Line Conductor For Open Wire Transmission, Local Loop and Exchange Construction
A little history on conductor design and manufacturing.
Open “Wire” means just that: the Wire Plant. Transmission of telegraph signals relied upon metalic, or early iron wire strung between supports in rural areas. Where signal circuits were arrayed in urban areas, poles were relied upon less, and supports were generally rooftops and sides of structures, buildings and homes.
In Europe, this practice continues to the present day. However, in the United States and Canada, urban congestion, heavier conductors, necessity of supporting adjunct facilities, such as loading coils, terminals, and the like, along with the challenge of construction and repair access, made this impossible. Even more importantly, with the advent of personal real property rights and need of special easements, joint use aspects and the like, such construction was swiftly made obsolete.
In the old days with telegraph, one single conductor (usually bare) was hung suspended by poles and a single wooden bracket or similar fixture, and the ground beneath the circuit furnished the “ground” return for it to operate.
Telegraphy operated at very low frequencies. Losses were minimal and successful long distance telegraphy was possible from the earliest days of this technology. Repeating, or signal regeneration locations at certain distances along the path of the line, provided with a telegrapher and additional sources of current, made long distance transmission possible. Unfortunately, with the high attenuation, or losses, associated with higher frequency voice wire transmission, could not be accomplished so easily.
Very early pioneering “fence line” telephone system, typical of western Nebraska.
Telephone voice transmission implied higer frequencies–sometimes as high as 100 times that of telegraphy. When the voice circuits were amplified, so in turn, was interference, and remained a problem with wire transmission plant up until the evolution of electronics in the immediate pre-World War I era.
The medium of early voice communication consisted of iron, steel and galvanized steel strand, as well as various sizes of copper conductor. Intermediate supports of wooden poles, to which were attached wooden brackets and screwed upon them, glass or dry process porcelain insulators, prevented the conductor from contacting the ground.
The telegraph industry had relied upon freshly cut, seldom preserved, wooden poles of varying lengths and strengths. It wasn’t until February 1891, that the American Telephone & Telegraph Company began to strictly specify pole line construction. Cedar and Chestnut were early tree species called for in these 1891 requirements and 40 foot lengths were demanded.
Within a few years after this, the specifications became more rigorous and involved, heights lengthened, and strengths proportioned to the standard line spans of tangent pole line construction: 130 feet or 40 poles per mile.
Crossarms, too began to take on their traditional “American” feel, with the first ten foot fur arms incorporating wooden locust pins of once inch diameter threads and inserted at 12″ intervals (with the exception of the “pole pair” which were placed on either side of the pole at 16″ distances between the wires).
109 galvanized steel line wire in the field. Photo by D. G. Schema.
Iron wire and steel wire development were in their infancy. Iron wire had been used with considerable success in the barbed wire industry and the settling of the western frontier.
As the great western frontier was being tamed, the iron and steel industries emerged to offer greater strength and resistant materials for line conductors. While the telegraph industry within the first 40 years of its inception, used iron line wire of two sizes: 12 guage and 14 guage, the burgeoning telephone industry found itself with an array of newer, higher strength and less current resistant materials for conductors.
The introduction of “galvanizing” to steel line wire open up many opportunities to place line wire which was not only physically stronger, but was corrosion resistant and could be made in various sizes unknown to the earlier signals and railroad industries. Iron wire was notoriously difficult to splice, allowing weakness where the ends were twisted, fatigue potential at the beginning of the earlier “twisted” splice, and simply were not electrically sound. These splices, when placed along hundreds of miles of line, created further distortions in the signal, amassed considerable interference and were not very electrically conductive.
With the diversity in line wire sizes, came new measurement aids. In the past, diameters were measured in “guage” sizes exclusively. Now, with the advent of steel and galvanized steel wire, “mils,” came into vogue. So, for example, the commonly used telegraphic 12 guage now became “109 mils” for telephone; the frequently applied 14 guage became “83 mils.”
There were several “universal” wire measurement size classifications. One nomenclature, known as the Birmingham Wire Guage or B.W.G., was dominant to Europe. The American Wire Guage or A.W.G., dominated North America’s open wire conductor diameter and strength standards to the present.
The use of “mils” is an expression of the diameter of the wire in decimal fractions of an inch, or mils. Variations to that measurement were accepted for nominal sizes of wire, e.g. for wire 0.100 inch in diameter and larger, plus or minus one and one-half (1 1/2) per cent; for wire less than 0.100-inch but larger than 0.060-inch nominal diameter, plus or minus one and one-half (1 1/2) mils; for wire less than 0.060-inch but larger than 0.030-inch nominal diameter, plus or minus one (1) mil.
With the onset of noisy circuits caused by simple physical twist physical connections, there had to be a better way to resolve these problems.
The first was to re-define the conductor itself, in order to make it more resistant to corrosion, have superior physical strength and more conductive to the electrical voice signal. This is where “galvanizing” steel wire became highly critical to the progress of the early telephone industry.
To quickly define the art of “galvanizing” is to apply a thin coating of zinc, which is a corrosion-resistant to the outside diameter of the steel surface. Sometimes called electroplating, this practice uses the coating of zinc by a “galvanic cell.” However, there are some subtle differences between this general definition.
When a steel line wire, say of 109 mils, is “galvanized,” it means the ferrous steel is protected from galvanic corrosion. Zinc is nearly rust-resistant–although ultimately, it does corrode over time–but much less than iron or non-treated steel. The zinc is in effect, a “sacrificial anode,” as it cathodically emerses the steel interior with a coating protecting it from superficial physical attacks.
Some people have remarked that “galvanizing” is the same as “electroplating.” This latter type of treatment usually includes “hot-dip zinc coating.” Galvanized steel wire typically uses zinc and is nearly always recognized for this ingredient inclusion.
Metallic Conductivity of Aerial Wire
For short-haul transmission requirements, galvanized steel was useful and applied to many telephone circuits. However, one large challenged still confronted early telephone engineers: conductivity of the line wire material.
If one looked at solid drawn copper conductor, with a resistance about ten percent that of steel, a major step could be taken in order to increase conductivity and decrease attentuation to some extent. But while the solution was fairly simple, the industrial processes which might produce this solution, simply did not exist.
