IEC TR 62691:2011

IEC/TR 62691 ®
Edition 1.0 2011-12
TECHNICAL
REPORT
colour
inside
Optical fibre cables –
Guide to the installation of optical fibre cables

IEC/TR 62691:2011(E)
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IEC/TR 62691 ®
Edition 1.0 2011-12
TECHNICAL
REPORT
colour
inside
Optical fibre cables –
Guide to the installation of optical fibre cables

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
U
ICS 33.180.10 ISBN 978-2-88912-817-4

– 2 – TR 62691 © IEC:2011(E)
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Installation planning . 7
3.1 Installation specification . 7
3.2 Route considerations . 7
3.3 Cable installation tension considerations . 8
3.4 Cable tension predictions – duct installations . 8
3.5 Maximum cable tension . 9
3.5.1 General . 9
3.5.2 Total cable tension – pulling applications . 9
3.5.3 Total cable tension – pushing, blowing, or pulling applications . 11
3.6 Installation temperature . 15
3.7 Information and training . 16
4 Cable installation methods. 16
4.1 General considerations . 16
4.2 Safety in confined spaces . 16
4.3 Pre-installation procedures . 16
4.4 Installation of optical cables in underground ducts . 17
4.4.1 Application . 17
4.4.2 Installation using trenchless technique . 17
4.4.3 Cable overload protection methods . 17
4.4.4 Cable bending and guiding systems . 17
4.4.5 Winching equipment and ropes . 18
4.4.6 Cable friction and lubrication . 18
4.4.7 Cable handling methods to maximise installed lengths . 19
4.4.8 Jointing length allowance . 19
4.4.9 Blowing techniques for the installation of fiber optic cables into ducts. 20
4.4.10 Optical fibre cable installation by floating technique . 20
4.5 Installation of aerial optical cables . 20
4.5.1 Application . 20
4.5.2 Installation methods . 20
4.5.3 Cable protection methods . 21
4.5.4 Winching and guiding systems . 21
4.5.5 Methods to maximise lengths . 21
4.5.6 Jointing length allowance . 21
4.5.7 In-service considerations . 21
4.6 Installation of buried cable . 22
4.6.1 Installation methods . 22
4.6.2 Cables in trenches . 22
4.6.3 Installing cables by ploughing . 23
4.6.4 Methods to maximise lengths . 23
4.6.5 Jointing length allowance . 23
4.7 Installation in special situations . 24
4.7.1 Tunnel and building lead-in . 24
4.7.2 Bridges . 24

TR 62691 © IEC:2011(E) – 3 –
4.7.3 Underwater . 24
4.7.4 Storm and sanitary sewers . 24
4.7.5 High pressure gas pipes . 24
4.7.6 Drinking water pipes . 24
4.7.7 Industrial environments . 25
4.8 Installation of indoor cables . 25
4.8.1 General considerations . 25
4.8.2 Cable routing . 25
4.8.3 Confined spaces . 25
4.9 Blown systems . 25
4.9.1 General considerations . 25
4.9.2 Installation of cables in the vertical riser area of buildings . 26
4.9.3 Tube installation . 26
4.9.4 Fibre and cable installation . 27
4.10 Cable location . 28
5 Lightning protection . 28
Bibliography . 29

Figure 1 – Cable tension calculations (equations. 1 through 3) . 10
Figure 2 – Cable tension calculations (equations. 4 through 9) . 12
Figure 3 – Cable tension calculations; Series1 = blowing; Series2 = pushing;
Series3 = pulling . 15
Figure 4 – Optical fibre cabling in an underground duct . 20
Figure 5 – Aerial cable installation . 22
Figure 6 – Cable installation by cascade blowing . 28

Table 1 – Calculation for total tension . 10
Table 2 – Calculation for pulling force in Figure 2 . 12
Table 3 – Calculation for pushing force in Figure 2 . 13
Table 4 – Calculation for blowing force in Figure 2 . 14
Table 5 – Minimum installation depths . 23

– 4 – TR 62691 © IEC:2011(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL FIBRE CABLES –
Guide to the installation
of optical fibre cables
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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with the International Organization for Standardization (ISO) in accordance with conditions determined by
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC 62691, which is a technical report, has been prepared by subcommittee 86A: Fibres and
cables, of IEC technical committee 86: Fibre optics.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
86A/1415/DTR 86A/1426/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.

