INDEX
UNDERGROUND CABLES
SERIAL
NUMBER
TOPIC
PAGE
NUMBER
1 INTRODUCTION TO UNDERGROUND CABLES
2 to 21
2 CABLE LAYING
22 to 38
3 CABLE JOINTING
39 to 70
4 CABLE TERMINATION
71 to 81
5 POWER TELECOMMUNICATION CO-ORDINATION
COMMITTEE AND PROTECTIVE DEVICES
82 to 96
6
PREVENTIVE MAINTENANCE &CABLE RECORDS
97 to 111
7 COMPUTERISATION OF CABLE RECORDS
112 To 114
8 FAULT REPAIR SERVICE, TRAI PARAMETERS
115 To 135
9 UPGRADATION & REHABILITATION OF
EXTERNAL PLANT, POLELESS SCHEME
136 To 150
10 INSPECTION PROCEDURE
151 To 160
11 TESTING OF CABLES, CABLE FAULTS &
LOCALISATION
161 To 172
12 QUESTION BANK FOR UNDERGROUND TELECOM
CABLE
173 TO 185
INTRODUCTION TO UNDERGROUND CABLES
Objective of the lesson:: This chapter provides the insight into the basic requirements of any
underground cable to survive the expected life period and needs. The chapter also deals extensively with the different types of cables in use in telecommunication networks and the parameters offered for various utilities.
1.0 BROAD CONSTRUCTION OF ANY TELECOMMUNICATION CABLE
• Core ::
All the insulated conductors compactly arranged in pairs, units and super units constitute core of the cable
• Moisture Barrier :
As the presence of moisture deteriorate the quality of insulation of the telecom cables, moisture barrier protects entry moisture into the core of the cable.
• Protection ::
Telecom cables require Protection
o from probable mechanical damages
o from water and chemicals or soil conditions o from Induction due to Electrical lines
o from diggings by different agencies and individuals o from damages while handling
1.1. THE CLASSIFICATION OF UNDERGROUND CABLES WITH REGARD TO DESIGN FEATURES ARE ::
Place where it is used - Underground / overhead / submarine Insulation material used - Paper / polythene cables
The filling compound - Dry core / jelly filled cables Mechanical protection - Armoured / unarmoured cables
System for which used - Co-axial / PCM
Type of conductor - Copper cable / Optical fibre cable Gauge of the conductor - 0.40 mm / 0.50 mm 0.63 mm / 0.90mm Pressurization of core - Pressurized / unpressurised cables
1.2 DESIGN FEATURES ::
Before discussing the above classifications in a nutshell let us know what are the purposes of the above Design features in a underground cables.
1.3 PURPOSE OF INSULATION UNDERGROUND CABLES ::
(1) The insulation is used to separate the conductors bunched in a unit to prevent short circuit between two conductors in a pair or between conductor of one pair with the conductor any other pair in the unit or core in the cable.
(2) The insulation is used as SHEATH to separate the insulated conductors from being corroded or eroded in soil.
(3) The insulation is being used for marking / identifying the pair or conductor in the unit and in the cable as a whole for that matter.
(4) The insulating material is used for preventing the grounding or earthing of the conductors. (5) The insulating material is used for preventing the corrosion of armouring .
RTTC, NAGPUR Page 3 of 185 Diagram 2 1st pair B Limb 3rd pair A Limb 2nd pair B Limb 1st pair A limb Insulating material PVC / PAPER
Annealed Copper
Conductors
Sheath LSDC / PVC C O R E Filling material Dry air / JellyMECHANICAL PROTECTION 2 LAYERS OF GI STRIPS
specific inductive capacity which is about 1.5. Its physical properties also enable large proportion of air as dielectric. The ideal dielectric for telecom cable is air which has specific inductive capacity of 1.0. The thickness, width and number of wraps per meter of insulating paper is selected to achieve the required mutual capacitance of cables.
The Polythene insulation is easy to apply and have desired electrical characteristic such as low dielectric constant, lo dissipation factor (loss) and high dielectric strength. Mechanically it is tougher than paper and has abrasion resistant with ample tensile strength and elongation. The insulating resistance measurement shall be measured with a DC voltage of magnitude not less than 500V after steady electrification for one minute. The insulation resistance values between each conductor in the cable and all the other conductors connected together and to the screen and earth shall not be less than 5000 Mega ohms / km at Room temperature.
( Cable length in Km x observed insulation in Mega ohms ).
1.4 Pairing and Overlay ::
Two insulated conductors shall be twisted together with uniform lay to form a pair. The length of the lay of any pair shall be different from that of adjacent pairs. The lay of various pairs shall be so chosen as to satisfy the capacitance unbalance requirements and cross-task requirement.
1.5 Unit Formation ::
The pairs are then assembled into units with different length of unit twists assigned to different units. These units are then assembled into a completed cable core.
1.6 Core wrappings are applied to the completed cable core to hold the units together and
provide high di-electric strength from core to shield and to protect the conductor insulation from damage due to the heat of sheathing operation. In PIJF cables hygroscopic and non-wicking polyester tape is used as core wrapping.
1.7 Filling compound ::
The cable should be filled with suitable water resistant compound which shall be compatible with the insulation, binders and tapes used in the cable. It shall be homogenous and uniformly mixed material containing an anti-oxidant. It shall not contain dirt, metallic particles or other foreign matter.
Paper insulated cables :: Dry air only Polythene insulated cables :: Jelly compound.
1.8 SCREEN ::
An aluminum tape coated with polythene / copolymer on both sides shall be applied over the cable core with a minimum overlap of 6 mm for all sizes of cables. The nominal thickness of the aluminum tape shall be 0.2 mm and that of polythene / copolymer coating on each side 0.05 mm.
The aluminum tape shall be sealed at the overlap and bonded to the inner surface of polythene sheath extruded over it. The tape shall be electrically continuous throughout the length of cable.
1.9 SHEATH ::
A moisture resistant , gas tight sheath must be applied to all the paper insulated cable other wise relative humidity conditions throughout will increase and insulation resistance will decrease. The sheath also protects the cable form damage during installation and service. The sheath shall be reasonably circular and free from pinholes and other defects. The variation between maximum and the minimum diameter at any cross section shall not exceed 5mm.
Paper insulated cables :: Lead sheath or Polythene sheath Polythene insulated cables :: Polythene sheath only.
1.10 CONDUCTOR::
Each conductor is a solid round wire made of annealed high conductivity copper of diameter 0.32 mm, 0.40 mm, 0.50mm, 0.63mm and 0.90 mm.
1.11 ARMOURING ::
In the armoured cables bedding and armour are provided over the sheath to be followed by jacket. Then the cables are called Armoured cables.
If this arrangement is not done then we call them as un armoured cables.
BEDDING
two close helical lapping of polythene or polypropylene tape is applied over the sheath to provide sufficient mechanical protection during armouring. Each take is applied with a minimum 5% overlap. The second tape will cover the overlap of the first tape evenly.
Nominal thickness of the Galvanised steel Tape armouring
Diameter of cable
over Polythene sheath Thickness of Steel tape
Upto 40 mm 0.5 mm
Above 40 mm 0.8 mm
Armouring is the application of two layers of galvanized steel tape both applied helically in the same direction with a gap in the first tape of 25% +/- 10 % of the nominal width of the tape, the second tape evenly covering the gap of the first tape. The overlap of the second over the first shall not be les than 15% of the nominal width of the tape on either side.