Let’s just consider how wire–of any metallic material–is made: Strips of metal are drawn successively through smaller and smaller dies until the proper diameter is achieved. There was one hitch: copper, for example, suffered from successive decreases in physical strength as it was drawn through dies to its ultimate needed diameter. Soon, at very small diameters, it became hard and brittle.
Metalurgical engineers worked on the problem and deduced that heat would mend the successive draws through the dies, whereby cracks and spaces would merge and achieve a much stronger final product. They also found incidentally–without striving for this express purpose–such heating also created a more conductive metal by a few percentage points.
This “hard drawn” wire goal could be achieved, Thomas B. Doolittle discovered, by drawing the line wire through additional “passes” and substantially altering the strength of the wire. Metallic wire’s strength is determined by one of the three factors to measure “stress.” This was “tensile” strength. Regular mined copper in its basic un-refined state has a “tensile” strength of about 28,000 lbs per square inch.
Such wire also has an “elongation” factor, e. g. “ductility” test, to determine the amount of extension of the metal vs. its original guage length. The necessity of this particular test is clearly seen when a wire is hung between two poles. In this test, two wires are placed parallel. Punch marks are made on the material to be tested to a specific length. A pull test begins. The amount of extension beyond the original location of the marks is measured pre-test and after-test in a manual procedure. A device called a extentiometer can be used on small test pieces to achieve results mechanically and with greater precision.
Doolittle’s ductility test achieved highly impressive results with this new copper drawing procedure. Instead of an elongation of 36% on the original wire sample, he found that strength of the same wire with this new process increased its strength to 65,000 lbs per square inch while decreasing the elongation factor down to about one percent!
Executives in the early telephone industry, most notably Theodore N. Vail, took notice and ordered testing to confirm these astonishing results. As a result, a significant order was placed for this type of conductor in 1883. Positive results were reinforced when the line was completed, put in to operation and the first call placed.
By the turn of the preceding century, the practical use of copper for longer span telephone construction could be demonstrated. Copper clearly demonstrated its essential place in the exchange and toll telephone transmission open wire plant of the next one hundred years.
Advent of “Cladded” Copper and Aluminum Surfaces to Steel Line Wire
The advent of rural electrification in the mid-1930s, brought about a maturing of the electric power industry and consequent evolution of conductor design. Because the Rural Electrification Administration demanded engineering standards and specifications of high quality and durability in the rural environiment, manufacturers were challenged to create new line design products.
As an effect of this technological evolution in the electric power industry, many inventions and standards in the emerging rural cooperative movement had positive repercussions to the telecommunications market as well.
Long span construction for rural electric systems required high strength conductor with an efficient degree of inherent electrical conductivity. It was quite clear that pure copper primary conductors would be extremely expensive. Additionally, with 350 to 500 foot spans, copper would not have the breaking strength to resist the span weight and impacts of climate upon the line conductor.
A manufacturer, Copperweld Bimetallics Group, arrived at a solution to this problem by creating a superior product for the rural electrics, which with a few modifications, was also successfully applied to the farmers’ mutual, independent telephone companies and by the late 1940s, the rural telephone cooperative movement. This was the introduction of a copper clad, later aluminum clad, coating to high strength steel core wire.
Additionally, the coating of copper and alumninum, afforded protection to the steel core, eliminating many problems associated with corrosion. Furthermore, theft of copper wire was virtually eliminated when copperweld conductor is strung, as the high scrap value of pure copper is mitigated.
Copperweld Bimetalics Group products could be specified and available for purchase with two differing types of steel cores: one a strong, heat-treated internal type for both the “High Strength” and and the “Extra High Strength,” while a low carbon steel was available for the “LC” grade wire.
What was even more important for the communications and power industries was the ability of several strands to be joined in lays to create multi-strand cable for guy wires, cable support strand, messengers for power distribution, and a host of other applications.
Aerial bare conductor could be selected and applied to systems based upon five major criteria:
Minimum Breaking Strength (MBS) is defined, based upon a legitimate testing program of various samples, is the minimum value of in-line tension required to break the wire.
Elongation is particularly important when studying the impact of climate upon spans of line wire between supports. The length of the wire is made longer by the stress of loads applied to the conductor, such as ice, snow, rain, wind, sleet or other factors. A physically unbalanced line, due to loss of a support from weather, a traffic accident or other event, can stress the strenth of line wire.
Elastic Limit. Line wire can only be stretched so far and for so much time before it is effected and suffers permanent and fatal collapse. Unless a tension of approximately 60% is applied in breaking strength to the line wire and exceeded, will either require physical “re-sagging” of the wire, or replacement of such spans affected. Another issue is clearance. If a line is permanently distorted, then traffic beneath the affected span, is endangered.
Temperature Coefficient of Expansion (TCE) is the effect upon the conductor with the advent of cooling or heating ambient atmospheric temperatures. Sags and tension of the existing line wire will be impacted by a unit length of the wire per degree of temperature variation. With improper sag resulting from these weather changes, both ground clearance and failure of the line conductors may be experienced.
Fatigue Endurance Limit (FEL). Defined by the REA as the “limit of undamped line wire, defined as the maxium stress that may be applied for an indefinitely large number of cycles ithout producing a beak, is expressed in lbs. per square inch of cross-sectional area of aerial wire.” What confuses many readers is that FEL is not to be confused with Minimum Breaking Strength (MBS). In MBS, the failure is due primarily to exceeding static tension alone. With FEL, both static stress and factors such as “aeolian vibration (wind),” in combination with each other.
F = KV
Where: F is in cycles per second
V is the wind velocity in feet per second
D is the conductor diameter in feet
K is an emperical constant of approximately 0.21
One benefit of brazed or soldered connections on the “LC” type of conductor was that weakening of the line wire through deflection or sag would not be affected.
Copperweld Bimetalics Group published a table demonstrating the physical and conductive properties of their conductor in regards to telephone open wire styles. For example, if we look at three major aerial wire catagories in exchange and transmission wire plant we see:
For 104 mil line wire (bare solid Copperweld Bimetalics Group Wires) both HS and EHS types:
With a diameter of .1040 of an inch, its breaking load in lbs. at 40% conductivity: 1,177 lbs and at 30% conductivity: 1,283 lbs. At EHS around 30% conductivity: 1,325 lbs.
