TC 1
TELECOM CABLES
P V R SAGAR,
ILP-2/IRISET
7013 416 426
TELECOM CABLES (COPPER)
VER 1.0
1
TC1: Telecom Cables (copper) for POSC - 06hrs
Sl No
Course Contents
1
Introduction of telecom cables
2
Paired Telephone cables
3
U/G PIJF cables
4
Effects of Railway Electrification on
Telecom circuits
5
Telecom Quad cables
6
Cable laying practice
CABLES
VER cables
10
7TELECOM
Jointing
of underground
(COPPER)
2
Telecom transmission media
1. Aerial Lines (Over Head Lines): GI wires & ACSR (Aluminium
Conductor Steel Reinforced).
2. Micro Wave System: Analog & Digital Systems are in use for
Radio Patching for Control Communication and long distance
Administrative trunk circuits.
3. RE Main Telecom Underground Cable: 0+12+2, 0+17+3, 0+18+2
etc. are in use in RE areas.
4. Underground 4 Quad and 6 Quad Cables: These are in use as
standalone or along with OFC in many Zonal Railways.
5. OFC Cable: 24 Fiber Underground OFC Cable is in use for high bit
rate Telecom traffic with enormous applications over Indian Railways.
TELECOM CABLES
(COPPER)
VER 10
3
UNDER GROUND CABLES
TELECOM CABLES
(COPPER)
VER 10
4
CLASSIFICATION OF TELECOMCABLES
TELECOM CABLES
(COPPER)
VER 10
6
Special Features of Telecom
Cables
•PVC insulated
•Twin Twisted paired / quad cables
•Screened cables
•Balanced cables
•Loaded Cables and
Colour coded
TELECOM CABLES
(COPPER)
VER 10
7
Electrical characteristics of Telecom
Cables
The four primary elements
R = Series Resistance
L = Series self inductance
C = shunt capacitance
G = Shunt conductance [Leakage]
TELECOM CABLES
(COPPER)
VER 10
8
Distortion less condition of a
transmission line
GL = CR
TELECOM CABLES
(COPPER)
VER 10
9
PAIRED CABLES
TELECOM CABLES
(COPPER)
VER 10
10
TELECOM CABLES
(COPPER)
VER 10
11
How Cross-talk is Eliminated ?
ADJACENT CIRCUIT
L1
3v
3v
3v
2v
Span-1
L2
2v
2v
Span-2
L1=3+2+3+2= 10V
span-3
2v
Span-4
L2=2+3+2+3= 10V
Net induced voltages on L1&L2 are the same, no potential
difference, no current flow at telephone and no cross-talk from
adjacent Circuits.
TELECOM CABLES
(COPPER)
VER 10
12
ADVENTAGE OF PAIRED CABLE
• Paired cables are balanced, by using two closely
spaced conductors twisted together, audio is
balanced equally on these wires. Since the flow
of induced emf on both wires are equal and
hence no potential difference, no current flow at
telephone and no cross-talk develops from
adjacent Circuits.
• A ground shield used to prevent high frequency
noise and balanced wires also rejects noise
coming from ground loops.
TELECOM CABLES
(COPPER)
VER 10
13
TYPE OF PAIRED CABLES
• SWITCH BOARD CABLES
• UNDER GROUND PIJF CABLES
 PVC Twin flate-2 core
 10 pair-.4/.5mm/.63mm
 20 pair-.4/.5mm/.63mm
 50 pair-.4/.5mm/.63mm
 100 pair-..4/5mm/.63mm
 DATA COM. CABLES
 10 pair-.5mm/.63mm
 20 pair-.5mm/.63mm
 50 pair-.5mm/.63mm
 100 pair-.5mm/.63mm
 Note: These cables are used for
) UTP (Un shielded twisted pair)
b) STP (shielded twisted pair)
COAXIAL CABLES
RG 58- 180 mtrs, RG 8-500 mtrs
These cables are used for Indoor
a


outdoor wiring, RDSO SPEC.
IRS:TC 41/97(Adm. 2)
wiring.TEC SPEC.NO:GR/WIR/06/03 OF March 2002
TELECOM CABLES
(COPPER)
VER 10
14
Colour code of Paired Cables
 Switch board cable are terminated





•
•
•
•
•
•
•
•
•
•
•
•
BLUE
-
WHITE
on krone cable termination box
ORANGEWHITE
(CTB)
GREEN WHITE
Under ground PIJF cables
BROWN WHITE
terminated on CTB
SLATE WHITE
UNDER ground 6 quad cables are
terminated on CTB or wago
BLUE RED
terminals.