The standard armouring types are
Aerial tape armour Jute protection Burried tape armour Modified tape armour
Steel armouring and polyjacketing
1.12 Jacket ::
Most cables serve their lives with a basic sheath but after armouring the armouring is to be protected from getting rusty and corrosion and jacket is the protection which does the job. It should be reasonably circular, free from pinholes and other defects.
Nominal thickness of the Jacket
Diameter of cable over Polythene
Jacket Thickness of Polythene Jacket
Upto 46 mm 1.4 mm
Above 46 mm up to 64 mm 1.8 mm
Above 64 mm 2.2 mm
1.13 Identification and Length markings on a Cable
To enable proper identification of Telecom cables the following markings shall be embossed, engraved or printed on the polythene jacket in case of armoured cable and on the sheath for unarmoured cables. These markings are at an interval of one meter throughout the length and are distinct and visible to the naked eye from a distance of about 1 meter.
Telephone handset emblem Name of the Manufacturer Year of Manufacture
Capacity of the cable in pairs Size of the conductor
Length marking
1.14 Sealing of the Ends::
The cables will be sealed with thermo shrinkable end caps of adequate thickness after completion of all tests in factory before dispatching to various stores and workplaces directly.
2.0 POLYTHENE INSULATED JELLY FILLED CABLES ::
These are popularly known as PIJF cables and consist of twisted pairs of polyethylene insulated copper conductors.
Paper insulated cables (LSDC, PCUT, PCQT, PCQL & PCQL ) are the primitive underground cables that are used in the Telecommunications network. These cables are available up to 1800 pairs. Later on due to various factors like escalation in the cost of Lead and more incidence of faults due to paper insulation the Polythene insulated Jelly filled cables ( Popularly known as PIJF ) are used extensively now a days in the telecommunication networks. The PIJF cables are available up to 3600 pairs.
Some constructional features of Paper insulated cables are dealt in Job Aid – I, for academic interest and as still a few number of these cables are still serving some of the telecommunication networks.
The Pressurization of dry core paper insulated cables is now a avoidable feature as the replacement of paper-insulated cables with PIJF cables is nearing completion. As the PIJF cables are filled with Jelly as filling compound which takes care of prevention of entry of moisture / water into the core of the cable.
2.1 POLYTHENE INSULATED JELLY FILLED POLYTHENE SHEATHED UNDER GROUND CABLE (VIDE ITD S/WT -129 DT. 2.3.83 & ITD SPECIFICATION NO S/WT - 143 DT. 30.7.88 )
(a) Number of Pairs
The cables shall be in sizes 5, 10, 20, 50, 100, 200, 400, 800, 2000, 2400, 2800, 3200 and 3600 pairs.
(b)
ConductorsEach conductor shall be insulated with polyethylene of insulating grade. Different gauges of conductors 0.32mm, 0.40mm, 0.50mm, 0.63mm, and 0.90 mm are used in the cables.
Each conductor shall consist of a solid wire of annealed high conductivity copper smoothly drawn & circular in section, uniform in quality, resistance and free from all defects.
The average resistance of all the conductors in the cable shall not exceed the values shown in Table given below.
Nominal diameter of conductor Resistance per km per conductor at 20 0 C Tolerance on conductor Resistance Minimum elongation of conductor Min % conductor Resistance unbalance Attenuation at 20 deg C
in mm ohms/km Ohms /km percentage Average Db/km
0.32 223 - 15 1.5
-0.40 135 +/- 4 15 1.5 12.0
0.50 86 +/- 3 15 1.0 8.25
0.63 58 +/- 2 18 1.0 6.30
0.90 28 +/- 1 18 1.0 4.40
2.1.1 The Percentage of Resistance Unbalance of any individual pair tested shall be
calculated as follows::
Percentage of Resistance Unbalance =
Where R1& R2 are the resistances of individual conductors of pair under test and R1 > R2
RTTC, NAGPUR Page 7 of 185
( R1 - R2 )
x 100 R1 + R2
Attenuation at 20 0 C =
2.1.3 CORRECTION FACTOR FOR CONDUCTOR RESISTANCE ::
Temperature in deg C at which
conductor Resistance is measured 10 20 30 40 50
Multiplier constant for conversion to 20 deg C 1.041 9 1.000 0 0.962 2 0.927 1 0.8945 (c) Insulation
Each conductor shall be insulated with solid medium density polythene of density 0.926 to 0.94 to a thickness. The insulation should be uniform, smooth and free from all defects. The insulation will have following color for identifying pairs /conductors under normal lighting conditions.
2.1.4 CODE FOR WIRE IDENTIFICATION
Primary colors Secondary colors
For 1st wire in a pair For 2nd wire in a pair and binder tape of unit in 50pr/100pr unit White Blue Red Orange Black Green Yellow Brown Slate / Gray
(c)
UnitA number of twisted pairs laid up to form a group shall constitute the unit. The color scheme of pairs and wires in a unit shall be read as below.
2.1.5 CODE FOR TAPE OR BINDER FOR UNIT IDENTIFICATION
Unit number 1 2 3 4 5
Color of Binder Blue Orange Green Brown Slate / Gray
2.1.6 CODE FOR CONDUCTOR INSULATION Pair No Color
First Wire Second Wire
1 White Blue
2 White Orange
3 White Green
4 White Brown
5 White Slate / gray
6 Red Blue
7 Red Orange
8 Red Green
9 Red Brown
10 Red Slate / gray
11 Black Blue
12 Black Orange
13 Black Green
14 Black Brown
15 Black Slate / gray
16 Yellow Blue
17 Yellow Orange
18 yellow Green
19 Yellow Brown
20 Yellow Slate / gray
21 Natural Blue
22 Natural Orange
Note:
(a) In 5 pair cable, color code specified for pairs 1 to 5 above is used.
(b) In 10 pairs cables and 10 pairs units of 50 pair cables, color code specified for pairs 1 to 10 is used.
(c) In 20 pair cables and 20 pairs units of 100 pair cables, color code specified for pairs 1 to 20 shall be used.
(d) The number of the pairs with respect to the color scheme is only for the purpose of identification of pairs, the actual numerical sequence of the pairs varies as the size increase.
The different colors of the binder shall be readily distinguishable under normal lighting conditions.
(e) Stranding
A 50 pair cable consists of 5 number of 10 pair units A 100 pairs cable consists of 10 number of 20 pair units.
These units shall be stranded into a compact and symmetrical cable. the sequence of the units in the cable shall be same throughout the length of the cable.
An open lapping of 0.02 mm miler tape of any other suitable material of appropriate thickness shall be applied for each unit.
The tapes shall be so colored and have lay not exceeding 200 mm. This tape is not necessary on the 5 pairs, 10 pairs and 20 pairs cables.
RTTC, NAGPUR Page 9 of 185
C
B
A
above table .
In the case of 100 pair cable, 2 spare pairs shall be provided. the color of the pair shall be as specified for pair No. 21 & 22 of above table. The spare pairs in the case of 50 pairs and 100 pairs cables shall be provided within the cable core, but shall not be within any unit.
The 200pair and 400 pair cables ( cables above 100 pr and unto 400 pairs) will be formed by super units of 50 pairs. and the units stranded in the form of layers
The cable over 400 pairs is formed be the super units of 100 pairs and the units stranded in the form of layers.