The weight of EHS at 1,000 ft. is 30.01 lbs and at one mile per length: 158.5 lbs.
The resistance of 104 mil line wire was 2,445 ohms per 1,000 feet at 40% conductivity; and at 30% conductivity 3,260 ohms per 1,000 feet.
For 128 mil line wire (bare solid Copperweld Bimetalics Group Wires) both HS and EHS types:
With a diameter of .1280 of an inch, and a 40% conductivity level, the breaking load in lbs. was 1,647. The breaking load in lbs for 30% conductivity in EHS for 128 mil wire 2,188 lbs.
The weight of 1,000 feet of 128 mil line wire was 45.47 lbs. Per mile the weight totalled: 240.1 lbs. per mile.
Resistance in ohms per 1,000 feet at 68-degrees ambiant temperature was 1.614 at 40% conductivity and 2.152 at 30% conductivity per mile.
For 165 mil line wire (bare solid Copperweld Bimetalic Group Wires) both HS and EHS types:
With a diameter of .1650, the breaking load in lbs. at 40% conductivity was: 2,523 for High Strength line wire and 2,780 lbs. for 30% conductivity line wire.
Weight of 165 mil line wire per 1,000 feet was 75.55 lbs and a full mile of the stuff was 398.9 lbs.
Resistance in ohms pwer 1,000 feet was .9715 for 40% conductivity level and 1.295 ohms for 30% conductivity.
This information was taken from “Tables of Physical Properties,” Copperweld Wire Tables and N.E.S.C. Loading Tables; c. 1977. Bulletin: E.D. 1899.
By the 1960s, some telephone companies had adopted, with some success, the aluminum-covered steel wire. With one third the conductivity and eight times the strength, this aluminum welded wire carried with its application significant corrosion resistance for an operating telephone company.
In the Copperweld Bimetalics Group advertising of the period, this aluminum welded conductor was marketed to utilities with the unique property of a ductile and permanent weld, due to a unique manufacturing process. This process “provides a thin ductile diffusion zone between the two metals which permts the bimetallic rod to be cold drawn to wire sizes . . . be[ing] formed . . . without danger of the bond being destroyed or damaged.”
The fatigue-resistant nature of this line wire made it popular in sea-side districts of both coasts, where open wire was strung. Because Copperweld Bimetalics Group guaranteed their wire against surface flaking and peeling, it was clear that they did not use the traditional hot-dipped process of cladding aluminum to steel. The layer laid was a much thicker one, which during tests in marine environments, proved that it was nearly identical in performance over years of use as that of a high purity aluminum Alloy 1350 of the same diameter.
The Rural Electrication Administration (REA) and later the Telephone Borrowers Division of the Rural Utilities Service (RUS), allowed only certain types of bare open wire conductor for use by cooperatives:
The attraction of rural telephone borrowers to these types of conductors were long span application use, the fact that galvanized steel wire could be specified for use with any of the three classes of zinc coating. Copper-clad steel wire also demonstrated to REA Engineering folk that it could be requested in various strengths and conductivities. The “skin effect” of copper-cladded steel wire could render a line with nearly the conductivity of pure copper, if care was taken in shipping and construction use of the product. High frequency carrier systems easily took advantage of this operational characteristic.
Line wire selection criteria included not only a differentiation between copper-clad aerial wire, galvanized steel or aluminum-clad conductor types, but demands of service vs. aerial wire types. For example, toll and EAS trunk circuits, with their special circuit designs, were not recommended to be placed on galvanized steel conductors of any guage. If carrier was to be placed on these circuits then it was essential that copper-clad and aluminum-clad conductors be selected. Additionally, for low frequency voice circuit use, galvanized steel did not impose a significant quality of sound problem.
The Skin Effect
In designing telecommunications openwire transmission, exchange and local loop plant, the “Skin Effect” is a genuine phenomenon and is associated with both voice frequency circuit transmission and high frequency transmission. But first, we need to explore the electrical physics associated with a simple openwire pair.
Let’s talk first about “Ohm’s Law.” We have a single pair wooden bracket lead serving eight farms and some acreages beyond a city limit. It is a simple party line circuit using high strength steel wire and runs for about five miles. This three-mile line has a d.c. resistance of 10 ohms per 1000 feet of wire. To find this we take 15,840 feet (3 miles) X 10 (ohms)/1000 (feet) = 158.4 ohms for one conductor; however, we have a pair, so we multiply 158.4 x 2 = 316.8. Now you have the TOTAL resistance of this small lead.
Because we call the dedicated pair from the subscriber to the central office and back again a “local loop,” this resistance we’ve determined in the previous paragraph is called “ohms per loop mile.” This is how we find the d.c. resistance of this particular bracket lead.
Now, our little party line doesn’t carry phantoms, nor carrier, so it is a relatively easy line to design. However, let’s say the pair we’ve designed for resistance is part of a longer lead–say a ten pin arm pair–and carries high frequency carrier.
Here’s the rub. On a typical exchange lead, with say two ten pin arms and some brackets below, these circuits have O-Carrier on the top four circuits. Since carrier is an alternating current combined with d.c. circuits (the two never mix), resistance distributed along the line will depend upon the frequency of these currents. Add to that, the sizes of conductor used–and these might be significant if miles from the central office–with many splices, adding further to the resistance. Thus, we find that the higher the frequency of an a.c. current the more current wants to “hug” or travel along the outside surface of the conductor, and less does it want to run down the center of the line. “R” the series resistance of this telephone pair will be greater than its d.c. resistance to the voice frequency currents.
Conductors And Their Characteristics On Open Wire Lines
Let’s talk a little about a conductor–not on a train–or leader of an orchestra . . . although in the latter, it is the conductor which carries the music of speech, so to speak.
If you were a GTE, REA-affiliated telco association, Independent or Bell company outside plant engineer, it was important to specify the proper conductor for the need of the particular line you were designing. It’s important to have all the facts, so that in the estimate sheet, ordering will be less haphazard and potential for mistakes limited.
So, we have a selection of line wires to choose from. Sizes of line conductor (wire) are based on the various needs and we’re going to simply limit our choice to the most widely specified conductors by the telcos when it came to open wire plant.
