larry@uunet.uu.net (Larry Lippman) (10/16/89)
In article <telecom-v09i0445m05@vector.dallas.tx.us> gentry@kcdev.uucp (Art Gentry) writes: > > 2. When one of those lines is damaged out in the middle of nowhere, > > and the damage is _inside_ the cable, how do they locate it? > > Moreover, how do they splice in a new piece of cable? In other > > words, how do they connect up those hundreds of individual lines? > > It would be like trying to rewire a spinal cord. > Ahhhh, back in the good-ol-days....:-} All the wires within a cable > are color coded, in pairs. In larger cables, pairs were grouped into > bunches, which in turn, were color coded themselves. So while tedious, > it was not overly difficult to match pairs in a splice. Many Telecom readers are, to some extent, familiar with the color code used on polyethylene insulated cables (PIC) in which each pair is individually color-coded and arranged in groups of 25-pairs, with these groups in turn being identified with colored binder strings. The above color code uses ten colors, and begins with white/blue for pair 1, white/orange for pair 2, white/green for pair 3, etc., ending with violet/slate for pair 25; binder group identification is made with colored tape or string using the above ten colors. The complete color code has already been posted by others to Telecom, and it is not my intent to repeat it here. The above color code with individual pair identification is used on both inside station wiring and outside PIC distribution cable. However, pulp-insulated cable does NOT have identification of individual pairs. There is still a significant amount of pulp-insulated cable in service, especially with high pair counts of 1,500 to 2,700 pairs. Pulp-insulated cable uses only three pair colors: white/green, white/red and white/blue. Binder groups within the cable come in sizes of 25, 26, 50, 51, 100 and 101 pairs, depending upon the wire gauge, pair count and style of the pulp-insulated cable. For cables with 400 or more pairs, the binder group size is generally 100 or 101 pairs. Each of the pairs in such a binder group has the SAME color code! As an example, a 404-pair pulp-insulated cable will typically have four binder groups: (1) 100 pairs of white/green plus a red/blue tracer pair; (2) 100 pairs of white/red plus a red/blue tracer pair; (3) 100 pairs of white/blue with a red/blue tracer pair; and (4) 100 pairs of white red with a red/blue tracer pair. The total pair count in this example is 404 pairs, and note that there are 200 pairs which have a white/red color code. The tracer pairs are generally reserved as spare or maintenance pairs. To make matters even more confusing, many pulp-insulated cables have no binder strings or tape! The binder groups have a twist which allows their identification as a unit, and the relative position of the binder groups when the cable is viewed in cross-section allows the identification of the particular binder group. Such binder groups are therefore arranged in concentric layers, with each layer being divided into binder segments. There are also umpteen different binder coding schemes used for pulp-insulated cable. For the sake of simplicity, while I am using the term "binder group" in this article, in reality I am referring to a cable "unit", which may in fact not have any binding strings or tape. As a result of the above, believe me, a damaged pulp-insulated cable is a real mess! Also, bear in mind that PIC cable did not come into general use until the 1950's, so prior to that time pulp-insulated cable was the ONLY type of outside plant cable. Restoration of a damaged pulp-insulated cable is performed by tone tracing or other electronic identification means on EACH AND EVERY pair. Restoration starts by picking a red/blue tracer pair as a means of establishing telephone communication between the cable splicer and the central office. At least there aren't that many tracer pairs to choose from. :-) The cable splicer cuts back the cable and attempts to identify the binder groups, starting with the CO-side FIRST. Picking one binder group at a time, a craftsperson in the CO sends tracing tone on the first pair in a binder group. A test probe with a sensitive amplifier is used at the cable site to detect this test tone and therefore identify the pair. Such a tone tracing arrangement works by capacitive coupling between the test probe and the cable pairs, so a cable splicer can rapidly scan for tone by merely brushing the test probe against fanned-out cable pairs. As soon as the CO-side of a pair is identified, the pair is placed in a numbered slot on a "restoral board", and a connection is made to the pair using insulation-piercing clips. A restoral board consists of two boards (a CO-side and a subscriber-side) with 100 pairs of insulation-piercing connections on each board, with several feet of cable between the two boards. The restoral board has two functions: (1) to temporarily tag the identified conductors of a binder group; and (2) to provide a temporary electrical connection prior to splicing of the CO and subscriber sides of the severed cable. More than one set of restoral boards may be used in a cable break, but it does get crowded around the splice area pretty fast! Identifying the CO side of the severed cable is the EASY part, made even easier with the use of a "front tap shoe" which connects to a protector block in the CO. A front tap shoe may make contact with as many as 100 pairs at a time, and using a test cable will conveniently terminate the pairs on a test panel used to apply tracing tone. There are also semi-automatic cable identification devices, like those made by Automation Products, which send a coded signal on each of 100 pairs, so that no craftsperson is necessary in the CO other than to change the front tap shoe to another 100 pairs. A cable splicer uses a field identifier unit with a digital readout to identify the pair number on a given pair in the binder group under test. After the CO side of the binder group has been identified using the above method, next comes the NOT SO EASY part. A second cable splicer then heads for the closest cross-connection box on the subscriber side of the severed cable. The first task is to establish a talk pair to the cable splicer at the break. Local battery for talking is provided by a cable-splicer's test set, traditionally the WECO 76C, although newer devices are now available. The second cable splicer then successively sends tracing tone across each pair at the cross-connection box, which the first cable splicer identifies at the site of the cable break. The identified pairs are then placed on the subscriber-side of the restoral board, which not only tags their identity, but makes a temporary electrical connection. What makes identification of the pairs on the subscriber-side of the cable break difficult is that it is unlikely that the full pair count of the cable will terminate at just one cross-connect location. A high pair-count