ORANGE RED
AFTER TERMINATION of cable pairs
soldering shell be don other than
GREEN RED
krone and wago CTB s.
BROWN RED
AFTER TERMINATION of cable pairs
SLATE RED
circuit details to be painted.
_____________________________________
ALL cables to be tested( end to end)
Main colours: Bl, Or, Gr, Br, Sl.
once in year. and record the
Mate colours: Wh, Rd, Bk, Ye.
parameters.
TELECOM CABLES
(COPPER)
VER 10
15
Colour Code of Conductors
Main / -> Mate
White
Red
Black
Yellow
Blue
1
6
11
16
Orange
2
7
12
17
Green
3
8
13
18
Brown
4
9
14
19
Gray / Slate
5
10
15
20
5 pairs
10 Pairs
50 pairs
5 number of 10 pair units
100 Pairs
5 number of 20 pair units
20 pairs
Each UNIT has it’s own coloured binder : 1. Blue 2. Orange 3.Green 4.Brown 5.
Gray
TELECOM CABLES
(COPPER)
VER 10
16
QUAD CABLES
• “STAR QUAD” is Four conductor balanced
cable, four wires form a tighter, more
consistent pack then two wires can and can
resist even more noise.
TELECOM CABLES
(COPPER)
VER 10
17
QUAD CABLES
TELECOM CABLES
(COPPER)
VER 10
18
Impedance Vs Frequency.
• The impedance, which describes the
combined effect of resistance (R), inductive
reactance (XL) and capacitive reactance (XC) in
an AC circuit, whether it occurs in a single
component, or in a whole circuit.
• Because impedance is affected by reactance
(X), as well as resistance (R), it is also affected
by frequency (ƒ) and the value of impedance
will change at different frequencies.
TELECOM CABLES
(COPPER)
VER 10
19
The component or circuit will not have the
same impedance at all frequencies. It is
common for inputs and outputs on many
types of equipment to have their impedances
quoted in Ohms and to assume a common
frequency for that particular type of
equipment.
TELECOM CABLES
(COPPER)
VER 10
20
RAILWAY ELECTRIFICATION
Effects of 25kv 50 cycles AC Traction on
Telecommunication.
1.Electromagnetic induction:- The currents flowing in the
Catenaries return to the feeding point via Rails, the rails are not specifically
Insulated from the earth therefore some portion of currents fined a path or
induces emf in cable sheath and conductors. It is Dangerous to working people
and Equipment.
2.Electro static induction:- cable conductor insulated from
earth and situated in this filed will get charged to certain
potential with reference to the earth due to capacitance coupling.
The magnitude of this potential depends on the catenary current
and distance.
3.

.
TELECOM CABLES
(COPPER)
VER 10
21
DIRECTIVES OF ITU-T FOR TELECOMM SYSTEM DESIGN
ON 25KV AC ELECTRIFED SECTION
 Recommendations on permissible voltages, calculating method and
protective measures have been issued by the I.T.U-T.
 Accordingly the following voltages may not be exceeded in the circuit
formed by cable conductors and ground.
 Psophometric voltage shall not exceed 2mv.
 During the normal functioning of traction system, the longitudinally
induced voltage in telecomm circuit shall not exceed 60 volts.
 Under conditions of particular difficulty and as far as the telephone
working condition permit, the limit of longitudinally induced voltage may
raised to 150 v rms subject to spl. precautions being taken. (Tapping
Transformers at Derivation point to be used)
 fault in traction system. To avoid danger to person ,cable and equipment
the longitudinally induced voltage in telecomm circuit shall not exceed430
volts. During the time of short circuit
TELECOM CABLES
(COPPER)
VER 10
22
Difference between PIJF underground Paired
and Quad Cables
Sl.No
Telephone Paired Cable
Telecom Quad Cable
1
Conductors are available in the form of
Pairs. Twin Twisted
Conductors are available in the form of
Quads. Twin Twisted pairs.
2
3
4
5
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Used for long distance Signalling and Telecom safety circuits between two Block stations.
7
Loop Resistance of the pair is important criteria.
Transmission loss in pair of quad is important criteria.