Some of the sizes of line wire were:
083, 109, 134, 165, 203 – for various types of steel wire (Steel line, H-steel line, E-steel line)
080, 104, 128, 165 – for various styles of copper conductor
080, 104, 128 – for various copperweld conductor types
To give you an idea of the weights involved–whether you were putting it up on poles, or as a linewrecker, deciding how much vehicular load you were needing to cart it away, here are some facts.
083 type steel line is about 99 lbs. per mile. Doesn’t weigh much, about .019 lbs per foot. But you have to order it in coils of one half mile which consists of a 50 lb coil for a half mile. Pretty hefty! In feet per pound it isn’t much: 53.3.
Now, take 109 steel line, which is used for a lot of old farmer bracket leads–a very common diameter guage: as a little thicker wire, it is 170 lbs. per mile and a little more per foot, say .032; pounds per foot is 31.1 and one half mile will be 85 lbs. in a roll with an inside “eye” diameter of 19 inches.
Let’s say we are building an exchange line between two small towns. Let’s specify our linewire: 134 steel line, which is 258 lbs. per mile, .049 per foot lbs., about slightly over 20 feet per pound and purchased for one half mile rolls–which is a hefty roll: 150 lbs. Let me see you pick that up and throw it in the trunk of your car!
On a major toll lead, selection of steel line conductor might require a little longer spans and greater strength. We’ll use the 165 sized diameter guage. It is 390 lbs. per mile! .074 lbs. per foot, and 13.5 feet per pound with a length of a half mile roll weighing in at almost 200 lbs.!
Copper is another animal altogether. On a hard-drawn copper conductor of let’s say, 080 diameter guage, it is 102 lbs. per mile; about the same as .083 steel, at .019 lbs. per foot, 51.7 feet per pound, and is available in a roll not quite the length of a mile, say .83 of a mile. Weight is slightly more than a comparative steel wire, at 85 lbs. a roll.
Again, we’ll use 104 diameter copper conductor: it is 173 pounds per mile, .033 pounds per foot, 30.5 ft. per pound, available in lengths over a mile: 1.07. A roll of this stuff weighs in at 185 lbs. Try to lift that into your car trunk!
128 is again a little more, at 262 lbs. per mile, .050 pounds per foot, 20.2 feet per pound and available at about .71 of a mile in rolled shipping length. It weighs the same as the 104 in a single roll.
165 is used for high grade, high frequency carrier toll systems. The Nevada Transcontinental Line used this, and so did the Council Bluffs to Sioux City, Iowa 7-armed toll lead. Let’s look at its stats:
435 lbs per mile, .083 lbs. per foot, 12.1 feet per pound and available in a big roll not quite a half mile: .42 of a mile. This big coil would weigh in at exactly 100 lbs.
Copperweld made by the Copperweld Bimetalics Corporation is a registered patented linewire incorporating the conductivity characteristics of copper but coated very lightly on a high strength steel core. This gives it conductivity as well as great strength over long span construction. Say, through mountains or rugged terrain.
Let’s see how this Copperweld-type conductor stacks up against the other styles of conductors.
080 sized Copperweld is about 93.5 lbs. per mile, .018 pounds per foot, 56.5 feet per pound, 1.07 of a mile in coiled lengths. Total weight of coil? 100 lbs. Not bad!
Let’s try 104, a very common bracket lead conductor? 158.5 lbs. per mile, .030 pounds per foot, 33.3 feet per pound available at over a mile in a coiled length of 200 lbs at 1.07th of a mile.
128 is a carrier-type conductor and for pounds per mile, it comes in at 240, .045 pounds per foot, 22.0 feet per pound, .83 of a mile. Rolled into a coil, its weight is about 200 lbs.
If you noted above we provided two key items of knowledge to the I & M (Installation & Maintenance) personnel (the guys and gals who put up this stuff): the inside coil diameter, which is standard: 19-inch “eye” and the weight of the roll.
Now you may roll your eyes at 200 lbs for a single roll, but when you are spinning out openwire for a toll lead’s, or smaller exchange lines’ construction, you are not spinning out one conductor at a time–you are spinning out four (4!) at a time. By doing this you are compounding the amount of labor in less time, equalizing the balance of the pole structures on the weight to be evenly distributed, and maintaining spans at equal drops. Your device for drawing wire consists of placing spools on a trailer which pays out the conductor from the terminal pole to the field at the construction site.
Splices and Wire Termination Devices
Line wire, bridle wire taps, splices and dead-end devices…
Note Hemingray Toll Insulators and simple tie arrangement. Photo by D. G. Schema.
Let us transition from the evolution and history of line wire evolution to the simple act of joining two line conductors together. Sounds simple, right? Every cable reel has an end and so it was with bare open wire line conductor.
The term “Western Union” splice says it all; namely that this formerly mamoth communications organization, devised the most common and perhaps oldest, splice for aerial wire. And . . . for many decades, it was an effective splice for line wire. This style of joining conductors endured until around 1906. It was around that time, some ardent telephony engineering types, decided that for both purposes of physical resiliancy as well as improving the sound quality of open wire systems electrically, it was time to turn a corner on splicing.
There were thoughtful telephony personnel in many independent telcos who aimed their trusty soldering equipment on improving the Western Union type splice so as to create a much more substantial joint. One of the first in Iowa, at Clarinda, sought to make their independent telephone company one of high transmission sound and reception quality by literally . . . soldering . . . all their open wire splices. In fact, this independent telephone company was known for its high business and technical reputation over many decades. It wasn’t until 1965, that the family owning it, sold out to GT&E.
By the early 1900s, the “shotgun” approach heralded a better means to join two (or sometimes three wires) together at a point. This was the “double barreled” parallel sleeve assembly which could mate two similarly sized conductors and then by use of a tool, the Sleeve Twister, build a pretty impressive simple compression joint.
Double barrel shotgun style twisted splicing sleeve.
109 aerial galvanized steel wire with double barrel type twisted splice. Photo by D. G. Schema.
One problem associated with galvanized steel line wire, as opposed to hard drawn copper, was the marring and scratching of the zinc surface of the steel, allowing rust and subsequent corrosion to begin. With two dual tubes, which covered the ends of the line wire for a significant length, any scratches would be covered and consealed. The paralleling of the two conductors with an overlay, also made the joint actually stronger than the actual line wire itself as opposed to previous mechanical hand splices which actually placed a “weak” link in the line wire at point of splice.