Identification of 50 pair super units in cables of 200 pair and 400 pair & 100 pair super units in cables of over 400 pairs
Position of the unit in the layer Color binder
First (Marker) Red
Intermediate White
Last (Reference) Black
Note:: The numbering of the units will be clock wise as running end.
Different configurations of PIJF cables availability is given in table.
Cable
size No of Units / Super units
Nominal length in a drum
In pairs Centre layer Middle Layer Outer Layer 0.50mm 0.40mm
5 1x5 (unit) 1000 -10 1x10 (unit) 1000 -20 1x20(unit) 1000 -50 5x10 (SU) 1000 -100 5x20(SU) 500 -200 4x50(SU) 400 -400 2x50(SU) 6x50(SU) 400 -800 2x100 (SU) 6x100 (SU) 200 200 1200 3x100(SU) 9x100(SU) 200 200
1600 1x100(SU) 5x100(SU) 10x100(SU) - 200
2000 1x100(SU) 6x100(SU) 13x100(SU) - 200
2400 2x100(SU) 8x100(SU) 14x100(SU) - 200
When required the cable sheath shall be armoured. For armoured cable a close helical lapping of waterproof cotton tape shall be applied over the inner-sheath. The cable shall than be armoured with two applications of galvanized steel tape each applied helically with a gap of 25% + 10% of the width of the tape, the second tape covering the gap of the first.
(g) Overall Polythene Jacket
A tightly fitting jacket of polythene shall be applied on the armoured cable. The minimum thickness of the jacket shall be 1.2 mm.
3.0 USES OF DIFFERENT TYPES OF CABLES
Gauges 0.32 mm and 0.44 mm for primary cable. Gauges 0.4 mm and 0.5 mm for secondary cable. Gauge 0.5 mm and 0.63 mm for distribution cable. Gauges 0.63 mm and 0.9 mm for distribution cable.
Higher gauges of cable for distribution side having longer lengths. Unarmoured PCUT cable to be laid in duct and to be pressurized.
Armoured jelly filled cable may be laid direct in the ground and and Unarmoured jelly filled in Ducts not to be pressurized.
4.0 DISADVANTAGES OF PAPER INSULATED CABLES WITH POLYTHENE INSULATED CABLES
4.1 Numbering of pairs is in coded form. Require more skill. Color markings also fade with due course of time.
4.2 Jointing of cables require skill and perfection is required while plumbing as even a slight pinhole will cause entry of moisture / water and damage all the pairs.
4.3 Extra care is required for handling like coiling, uncoiling to avoid damage. 4.4 Water / moisture entry will affect the complete cable at once instantaneously. 4.5 Termination in cabinet / pillars / DPs and at MDF is very expensive and time
consuming & increases number of joints.
5.0 ADVANTAGES OF POLYTHENE INSULATED JELLY CABLES.
5.1 Counting of pairs is easy and human mistakes are avoided. 5.2 Jointing is easy and require no chamber or additional place. 5.3 Failure of joints is less.
5.4 Entry of moisture / water is prevented by Jelly in the core.
5.6 Handling of cable is easy not delicate like paper insulated cables. 5.7 Life of cable is more.
NOTE :: The systems used in our telecommunication underground network other than PIJF cables are discussed in brief at the end of this chapter.
6.0 CO-AXIAL CABLE
in a lead sheath. The cable is recognized with 1. Number of cores i.e. either 2 core or 4 core
2. Size of the inner diameter of tube - r i.e. 0.375 type ( large tube – 0.375” ) or 0.174 type (small tube – 0.174”).
The interstice Quads or pairs having diameter of 0.9mm TWO CORE 375 coaxial cable
7.0 OPTICAL FIBRE CABLE ::
Optical fiber is the latest underground cable that is being used extensively in all the networks including long distance trunks, junction circuits and even the local subscriber loops to enhance the data transmission.
The OF cables are detailed extensively in the other modules of the basic course. How ever for academic interest the advantages of OF cables over copper cables are discussed here under
1. Optical Fibers are non conductive, hence does not require ground and surge suppression 2. Optical Fibers are immune to electromagnetic interference
3. Un authorized tapping is not feasible. 4. Easily upgradeable to higher bandwidth.
5. Low loss ( 5db per km to < 0.25 db per km on a typical fiber) 6. Long and unrepeated links , hence inexpensive
7. Small light, and hence cost is less and easy for installation.
8. It does not attract lightning, It does not carry electricity hence not hazardous
The Application of the Fiber Optical cable in communications are ::
1. Is the common carrier nation wide networks 2. Inter connecting all Trunk automatic exchanges 3. Inter connecting all the Exchanges.
4. Under sea cable 5. Control systems
Coaxial core Lead sheath
Quads of 0.9 mm
6. Customer premises communication networks. 7. SDH systems
• 8 MB MUX for 120 channels
• 34 MB for 480 channels
• 140 MB for 1920 channels
8.0 PAIR GAIN SYSTEMS ::
The pair gain systems are introduced in to the local network to provide temporary relief to the Technically not feasible (TNF) areas. The PGS is a switching system which provides more subscriber lines using a single cable pair. The numerical value of pairs gained is therefore defined as
Pair gained = No of customers connected – No of network pairs connected . The types of PGS are divided into basic groups depending on how pair gain is achieved
Concentrator
Grade of service requirement will limit the degree of concentration practically possible.
Multiplexer
Uses FDM or TDM technique to assign a dedicated frequency or time slot resulting in non-concentration. Better pair gain is possible.
Concentrating Multiplexer
It is a combination of multiplexer with concentrator. The different types of PGS are given in the table. PGS Description Customer pairs to network pairs Break even distance in Km
1+1 FM Analog customer carrier 2 / 1 0.02
4D PGS-1 4 channel Digital PGS phase I 4 / 1 0.04
4DPGS –2 4 channel digital PGS phase II 4 / 1 0.03
SLC Small line concentrator 14 / 5 0.08
LCU Line concentrator Unit 96 / 16 5.2
RCM Remote customer multiplex 30 / 2 2.0
Benefits of PGS units :
Primary Benefits : Flexibility to provide rapid service as less effort is needed to install it than
conventional cable .
9.0 CONSTRUCTION OF solid polythene insulated fully filled under ground
pcm telecom cables used for 2mbps digital system.
The cables are available in sizes 10+2, 20+4, 48+6, 96+8 and the nominal conductor diameter of 0.63 mm. The core shall be formed in units o 5 pair in the case of 10+2oair cable, units of 10 pairs in case of 20+4 cables and units of 12 pairs in case of 48+6 and 96+8 pairs.
The conductor material and insulating material are same as PIJF cable construction.
The color code for conductor insulation is :
Pair No 1 2 3 4 5 6 7 8 9 10 11 12
Color 1st wire W W W W W W R R R R R R
2nd wire B O G BN S BK B O G BN S BK
Color code for Binder for Unit identification :
Unit No. 1 2 3 4 5 6 7 8
Color of
Binder Blue Orange Green Brown Grey White Red Black
Cable Laying Up :: As shown in the diagram
Size of cable No of Units Size of unit No of Extra pairs
10+2 pairs 2 5 pairs 2
20+4 pairs 2 10 pairs 4
48+6 pairs 4 12 pairs 6
96+8 pairs 8 12 pairs 8
Color code for conductor insulation for Extra pairs ::
Pair No 1 2 3 4 5 6 7 8
1st Wire
COLOUR BK BK BK BK Y Y Y Y
2ndWire
COLOUR B O G BN B O G BN
Core separator Tape (Screen)
A poly-al core separator tape screen is in continuous length to physically separate the core into two compartments. The thickness of the tape shall be suitable to meet the cross-talk requirements. In addition a Poly-al tape shield if provided with 0.2 mm thickness of al tape and 0.05 mm coating of polythene
PCM CABLE LAY
1.1 LEAD SHEATH CABLE (FOR REFERENCE ONLY , OBSOLETE)
There are various types or lead sheath cables i.e. PCUT, PCQL, PCQT etc.