8
RDSO spec. of Cable: IRS-TC: 41/97
RDSO spec. of Cable: IRS-TC: 30/2005
9
Jointing is in the form of Straight Through Joints.
Jointing is in the form of Straight Through/ Derivation/Transformer/Condenser/Loading Coil Joints(as required in the section).
10
(TSF) Thermo Shrink Filled Jointing Kits for different size of cables used as per RDSO spec. no: RDS0/SPN/TC/57/2006
(RTSF) Reinforced Thermo Shrinkable Jointing Kits for 4/6 underground Quad Cable as per RDSO spec. no: IRS:TC:77/2012
11
Terminated in Krone/Wago type modules and terminal strips.
Terminated in 10 Pair/20 Pair CTBs and Wago type modules
12
Generally used by all Telecom Service providers.
Exclusively designed for Signaling and Telecom applications of Indian Railways.
Available in 10/20/50/100 pairs
Available in 4/6 quads
Dia of conductors : 0.51/0.63 mm
Dia of conductors : 0.9/1.4 mm
Z o of the pair : 600 Ohms
Z o of the pair in the quad: 470 Ohms (0.9 mm
dia) / 310 Ohms (1.4mm dia)
Induced Voltage reduction in two
stages by earthing Al foil & armour
Induced Voltage reduction in three stages
by earthing Al foil, Aluminum screen &
armour.
TELECOM CABLES
(COPPER)
VER 10
23
Difference between PIJF underground
Paired and Quad Cables
Sl.No
Telephone Paired Cable
Telecom Quad Cable
6
Used for short distance Telephony/
Data Circuits applications in station
area as last mile connectivity.
Used for short distance Telephony/ Data
Circuits applications in Railway station
area as last mile connectivity.
7
Loop Resistance of the pair is
important criteria
Transmission loss in pair of quad
is important criteria
8
RDSO spec. of Cable: IRS-TC:
41/97
RDSO spec. of Cable: IRS-TC:
30/2005
Jointing is in the form of Straight
Through Joints.
Jointing is in the form of
Straight Through/derivation
Joints
TSF Jointing Kits for different size of
cables used as per RDSO spec. no:
RDS0/SPN/TC/57/2006
RTSF) Jointing Kits for 4/6 u/g
Quad Cable as per RDSO spec.
no: IRS:TC:77/2012
9
10
TELECOM CABLES
(COPPER)
VER 10
24
Difference between PIJF underground
Paired and Quad Cables
Sl.No
Telephone Paired Cable
Telecom Quad Cable
11
Terminated in Krone/Wago
type modules and terminal
strips
Terminated in 10 Pair/20 Pair CTBs
and Wago type modules
12
Generally used by all
Telecom Service providers
Exclusively designed for Signaling
and Telecom applications of
Indian Railways
TELECOM CABLES
(COPPER)
VER 10
25
What is Psophometric noise .
• When cable is in close proximity to strong electromagnetic fields,
unwanted current and voltage may be induced on it. If the power
level is high enough, the electrical "noise" can interfere with voice
and data applications running on the cabling.
• In data communication, excessive electromagnetic interference
(EMI) hinders the ability of remote receivers to successfully detect
data packets. The end result is increased errors, network traffic due
to packet retransmissions, and network congestion.
• For analog voice communication, EMI can create psophometric
noise, which degrades transmission quality. This will be measured
with psophometric meter.
• Psophometric voltage readings, V, in mill volts, are commonly
converted to dBm(psoph) .
TELECOM CABLES
(COPPER)
VER 10
26
PSOPH CURVE
TELECOM CABLES
(COPPER)
VER 10
27
Effects of 25kv 50 cycles AC Traction on
Telecommunication.
It is reduced by the following..
 Changing over Overhead system to Under Ground Cables.
 It is consider that a normal filed strength of 87.5v/km exists in vicinity of
telecom cable . This induces a voltage of 8.75 v/km in each wire of cable
,because of its screening factor is 0.1 as cable length increase this voltages
also increases proportionately. If this longitudinally induced voltage
exceeds 150 v the safety and equipment becomes hazardous as per the
recommendations of ITU-T. It is essential to isolate all circuits from
induced voltage, so that its value will not raise above 150volts . For that
divide 150v by per-kilometer induced value 8.75/km of the cable, gives
17km of max. permissible length for cable circuits .Hence Isolating
circuits physically by providing Isolation Transformers at distance of 17km
on each circuit at cable Hut. By doing this accumulation of induced voltage
on the cable pairs is brought to Zero.