These twisted sleeve type joining techniques worked pretty well . . . until the advent of carrier systems and their attendant high frequency attentuation sometimes associated with bad splices, dead-ends and other potential sources of interference. Customers demanded a higher quality of sound transmission and reception. Telephone transmission engineers also were engaged in a battle over resistive unbalances in open wire circuits. Each twisted sleeve created these imbalances, which were usually marginal in effect, but added in total to a 200 mile toll lead, became an accumulative problem.
The test board personnel also did their best to locate faulty splicing, however when the surface of the conductor or splice itself, protected with a thin film of anti-corrosive material was abused by contact with trees, buildings or other physical objects, problems began to re-occur. Additionally, just the act of a lineman’s moving a connection, could cause further problems.
Many telephone companies found themselves judiciously inspecting these Western Union splices and double barrel sleeves for problems and subsequently soldering them for a firmer connection. The soldering would, for the near term, hope to eliminate higher resistance. These tactics served to correct unbalanced electrical resistance for the future, but raised significantly the labor costs required to correct the problem. There had to be a better solution.
Perhaps the first compression-type, non-twisted, non-soldered, aerial wire joint, was that introduced in 1927. By creating a “gas tight” connection between the sleeve and the conductor, little if any moisture could permeate the splice containment and cause resistance problems or corrosion. Additionally, when traditional splices had been cut out of old circuits due to problems, it was often found the circumference of the existing line wire had been corrosively affected–hence the line wire was now of a smaller size than when originally strung. With connectors introducing this new compression joint, the centers could be enlarged to accomodate older wires reduced in size by corrosion. Where line wires were of the same diameter to be inserted to the sleeve, the term “combination” was applied. “Maintenance” sleeves were those used when line wires had been reduced by rust and corrosion.
Where copper conductors were to be joined, the interior of the tubes were made from soft copper which could be compressed with a lineman’s tool. Where galvanized steel line wire was applied to these “rolled” splices, a softer steel material allowed joining. Around the outside of the splice was a layer of zinc, to combat corrosion.
Where bridling runs were joined to sleeves, annealed brass was used. Brass also afforded a higher tolerance for lines under tension and gripped the conductors well.
The Sleeve-Wire Guage
The “B” Bell System Sleeve-Wire Guage
Every I & M employee has to have a guage! Well, when working with open wire, that was. Before we enter into a lengthy discussion about joints within open wire lines, we need to talk a little about this pocket held measuring device. Every teleco construction guy had one in his pocket and was a common issuance in all communications companies working with open wire construction. In the Bell System they called it a “B” Sleeve Wire Guage. Whatever the name, this guage would quickly furnish the proper information in order for the compression connector to be chosen for use joining two line wires together. Can’t have them loose!
The sleeve guage, no matter who issued it, was used primarily in two functions:
Does your existing, but corroded copper line, have sufficient diameter to make a clean rolled joint with the specified copper sleeves available?
To confirm whether or not your Sleeve Rolling Tool has become too worn to properly roll good sleeve joints.
In the World War II and immediate post war days of the 1940s, the telcos used a useful–however slightly ungainly–device called the Rolling Sleeve Tool. It is pictured below:
This is how it was used:
Use an abrasive medium to clean the ends of the linewire until bright and shiny on the surface.
Take the mechanical sleeve joint with one hand and shove the linewire which has been cleaned to one inch into one end. Sometimes it is not easy to do by hand and a tool, such as a wire cutter can hold the sleeve unerringly.
Nick and deform the sleeve with the cutting pliers at the midpoint about 1/4 inch from the outer ends; this will secure the one wire inside without pulling out.
Take your other conductor and repeat the same process.
Now it is ready to be rolled. Take the ratchet wrench and turn it so the flat portions of the rolls are opposing one another.
Push on the roll stop and turn the wrench until the roll stop slides into position without spinning the wrench.
Hold the tool beyond the sleeve ends and place the open wire line between the flat areas of the rolls using the properly sized sleeve connector.
Release the roll stop which will ensure an air-tight connection and centered in the groove.
The sleeve should again be rolled by operating the ratchet with some force, but not overdoing it.
A straight and non-distorted sleeve should be the result.
The Nicopress Tool
No. 31-QC Nicopress Sleeve Pressing Tool
By 1947, a new tool had succeeded the rather awkward press type mechanism illustrated above. The use of pressed sleeve joints was preserved for open wire lines, but the tool changed. This was a tool called the 31-QC in some Bell System quarters, or Nicopress tool to others. Its actions were easily understood and with proper practice, could provide similar compression splices easily without the mess and fuss of the old tool.
How the Nicopress Tool Was Used
The Nicorpess Sleeve Pressing Tool was made by the National Telephone Supply Company, and appears similar to a pair of bolt cutters. The action was simple:
Bring the handles together and the groove in the jaws brings great pressure on the sleeve and wire within.
The tool is designed for several different types and sizes of linewire sleeves. There are two grooves: the “Q” groove will take sleeves with could be rolled in the middle groove of the standard sleeve rolling tool outlined above. However, to best the tool above, there was a second insertion point: the “C” groove which can roll smaller diameter line wire.
Let’s make a joint!
Clean the ends of the line wire to a shiny texture first
Check the line wire dimensions, using the little guage above
Select the properly designed sleeve for the wire guage used
Place the end of one wire into the sleeve–the modern sleeves introduced in the late ’40s, incorporated a permanent “stop” inside the new sleeves to limit the wire’s exposure inside the sleeve
To secure the wire on the sleeve, use your side cutter pliers to make an indentation about 1/4 inch from the sleeve’s center, this won’t allow any play within the unit
Add the second wire to the opposite bore on the sleeve, repeat
Continue using your wire cutter to compress the joint
Don’t make a partial press on the sleeve ends but use the tool with a consistent pressure so that the compression joint looks like this:
Now you have the line secure and the completed splice should have these marks.
By using the B-Sleeve Wire Guage, check the indented portions of the completed compression joint. It should enter the guage without much clearance left. This is not done with every compression sleeve, but should be practiced every couple of sleeves to ensure the tool is properly adjusted so that it is consistently applying pressure to each joint.