1.1.1 PCUT (PAPER CORED UNIT TWIN) CABLE
(a) PCUT cables are used for all local telephone underground cables.
(b) In this type of cable each unit is a self-contained group of pairs of conductors.
(c) The insulating paper covering each conductor is painted with colored lines forming a group of rings on the outside of the covered conductor. The color and spacing of the marking is given in table-I.
(d) Two insulated conductors are twisted to form a pair.
(e) The lays of the conductors forming the pair are different for adjacent airs and pairs in adjacent layers have different lengths of lays. The lays are so chosen as to ensure that cross talk between pairs is kept down to the minimum.
(f) Cables of less than 102 pairs dealt with one unit. The cable having more than 102 pairs are divided into groups of 51 pairs. Cable containing more than 408 pairs are in units of 102 pairs. The direction of stranding is reversed in successive layers.
(g) All the units of the cables are stranded in rope like fashion to form the cable.
(h) In all the large size cables with more than 51 pairs, one open helical whipping of cotton of not less than 3 strands is applied round each layer.
(i) Each complete unit is covered with an open helical whipping of paper marked with black (or blue) printed figures repeated through out the length to identify the unit. Over this there is a helical whipping of cotton.
(j) A final closed helical lapping of two thickness of insulating paper is laid over the formed cable core.
(k) Table - II gives the lay up of pairs in the unit.
TABLE-I
Pair numbers in
layer No. of lines Color of lines
A-wire B-wire Central & even layers Odd layers
1. Marker 1 2 Green Orange
2. Marker 3 4 Green Orange
3. 1 2 Red Blue
4. 3 4 Red Blue
5. 1 2 Red Blue
6. and so on 3 4 Red Blue
of cable Layer
Ist 2nd 3rd 4th 5th
20 2 6 12
51 4 10 16 21
102 2 8 14 20 26 32
Different sizes of the PCUT cables used in the DOT are 20,50,100, 150, 200, 300, 400, 600, 800, 1000, 1200 pairs
1.1.2 PCQL (PAPER CORE QUAD LOCAL) CABLE
(i) Lead covered paper core quad twisted local cables (PQCL) are used for junction circuits between local exchanges.
(ii) In this type of cable, the pairs are twisted in Quad formation i.e., four insulated conductors of each core are twisted together in one operation so as to occupy the four corners of a square. The conductors diagonally opposite to each other in the quad form a pair.
Inductive interference is kept down to minimum by this formation. (iii) Gauges on conductor are 0.63, 0.9 & 1.27 mm.
(iv) Stiffening of the paper tubes has resulted in the accurate and permanent centralization of the conductors whilst a central string upon which the covered conductors are bedded is used to ensure symmetry of cable.
(v) Numbering scheme is given by Table - III.
(vi) The A wire of a pair is the one having the odd number of ink lines upon the paper insulation. Wires in alternate quads have the paper marked with red and blue lines respectively.
(vii) PCQL cable are available of 14, 38, 54, 100, 200, 300, 400, 500, 600, 800 pairs. Position of quad in
layer color of marking on insulation paper Color of quadCentre and even layer
Whipping Odd layer
First marker Red White with
orange strands
Black with orange strands Intermediate 2,4,6
etc. Blue White Black
3,5,7 etc Red White Black
Last reference Blue White with
orange strands
Black with orange strands
(vi) The lays of the conductors forming the quads differ for adjacent quads. The quads are then stranded into a compact and symmetrical cable. The direction of the stranding alternates in successive layers.
(vii) A final close helical lapping of two thickness of insulating paper (red color) laid over the formed cable core.
1.1.3 PCQT (PAPER CORE QUAD TRUNK) CABLE
1. Lead covered paper core quad twisted trunk cables (PCQT) are used for trunk circuits. The construction of these cables is similar in all respects to PCQL cables. The essential points of difference between the PCQL & PCQT type cables are:
2. 0.90 mm and 1.27 mm dia copper conductors are used in PCQT as against 0.63, 0.90 & 1.27 mm dia in PCQL.
3. The mean mutual capacity in PCQT cables is smaller than in the case of PCQL.
4. The permissible capacity unbalance in PCQT cables is much less than in PCQL cables. The higher gauges of wire and lower mutual capacity keeps the attenuation constant of cable low and the reduced permissible capacity unbalance serves to minimize cross- talk.
5. PCQT cables are in sizes of 6,14, 38 and 54 pairs.
1.2 COMPOSITE SHEATH CABLE
During the last two decades the DOT imported various steps of composite sheath cables and the cables are named as per the construction of sheath.
a) Al Path -sheath construction
(Aluminum- Polythene) b) PAP -do- (Polythene-Al - polythene) c) Stall path -do- (Steel-Aluminum - Polythene). d) PASP -do- (Polythene - Al -Steel - Polythene)
Now the composite sheath cable is being manufactured in HCL indigenously on the ITD specification No. S/WT-129 dt 2.3.82 & ITD S/WT-143/B dt 30.7.88 and the name of the cable has been standardized as ‘Polythene insulated fully filled polythene sheathed underground cable’ (Jelly filled cables).
PRACTICE
Identification and constructional and Design features Polythene insulated Jelly filled cables, PCM CABLES, which are discussed in Chapter I are to be practiced in the practical classes.
CABLE LAYING
OBJECTIVE :: THE LAYING METHODS, THE PROCEDURES AND STEPS INVOLVED
ALONGWITHCERTAINPRACTICALPROBLEMSTHATAREENCOUNTERED INTHEFIELD AREDISCUSSED AT LENGTH FOR ADOPTING BETTER TECHNIQUES.
* * *
1. INTRODUCTION :
In any large telephone exchange system, cable component constitutes nearly 50% of the capital outlay. Hence proper and standard cable construction can obtain economy and reduce the cost of maintenance and over and above help rendering efficient and un-interrupted service.
2 CABLE CONSTRUCTION PRACTICE MAY BE BROADLY CLASSIFIED INTO:
(a) Receipt, storage, handling and transport of cable (b) Surveying and selection of routes, trenching and laying (c) Jointing of cables and termination
(d) Preparation of cable plan, cable diagram and other relevant records (e) Acceptance testing
2.1 SURVEYING THE SELECTION OF ROUTE :
(a) The routes should be as short as practicable provided other requirements viz., future requirements and expansion of other services are take in to consideration. Normally the cable should be laid along road and railway tracks.
(b) Corrosive soil should be avoided. If unavoidable measures like covering the cable with sand or drawing the cable through non-reactive duct should be adopted.
(c) Opening of expensive pavements and roads should be avoided. (d) The consideration should be given to the existence, alternation and
growth of other services.
(e) While surveying along a new road under construction or newly
developed area, proper coordination should be maintained with other underground services like water, electricity, sewage, gas etc.
2.2 DEPENDING UPON THE ROUTE SELECTED, PERMISSION FOR DIGGING TRENCHES ARE TO BE TAKEN FROM THE RELEVANT AUTHORITIES LIKE :
(1) Municipal or local authorities (2) Traffic authorities
(4) Railway Department (5) Post trust authorities.