TELECOM CABLES
(COPPER)
VER 10
28
It is reduced by the following
 Provision of Earthing and SPD`s for all
telecomm Equipments as per RDSO
guidelines.
 By using seethed cables(Al or Pb) having good
screening factor.
 Screening factor is the ratio of induced
voltage of cable in presence of cable sheath
and induced voltage cable with out cable
sheath.
TELECOM CABLES
(COPPER)
VER 10
29
PRECATIONS TO BE TAKEV FOR PROTECTION OF STAFF AND EQUIPMENT IN
25kv 50 cycles AC TRACTION TERRRITORY.
Precaution are required on account of the flowing.
1. Proximity of Live Conductor
2. Pressure of return current in rails.
3. Induction in all metallic bodies situated close to overhead
equipment.
Precautions to be taken:1. Use Insulated Tools.
2. Use Rubber Gloves.
3. Use Rubber Mats.
4. Before cutting the armour or sheath of cables an electrical
connectivity to be made between two ends of the cable
through an external wire.
TELECOM CABLES
(COPPER)
VER 10
30
SIZE OF RE CABLES (l+m+n)
0 = No of carrier quads
3 = No of pet quads
17 = No of paper insulated quads
0 = No of carrier quads
2 = No of pet quads
18 = No of paper insulated quads
TELECOM CABLES
(COPPER)
VER 10
31
CONSTRUCTION OF 6Q CABLE
1. Conductor
2. Petroleum jelly
3. Dummy tube
4. Binder
5. Polyester tape
6. Poly aluminum tape
7. PVC inner jacket
8. Aluminum wire screen
9. Woven tape(yellow color)
10. PVC intermediate jacket
11. G.I. Steel armour
12. PVC outer jacket
TELECOM CABLES
(COPPER)
VER 10
32
SPECIFICATIONS OF 6Q CABLE RDSO SPN.N0:IRS-TC
30/2005
Version I.W.E.F:1-1-2006
1.
2.
1.
2.
3.
4.
5.
6.
7.
8.
9.
Loop resistance : 56Ω/Loop Km
Transmission loss : 0.25 dB/Loop Km( When loaded)
: 0.63 dB/ L.Km (When not loaded)
Impedance
: 470 Ω
Insulation resistance : >100 MΩ with 100V Megger
Conductor diameter : 0.9 mm
Thickness of sheath (PVC): 1.8 mm
Thickness of G.I. Armour: 4 X 0.8 mm
Thickness of inner PVC sheath: 1.8 mm
Thickness of Aluminum tape: 0.2mm±10%
Aluminum Screen : 36 no. of wires / 13 no. of strips
( depends on dia
/ thickness)
Mutual Capacitance : 0.05 uF/Km
TELECOM CABLES
(COPPER)
VER 10
33
Schematic representation of the elementary
components of a transmission Line.
where
R-is the resistance per unit length, L- is the inductance per unit length,
G- is the conductance of the dielectric per unit length, C-is the
capacitance per unit length,
TELECOM CABLES
(COPPER)
VER 10
34
WHAT IS LOADING OF CABLE
• For Attenuation free Transmission line. These line parameter
should Justify the follow equation.
•
LG=RC
but R C > L G
• R and C are very high due to thin and very closely spaced
conductors in the cable. It can not be
decreased by
increasing dia and spacing of the conductors due to limitation
of cable size. G- is the conductance (leakage) can not increase
due to low insulation of cable. The possibility is only adding
the Inductance to the transmission line. It is known as Loading
of cable.
TELECOM CABLES
(COPPER)
VER 10
35
LOADING
• Connecting the loading coils of value 118mH
in series with each conductor to reduce the
original attenuation of 0.63 dB to 0.25dB is
known as “Loading”
for 0.9 mm dia conductor
: 88 mH/ 1830 mtrs. ( RE Cable)
: 118 mH/ 2Km ( 6 Quad)
TELECOM CABLES
(COPPER)
VER 10
36
LOADING SECTION IN CASE OF 6Q CABLE
1. Loading section –
2000 Mtrs.
2. Normal joint -500
m
3. Condenser joint –
1000 Mtrs.
TELECOM CABLES
(COPPER)
VER 10
37
BALANCING OF CABLE
•
Bringing down the various capacitance unbalances below
the nominated value to reduce the noise & cross talk in
known as “Balancing”
• Permissible limits of capacitance unbalance for full and half
loading are 40 pF and 20 pF respectively.