If the guage shows some inconsistency in pressure and collapsing of the compression splice, then it may be time for the tool itself to be adjusted. When you bought this little tool, an Allen Wrench was supplied with it. You simply loosened the locking screw after a couple of turns, then in a clockwise way, turn the adjustment screw just slightly–checking with a guage to ensure it is accurate. By using a junk piece of line wire and using the guage, will ensure it is perfectly adjusted back to its manufacturing status. If you do not find this first adjustment works, continue to turn the adjustment screw a small amount each time juntil the compressed sleeve with just pass into the guage slot. When the correct adjustment is obtained turn up the locking screw HARD so that the tool will hold this new adjustment.
Sleeves for accomodating differing sizes of conductor. These were used primarily for connecting drop wire, bridle wire runs and regular line wire. Note 1950s prices.
Conductors which were common galvanized type utilized this splice style.
Conductor sleeves for jumpers at dead-ends.
Multiple compression splices on wooden bracket construction view. Photo by D. G. Schema.
Galvanized steel line wire compression splicing on crossarm pairs.
Sizing the proper sleeve for the conductor to be compressed and spliced.
A Chinese Puzzle Made Practical
Remember this technique as a toy when you were young?
The Wire Link
Remember the old Chinese puzzle game where you stuck your fingers in each end of a tube? When you slowly drew your fingers out, the device tightened around your finger and made it impossible to remove your much needed appendages?
Well, this playful gimmick was made practical in a number of ways, the least of which was this little patented device called the “wire link.” While these were not seen in great abundance on open wire lines for joining the ends of conductors, they did play a role in later 1950s construction and into the 1970s, when the Bell and Indendent telcos removed their open wire outside plant medium.
Here’s how it was made and works. First of all, it was used only on 109 steel wire, so that limited its use to farm service station bracket leads and a few exchange lines. It was basically a shell of aluminum tapered at the ends and about five and a half inches long. Once you stuck the cleaned ends of a line wire in either end and pulled that conductor was there . . . forever! Obviously, they were not reusable, and once you made the connection, or made a mistake, they simply could not be removed from the line without simply physically cutting them out.
One of their drawbacks was use in contaminated areas. So forget about installing them on sea coasts, industrial areas or places where lots of water was present. The insides would rust and decay.
However, for the majority of rural areas across the United States, they performed an admirable place in maintaining the line wire in place despite strong storms and lots of other climate foes.
To install the little wire link, you had to completely clean the cut ends of the line wire so that any rust or galvanizing was clear. The wire would appear shiny on the surface to about one inch. Then you inserted the wire ends to a physical stop inside the link. Then pull back on the wire hard! This would lock the jaws of the little device making it IMPOSSIBLE to remove the linewire. On the other side, you repeated the operation so as to make both line wires meet within the wire link.
Pretty nifty little device!
S-type connectors to join line wire with bridle or other line wire.
1890-1910 means of using two piece transposition insulator for dead-ending.
Single piece HG 1890s (left) and Two-piece AT&T transposition (right). insulators. Photo by D. G. Schema.
Using single Pony-type insulator for loop dead-ends and bridling run.
A typical 109 guage strand vice used by Northwestern Bell on open wire exchange circuits. See also the briding sleeve. Photo by D. G. Schema.
REA specifications for bridging connectors at c-type dead-end assemblies.
REA-accepted bridging connector sleeve from line wires to bridle wires.
Threaded connector tap nut and bolt for bare wire to bridling wire.
Tangent crossarm bridging connectors from line wire to bridling run.
Bridging connectors used on obsolete railroad lead.
Loop-type dead-ends for c-type spool bracket.
Steel line wire loop dead-ends for galvanized aerial conductor.
Continuous loop bail for spool-type deadends.
This “strand vice” was a smaller component of its larger brother used by nearly all utilities and railroads for dead-ending 6.6 strand as guy wire. Early versions of the guy attachment were prone to premature failure. Later versions are satisfactory.
Northwestern Bell four wire, exchange lead with BDE crossarm, C-type dead-ends and strand vice dead-end loops. Note the larger version of strand vice on guy attachment. Photo by D. G. Schema.
Series Inductance of an Open Wire Lead
Inductance is when one current flows through a coil of wire an opposing counter electromotive force is induced in the coil opposing the a.c. voltage. We call this electrical inductance. Now a telephone line may be of significant local loop length. Throughout this and other pairs, a current is flowing–which also may be changing in character because of its use and non-use–thus building an induced voltage along its length. In series, the Series Inductance(L), can be deduced by two factors: the guage of the wires and the separation. Remember we talked about W6 and W8 crossarm design. . . this is where such issues are important.
Hence, the inductance of the line will increase as the distance between the two wires increases; it decreases as the diameter of the wires decreases. In the telephone culture, we calculate series inductance in millihenries (mh) per loop mile. Here’s the calculation:
L = 2 TT F L
L is the Inductive Reactance (ohms)
2 TT is the constant, expressed as 6.28
F is the freqency (CPS)
L is the henries of series inductance
So for a long toll lead, the series inductance opposes the voice frequency and carrier traveling along the line because of its own inductive reactance properties.
Open Wire’s Capacitive Reactance
Like power transmission lines where air fills the distance and clearances between the energized phase conductors of an 115-kV H-Frame line combined with the metalic fittings on a suspension insulator string and the intervening dialectrics, such features act as “capacitors.” A telephone line, of much lower voltages and currents, also possesses such physical characteristics.
On an openwire lead, each pair is separated not only by air between the pairs, but air between pairs throughout the structure design. Just as air and porcelain in our above example act a dialectric with comparative energized conductors between, we have a simple capacitor. Capacitance is increased with the sizing of the conductors and when the distance between conductors is made closer.
Now, when you also add glass insulators at support points, the capacitance increases noteably. This occurs because the glass is an abruptly greater dialectric (or insulator) than the air itself. Glass doesn’t break down in a voltage arc as readily as air does. Because a multi-pair cable has no air separation and only plastic jacketed insulation is present with a high degree of closeness between the conductors, very high capacitance can result. This was unknown at the time the earliest cables were built and on which ignorance, these early cables failed in service (among other reasons).