2.3 AT THE TIME OF TRENCHING OPERATION CO-ORDINATION WITH THE FOLLOWING AUTHORITIES ARE TO BE
MAINTAINED:-(1) Electric supply. (2) Water supple. (3) Gas pipeline. (4) Sewage system.
3 TRENCHING :
The following are some important points to be given due consideration at the time of trenching
(a) Trenching should be such that the top of the cable should not be less than 60 cms. from the soil surface.
(b) The alignment should be straight at least 50 m at a stretch. (c) It should be at least 0.3m away from the boundary walls. (d) The depth of the trench should be 1.2 m.
(e) The width of the trench should be between 30 cm and 40 cm minimum. (f) (i) A separation of 0.6 m (relaxable upto 0.2m) should be maintained
While cable laid parallel to electric cables.
(ii) Parallelism exceeding 0.8 km with 11KV and above should be referred to PTCC.
(iii) At the crossing with electric cables, the telephone cable should be laid solid in between for 90 cm on either side. Cross-trenches (trial
pits are to be made if records for existing services are not available. IMPORTANT NOTE :: The min. bending diameter for armoured cables should be 15 times of the diameter of the cable
4 ROAD CROSSING
(a) Cable should be laid through G.I. pipes of suitable sizes.
(b) The depth of the pipe from the surface of the road should be 1m and with a slight slope to pass away water.
(c) The number of pipes laid at a time should be sufficient to cater to the requirements for 20 years.
(d) No jointing in the middle of the road.
5. GUIDELINES FOR LAYING OF CABLES ALONG NATIONAL HIGH WAYS, OVER BRIDGES AND CULVERTS
5.1 ALONG NATIONAL HIGH WAYS
(a) Permission from the Chief Engineer PWD is to be taken.
(b) The cables should be laid at distance not less than 457 cm from the Centerline of the road on formation.
(c) The depth of the cable from the soil surface should not be less than 120
5.2 Along over bridges culverts & Fly– over
1. A culvert should be paid by a concrete channel of 12” depth below the bed of the culvert to correspond to the footpath alignment so that all the cables can be drawn through this opening.
2. In order to lay the cable across small bridges with piers the piers should be extended beyond the width of the road so that pipe for cables may be securely clamped on the piers.
3. In case of long bridges and fly over in cities, liaison should be kept with proper authorities to ensure that suitable arrangements are provided for laying cables. the present practice is to have a concrete channel 20 to 30 cm in depth 90 cm in width along the footpath with removable covers.
6.0 LAYING OF CABLES ALONG RAILWAYS
1. Instructions laid vide paras 464 and 465 of P & T Manual Volume X should be strictly followed.
2. Side of the track will be selected by DET in consultation with proper Railway authority e.g. either Divisional Operating superintendent or district Engineer, if the alignment falls within 3 to 5.5 meters from the centre line of any Railway Track.
3. Excavation and reinstatement for any underground cable within 3 meters of the centre of any Railway track or any attachment to any Railway structure should be attended by the Railway staff at the cost of DOT.
6.1 RAILWAY CROSSING
1. Railway track should be crossed by G.I. pipes of 75 mm dia.
2. Minimum depth of the GI pipe from below the rail level should be 1.25 meters. 3. The length of the pipe should be sufficiently long so that work on telecom
alignment can be carried out without any hindrance to the railway traffic. This should extend at least 4.5 meters from the center of the last track.
7.0 OPEN GUTTER CROSSING
In partly developed metro cities. wherever open gutters are constructed for storm water drainage for sewage, it is difficult to lay small cables across the gutters to multistoried buildings. It should be preferable to recommend to the local authorities to provide a small 25 to 30 mm dia. crossing GI pipes below the bed of the drainage opposite each multi storied building.
8.0 LAYING METHOD OF THE CABLE
There are three methods normally adopted by the DOT for laying the cable which are :
(a) Laying direct in the ground (b) laying solid
(c) Drawing through duct or duct laying
8.1 LAYING DIRECT IN THE GROUND (DIRECT LAYING)
(a) This method of laying is comparatively suitable and also cheap from the point of view of initial investment.
(b) It involves
:-(i) Digging the trench as per standard vide Rs. 3. The digging may be done manually or be thrust boring or by other mechanical means.
(ii) Preparation of a bedding 5 cm high of soft soil (sieved earth) free from stones and corrosive elements.
(iii) Thorough checking of cable which is to be laid.
(iv) Paying out the cable in the trench by taking the help of cable wheel. If the wheel is not available the cable drum is to be mounted on a spindle supported by jacks on either ends. the jacks should be properly positioned on level surface and the rotation of the spindle should be smooth. Laying out of the cable is done by either moving the cable wheel along the trench of keeping the drum stationary at one end of the trench and pulling the cable
At the time of paying out special precautions to be taken so that
:-(a) There should not be any twist in the cable and there should not be heavy strain (specially in the case of unarmoured cable)
(b) Laying should be as far as practicable straight and along one side of the bed of the trench .
(c) If more than one cable are to be laid at a time, there must not be any criss-cross of the cables.
Cable rollers at every 10 m in straight section and at all bends and corners are to be used on the bed of the trench to avoid strain on the cable at the time of pulling. In pulling unarmoured lead sheath cable it should be ensured that the lead sheath is gripping the wires of the cable finally so that pull is shared equally be the lead - sheath and conductors.
Unless otherwise indicated in the drum the free end of the cable should be laid near the exchange which is called the UP end of the cable route. The inner end of the cable should be laid away from this exchange i.e. Down end of the cable route. (v) Identification callers :
number of the cable should be fixed are every 5 m along with length of the cable and at all joint locations. Whenever cables pass through pipe or duct cable marker should invariably be fixed at about 1 m away from the mouth of the pipe.
(vi) Pressure testing :
It is sound practice to deep the cables under a pressure of 8 to 10 p.s.i. after laying. A fall in pressure signifies the damage in the sheath of the cable which is to be corrected.
(vii) Flooding the trench : Sometimes it may happen that trench is dug along
the existing cable route. In order to detect if any damage is caused to the existing cables, the trench is flooded with water and the cables are allowed to be immersed in water for 24 hours. After the lapse of 24 hrs the existing cables are tested from the test desk in order to detect any fault come up due to trenching.
(viii) Back filling & Reinstatement : After laying out the cable it should be covered by a consolidated layer of 80 mm of soft earth which should be free from stones or other sharp object, carefully pressed and lightly rammed.
(ix) Warning Bricks or tapes : As a protective measure a row of bricks
(length wise or width wise depending upon the number of cables) or stone slabs are to be placed along with cable alignment. The modern practice is to lay a plastic tape with name of the Department printed on it at about 30 cms above and along with cable alignment.
After placing the protective arrangement , remaining portion of the trench is filled in and well rammed. It is advisable to leave a crown of earth rising not less than 5 cm in the centre and tapering towards the sides of the trench. This allows for natural subsidence.
(x) Route indicators & joint indicators: There are different types of
indicators used in the department. The appropriate type of route indicators should be placed 200 m apart in the straight and at every point where the direction of the cable route changes. Joint indicator are to be used for each joint.
(xi) Preparation of diagrams & records : All the diagrams relating to the
cable alignment viz. line diagram for primary secondary and distribution side, cable plan for primary secondary and distribution side, records for Pillars and DPs etc. are to be prepared. A careful record of the dispositions of the underground structures of other utility concerns such as water, mains electricity, sewage etc. coming in close vicinity of, or crossing the departmental cables should be maintained.
