[Trade Journal]
Publication: Bell Laboratories Record
Murray Hill, NJ, United States
vol. 32, no. 4, p. 121-125, col. 1-2
The author, (right) and V. P. DiLullo examine one of the new wire supports. Mr. DiLullo holds a standard glass insulator.
A New Type Open-Wire Line for Rural Areas
R. G. WATLING Outside Plant Development
New equipment and techniques for installing rural open-wire lines have been developed to a point where a general field trial by the Operating Companies is getting under way. The unique feature of the new line is that it can be constructed entirely from the ground. For this purpose a newly designed wire support permits the wires to he strung, tensioned, and clamped without the necessity of climbing poles.
The extension and improvement of rural telephone facilities have always been important Bell System objectives. Since the war, Operating Companies throughout the nation have put special emphasis on a construction program to meet the unprecedented demand of residents of sparsely settled areas for telephone service. Between one and one-half and two million telephones have been installed on farms and ranches since 1945. For this increased service the Bell System has built thousands of miles of new pole line and has strung over a million and a half miles of wire.
Bell Laboratories has contributed to this vast construction program by developing new equipment and Systems needed to furnish additional service of a better grade to farmers. New high-strength steel line wire has made possible long-span construction in many areas and has resulted in substantial savings in material costs by decreasing the number of poles required per mile; a new form of distribution wire, which is buried directly in the ground, has afforded construction economies in certain areas; new types of carrier systems have been developed for installation on telephone lines and on power lines; radio telephone links have been made available for extending telephone service to remote customers — these are representative developments which have helped the Bell System carry out its aims of incorporating in rural service as many of the features of urban service as is practicable.
Recent studies of rural outside plant indicated that greater economies in construction costs are more likely to result through the introduction of new structures and techniques than through modifications of present materials. Development efforts have therefore been pointed in the former direction, with the result that a new type of light open-wire line has been designed. This line can be constructed entirely from the ground and can carry from one to four pairs of conductors, which, with the multiparty System, affords capacity to serve adequately many of the rural areas in the country. In those cases where more circuits are needed, carrier systems suitable for use on this as well as on other types of construction are being considered.
Fig. 1 — Prior to erection, the pole and all of its fittings are being assembled on the ground by J. D. Apgar (left) and V. P. DiLullo of the Chester Laboratories.
The elimination of pole climbing in line wire installation operations is made possible through the design of a new type of insulator used to support the wires. Unlike the conventional glass insulator, which is mounted on the top of the crossarm, the new insulator is mounted underneath (or suspended from a bracket) to facilitate installation of line wires from the ground.
The new line was developed primarily to reduce construction costs through the simplification of labor operations. Although designed for long-span construction, the line uses the lightest poles, cross-arms, and guys consistent with strength and clearance requirements. All construction work can be done by a crew of three or four men.
In terrains suitable for the operation of motor vehicles, pole line construction operations, such as hole digging, pole setting, and guy anchor installation, can be expedited by the use of Standard truck-mounted digging and hoisting equipment. In areas where these trucks cannot be conveniently used, the operations described are performed manually.
Fig. 2 — A completely equipped pole being raised to a permanent position at the Chester Laboratories by (left to right) V. P. DiLullo, J. D. Apgar, and T. W. Rolph.
Poles, as in Figures 1 and 2, are completely equipped with pole brackets or crossarms, insulators, transposition brackets, and guy attachments before they are erected. The wooden crossarms carry two or four pairs of wires. In the case of the two-pair line (Figure 3), the wires on one side of the pole are in a horizontal position below the arm, and the wires on the other side are arranged vertically, one above the arm and one below. At each succeeding pole the position of the wires alternates between horizontal and vertical so that, in four spans, the wires of each pair make a complete helical turn, each around the other. This provides a transposition system that — protects each Circuit against noise and crosstalk interference. Wires of the four-pair line are transposed in a similar manner. Where only a single pair of wires is required, these are supported by means of brackets of strap steel attached to the poles with lag screws or through-bolts.
Fig. 3 — A complete ground-erected, two-pair line, showing horizontal and vertical mountings of suspension insulators.
The advantages of the new construction methods are, of course, most fully realized in the wire-stringing operations. Line wires are payed out along the right-of-way by one of two methods, depending on the nature of the terrain along the route. If the right-of-way permits the use of motor vehicles, the line wires may be payed out from trailer-mounted reels, as the trailer moves along the lead. If the use of motor vehicles is impracticable, the wires may be pulled along the lead by hand, or by horse teams, from reels located at accessible positions along the right-of-way. Usually one-half mile lengths of line are pulled in at one time. As the wires are pulled along the lead, in every span the relative position of each wire of a pair is changed, to provide for the helical turns of the transposition System.