Now our toll lead is composed of many, many pairs–sometimes as many as 40 pairs on an 80 wire lead. Capacitance becomes considerable when it isdistributed between the adjacent wire pairs above and below on arms within the structured medium of openwire construction. The combined capacitance of these various combinations of pairs is called the shunt capacitance.
Again, in calculating these lines, we use the letter “C” for capacitance. The amount of capacitance per mile results in what we call microfarads per loop mile. When we combine all these factors of all the various combinations of line and wire pairs in their immediate vicinity along a toll lead, their operation causes a capacitive reactance or Xc to occur across these wires.
. . . and you thought we were finished . . . ?
We talked previously about the insulating constant or dialectric constant. We know what insulators are: sometimes ceramic, glass, plastic, air, liquids like very pure mineral oil or PCBs, or vacuums.
But none of these are perfect insulators. In fact all can break-down under severe conditions of lightning, overvoltges and overcurrents, changes in their purity, contamination or mechanical failure. Water, for example, would be a near perfect conductor if it weren’t for the added chemicals and bi-metalic salts which permeate the liquid. Lightning can strike, flashing over insulators–literally blowing them up explosively–by exceeding their insulating properties. In oil, moisture can enter an apparatus tank because of a faulty seal, gasket or insecure bolting/welding of unit and cause the oil to break-down and flashover, causing insulation failure or case rupture.
And on that note, we proceed to our little open wire pair–either alone on a bracket lead–or among many of its companions on a 80 wire transcontinental line. The weather along most of its route might be very good . . . one day . . . and very bad the next. Here’s where telephone engineers had to battle the forces of nature. During heavy rains, snow, clinging sleet and ice storms and their aftermath, humidity and temperature changes markedly. Not only does the humidity cause leakage between the pairs through the air, but water on glass insulators furnishes a good path to the steel or wet wooden pin for signal strength to degrade and shorts to occur. For older cables, despite their protective sheath of plastic or lead or copper, humidity can enter, causing significant changes in the amount of leakage through the cable’s interior.
No openwire line is immune to these conditions, as aerial wire crossed various regions, urban and non-urban areas, industrial and rural, mountainous and desert locations throughtout the United States. This leakage issue dominated openwire design throughout its lifetime.
This leakage, or we will call it shunt leakage (G), is a shunt across the voice frequency telephone lines just as resistance acts upon these same wires. We call this part of attenuation, or loss, to a telephone signal. There is a simple way to determine the ohms per loop mile resistance for this shunt conductance:
What is Characteristic Impedance?
Our openwire lead could not operate properly if we ignored one of the most important characteristics of its design: characteristic impedance or:
This simple symbol denotes the combination of previously explored phyiscal issues associated with telephone design:
A line’s construction is based upon this final analysis. Despite whatever equipment might be placed on the line at the terminals, the length of the openwire lead, or interconnecting terminals, the characteristic impedance is independent of this. Because of the characteristic impedance of any openwire lead, this resulting calculation and derivative dictates to the telephone transmission engineer, the specific required values of equipment connected to the telephone line. Since the amount of power between terminals of a pair, the connecting equipment must have the same characteristics as that of your specifically designed line. For example, in the carrier world, the Bell System’s O-Carrier for 16-channel openwire carrier could not be re-used and connected to cable pairs. N-Carrier was the 16-channel system for cable pairs only. It could not be connected up to be used on openwire. The same for J-Carrier (12-channel openwire) and K-Carrier (12-channel multi-pair cable) could be said for this previous technology. Lenkurt 34A Carrier also was manufactured for only openwire and a companion technology for cable and so forth.
Carrier for open wire imposed some variables to this calculation. For example, a distantly served openwire toll lead might have 600 ohms at 1000 cycles. Because the frequency of the J-Carrier 12-channel system was high, the characteristic impedance was pretty high. So let’s design carrier for both the sending (C. O.) and receiving end (C. O.) of a long aerial toll lead. If the input equipment were 700 ohms impedance, then the output equipment must have a like number of resistance ohms.
We talked about attenuation in a telephone line–or the losses–it suffers when a speech pattern is transmitted through its length. A signal starts out at the C. O. with considerable strength. However, because of resistance, capacitance and inductance along this route, it seriously degrades. Current and voltage waves decrease with distance because of resistance along the conductor. This is Current X Resistance (IXR=voltage drop) along a circuit. This was theseries resistance we previously encountered in our discussion.
Also, we have “leaking” insulators, steel pins which conduct electricity much more fluently than wooden pins and perhaps wet wood arms with steel braces. This also prevents the signal from traveling easily the whole distance at full strength. We use a calculation which describes the power decrease from one end of the line to the other:
E x I = Power
Telephone openwire systems on long-haul transmission plant did not just go from terminus at one large city to a terminal in another large city. They passed through various towns along the way. Because the towns were spaced inconsistently, the toll lead would be broken into “line sections” whereby the various sections might be eight miles for the first, 15 miles for the second, 22 miles for the third, nine miles for the fourth and 28 miles for the last.
Telephone Transmission Engineers would design a toll lead so that the intervening sections would have uniform values. Naturally, an eight mile section would be different in electrical values from the 22-miles of toll lead in another. Because of this difference between each section, the final output at the far end terminus, might have severe attenuation–causing indistinct voice comprehension or a large degree of static and interference.
No Transmission Plant Engineer would allow this to happen and so corrective management was undertaken to prevent this problem and allow clear comprehension of speech.
Not Quite . . . “Warp” Speed . . .
Light travels at a breathtaking amount of speed–unhindered: 186,000 miles per second! When electricity travels along a power line at 60 cycles, the speed is slightly reduced–but no less exciting and invigorating a feat: 176,000 miles per second!
In telephone scale, things get up to speed quickly: an open wire line is NASCAR log 10 and over! In high frequency carrier systems, the signal moves at nearly the speed of unhindered light itself. This occurs with carrier signals over 4000 cycles. Higher speeds equate with higher frequencies; lower voice frequency waves move much slower.
The “skin effect.” Higher speeds are possible with the higher frequencies tending to “hug” the outside of the conductor. Lower speeds of voice-frequency systems whose amplitude and wave heights are not as frequent, travel through the conductor, suffering the effects of resistance.