TR 62691 © IEC:2011(E) – 5 –
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
A bilingual version of this publication may be issued at a later date.

– 6 – TR 62691 © IEC:2011(E)
OPTICAL FIBRE CABLES –
Guide to the installation
of optical fibre cables
1 Scope
Optical fibre cabling provides a high performance communications pathway whose
characteristics can be degraded by inadequate installation. This technical report provides
guidance to assist the user and installer with regard to the general aspects of the installation
of optical fibre cables covered by the IEC 60794 series of specifications, and the particular
aspects of the 'blowing' technique.
Optical fibre cables are designed so that normal installation practices and equipment can be
used wherever possible. They do, however, generally have a strain limit rather lower than
metallic conductor cables and, in some circumstances, special care and arrangements may be
needed to ensure successful installation.
It is important to pay particular attention to the cable manufacturer's recommendations and
stated physical limitations and not exceed the given cable tensile load rating for a particular
cable. Damage caused by overloading during installation may not be immediately apparent
but can lead to failure later in its service life.
This guide does not supersede the additional relevant standards and requirements applicable
to certain hazardous environments, e.g. electricity supply and railways.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60794-3 series, Optical fibre cables – Part 3: Sectional specification – Outdoor cables
IEC 60794-3-40, Optical fibre cables – Part 3-40: Outdoor cables – Family specification for
sewer cables and conduits for installation by blowing and/or pulling in non-man accessible
storm and sanitary sewers
IEC 60794-3-50, Optical fibre cables – Part 3-50: Outdoor cables – Family specification for
gas pipe cables and subducts for installation by blowing and/or pulling/dragging in gas pipes
IEC 60794-3-60, Optical fibre cables – Part 3-60: Outdoor cables – Family specification for
drinking water pipe cables and subducts for installation by blowing and/or
pulling/dragging/floating in drinking water pipes
IEC/TR 62362, Selection of optical fibre cable specifications relative to mechanical, ingress,
climatic or electromagnetic characteristics – Guidance
IEC/TR 62470, Guidance on techniques for the measurement of the Coefficient Of Friction
(COF) between cables and ducts
ISO/IEC 24702, Information technology – Generic cabling – Industrial premises

TR 62691 © IEC:2011(E) – 7 –
ISO/IEC TR 29106, Information technology – Generic cabling – Introduction to the MICE
environmental classification
ITU-T Recommendation K.25, Protection of optical fibre cables
ITU-T Recommendation L.35, Installation of optical fibre cables in the access network
ITU-T Recommendation L.38, Use of trenchless techniques for the construction of
underground infrastructures for telecommunication cable installation
ITU-T Recommendation L.57, Air-assisted installation of optical fibre cables
ITU-T Recommendation L.61, Optical fibre cable installation by floating technique
ITU-T Recommendation L.77, Installation of optical fibre cables inside sewer ducts
3 Installation planning
3.1 Installation specification
The successful installation of an optical fibre cable can be influenced significantly by careful
planning and assisted by the preparation of an installation specification by the user. The
installation specification should address the cabling infrastructure, cable routes, potential
hazards and installation environment and provide a bill of materials and technical
requirements for cables, connectors and closures.
The installation specification should also detail any civil works, route preparation (including
drawpits, ductwork, traywork and trunking) and surveying that are necessary, together with a
clear indication of responsibilities and contractual interfaces, especially if there are any site or
access limitations.
Post installation requirements for reinstatement, spares, ancillary services and regulatory
issues should also be addressed.
3.2 Route considerations
Whilst optical fibre cables are lighter and installed in longer lengths than conventional metallic
cables, the same basic route considerations apply.
Route planning and cable handling methods must carefully take into account the specified
minimum bending radius and maximum tensile loading of the particular optical fibre cable
being installed so that fibre damage, giving rise to latent faults, can be avoided.
Some of the most difficult situations for the installation of optical fibre cables are in
underground ducts and the condition and geometry of duct routes is of great importance.
Where the infrastructure includes ducts in poor condition, excessive curvature, or ducts
already containing cables or access points with abrupt changes of direction, the maximum pull
distance will be reduced accordingly.
Provision of long cable lengths in underground duct or aerial situations may involve
installation methods that require access to the cable at intermediate points for additional
winching or blowing effort, or “figure 8” techniques, these sites should be chosen with care.
Consideration should also be given to factors of time and disturbance. Installation equipment
may be required to run for long periods of time and the time of day, noise levels, and
vehicular traffic disruption should be taken into account.