Before the wires are raised to their insulators, vibration dampers (Figure 4) are placed on each wire in each span. The damper is a short length of plastic tubing, split helically along its length to facilitate its installation on the wire. This damper, by its flexing action as the wire moves under wind-inducted vibrations, will absorb energy as fast as the the wind puts energy in, thus damping out high-frequency, low-amplitude vibrations which might result in injury to the wire at the point of its support. The damper is effective at any position on the wire in the span.
Fig. 4 — P. T. Packard demonstrates how a helically split vibration damper is placed on an open wire line prior to raising it to the insulated wire support.
The wires are then lifted from the ground with wire-raising tools and placed in the wire supports. This Operation is shown in Figure 5. The wire-raising tool is of light and strong construction and has insulating sections to protect workmen against electrical shock in case of accidental contact with power wires. The head of the tool is designed to perform several functions: to hold the wire while it is being raised from the ground, to guide the wire into its support, to tighten the support after the wire is tensioned, and to open the support and remove the wire therefrom if this is ever required, either while construction is in progress or as a maintenance operation.
Fig. 5 — Left, two views of the wire-raising tool being used to place a wire on the insulated support.
The wire support is the heart of the new system because its unique design makes it possible to install line wires without the necessity of pole climbing. The complete support consists of three major components: the mounting bolt, the insulator, and the wire clamp assembly. Supports can be seen in several of the accompanying photographs, and the parts are identified in Figure 6. The insulator is made of a tough plastic of the filled styrene polyester casting resin family which possesses excellent electrical and mechanical properties. The metal parts are molded into the insulator, which is in the form of a cylinder. Unlike the standard form of glass insulator with its flared petticoat designed to keep the under-surface dry, the new insulator does not have such a “dry path,” but depends on rain to keep its surface clean. A clean surface, even though wet, does not permit much electrical leakage.
Fig. 6 — Drawing of the new insulated wire support, showing parts.
The wire clamp consists essentially of a hook member of aluminum, a keeper, also of aluminum, which pivots on and moves across the hook, and a steel locking screw. As the wire enters the hook, it pushes the keeper aside and drops into the slot of the hook. The keeper then restores, trapping the wire so that it cannot escape, but allowing it to move freely through the hook longitudinally to permit tensioning.
Fig. 7 — Below, tensioning gear used to get correct tension in open wire lines from a ground position.
The wires are tensioned from the ground. The tensioning gear, seen in Figure 7, consists of a system of ropes and pulleys designed to equalize tensions in all four of the wires, grips for holding the wires, and a dynamometer to measure wire tensions. After the line wires are tensioned, the final construction Operation, that of tightening the wire-support locking screws with the wire-raising tool, is performed as in Figure 8. The locking surfaces of the keeper and hook are such that a slight bend is put in the wire, thus helping to hold it tight. The keeper and hook have been designed to guard against injury to the wire surface.
Fig. 8 — The wire-raising tool is here being used to tighten the locking screw of the insulated wire support.
Field trials of the new construction methods have been made in Virginia, Colorado, and Louisiana. The line in Virginia was built under difficult terrain conditions where the construction techniques of the new type line could be tested most effectively. The Colorado installation is in a dry region of extreme temperatures and high prevailing winds that will test the fatigue endurance qualities of the new line. The Louisiana line will operate under hot and humid conditions, and therefore will test the insulating qualities of the wire supports. Meanwhile, preparations are being made for a general field trial of this new rural line by the various Operating Companies of the Bell System.
THE AUTHOR
R. G. WATLING received a B.A. degree from Occidental College in 1923 and the following year joined the Southern California Telephone Company. He was transferred to the Laboratories in 1926, serving first as an instructor in the training course for Technical Assistants, and later joining the administrative staff of Outside Plant Development. In 1940 he became supervising engineer in Switching Apparatus Development. The following year, on leave from the Laboratories, he served as assistant to the Director of Research at the U. S. Navy Underwater Sound Laboratory, New London, Conn. Returning to Outside Plant Development in 1946, he was concerned with the development of hardware and tools, and two years later was assigned to the plant Systems studies group. He is currently in charge of a group working on wire and cable development problems. Mr. Watling is a member of the A.I.E.E., the A.S.T.M. and the New Jersey Society of Professional Engineers.