9.0
RESPONSIBILITIES FOR CABLE CONSTRUCTION
a) Checking the condition of the cable on drum which is to be laid and ensured that it is healthy and in pressurized condition.
b) Ensuring that the trench is of standard dimensions, in case standard dimensions, cannot be maintained, additional protection is to be given.
c) Offering the trench for A.T. before starting cable laying. d) Laying the cable as per standard method.
e) Offering drums length and laid cable to A.T.
f) Provision of mechanical protection, such as bricks, RCC tiles, split ducts, warning tapes etc., temporary re-instatement.
g) Offering to A.T.
h) Continuity and insulation test of all the pairs before jointing and ensuring that all conductors are in good condition.
i) Offering joints to A.T.
j) Termination the cable as specified. k) Offering to A.T.
l) Updating the cable records including
m) Location, sizes, gauges and code number of cable n) Location of the joints including branch joint o) Cable pair records for the entire route
p) Average value of loop-resistance, transmission loss and Insulation.
CABLE CONSTRUCTION
Any communication cable laid underground forms part of the network of telecommunication infrastructure and is a permanent asset which is expected to live up to its theoretical life span, if not beyond, with a reasonably satisfactory service to the user. Needless to say that telecommunications and in this modern information area, when entirely new services are being planed and more and more information carrying capability is envisaged, the manufacture of modern telecommunication cables and their induction into the existing network should be in line with the needs of the new technologies. Therefore, it is imperative on the part of the construction staff to look into carefully every stage of construction activity, right from selection of appropriate type of cable for a particular application up to testing and commissioning of each pair so as to plug all gaps of vulnerability leading to deterioration of characteristics of the cable.
3.0. PARAMETERS.
The copper based telecom cable is required to meet certain standards set on the following parameters, so as to consider it suitable for satisfactory transmission and reception of speech and data in the form of analogue or digital signals.
I. Insulation resistance II. Conductor resistance III Mutual capacitance
A thorough check on the following points must also be carried out before being recommended for network suitability.
I. Conductor open fault II. Conductor cross fault
III. Shield/sheath/core-separator tape continuity IV. Low dielectric strength
3.0 STAGES OF CHECK
To keep the cable healthy in operation and satisfactory in Its set parameters, checks are to be carried out at every stage by the Construction staff. The following stages require careful analysis.
I. Receipt, transport and storage.
II. Physical deformity or manufacturing defects unnoticed by the QA wind. III. Laying activity.
IV Jointing activity
V. Acceptance testing activity.
3.1 Receipt, Transport and Storage
Right from the dispatch of cable from the factory, duly cleared by the Quality Assurance ( QA) wing, the telecom cable should be carefully loaded transported, unloaded and stocked at the intermediate Stock Depots and finally brought to the Unit stores where detailed inspection of the received cable is carried out. Every drum length should be checked for correct length, visible damage, manufactures code, type & size and condition of end seal. These checks may be conveniently carried out by the JTO ( MM) at the Unit stores and the data fed into a computer memory, to be used for various management purposes, including giving feedback to the manufacture, QA Store Depot etc. The flow chart depicted at Figure 1 illustrates a typical method of checking the cable drums and follow up action in Unit store.
3.2 Physical Deformity and Manufacturing Defects
Physical deformities occurred during manufacture and overlooked by the QA wing rarely come across in the field units. There may be other damages that occur during transport or handling, which should not go unnoticed. This will help in taking up the defects with the manufacture or Central Store Depot immediately and either get replacement or claim compensation for loss/damage. This extra check is necessary to avoid problems at a later date during maintenance.
FLOW CHART FOR CHEK ON RECEIPT OF CABLE ::
START
Is the cable drum received in tact If , yes note down Drum No length, etc Want to ensure correct length Test length by APLAB Any difference with markings Uncoil the drum and inspect
Any defect observed
If no issue for usage in work Ear mark duct section or route section according to length
3.3 Laying Activity
Great deal of attention is to be paid during laying of cables. As the cable laying is resorted to through outside agencies, departmental officials should exercise a close supervision of activities in progress . The contractor may be considered as a businessman interested in getting maximum profit for minimum effort. His as well as his worker’s intention, therefore maybe more on completion of work speedily rather than caring for standards, precautions, warning to pedestrians and vehicular traffic, damage to existing cable etc. Therefore supervision by departmental officials is necessary. Being an underground activity. once laid and the trench back filled, it is difficult for an inspecting official to see the defect directly. It is necessary to dig trial pits at suspected spots to check for correct depth, warning layer. GI Pipe, clearance between water pipe and cable etc. Alternatively the best way of supervision however will be to see on day-to-day basis and conduct surprise checks at random. It is suggested that the following nine commandments may be enforced on the contractor so as to achieve satisfactory results.
I. Mark the route where cable is to be laid and a route map issued to the contractor who has to strictly follow the same.
II. Mark the route where Telecom and Electric cables exist and ask him to take special care to avoid damage/accidental contact.
RTTC, NAGPUR Page 29 of 185
no Furnish feed back to
QA /store and all
concerned officers to get replacement
Append stock file
Acknowledge Store Receipt
IV. Earmark BT/Berm cutting for strict compliance and avoid inconvenience to smooth flow of traffic or pedestrians.
V. Enlighten contractor about precautions such as drawing cables using cable grip & cable rollers where necessary. Let him engage more men for paying out and laying in cities to avoid damage to the cable and inconvenience to traffic.
VI. He should use winch, cable rollers, pulley blocks, nylon rope etc while higher size cables are drawn in ducts. he should ensure that draw hooks are attached to the cable ends and only moderate pulling tension is applied on the cable.
VII. He should use proper warning layer over cable as per instructions and should the identification tags/collars at specified intervals before closure of trench.
VIII. He should properly mark all jointing spots and leave only optimum joint length on each cable as per requirement of DOT so that no cable is wasted at the time of jointing.
IX. He should immediately report to construction Officer DOT any instance of objection raised by PWD/Local Authority or private individual so that such grievances can be settled by the construction Officer amicably.
3.3.1 Tender Conditions.
The practice of calling sealed tenders, accepting the lowest rates and awarding the work for more than one financial year creates some practical difficulties. Since the labor rates and other incidentals are subjected to change year after year, the successful tenderer may try to backout after one year’s work or ask for enhanced rates. So it is desirable to call for tenders on year-to-year basis for cable laying work. In rural areas where close supervision is difficult, contractors may try to maintain insufficient depth for trench and avoid using warning layer. In semi urban and other developed cities, it is advisable to engage more men for laying so that the entire operation progresses quickly and gets completed with barest minimum inconvenience to shopkeepers and general public Unlike other civil construction works, tender conditions for carrying out cable laying works should take into account all these important aspects and give more stress on precautions to be taken while laying, as any defective practice will lead to network instability at a later date.
3.3.2 Some Common Wrong Practices and Their Remedies.
Some of the wrong practices often noticed in laying cables on public roads by contractors are enumerated in the following paragraphs, which can be rectified as suggested.
3.3.3. Crossing Water Pipes.
Wherever water pipes exist at insufficient depths and the contractor lays the cable over it, it causes unequal dynamic stress on the cable by vehicular traffic , ultimately developing a sheath crack and consequential failure of circuits. In such cases, the contractor should get specific instructions from the Construction Officer and lay the telecom cable through GI pipe further below the level of water pipe with a soft earth cushioning between water pipe and cable terrains may preferably be made using
water blocking powder on the upstream side and protect the ends of cables by using insulation tapes during laying.