– 8 – TR 62691 © IEC:2011(E)
Because the condition of underground ducts intended for optical fibre cable is of particular
importance, care should always be taken to ensure that ducts are in sound condition and as
clean and clear as possible. Consideration can also be given to the provision of a sub-duct
system, either in single or multiple form, to provide a good environment for installation,
segregation of cables, extra mechanical protection and improved maintenance procedures.
Sub-ducts can be more difficult to rope and cable than normal size ducts, particularly over
long lengths, and the diameter ratio between the cable and subduct should be considered.
Note that in ducts or subducts, bundles of microducts can also be installed, e.g. by pulling or
blowing.
For overhead route sections, a very important consideration is the need to minimise in-service
cable movement. Movement of the cable produced by thermal changes, cable weight, ice
loading, wind, etc. may have a detrimental effect. A stable pole route, with all poles set as
rigidly as possible, is therefore an important element in reducing possible movement and
consideration should be given to purpose-designed, optical fibre-compatible, pole top fittings
and attachments.
Although optical fibre cables are generally light in weight, their addition to an existing
suspension member can take the optical fibre beyond its recommended strain limit and the
added dip and extension should be calculated before installation.
Where it is planned for long lengths of optical fibre cable to be directly buried or ploughed,
those sections involving ploughing can, with advantage, be pre-prepared using specialised
slitting or trenching equipment.
3.3 Cable installation tension considerations
The potential for providing very long lengths of optical fibre cable can lead to the need for
confidence that a particular installation operation will be successfully achieved, particularly in
underground ducts, and a good indication can be provided, in some cases, by calculating the
maximum cable tension. This maximum tension can be compared with the stated mechanical
performance of the cable and, where these values are close, consideration can be given to
methods for providing a greater margin of safety such as an alternative cable design,
shortening the route, changing the route or direction of cabling, provision of intermediate
winches, or by taking special precautions at particular locations. Calculation considerations
are indicated in the clauses which follow.
Cable tensions in overhead installations where the cable is lashed or clipped to a messenger
strand or other supporting members are generally minimal. Rollers or similar types of
hangers are used to support the cable at frequent intervals such that it does not sag during
the installation process. Rollers, quadrant blocks, or other guides should be used when the
cable line changes direction in order to minimize cable tensions and support the cable’s
minimum bend radius. If cables are pulled from the end, many of the same considerations for
pulling into ducts are present, though generally with lower tensions. Changes in elevation
may increase the tension, and must be considered. Moving reel installation methods
generally exhibit minimal cable tension, but jerking of the cable due to reel inertia and
movements must be guarded against. See the further discussion in 4.5. Considerations for
self-supporting cables (figure-8 or ADSS, for example) are addressed in 4.5.
Cable tensions in ploughing or trenching are generally minimal, much smaller than the rated
tension of the cable. Momentary tensions and jerking due to cable reel inertia when paying
off cables, which result in tensions in the immediate area being installed, should be
considered. In ploughing, frictional tension through the plough chute must be considered, but
is generally small. See also 3.6.
3.4 Cable tension predictions – duct installations
It should be noted that the tension calculations for duct installations are of necessity inexact
since the actual geometry and characteristics of the ducts are seldom well known. The

