INTRODUCTION TWISTED PAIR CABLING COLOR CODING JOINTING OF CABLES OUTLINE
INTRODUCTION A cable is two or more wires twisted together to form a single assembly. It is used in the telephone industry to connect lines from telephone exchanges to pillars and from there to distribution points (DP) and then to user sets, finally connecting subscriber lines with the exchange system. Cable used in telecommunication system The heart of cable is the transmission medium, which may be optical fibers or twisted copper wire pairs. A mechanical structure or jacket protects the medium against the external environment.
Underground laying of Cable Underground cables have pairs of copper wire paired with the help of color coding. For e.g. 5-pair, 10-pair, 20-pair, 50-pair, 100- pair, 200-pair, 1000-pair, 1200-pair wire etc. In 5-1000 pair, the thickness of copper wire is 0.6mm. In 1200 pair wire, the size is 0.4mm. INTRODUCTION Two types of underground cables laid in two parts between exchange and telephone set : - Primary cable (lies between main exchange and pillar) - Secondary cable (lies between pillar and distribution points or DP )
TWISTED PAIR CABLING I n twisted pair cabling two conductors are twisted together (forward & return conductors) for canceling out electromagnetic interference, noise etc. from external sources. The twist rate or pitch (twists per meter) is specific for given type of cable. Types of twisted pair cabling used – FTP (foiled twisted pair) STP (shielded twisted pair) UTP (unshielded twisted pair) UTP - primary wire type for telephone usage, it is not surrounded by any shielding. 1 st wire - "tip" connected to the positive side of the circuit 2 nd wire - "ring" connected to the negative side of the circuit It was introduced by Alexander Graham Bell in 1881.
COLOR CODING Color coding is a system in telecommunication wiring for identifying individual conductors in twisted pair of cables, using different colors. The most common is the 5 – pair twisted cable which contains five colors – Blue, Orange, Green, Brown and Slate for the ring wire and white for tip wire common with each ring wire making a total of 10 conductors. 5 – PAIR CABLE Each pair has five different ring wire colors but tip wire color depends on size of cable though common in one 5-pair set. The colors are applied to the insulation that covers each conductor.
COLOR CODING 10 – PAIR CABLE The next pair is the 10 – pair twisted cable which contains five colors – Blue, Orange, Green, Brown and Slate in two sets for the ring wire and white and red colors for tip wire of each set respectively making a total of 20 conductors.
COLOR CODING 20 – PAIR CABLE The 20 – pair cable has colors - Blue, Orange, Green, Brown and Slate in 4 sets for ring wire and white, red, black, yellow colors for tip wire in each set making a total of 40 conductors.
COLOR CODING 25 – PAIR CABLE The 25 – pair has similar four sets as 20-pair and a 5 th set with violet colored tip wire making a total of 50 conductors.
LARGE PAIR CABLE Large pairs cables include 50-pair, 100-pair, 800-pair, 1000-pair cables etc. They follow the same color coding repeating ring and wire colors for specific sets. For e.g. 200-pair cable -> 4 groups -> 50 wires each -> 5 sets -> 10 wires each -> 2 subsets -> 5 wires each -> 5 ring colors and one tip color for each subset. To more easily identify, which pair, a wire belongs to. Otherwise, one has to note which color codes are physically twisted together. BINDER GROUPS For cables over 25 pairs, first 25 pairs (called binder group) are marked with mylar ribbons using the color code starting with a white/blue ribbon, the second 25 pairs with a white/orange ribbon, and so on through the 24th binder group (600 pairs), which has a violet/brown ribbon, and forming a "Super" binder. The super binder is distributed in 100 pairs tied with a tip color coded ribbon. The pattern then starts over. COLOR CODING
JOINTING OF CABLES NEED OF A STANDARD Important to follow standard construction practices and good workmanship. Difficulties to maintenance staff in tracing circuits at the time of faults if joined haphazardly, also impairs the performance quality of the network Transmission properties can be maintained at satisfactory level when the conductor jointing is done in perfect 1:1 order. TYPES OF JOINTING Limited lengths available for different sizes of cables and occurrence of damage to working cables resulting in a joint or two called Straight Joint. STRAIGHT JOINT Operation on new or working cable made for diverting part of cable pairs to another direction / area resulting in a Branch Joint. BRANCH JOINT
JOINTING OF CABLES TEE OR PARALLEL JOINT Transfer the cable pairs of one area in exchange (old pillar) to another area (new pillar ) in same exchange or to transfer the cable pairs from existing exchange in the area to another exchange (area transfer) results in a Tee Joint or Parallel Joint. Old Exchange New Exchange JOINTING TECHNIQUE Same colored wires are jointed together by twisting them uniformly and dressing with a sleeve. Gel/grease is pasted over the whole sleeve. Then, polythene is wrapped over the greased sleeve which is again wrapped with tape to firmly hold polythene. Cable pair is fitted in klastar (aluminum metal holder), then covered with a black jacket. A metal channel is slided over the edge of the jacket and heated with a blow lamp to firmly fix jacket. This procedure thus joins two wires according to standards.