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

® Registered trademark of the International Electrotechnical Commission

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– 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

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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

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– 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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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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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.

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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
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related to the specific publication. At this date, the publication will be
• reconfirmed,
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colour printer.

A bilingual version of this publication may be issued at a later date.

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– 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

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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.

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– 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

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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:

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– 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
...