TR 62691 © IEC:2011(E) – 9 –
calculations, therefore, should be utilized with regard to experience and empirical data from
similar installations.
Two sets of equation are presented below. The first, presented in 3.5.2, is used to calculate
cable tension in pulling applications. The second, presented in 3.5.3, is used to calculate
cable tension in cable pushing and blowing applications; it may also be used for pulling. Note
that the first set, for pulling only, is much simpler and neglects cable weight in Equation 3.
The second equation, for any of the duct installation methods, comprises very complex
equations involving much more data, including amplitude and frequency of innerduct
undulations. Much of this sort of data are generally not known and must be estimated from
cable experiments and empirical data from similar installations.
3.5 Maximum cable tension
3.5.1 General
The following main contributory functions need to be considered when calculating cable
tensions:
– the mass per unit length of cable;
– the diameter of the cable;
– the stiffness of the cable;
– the coefficient of friction between cable sheath and surfaces with which it will come in
contact;
– the inner diameter of the duct;
– deviations (bends and undulations) and inclinations.
3.5.2 Total cable tension – pulling applications
Using the routes and common tension formulae in Figure 1 as an example:

– 10 – TR 62691 © IEC:2011(E)
Feed end
A
Pulling end
30°
200 m
G
45°
1 in 8 down
1 in 10 up
250 m
F
60 m
Level
90°
20 m
E
100 m
160 m
B
Level
1 in 6 up Level
C D
IEC  2576/11
T is the tension at end of section (N);
T is the tension at beginning of section (N);
i
µ is the coefficient of friction (between cable and duct or guide);
l is the length of section (m);
w is the cable specific mass (kg/m);
θ is the inclination (radians, + up, – down) or deviation (radians, horizontal plane);
g is the acceleration due to gravity (9,81 m/s²);
T = Ti + µlwg Equation 1 (for straight sections)
T = Ti + lwg (µ cosθ + sinθ) Equation 2 (for inclined sections)
T = Ti eµθ Equation 3 (for deviated sections and bends)
Figure 1 – Cable tension calculations (equations. 1 through 3)
The resulting total tension calculations are shown in Table 1:
Table 1 – Calculation for total tension
Section Length Tension at Inclination Deviation Equation Tension at end
beginning of of section
section T (cumulative) T
i
m N rad rad N
A – 0 – – – 0
A – B 250 0 0,100 – 2 1 460
B – 1 460 – 1,571 3 3 464
B – C 160 3 464 0,165 – 2 4 484
C – 4 484 – – – 4 484
C – D 100 4 484 – – 1 4 980
D – 4 980 – – – 4 980
D – E 20 4 980 0,785 3 7 669
E – 7 669 – – – 7 669
E – F 60 7 669 – – 1 7 967
F – 7 967 0,524 3 10 628
F – G 200 10 628 – 0,124 – 2 11 390

TR 62691 © IEC:2011(E) – 11 –
NOTE Where more than one cable per duct is installed, tension can be greatly raised and it is necessary to take
account of this by applying a factor before the deviation calculation. Factors vary with the number of cables,
sheath/cable materials, cable/duct sizes, cable flexibility, etc. Values can be in the order of 1,5 to 2 for two cables,
2 to 4 for three cables and 4 to 9 for four cables.
3.5.3 Total cable tension – pushing, blowing, or pulling applications
Total tension can be calculated on a cumulative basis working through each section from one
end of the route to the other. Calculation is done using the common tension and blowing
formulae listed below:
 
 
WP 8πAfl 8πA 3AB 48B
−1
F= sinh +sinh  F+  − Horizontal pulling, Equation 4
 i 
2 2 4 2
 
8πA P WP 2W(P/4) πP
 
 
8πfA
2 2
l
 
WP 48B 2 WP 48B
P
F=F± + e  − (+ . – for upwards)  Vertical pulling, Equation 5
i
 2 2
8πfA πP 8πfA πP
 