• The capacitance unbalance exists between,
a) Conductors of a quad and sheath(Earthed). This is called
“Earth Coupling”.
b) Conductors of a quad and between adjacent quads. This is
called “Cross-talk Coupling”.
• Cross-talk couplings causes cross-talk and Earth couplings
cause ‘Noise’ in VF circuits.
TELECOM CABLES
(COPPER)
VER 10
38
COLOUR CODE & QUAD ALLOCATION IN NON-OFC SECTION AS
PER RLY.BOARD GUIDE LINES.LTR. NO.2003/TELE/TP/1 DT.8/8/03
Q.No
COLOUR OF INSULATION
Circuit
A-Wire
B-Wire C-Wire D-Wire
1
Orange
white
Red
Grey
BLOCK
2
Blue
White
Red
Grey
SEC.CTO
3
Brown
White
Red
Grey
EC
4
Green White Red
Grey
4/1-BPAC 4/2GATE PHONE
5
Yellow
White
Red
Grey
BPAC
6
Black
White
Red
Grey
TAWS
TELECOM CABLES
(COPPER)
VER 10
39
COLOUR CODE & QUAD ALLOCATION IN OFC SECTION
Q.No COLOUR OF INSULATION
Circuit
1
A-Wire B-Wire C-Wire D-Wire
Orange white Red
Grey Block
2
Blue
White
Red
Grey
Spare for
Block
3
Brown
White
Red
Grey
E.C CKT
4
Green
White
Red
Grey
4/1-LC GATE
4/2-BPAC
5
Yellow
White
Red
Grey
BPAC
6
Black
White
Red
Grey
TAWS
TELECOM CABLES
(COPPER)
VER 10
40
LAYING OF TELECOM QUAD CABLE
ASPER TELECOM MANUAL CHAPTERX III
TELECOM CABLES
(COPPER)
VER 10
41
Checks on receipt of drum
•
•
•
•
•
•
•
•
•
Drum length 1 Km Wt. 2MT approx
Drum no. , size of cable & diameter of conductor.
Manufacturer’s details
Length of cable
Address of consignee
Year of manufacturer
Net & Gross weight
Arrow indicating direction of rolling
End seal shall be checked & RDSO inspection marks
shall be seen
TELECOM CABLES
(COPPER)
VER 10
42
Handling cable drum
 Use crane / ramp for loading & unloading
 Use centre bar for carrying
 Drum shall not be dropped
 Cable shall not be kept flat
 Do not stock drums closely
TELECOM CABLES
(COPPER)
VER 10
43
Planning for laying
•
•
•
•
•
•
Survey of cable route
Mark details on 200m charts
– Track
– Yard
– Buildings
– LCs
– Bridges
– Water bodies
– Existing cable paths
– Likely track crossings
Consider 1 drum length (1 km) to cover 0.96 RKm (the margin take
scare of detour, crossing etc.)
Joint on either end of bridges
Locate ECs rationalizing no. of joints
Get approval of Engg. & S&T (Open line)
TELECOM CABLES
(COPPER)
VER 10
44
General precautions while laying
•
•
•
•
•
•
•
•
•
Do not drag the cable on ground
Cable to be carried using centre bar
Drum to be lifted with jack and rotated freely
Measure insulation before laying
Cable end sealing after laying
Drum no. & km no. to be noted
Straight line laying
Overlap to be left for jointing
Extra loop of 5/10 mtrs near
bridges/culverts/repeaters
TELECOM CABLES
(COPPER)
VER 10
45
Specific precautions while laying
•
•
•
•
•
•
•
•
Criteria
– At least 5.75 mtrs away from centre of track
– Beyond embankment
– Close to Railway Boundary
Normal soil - Trench depth 1 m, width 30 cm (depth shall not
be less than 70 cm in any case)
Rocky area – at least 30 cm depth & use of DWC/HDPE/RCC
pipe & concrete protection
Use of MS channels & GI trough on girder bridges
RCC / GI pipe protection on RCC culverts /bridges
Check for availability of cable duct on RCC bridges
LC gate crossing / track crossing – Use of GI pipes
Insulation test of drum before laying & jointly signed by
Maintenance & Construction representatives
TELECOM CABLES
(COPPER)
VER 10
46
No OFC or Quad Cables shall be laid
close to the existing track. It shall be
laid close to the Railway boundary on
one side of the Railway track to the
extent
possible
to
avoid
any
interference with the future works.
