the proposed pin with this size of shank has a stem 13 inches long. For a shank of 21⁄4 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.