Speech comprises a broad array of frequencies. These velocities differ dramatically with these patterns. For example, the speed of some speech velocities can reach almost 3,000 cycles–nearly the speed of light. But it can also be low, in the 200 cycle range on voice frequency (only) pairs. Carrier is the big dependent upon speed: various carriers comprise operating efficiencies from 4,000 to 132,000 cycles per second.
Echo . . . Echo . . . Echo . . . Effects
Ever listen to a conversation on a phone where your spoken speech is heard intelligently, but less audibly, as an “echo”? This is a result of a long telephone line with locations within its length where impedance is not the same in all sections. Lots of intervening activities cause this disturbance. Toll cable connections to openwire pairs at junction or terminal structures, changing wire guages with different technical values between sections, excessively long bridle wire runs, installed equipment without equalizing impendance between them.
This is what happens: the power carrying the voice signal or carrier wave travels from its C. O. beginning through a toll lead to a section point where there is a direct connection of a buried (in our little example, perhaps an ANTW-type) cable to an open wire terminal with bridling runs. The cable dips down the riser and comes up where a pedestal splice/with (or without) terminal is seen next to the pole. It in turn, is spliced into a 600-pair 19-guage copper cable which then feeds to the central office in that location. The power hits those rough points and not all the power is transmitted through to the buried cable and c. o. Some is bounced back or reflected back along the telephone line to the transmitting c. o. terminal. This is an echo effect. Sometimes this problem is termed “reflection loss.”
Since this small amount of power is reflected back to the C. O., it conforms to our previous discussion of power transmitted: that is, it consists of voltage and current waves. This is like a trough of water and swishing it back and forth as you lift up on either end. The received voltage and current is less, as it encountered some resistance traveling back towards the C. O. This lost power occurs because there is a mis-match between the impedance of the cable, bridle wire, other cable pair guage sizes and so forth. As in our previous discussion of end-to-end terminal-to-terminal design of openwire toll leads, equal impedance must be designed into that line section–matching apparatus’ impedance qualities as well.
Voice Signal Attenuation
In some systems, especially dense urban areas where many risers, connected cables and coax systems are introduced, it is not always possible to precisely match the impedance. This is where Echo Cancellers are installed in a central office. Now, just because openwire is no longer a medium for transmission technology for telephone, echo effects are still heard today. That is because translating from an electrical signal to converted optical signal on fiber and reduced back again to an electrical signal, can also subvert quality of speech. In fiber, all splices in a fiber cable are fused together–not connected with a crimping or tighening device as with wire. These glass fibers are hollow and hence the ends must be microscopically and with space-craft clean-room efficiency fused with lasers to make good connections.
However, that is not always supremely possible. Echo effects occur in fiber, too, because the light signal on a multi-mode fiber bounces along suffering both resistance and at points of connection, bounce or reflect back. That is called “reflection loss” in fiber–so you see, what has been learned in openwire directly translates to the modern era.
Reflection loss on openwire circuits is particularly aggrevating because:
Terminal Equipment received power is reduced
The distortion caused by the reflection and echo attenuates the speech quality.
Power Ratio and Decibels
Yeah . . . I know . . . more math–but meaningful to the Telephone Outside Transmission Plant Engineer. . .
N= 10 log ___
This is how we convert power to decibels. Yes, I know what a decibel is: basically it is common knowledge that this unit is defined as how we respond to sound waves through our ears.
Now, technically in telephone parlance, it is slightly a different matter. We use the term decibel in radio and telephone engineering based upon the amount of loss caused by one mile of standard copper 19-guage cable at a frequency of 886 cycles. Okay . . . ? But what about . . . open wire?
We use the decibel in both radio and wire communications (now also fiber) to express a basic ratio between:
E, I or Sound Level, or Power
When we amplify speech, or power, or sound, we use the term decibel. Since we don’t measure within our ear power per say, we do materialize the soundwave. That pecularity is reproduced in our head and translated into comprehensible language or tone. We measure the gain or loss of an openwire telephone line in decibels.
Back to our equation above. We need to design an openwire toll lead to conform to transmission characteristics which transmit intelligible speech at lowest loss ratios. Thus, the equation is based upon these constructs: Ndb: number of decibels; PI is the power (doesn’t differentiate between input or output); P2 is the smaller power. Log refers to 10 as a logarithm.
Here’s an interesting comparison between my lives with one foot in the telephone world and one foot in the power T&D domain: in my world of power distribution, for example, the losses of a 13.2-kV distribution feeder can be readily calculated through feeder instrument transformers and metering on its 60-Hz route. The frequency is always 60-Hz (and yes, there are some 50-Hz lines, too, but they are also inflexibly defined at that cycling).
With an ammeter and a voltage tester, it is possible to measure the current status of that distribution feeder quite adequately. However, with telephone systems, where the power levels are reduced markedly and the frequency is varied significantly, such measurements with these tools are not practical.
Can you imagine the difference between the load of a refrigerator on a 120-volt secondary to be compared with the output of your voice frequency? Substantially different in nearly all respects. When you speak into the phone receiver, your personal voice output is about 0.0001 watt! When you take that signal and transmit it to the far end of your caller’s phone, it becomes 0.000001 of a watt! This example used an openwire line around 9-10 miles in length.
Here’s the problem: due to the degradation of the line’s ability to transmit speech over long distances, the talking range decreases speech quality–although still comprehensible to the other subscriber.
But not all lines are within 5-10 miles of any subscriber. This is where the early telephone engineers sought to extend the practical limits of then openwire line construction to distant cities.
Now, loading coils or repeaters were inserted into the line connection, using inductance or electronic systems to “up” the signal. Then these decibels are amplified over 100 times with corresponding power levels increased.
Now . . . here’s where we get to the interesting part. Ever wonder where the term “decibel” was arrived at? The original unit was called the bel in deference to A. G. Bell, one of the telephone’s many inventors; dec (10:1) was the corresponding term preceeding bel to create the word decibel. Pretty neat, right?
Early engineers used the term bel on their calculations but found it to be too broad for practical use in their computations. That was because it was a ratio of ten to one. So it was decided early on to think of decibel as a unit of power ratio–not necessarily of power, per se.
I’m sure you’ve bought or seen stereo equipment or other audio equipment with the configurtion: –5 db or + 8 db? The minus (-) or (+) permutation signifies power loss or power gain.