The following diagrams in the next page illustrate better about the laying across water pipe lines and culverts.
CROSS- SECTION OF ROAD SHOWING TELECOM CABLE LAID
OVER WATER PIPE WITHOUT CLEARANCE AND SUBJECTED TO EXCESSIVE DYNAMIC LOADS FIGURE-2
3.3.4 Crossing Culverts
While laying cables across a culvert, the usual practice followed is by using GI pipes cut at the ends in V- shape on the outer surface and bend downwards so as to lead in the cable from end to the trench. This apart from weakening the strength of GI pipes, damages the outer sheath of cable due to abrasion. Moreover, the pipe itself is broken at this weak spot whenever any vehicle runs over it. The V-cut also reduces the inner volume of the pipe. making it difficult to draw further cables through it. the cut portion allows mud to enter the pipe and clog the inner space during heavy monsoon and in course of time renders the pipe unfit for further drawl of cables. The use of 45o bends of the same size as that of the pipe at the ends with necessary couplings
and sealing at both ends using plaster of Paris or light cement mortar mix, after all cables are drawn through the pipe, is found to be an advantageous method. A typical arrangement is shown in figure 3 Where the pipe could not be taken close to the wheel guard of the culvert or below it, the pipe may be enclosed inside the parapet wall by dismantling and reconstructing it with the specific approval of the PWD. Sealing the ends of pipes in both the above cases is an important precaution to avoid accumulation of mud and prevention of entry of harmful rodents, rats etc. Where the culverts are not provided with parapet walls, it is preferable to enclose the GI pipe along with cable in cement concrete through the length of culvert as shown in Figure 4 Care should be taken to draw further cables in the same pipes where sufficient space is available and finally seal the mouths so as to avoid wastage of pipes.
TYPICAL METHOD OF LAYING CABLE THROUGH PIPE OVER CULVERTS USING 45oBENDS FIGURE 3
3.3.5 Crossing 11KV Electric Cables
Instances we may come across where 11KV electric cables exist in parallel or across a proposed Telecom cable route. In respect of parallelism, it is advisable to take the telecom cable with maximum horizontal clearance as far as practicable but not less than 0.6 meters, so that the intensity of inductive interference can be minimized. Absence of sheath continuity and armour continuity in Telecom cable and it’s improper earthing in the vicinity of power cable will result in AC induction and consequent impairment of the telecom circuits. When the power parallelism is more than 0.8 kms the cable route should be referred to Power Telecom Co-ordination Committee (PTCC) for recommendation of protection measures. In case of crossings, care should be taken see that telecom cable crosses at right angles and at a vertical clearance preferably of 0.6 meters but not less than 0.3 meters at any point. When the specified clearances cannot be maintained, it is preferable to lay the telecom cable through cement concrete pipes for a length of 1 meter on either side of power cable at the crossing and seal the mouths at both ends. Electricity authorities should also be requested to lay the electric cable at crossing location in solid or through cement concrete pipe. Conventionally telecom cables are laid only on one side of the road and preferably on thru route through which telephone alignment runs. However if a 11 KV cable exists in any route, Electricity Board Authorities should be consulted and correct location of the electric cable, crossing location etc are to ascertained, before starting telecom cable laying work. Figure 5 shows a practical arrangement of telecom cable crossing an electric cable.
LAYING CABLE THROUGH GI PIPES EMBEDDED IN PCC ACROSS CULTVERTS HAVING NO PARAPETS FIGURE 4
4.0 JOINTING ACTIVITY
It is very important to follow standard construction practices and good workmanship in cable construction work. This important task is vested with the DOT staff who are given necessary training in conductor jointing, splice closure technique earthing protection, mechanical protection to joints etc.
Any physical cable pair can be jointed in a haphazard way in a number of through joints and made available at the distant end for working a circuit. This non standard practice not only causes difficulties to the maintenance staff in tracing the circuits at the time of faults, but also impairs the performance quality of the network, It is therefore necessary to follow standard construction practices only. Transmission properties could be maintained at a satisfactory level only when the conductor jointing is done in perfect 1:1 order. This means all pairs in layers should be jointed to the corresponding pairs in the other bit of cable in the same layer. Thus the correct pair jointing in through/ branch joints and in CT boxes and DPs forms a homogeneous medium for building up a satisfactory communication network. Unlike paper cored cables, polythene insulated conductors in the Jelly Filled ( JE) cables pose no problem, since the color of conductor insulation in polythene insulated conductors does not fade in course of time and identification of tip and ring conductors is easy. Making the joints hastily or without taking proper care should be avoided. Close supervision at every stage of cable construction activities is therefore necessary. Joints should not be allowed to be closed unless all cable pairs and sheath continuity are tested.
Some cable splicers may have a wrong notion that water does not affect the JF cable and therefore they sometimes make joints in rains, keep the end of cable in water till joints are made etc. Experience has shown that water trapped inside joints flows through the crevices of the cable core and gets collected in the lower most joint. Even through UY-connectors and splice - modules are theoretically supposed to be watertight, instances have been noticed where water trapped inside a joints finds it’s way into the splice modules and UY-connectors and cause low insulation faults. This is observed to be due to the fact that jelly filling inside some cables is not viscous in nature but crystalline, which allows water to travel through the core of the cable,
method. Therefore joints in JF cables in the sloppy terrains may preferably be made using water blocking powder on the upstream side and protect the ends of cables by using insulation tapes during laying.
4.1 Necessity of Using Proper Tools and Implements.
Due to adoption of newer technologies in cable jointing, cable splicers are required to use different and entirely new tools. It is necessary to make them realize that the tools must be used for the purpose for which it is meant. Splicing staff must refrain from using ordinary blowlamp in place of low heat modified blowlamp. They should use only flat face crimping pliers for connecting polythene-insulated conductors in UY- connectors instead of using ordinary pliers. There are imported as well as indigenous type LSA PLUS Krone connecting tools for use in Krone type CTBs and Dps. Such connectors should be exclusively used for those works only
4.2 Precautions to be taken during Jointing of a Cable.
The following points require careful attention when joints are made.
I. Do not hesitate to use a tent or tarpaulin to protect joint and splicing staff from Sun and rain. This will not only reduce the fatigue of workers but also will protect the cable joints from possible entry of moisture and dust.
II. Keep the cable on raised platform while joints are made, so that cable splicer is able to operate correct pair and layer conveniently.
III. Keep all tools and hands of splicing staff clean before starting jointing operation.
IV. Clean the ends of cables using abrading cloth and cleaning liquid before fixing XAGA.
V. When doing branch joints, take care to fix branch off clip properly and take extra care in shrinking the portion where branch off clip is fixed so as to avoid any gap through which water may enter.
VI. Remember tying the identification tags or collars on each and every cable at frequent intervals near joints.
VII. Do not operate all cables to trace a fault in a cable without referring to records or proper investigation and identification of faulty cable.
VIII. Ensure keeping finished joints on joint stands inside the duct manholes so that the joints are not subjected to tensile stress.