TELECOM CABLES
(COPPER)
VER 10
47
METHODS OF LAYING CABLE
 Methods of laying underground cables:
1. Laying direct in the ground
2. Drawing through ducts
3. Laying solid
4. Cable laying at road crossing
5. Cable laying on the long bridges
6. Cable laying at a railway track crossing
TELECOM CABLES
(COPPER)
VER 10
48
Laying direct in the ground
Digging the trench and putting the cable in it and
closing.
This method of laying cables is comparatively
simple and cheap, and is the one that is widely
used.
Depth of the trench is 100 cm and width is 30cm.
In case of Quad cable and OFC cable laying
together in same trench then the depth of the
trench is 120 cm with width of 30 cm.
TELECOM CABLES
(COPPER)
VER 10
49
Drawing through ducts
In this system, also known as the draw in
system, one or more ducts are laid together,
according to anticipated requirements and a
single or more cables according to size are
drawn through each pipe or duct. Manholes are
provided at definite intervals. The initial cost of
laying of ducts is high. The system is generally
used only in difficult location such as crossings,
railway bridges, culverts and in such situations
where subsequent excavation of a trench is both
very expensive and inconvenient.
TELECOM CABLES
(COPPER)
VER 10
50
Laying solid
• The places where the chemical soil is there,
the cable cannot be laid directly. After making
brick structure around it, the bitumen
compound to be filled around the cable, and
covered by bricks on the above.
• Laying solid is higher cost than laying direct.
TELECOM CABLES
(COPPER)
VER 10
51
Cable laying at road crossing
At road crossings cables should be laid in pipes.
Depth of the trench shall be 100 cm
RCC/GI/DWC Pipes should be laid with a slight
slope from the centre to the sides of the road
to prevent collection of water.
Trenching across roadways, for laying
cable may be by manual excavation, thrust
boring or tunnelling.
TELECOM CABLES
(COPPER)
VER 10
52
Cable laying on culverts and bridges
cables should preferably be laid in G.I. troughs /
DWC pipes.
Joints should be avoided, as far as possible, in
the middle of the bridge.
At the end of the bridge the cable should be
gradually sloped down to normal trench depth
through pipes. This is necessary to protect the
cable from theft and damage by pedestrians or
vehicular traffic.
TELECOM CABLES
(COPPER)
VER 10
53
Cable laying at railway track crossing
 It should be laid in RCC/ GI / DWC pipes of
not less than 75mm diameter at a minimum
depth of 1.25 meters below rail level.
The pipeline should extend on both sides of
the Railway track for sufficient distance to
enable repairs to the cable being undertaken
without the necessity of disturbing the
formation under the Railway track.
TELECOM CABLES
(COPPER)
VER 10
54
STEPS IN LAYING
1.
2.
3.
4.
5.
Trenching
Cleaning the trench
Drawing the cable
Putting the bricks over it if necessary.
Closing the trench with earth. Wlile closing
suitable cable marker to be installed over it.
TELECOM CABLES
(COPPER)
VER 10
55
Length of 6 Quad Cables
The Quad cable length is worked out on
following basis to arrive at the location of the
straight joints.
a) Route length as per actual measurement
plus contour allowances of 2.5%.
b) Extra length for track crossing including
2.5-meter loop on each side etc.
c) Extra length on approach crossing of the
bridges and 5 meters on measurement in the
detailed survey.
TELECOM CABLES
(COPPER)
VER 10
56
d) 10 meter of cable to be kept on either side of
major steel bridges and 5 meters on minor
bridges.
e) At every joint a loop of 10 meters on either
side.
f) At Station a loop of 10 meters in the cable pit.