2Bf
fθ
F= Fe + Deviations and bends, Equation 6
i
6(D −D )R )
d c b
 
dF 3AB 8πA
= f (W cosα) + + F +W sinα Inclined pulling, Equation 7
 4 2 
dx 2(P/4) P
 
dF  AB A  D −D
3 8π  
d c 2
= f (W cosα) + + F + F +W sinα  Inclined pushing,
 
 
4 2 2
dx 2(P/4) P π B
 
 
Equation 8
2 2
  D −D πD D(p − p )
dF 3AB 8πA  
d c 2 c d i
= f (W cosα) + + F + F +W sinα−
 
 4 2  2
dx 2(P/4) P π B
  x
 
2 2 2
8l p −(p − p )
i i
l
Blowing (inclined), Equation 9

F  = force at end of section (N)
F = force at beginning of section (N)
i
f  = coefficient of friction, COF (between cable and duct or guide)
m = cable specific mass (kg/m)
l = length of duct (m)
W = cable specific weight = gm (N/m)
g = acceleration of gravity (9,81 m/s )
B = cable stiffness (Nm )
D = cable diameter (m)
c
D = duct inner diameter (m)
d
A = amplitude of duct-undulations (m)
P = period of duct-undulations (m)
R = bending radius of bend (m)
b
θ = deviation of bend (radians, horizontal plane)

