Angle towers, used where the line makes a large change in direction at a single point, have three legs on each rectangular side, a width of 20 feet on each of these sides for some distance above the ground, and a width of 27 feet 2 inches at the top. In these towers the two legs on the triangular side that is in compression are each made up of four 3″ × 3″ × 1⁄4″ L sections joined by 11⁄2″ × 1⁄4″ lattices and rivets. Towers of this sort are used near the Toronto terminal-station, where the line changes 35 degrees at a single point, and near the crossing of Twelve-Mile Creek, where the angular change of the line on a tower is 45 degrees. Close to each terminal-station and division-house the transmission line is supported by terminal towers. These towers differ from the others in that each carries insulators for only three conductors, and these insulators are all at the same level. Each terminal tower has nine insulators, arranged in three parallel rows of three each for the conductors of a single circuit, and each conductor thus has its strain distributed between three pins. All three wires of a circuit are held 40 feet above the ground by a terminal tower, and pass to their entries in the wall of a station at the same level. As these terminal towers must resist the end strain of the line, they are made extra heavy, the four legs each being made up of 4″ × 4″ × 5⁄16″ and 4″ × 4″ × 3⁄8″ L sections. For the three cross-arms on one of these towers three pieces of 4-inch pipe, each 15 feet 9 inches long, are secured at its top with their parallel centre lines 30 inches apart in the same plane. Each of these pipes carries three insulator pins with their centres 7 feet 41⁄2 inches apart. On the bottom of each leg of a terminal tower there is a foot, formed by riveting on bent plates, that measure 15 and 18 inches, respectively, on the two longer sides. Each foot of this tower is set in a block of concrete 5 feet square that extends from 3.5 feet to 7.5 feet below the ground level.

Insulators for the transmission line, which are illustrated in [Fig. 104], are of brown, glazed porcelain, made in three parts, and cemented together. The three parts consist of three petticoats or thimbles, each of which slips over or into one of the others, so that there are three outside surfaces and three interior or protected surfaces between the top of an insulator and its pin.

From top to bottom the height of each insulator is 14 inches, and this is also the diameter of the highest and largest petticoat. The next or middle petticoat has a maximum diameter of 10 inches and the lowest petticoat one of 8 inches. Cement holds the lowest petticoat of the insulator on one of the steel pins previously described, and in this position the edge of the lowest petticoat is about 21⁄2 inches from the steel support. At the top of each insulator the transmission conductor is secured, and the shortest distance from this conductor to any of the steel parts through the air is about 17 inches.

From the step-up transformer house at Niagara Falls to the terminal-station at Toronto, a distance of seventy-five miles, each three-phase, 60,000-volt, 25-cycle circuit on the steel towers is made up of three hard-drawn copper cables with a cross section of 190,000 circular mils each, and is designed to deliver 12,000 electric horse-power with a loss of ten per cent, on a basis of 100 per cent power factor. Six equal strands of copper make up each cable, and this wire has been specially drawn with an elastic limit of more than 35,000 pounds and a tensile strength of over 55,000 pounds per square inch. This cable is made in uniform lengths of 3,000 feet, and these lengths are joined by twisting their ends together in copper sleeves, and no solder is used. No insulation is used on these cables.

Fig. 104.—Insulators.

Instead of a tie-wire, a novel clamp is employed to secure the copper cable on each insulator. This complete clamp is made up of two separate clamps that grasp the cable at opposite sides of each insulator and of two half-circles of hard-drawn copper wire of 0.187 inch diameter. Each half-circle of this wire joins one-half of each of the opposite clamps, and fits about the neck of the insulator just below its head. Two bronze castings, one of which has a bolt extension that passes through the other, and a nut, make up each separate clamp. When the combined clamp is to be applied, the sides are separated by removing the nut that holds them together, the half-circles are brought around the neck of the insulator, and each of the side clamps is then tightened on to the cable by turning the nut that draws its halves together. This complete clamp can be applied as quickly as a tie-wire, is very strong, and does not cut into the cable.

Each of the regular steel towers is designed to withstand safely a side strain of 10,000 pounds at the insulators, or an average of 1,666 pounds per cable. With the 190,000-mil cable coated to a depth of 1⁄2 inch with ice and exposed to a wind blowing 100 miles per hour, the estimated strains on each steel pin for different spans and angular changes in the direction of the line are given in the accompanying table:

Pounds Strain on Pins, 1⁄2-inch Sleet, 100 Miles Wind.

Span,
feet.		Degrees and Minutes.
00.3011.3022.3033.3044.3055.306
003569104138173207242276311345380414
100256291325360394429463498532567601636670
200512547581616650685719754788823857892926
3007688038378729069419751,0101,0441,0791,1131,1481,182
4001,0241,0591,0931,1281,1621,1971,2311,2661,3001,3351,3691,4041,438
5001,2801,3151,3491,3841,4181,4531,4871,5221,5561,5911,6251,6601,694
6001,5361,5711,6051,6401,6741,7091,7431,7781,8121,8471,8811,9161,950
7001,7921,8271,8611,8961,9301,9651,9992,0342,0682,1032,1372,1722,206
8002,0482,0832,1172,1522,1862,2212,2552,2902,3242,3592,3932,4282,462
9002,3042,3392,3732,4082,4422,4772,5112,5462,5802,6152,6492,6842,718
1,0002,5602,5952,6292,6642,6982,7332,7672,8022,8362,8712,9052,9402,974