TELECOM CABLES
(COPPER)
VER 10
57
TESTING OF CABLE
TELECOM CABLES
(COPPER)
VER 10
58
TESTING OF CABLE
TYPES OF TESTING:
1. Testing before laying of cable.
2. Testing after laying of cable.
3. Fault localization tests.
4. Testing of cable before commissioning of
BPAC/SSDAC/MSDAC( as per RDSO lr.
no.sts/e/ssdac/spn/177 dtd.28/30-8-6)
5. Routine Testing (as per Telecomm Manual)
TELECOM CABLES
(COPPER)
VER 10
59
TESTING BEFORE LAYING
a) Test the cable for proper end sealing.
b) Checking for any physical/Mechanical
damages during transportation, and during
manufacturing. Etc.,
TELECOM CABLES
(COPPER)
VER 10
60
TESTS AFTER COMPLETION OF CABLE
LAYING
a) Continuity test – Ohm-meter / Multi meter
b) Absence of crosses – Ohm-meter / Multi
meter
c) Absence of contacts – Volt-meter/Ohm
meter / Multi meter
d) Insulation testing – Insulation tester /
Insulation Megger.
TELECOM CABLES
(COPPER)
VER 10
61
ROUTINE TESTS in QUAD CABLE
AS PER TELECOMM MANUAL CHAPTER VIII
a)
b)
c)
d)
e)
Conduction test.- Monthly
Transmission loss test.- Monthly
Crosstalk (near end far end)- Quarterly
Psophometric Noise- Quarterly
Insulation test – Yearly
TELECOM CABLES
(COPPER)
VER 10
62
Mandatory Check &Tests to be don before
commissioning of BPAC/SSDAC/MSDAC Applications
on Quad/PIJF cables.
a)
b)
c)
d)
e)
f)
g)
h)
i)
j)
•
•
Conduction test.-56 ohms/loop km
Insulation Resistance – 10 M Ohms.
Transmission loss test.-At 2khz/600ohms Transmission loss should not be more
than 30 db for full length of quad cable.
Near end Crosstalk- Should be better than -55 dbm at 155khz &-61 dBm at 1KHz
Far End Crosstalk- Should be better than -55 dbm at 155khz & -65 dBm at 1KHz
Psophpmetric Noise- should not be more than 2mv.
Continuity of Armour - Should be Ensured
Earth Resistance at Armour-Should be Ensured less than 1 Ohm.
Position of one quad in quad cable
x(A)
x (C)
x (D) 1st PAIR-AB
x (B)
2ed PAIR-CD
Each Quad is binded by respective quad colour binder
TELECOM CABLES
(COPPER)
VER 10
63
Precautions to be taken while using quad cable
• Designated pair of wire of same quad should be used.
• Do not use one wire of one quad and another wire from other
quad.
• If any wire of a pair of the quad is broken then use fresh pair
of wire should be used.
• No wire should be paralleled for reducing the conductor
resistance.
TELECOM CABLES
(COPPER)
VER 10
64
CONDUCTION TEST
a)
Purpose of this test is to
measure the loop resitance of
conductors which indicates the
condition of joints.
b) Measuring instrument used:
Ohm meter or Bridge Megger.
c) Time of measurment: Hotest
period of the day in case of
Over Head lines / at any time in
cable.
d) Acceptance value: 5% more
than standard values.
+--
TELECOM CABLES
(COPPER)
VER 10
65
TRANSMISSION LOSS TEST
a)
Purpose of this test is to
measure the dB loss of the
system (cable). It also
indicates the insertion loss
of way station
equipments.
b) Time of measurement:
coldest period of night i.e. 4
AM to 5AM in case of over
head lines / any time in
case of cables.
c) Instrument used:
TMS Kit.
TELECOM CABLES
(COPPER)
VER 10
66
INSULATION RESISTANCE
a) Purpose of this test
is to know the
proper insulation of
the conductor.
b) Time of
measurment: Any
time of the day.
c) Instrument used:
Insulation Megger.
TELECOM CABLES
(COPPER)
VER 10
67
STANDARD VALUES
Sl No
Description
1
Loop Resistance in Ω
2
3
Insulation in MΩ
25.4 Ω /L.Km
a) G.I wire of 3.55mm dia
5.62 Ω / L.Km
b) ACSR wire of6/1/1.5 mm
c) cable conductor of dia 0.9mm 56 Ω / L.Km
2 mill volts
a) Psophpmetric Noisea)
b)
4
Value
100 MΩ
>1000 MΩ
>
With 100V Megger
With 500V Megger
Transmission loss in Db
a)
b)
c)
Cable conductor of dia 0.51 mm
Cable conductor of dia 0.63 mm
Cable conductor of dia 0.9 mm
TELECOM CABLES
(COPPER)
VER 10
1.379
1.107
o.63 (UN-LOADED)
0.25 (LOADED}
68
JOINTING OF TELECOM CABLE(6Q)
• Now a days to make any telecom cable joint
Thermo Shrinkable Jointing Kit is used (TSF
kit).