– 12 – TR 62691 © IEC:2011(E)
α = inclination (radians, + up, – down)
p = air pressure (absolute) at beginning of section (N/m )
i
)
p = air pressure (absolute) at end of section (N/m
x = position in the section (m)
Equations 4, 5 and 6 are analytical solutions, equations 7, 8 and 9 have to be solved
numerically.
The example in Figure 2 is given as an illustration.
A cable with diameter of 18 mm, weight of 2 N/m and stiffness 5 Nm is installed in a
40/33 mm duct of 2 000 m total length laid in the trajectory below (the red sections are
vertical):
400 600 1 950 1 990
400 600 1950 1990
2 000
1 960 1 980
1960 1980
1 850
1 900
1900 1850
1 600
200 1600
1 800
5 10 50
5 10 50
20 40
20 40
1 000 1 400
1000 1400
IEC  2577/11
Figure 2 – Cable tension calculations (equations. 4 through 9)
The COF between cable and duct is 0,1, the (right-angled) bends in the trajectory are of
radius of 1,2 m and the straight sections still make undulations with amplitude of 5 cm and
period of 8 m.
IEC/TR 62470 describes techniques to measure the coefficient of friction (COF) between
cables and ducts.
Pulling force:
The pulling force is calculated for the situation that the winch is placed at the beginning of the
trajectory. The cable is placed somewhere in the field. First the pulling force is calculated for
one location of the cable, at 1 100 m, with boundary condition that the cable enters the duct
without any tension as shown in Table 2.
Table 2 – Calculation for pulling force in Figure 2
Position (m) Pulling force (N)
1 100 0
1 000, before bend 20
1 000, after bend 26
600, before bend 127
600, after bend 151
TR 62691 © IEC:2011(E) – 13 –
Position (m) Pulling force (N)
400, before bend 236
400, after bend 279
200, before bend 421
200, after bend 495
150, before bend 547
150, after bend 642
100, before bend 709
100, after bend 833
50, before bend 920
50, after bend 1 079
40, before bend 1 080
40, after bend 1 266
20, before bend 1 317
20, after bend 1 544
10, before bend 1 595
10, after bend 1 869
5, before bend 1 887
5, after bend 2 210
0 2 232
In Figure 3 the pulling force is also plotted for other lengths.
Pushing force:
The pushing force is calculated for the situation that the pushing device is placed at the
beginning of the trajectory. The cable is placed at the same location. First the pushing force is
calculated for one location of the cable, at 450 m, with boundary condition that the pushing
force at the cable end is zero as shown in Table 3.
Table 3 – Calculation for pushing force in Figure 2
Position (m) Pushing force (N)
450 0
400, before bend 10
400, after bend 14
200, before bend 59
200, after bend 72
150, before bend 86
150, after bend 103
100, before bend 131
100, after bend 156
50, before bend 202
50, after bend 239
40, before bend 282
40, after bend 333
20, before bend 415
– 14 – TR 62691 © IEC:2011(E)
Position (m) Pushing force (N)
20, after bend 488
10, before bend 558
10, after bend 655
5, before bend 720
5, after bend 845
0 950
NOTE that the available software only gives the end-result of 950 N. In Figure 3 the pushing force is also plotted
for other lengths.
Blowing force:
The blowing force is calculated for the situation that the blowing device is placed at the
beginning of the trajectory. The cable is placed at the same location. The calculation is done
for a pressure at the cable inlet of 12 bar relative to atmosphere (13 bar absolute) and the
duct open at 2 000 m. Note that the calculation starts with the cable-end at the "critical point",
the position where the pushing force reaches a maximum, at the bend at 1 000 m (beyond this
position the airflow propelling forces become larger than the friction forces). The calculation
does not take into account the effect of the filling of the duct with cable on the airflow (which
shifts the critical point to a position further in the trajectory), which makes the calculation
worst case. In this example the full 2 000 m can be bridged by blowing. This is illustrated in
Table 4.
Table 4 – Calculation for blowing force in Figure 2
Position (m) Pushing force (N)
1 000, before bend 0
1 000, after bend 2.5
600, before bend 5
600, after bend 8
400, before bend 13
400, after bend 18
200, before bend 26
200, after bend 34
150, before bend 38
150, after bend 47
100, before bend 52
100, after bend 64
50, before bend 70
50, after bend 85
40, before bend 108
40, after bend 130
20, before bend 136
20, after bend 161
10, before bend 142
10, after bend 169
5, before bend 171
5, after bend 204
0 208
TR 62691 © IEC:2011(E) – 15 –
In Figure 3 the pushing force is also plotted for other lengths. Note that calculation is still
done with the duct open at the corresponding lengths. Also note that the plotted pushing force
in Figure 3 is a little higher than the force in the table. The forces plotted in Figure 3 are
obtained with software that also takes into account that the cable end needs a little higher
pushing force when exactly in the bend than when passed. This is why a bend is picked as
the critical point, while the airflow propelling forces were already a little higher than the
friction forces.
202 00000
1 500
1 000
Serie 1
Series1
Series 2
Series2
Series 3
Series3
0 500 1 000 1 500
0 500 1000 1500 2 0002000
-5–00500
-–101 00000
Position x  (m)
Position x (m)
IEC  2578/11
Figure 3 – Cable tension calculations; Series1 = blowing;
Series2 = pushing; Series3 = pulling
3.6 Installation temperature
Installation temperature may affect installation procedures and it is good practice to install
optical fibre cables, particularly in long lengths only when the temperature is within the limits
set by the particular cable manufacturer.
The mechanical properties of optical cables are also dependent on the temperature and the
materials used in their construction. Typically, cables containing PVC in their construction
should not be installed when their temperature is below 0 °C whilst cables incorporating
polyethylene can be installed when their temperature is down to – 15 °C. For most cables the
upper installation temperature limit is + 50 °C. Unless special measures are taken, cables
should not have been exposed to temperatures outside the specified installation temperature
range for a period of 12 h prior to installation.
NOTE Polyethylene which is used as a common sheath material starts softening around 50 °C. Thus the
coefficient of friction increases remarkably. This will impact installation performance (pulling, pushing, blowing)
negatively.
Cable tension F  (N)
Cable tension F (N)
– 16 – TR 62691 © IEC:2011(E)
3.7 Information and training
Methods and practices used in the handling of optical fibre cables during installation can,
without producing any immediately obvious physical damage or transmission loss, affect their
long-term transmission characteristics.
Technicians involved in installation procedures should be made fully aware of the correct
methods to employ, the possible consequences of employing incorrect methods, and have
sufficient information and training to enable cables to be installed without damage to fibres.
In particular, installation crews should be made aware of minimum bending criteria, and how
easy it is to contravene these when installing by hand.
4 Cable installation methods
4.1 General considerations
Optical fibre cable can be installed using the same or similar general methods employed for
metallic cables but with more attention required to certain aspects such as long lengths, cable
bending and cable strain and it may be necessary to employ particular methods and
equipment in some circumstances. Optical fibre must be protected from excessive strains,
produced axially or in bending, during installation and various methods are available to do
this. The aim of all optical fibre, cable-placing methods and systems should be to install the
cable with the fibre in an as near as possible strain-free condition, ready for splicing.
Other general precautions:
– delivery of cable to site should be monitored to ensure that no mechanical damage occurs
during off-loading from vehicles;
– storage conditions should be suitable, taking into account mechanical and environmental
considerations;
– documentation should be checked to ensure that cable delivered is in accordance with the
procurement specification;
– suitable protective caps should be fitted to the exposed ends of the optical cable. End
caps should be handled carefully to avoid damage during installation, and any damaged
caps should be repaired or replaced.
4.2 Safety in confined spaces
During the installation of optical fibre cables, it may be necessary to work in confined spaces
such as manholes, underground passageways, tunnels and cable ways and areas where air
circulation is poor or where entry and exit is difficult.
Where the possibility of working in confined spaces exists, it is necessary to consider any
health and safety hazards that may be present, such as explosive, asphyxiating or toxic
gases, lead, asbestos, etc. and ensure that any additional safety equipment and/or instruction
is provided prior to the commencement of work.
4.3 Pre-installation procedures
Before installation commences, the installer should carry out the following checks:
– establish that the routes defined in the installation specification are accessible and
available in accordance with the installation programme. The installer should advise the
user of all proposed deviations;
– establish that the environmental conditions within the routes and the installation methods
to be used are suitable for the design of optical cable to be installed;