IX. Ensure using exhaust fan and proper light inside duct manhole while joints are made.
6.0 CONCLUSION :
A reliable subscriber network is a basic requirement of any telecommunication installation. Taking into consideration the huge investment in the external plant, underground telecom cables used should be made less vulnerable to catastrophic faults. This could be achieved by adopting careful planning and construction practices and the impetus given on sanctioning sufficient field staff for patrolling, supervision of cable laying works, jointing operation, annual fault clearance checks etc. The success of introduction of any new technology switching systems largely
depends on the reliable and efficient cable network. With reliable external plant DOT will be in a position to meet the challenges of Global information Revolution.
MICRO TUNNELLING
The frequent digging of downtown areas invite criticism from town planner and civilians as well. In view of this situation the following issues received the attention of telecom professional
• How long the cutting and covering technique will be allowed and economical as well.
• Rehabilitation and repair of underground cables disfavors conventional cable laying in the crowded parts of localities.
• Ecological disadvantages are too much in cut and cover technique.
• Congesting at the depth 1 to 1.5 meters below the ground and prohibits further exploitation.
One of the options after studying the problems is MICRO TUNNELLING , which is trench less installation of piles and cables. It replaces the open cut trenching by using drilling suspension. The remotely controlled drill tool is advanced underground. High pressure drilling suspension is emitted from the three dimensions drill tool which rotates through the ground forming the pilot hole or tunnel. Larger spool are pressed against the walls of the tunnel and finer particles of earth are transported along the tunnel with aid of environmentally safe drilling fluid to start pit or the target pit.
The remotely controlled rotating drill tool reaches the target pit with complete accuracy, the relevant reamer of the job is then attached and the pilot hole is widened to enable the simultaneous instillation of the products.
The pipe or cable called product is attached behind the reamer. The Bentonite drilling suspension enables the installation to be carried out smoothly and without damaging the product. This drilling suspension acts as a lubricant and helps to reduce friction in the tunnel. The drilling suspension is a important part of the technique. Under high pressure, it forces it’s way through the ground, transports the spoils to the pit, supports the micro tunnel and reduces friction on the drill tool and products. This suspension consists of water mixed with Bentonite and water which is specially mixed for each job and the quantity depends up on the physical parameters of the ground. predominantly consists of natural clay minerals, which have swelling properties. This is determined in advance by a geological survey.
Location technique is based on electro-magnetic waves. These waves are transmitted from drill tool and measured above ground by receiver. The precise position of the tool can be located and obstacles of underground in line can be avoided.
Advantages of Micro tunneling technology:
• Ecological advantage, a little job-site waste to dispose off.
• Un-obstructive, No noise, no mess, no traffic disruption for the people.
• Economical Lowe costs but high instillation performance.
CHAPTER – III
CABLE JOINTING
Objective of the Lesson :: The necessity of a joint in telecom underground cable and
choosing of correct technique from the techniques available and adopting for better construction methods for jointing of conductors and joint closures for various types of cables available
.
* * *
Different types of Jointing Techniques for U/G telephone cables, using different types of connecting techniques for jointing conductors and joint closures.
One Of the oldest form of cable existing in our networks are lead sheath dry core (LSDC) paper insulated cable. As discussed its use has been discarded due to various reasons. These are being replaced by PIJF cables and OF cables in the networks.
1. Necessity of joints : The joint of a underground telecom cable arises due to a. Limited lengths available for different sizes of cables in new cables.
b. Occurrence of Damages to the working cables , resulting in a joint or two.
THIS IS CALLED STRAIGHT JOINT
c. An operation on a New cable or Existing working cable is made for diverting part of cable pairs to another direction / area.
THIS IS CALLED BRANCH JOINT
d. To transfer the existing cable pairs of one area in an exchange system ( old pillar ) another area (new pillar ) in the same exchange system
e. To transfer the existing cable pairs from existing exchange in the area to another new exchange called area transfer.
RTTC, NAGPUR Page 39 of 185 Old exchange New exchange AREA to be transferr
1.1 The jointing of the Local cables are described as detailed below :-a. Jointing of LSDC cables
b. Thermo shrink joint technique. c. Jointing with ALSS technique.
d. Jointing Jelly filled cables with TSF kits.
1.2 PRECAUTIONS TO BE OBSERVED FOR JOINTS
Very often a large size of cable is required to be jointed with another same size or more than one cable of smaller sizes of cables. While proceeding for jointing following precautions are to be taken particularly in case of Brach joints and ‘Tee’ joints.
• The jointing of conductors should be done as per jointing schme ensuring that the smaller branch cabe is jointed to inner layer or main cable.
• In case there is any spare cable pairs left, these should be bunched together and stumped in the joint, which can be utilized infutre (with recording )
• Dressing of main sleeve should be done in such a way that the man sleeve flushes on all sides as far as possible.
• In case of plumping of LSDC should be done proper at Branching point to fill any gaps or pin holes while dressing.
• Suitable size of Kits should be used depending on the specifications.
1.3 ARRANGEMENTS TO BE MADE BEFORE THE START OF JOINTING
• Cable jointing pit suitable size be dug so as to accommodate the cable splicer along with his assitants and tools and facilitage easy jointing.
• Guarding of work against public to avoid danger to vehicles , pedestrians and cable jointing personnel.
• Beware of existing cables and particularly existing joints at that place.
• Beware of underground Power cables at the place of joint.
• Protection against weather and water toavoid low insulation in joint.
• Pre arranging Joint tools and Joint materials.
1.4 GENERAL :
Other instances of requirement of Jointing of underground cable is for the following purposes
:-(a) Jointing of cable - drum lengths to obtain the desired length of cable and to direct different amount of pairs in different directions as necessitated by subs-density.
(b) Incorporating additional joint on some working cable for removing (c) faults.
(d) Replacement of a faulty portion of a cable length by incorporating two (e) additional joints.
(f) Replacement of faulty joint by a new one.
2.0 JOINTING TECHNIQUES
Any jointing technique consists of the following operations. (a) conductor jointing.
(b) Protecting the joint against moisture entry and / or making the joint airtight. (c) Protecting the joint against corrosion and mechanical damage.
2.1 CONDUCTOR JOINTING
A. CONVENTIONAL METHOD
:-It consists of twisting the conductor ( soldering also required for higher gauges) and putting a paper sleeve for insulation. This system though suitable for paper core cable is going to be abolished for the following
reasons:-(a) Not suitable for jelly-filled cable.
(b) Time consuming operation and hence the efficiency of the splice is decreased.
RTTC, NAGPUR Page 41 of 185
Paper insulated conductors Paper sleeve
Twisting of conductors
(a) B - wire connector (UK)
(b) Pica bond or AMP connector (USA) (c) Scotch or UY connector (USA)
(filled variety)
Out or these three DOT has accepted the scotchlok connector for the following reasons.
(1) Same connector holds good for all gauges of wire. (2) Smaller joint size.
(3) Jointing operation very simple, insulation on wire need not be removed. (4) No chance of imperfect joint, as we can see through the connector. (5) Plastic outer cover quite firm.
(6) Avoids corrosion as the connector is filled with jelly.
UY CONNECTOR BEFORE USAGE
One conductor from one direction and another conductors from another direction to be jointed are inserted into the UY connector without removing the insulation of the wires. The contact will be made by the plate after cutting through the insulation. This technique is used for Polythene insulated jelly filled cables.
UY CONNECTORS AFTER USAGE
RTTC, NAGPUR Page 42 of 185 PVC TRANSPARENT BODY Copper Conductors with insulation Contact plate Copper Conductors with insulation cut at plate
Contact plate PVC
TRANSPAREN T BODY