• To make 6quad cable joints universal TSF kit
under RDSO Specification IRS-TC-77/2012 is
used.
• To make cable joints for PIJF Under Ground
telephone cable universal TSF kit under RDSO
Specification IRS-TC-57/2006 is used.
•TELECOM CABLES
(COPPER)
VER 10
69
CABLE JOINTS
6 QUAD CABLE
TELECOM CABLES
(COPPER)
VER 10
70
JOINTS IN 6-QUAD CABLE
1. Normal joint: To join two lengths of cable.
2. Transformer joint / Derivation joint: This is
made whenever we want to extend the
control/block to any place.
3. Loading coil joint: To reduce the original
attenuation of the cable to a lower value.
4. Condenser joint: To minimize the noise and
cross talk in the cable.
TELECOM CABLES
(COPPER)
VER 10
71
JOINTING OF TELECOM CABLE(6Q)
Now a days to make any telecom cable joint
Thermo Shrinkable Jointing Kit is used (TSF
kit).
To make 6quad cable joints universal TSF kit
under RDSO Specification is used.
IRS-TC-77/2012. is the specification number of
the RTSF kit.
IRS-TC-57/2012 TSF JOINTING KIT FOR PJF
CABLES OF DIFRENT SIZES.
TELECOM CABLES
(COPPER)
VER 10
72
JOINTS IN LOADING SECTION
TELECOM CABLES
(COPPER)
VER 10
73
JOINTING PRECAUTIONS
1. The mud around the tent should protect the pit
from entry of water.
2. The joint should be kept at the same horizontal
level.
3. The end of the cable should meet the other end
of the subsequent cable length with
appropriate loops.
4. A heap of mud is to be placed over the buried
joint so that the water flows away from the
joint.
TELECOM CABLES
(COPPER)
VER 10
74
Causes for cable failures & precautions
 Manufacturing defects – Test the cable before laying.
 Laying of cable at lower depth – Check the depth of trench
before closing the cable trench.
 Joint failure due to sub stranded/ expired jointing kit used or
jointing done by un skilled jointer- Use RDSO approved RTSF
jointing kit and ensure skilled jointer before starting the
work.
 Cable joint burnt due to Lightning - Ensure the proper
continuity of metallic protection mechanism before closing
the joint and Earth Resistance shall be less than 1 ohm at
both ends of cable termination.
TELECOM CABLES
(COPPER)
VER 10
75
• Using of Quad cable without jelly – Water enters into the
joint along with cable core when there is any cable
damage(crow bar hit) in between two joints- Use the PIJF 6
quad cable as per RDSO spec no. IRS:TC 30-2005 ver.1.
• Exposing of cables on Bridges/ Culverts/Rocky areas- Regular
Cable route inspection shall be done by section
Technician/JE/SSE and strengthening of cable route shall be
carried out as per Railway Board Telecom Action plan.
TELECOM CABLES
(COPPER)
VER 10
76
Cable cuts and thefts- Ensure the cable is
with in Railway Boundary, avoid the exposing
of cable, implement the Railway Board JPO,
Update the cable route diagrams and upload
to web page for easy access to concerned
dept.
Codal life of Cable- Plan for replacement of
cable with in codal life (20 / 25 years).
TELECOM CABLES
(COPPER)
VER 10
77
Typical 6 Quad cable failures & their causes
1. Cable burnt at joint due to lightning and all
circuits failed- Armour connectivity at joint
is given up.
2. Cable is noisy while train passing in the
section BPAC circuit frequently failingimproper earthing of cable armour/ screen/
Al. moisture barrier.
TELECOM CABLES
(COPPER)
VER 10
78
Typical 6 Quad cable failure
contd.
• Abnormal delay (48 hrs) in restoring of 6 quad
cable fault: Cable not traceable because cable is laid
outside Railway Boundary and the Colony people
constructed culvert on the cable route for about
10mts. The drainage water was over flowing and
spread over the area and got covered with thick
bushes also. Staff not able to walk on the cable
route with cable route locater and could not locate
the cable the fault. Later, found Cable was in
damaged condition in the culvert.
TELECOM CABLES
(COPPER)
VER 10
79
Thank you
TELECOM CABLES
(COPPER)
VER 10
80