cable may in fact have its pairs terminated at a dozen or more different cross-connection points, EACH of which will have to be visited in order to send tracing tone to the cable break site and identify the full pair count. Sometimes pairs never even terminate at a cross-connect location, but instead terminate directly at a large customer location - which is yet another place that may have to be visited. In most instances, none of the above tracing effort is necessary in the case of a PIC cable break, since each pair in PIC cable is by its very nature self-identifying through its own color and that of its binder group color. One does not truly appreciate this "feature" of PIC cable until one experiences the effort necessary to repair a pulp-insulated cable. Installing new pulp-insulated cable was not so difficult since at intermediate splices pairs in a binder group were merely joined at random. Identification was only necessary at termination points. An additional problem is that in most cases it is not possible to pull enough slack in a damaged cable to reconnect the severed pairs. A length of jumper pair wire is therefore placed in the splice, and now one has TWO splices for every pair: one for each side of the jumper. Yet another problem is that the sheath must be cut back at least a foot in each direction of the cable break in order to "visualize" and therefore identify the binder group placement. For a badly mangled cable it may be necessary to splice a complete length of cable between the severed ends since 2-feet is about the limit to the length of any one splice case. And to make matters even worse, how would you like to be a cable splicer doing this work 15 feet above the ground working in a small tent in sub-zero weather? A motor vehicle accident that knocks down a utility pole will create this exact situation! While a cable splicer's job has little glamor, it does have some excitement and some hazards, and it is just as essential as that of a switchman in the CO. One of the most common hazards in working with aerial cable today is electric shock from streetlight fixtures with a broken ground that are attached to a utility pole. In large cities with extensive underground distribution, telephone cables may often share manholes with high-voltage electric power distribution cables. The ultimate nightmare of a cable splicer is to accidentally cut into a power cable instead of a telephone cable; a lead-sheathed power cable is indistinguishable from a lead-sheathed telephone cable. Such an accident has in fact happened on more than one occasion over the years. In previous years the job of a cable splicer was more artisan in nature, especially involving the working of lead used to join the lead sheaths of cables and make splice cases. The ultimate display of "lead craftsmanship" was in the "wiping of a joint" which formed the rounded end of a splice case where the cable entered the larger diameter splice. While many lead-sheathed cables still exist, today there is very little hot lead work; lead cables are usually fitted into conventional two-part separable splice cases using sealing tape and a compression-type closure. In previous years, many a cable splicer has been burned from spilled molten lead or spilled hot paraffin (used to "boil out" moisture from damaged pulp-insulated cable). I'll close this article with an interesting bit of "cable trivia". First, some background. Many CO buildings still in use in large cities were constructed between 1915 and 1930. Such buildings have seen many generations of telephone apparatus and have been "modernized" on a number of occasions. New apparatus is always installed and wired before old apparatus is removed. Telephone cable in CO buildings is supported on "cable rack", which may be as wide as 24 inches. Cable is built up in layers, with the oldest cable being at the bottom of the cable rack; the bottom layer is laced to the cable rack with waxed twine ("12 cord", for the benefit of any WECO people reading this who have "paid their dues" :-) ). Each successive layer of cable is laced to the previous layer. It is not unusual in a large CO to have a SOLID mass of cable 2 feet wide by 2 feet high on a single cable rack. In the above situation, much of the lower "layers" of cable in a cable rack will be non-working cable which connected apparatus that was removed years ago. The labor necessary to remove such old cable is significant, so usual practice is to just leave the lower layers in place. As a shortage of wiring space develops, an operation referred to as "cable mining" is performed to remove the bottom layers of cable and re-stitch the upper, working layers back to the cable rack, thereby freeing up space for new cable layers. Cable mining is only done when absolutely necessary, so if space is still available it is not unusual for a cable rack to have bottom layers of cable that are 60 or more years old. Such a situation still exists today in many older metropolitan CO buildings. An interesting "environmental" problem has been "discovered" in the past 10 to 15 years which now dictates that cable mining be conducted with the utmost care. There are actually two problems: 1. Plastic sheaths for central office power and signal cable did not come into general use until the 1950's. Prior to this time cable sheaths were made from cotton or silk. In the case of power cable, some styles of cable were covered with an asbestos sheath to prevent accidental fires. While asbestos-sheathed power cable has not been used since the 1950's, much of this cable still remains on cable racks. 2. While it may be hard to imagine today, large CO's were periodically plagued with mice during the 1920's and 1930's. These mice would chew on cable, thereby causing faults. Mice particularly loved the area around cord positions at DSA and toll operator facilities; the mice like to run on the inside multiples of such cord boards. Crumbs of food brought in by operators would attract such mice. In an effort to control this mice problem, some brilliant WECO engineer (who in all fairness did not know any better) during the 1920's came up with the clever idea of impregnating the cloth sheath of central office and switchboard cables with ARSENIC in order to deter the mice from chewing the cables. As a result, some CO cable installed during the 1920's and 1930's contains arsenic. So, today, some cable mining must be carried out with the utmost caution in order to avoid the hazards of asbestos and arsenic! <> Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp. <> UUCP {allegra|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry <> TEL 716/688-1231 | 716/773-1700 {hplabs|utzoo|uunet}!/ \uniquex!larry <> FAX 716/741-9635 | 716/773-2488 "Have you hugged your cat today?"
tad@beaver.cs.washington.edu (10/19/89)
I enjoyed Larry Lippman's description of cble splicing and mining. Wasn't it a cable mining operation that set off the Hinsdale fire? Tad Cook tad@ssc.UUCP