TR 62691 © IEC:2011(E) – 17 –
– determine any measures necessary to prevent the optical fibre within the optical cable
experiencing direct stress following installation. Where long vertical runs are proposed,
optical cables may need to deviate from the vertical at intervals as recommended by the
manufacturer (by the inclusion of short horizontal runs, loops or support arrangements);
– determine the proposed locations at which drums (or reels) shall be positioned during the
installation programme and establish the accessibility and availability of those locations;
– identify proposed locations of service loops and establish their accessibility and
availability in accordance with the installation programme;
– ensure that all necessary installation accessories are available;
– identify proposed locations of closures and establish their accessibility and availability in
accordance with the installation programme.
The closures should be positioned so that subsequent repair, expansion or extension of the
installed cabling may be undertaken with minimal disruption and in safety.
4.4 Installation of optical cables in underground ducts
4.4.1 Application
A typical underground duct installation is shown in Figure 4.
4.4.2 Installation using trenchless technique
Installation of ducts using trenchless techniques can reduce environmental damage and social
costs and at the same time, provide an economic alternative to installing ducts by digging
methods.
This technique is described in ITU-T, L.38.
4.4.3 Cable overload protection methods
Where all actions and precautions have been taken to protect the cable and its fibres from
excessive load as far as suitability of route, guiding etc. is concerned, then there still remains
the possibility, in the dynamics of an installation operation, for high loads to be applied to the
cable and it may be advisable to provide a cable overload prevention mechanism. Two
classes of device provide this protection: those situated at the primary or intermediate winch
and those at the cable/rope interface. Those at the winch include (depending on winch type)
mechanical clutches, stalling motors and hydraulic bypass valves which can be set to a
predetermined load and the dynamometer/cable tension monitoring type systems to provide
feedback for winch control. Those at the cable/rope interface include mechanical fuses
(tensile or shear) and sensing devices to provide winch control information. All these systems
have a common aim of limiting or stopping the winching oper
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