IEC TR 62959:2021

Optical fibre cables - Shrinkage effects on cable and cable element end termination - Guidance

IEC TR 62959:2021 which is a Technical Report, provides information on cable shrinkage characterisation of optical fibre cables that consist of standard glass optical fibres for telecommunication application. The characterisation is directed to the effects of cable shrinkage or cable element shrinkage on the termination of cables. Shrinkage can or cannot be a concern depending on the method of termination. Examples of different cable termination cases are included and described. Tests for the evaluation of cable shrinkage are recommended that can be used as indicators, and shrinkage classification by several grades are given.

General Information

• Status: Published
• Publication Date: 16-Feb-2021
• ICS: 33.180.10 - Fibres and cables
• Technical Committee: SC 86A - Fibres and cables
• Current Stage: PPUB - Publication issued
• Start Date: 17-Feb-2021
• Completion Date: 03-Mar-2021

Overview

IEC TR 62959:2021 is a Technical Report from the International Electrotechnical Commission (IEC) that provides guidance on shrinkage effects of optical fibre cables and their impact on cable and cable-element end termination. The report addresses cables built with standard glass optical fibres for telecommunication applications and explains how thermal and material-induced shrinkage can influence connectorization, splicing and other termination methods.

Key topics

• Scope and purpose
  • Guidance (informative) on characterising cable shrinkage and its effects on terminations rather than prescriptive normative requirements.
• Materials and mechanisms
  • Differentiation between reversible thermal expansion/contraction and irreversible thermal contraction (shrinkage) of plastic cable components.
  • Discussion of forces between cable elements caused by thermal changes.
• Cable types
  • Coverage includes simplex, loose-tube, unitube and other common telecommunication cable constructions.
• Termination cases
  • Examples and descriptions of practical termination scenarios: connectorized cables, hardened connectors, modules, dividers/fan-outs, splices and protective housings.
• Test methods and parameters
  • Recommended test methods for evaluating shrinkage with Method F11 and Method F17 highlighted.
  • Guidance on preconditioning, test parameters and shrinkage grades (including fibre protrusion grades).
• Recommended performance indicators
  • Tests to evaluate optical performance under thermal cycling, fibre protrusion, sheath shrinkage and element forces.
• Annexes
  • Extensive informative annexes with test templates, study results and tailored test recommendations for specific termination types.

Practical applications

Who uses IEC TR 62959:2021 and why:

• Cable manufacturers - to characterise shrinkage behavior during product development and for specification of shrinkage grades.
• Test laboratories - to apply recommended test methods (F11, F17) and report shrinkage/fibre protrusion results.
• System designers and installers - to select appropriate termination methods and protectors (modules, housings, hardened connectors) where shrinkage could affect reliability.
• Network operators and specifiers - to set procurement requirements and acceptance criteria for cable assemblies used in outdoor or varying-temperature environments.

Related standards (if applicable)

• This Technical Report complements IEC optical-fibre cable standards and test documents covering mechanical, environmental and optical performance. Users should consult relevant IEC normative standards for formal performance requirements and test procedures when specifying or qualifying products.

Keywords: IEC TR 62959:2021, optical fibre cables, cable shrinkage testing, fibre protrusion, connector termination, loose tube, simplex, shrinkage grades, test methods F11 F17.

Standards Content (Sample)

IEC TR 62959 ®
Edition 1.0 2021-02
TECHNICAL
REPORT
colour
inside
Optical fibre cables – Shrinkage effects on cable and cable element end
termination – Guidance
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IEC TR 62959 ®
Edition 1.0 2021-02
TECHNICAL
REPORT
colour
inside
Optical fibre cables – Shrinkage effects on cable and cable element end

termination – Guidance
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.180.10 ISBN 978-2-8322-9434-5

– 2 – IEC TR 62959:2021  IEC 2021
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 10
4 Abbreviated terms . 11
5 Characteristics of optical fibre cables . 11
5.1 General . 11
5.2 Cable materials . 11
5.2.1 Plastic materials . 11
5.2.2 Reversible thermal expansion and contraction . 11
5.2.3 Irreversible thermal contraction (shrinkage) . 12
5.2.4 Forces between cable elements caused by thermal changes . 13
5.3 Cable design . 13
5.4 Basic cable types . 14
5.5 Cable performance . 15
5.5.1 General . 15
5.5.2 Optical performance during temperature changes . 15
5.5.3 Cable shrinkage characteristic . 16
5.5.4 Cable shrinkage during connector termination process . 16
6 Test methods for cable shrinkage . 17
6.1 General . 17
6.2 Conditions before shrinkage testing . 17
6.3 Test method F11 . 17
6.4 Test method F17 . 18
7 Conclusions of the cable shrinkage study . 19
7.1 General . 19
7.2 Conclusion for simplex cables . 19
7.3 Conclusion for loose tube cables . 20
8 Termination cases of optical fibre cables . 20
8.1 General . 20
8.2 Different termination cases . 20
9 Recommended tests for evaluation of shrinkage effects . 21
9.1 General . 21
9.2 Limitation of tests for determination of shrinkage effects . 22
9.3 Cables terminated with connectors. 22
9.3.1 Performance indicator tests . 22
9.3.2 Cable shrinkage . 22
9.3.3 Cable thermal expansion and contraction . 22
9.3.4 Cable element forces . 22
9.4 Cables terminated with hardened connectors . 22
9.4.1 Performance indicator tests . 22
9.4.2 Cable shrinkage (fibre protrusion) . 23
9.5 Cables fixed into a module and fibres terminated with connectors . 23
9.5.1 Performance indicator tests . 23
9.5.2 Cable shrinkage (fibre protrusion) . 23

9.6 Cables fixed into a divider and fan-out cables terminated with connectors . 23
9.6.1 Performance indicator tests . 23
9.6.2 General . 24
9.6.3 Shrinkage (fibre protrusion) . 24
9.6.4 Shrinkage of fan-out cable . 24
9.7 Cables fixed into a protective housing and terminated with splices . 25
9.7.1 Performance indicator tests . 25
9.7.2 Cable shrinkage (fibre protrusion) . 25
9.7.3 Sheath shrinkage . 25
9.8 Cables fixed into a protective housing and terminated with connectors . 25
9.8.1 Performance indicator tests . 25
9.8.2 Cable shrinkage . 25
10 Recommended test parameters for shrinkage testing and shrinkage grades . 26
10.1 General . 26
10.2 Recommended test parameters for shrinkage testing . 26
10.3 Shrinkage grades for Method F11A . 27
10.4 Recommended shrinkage limit for Method F11B. 27
10.5 Fibre protrusion grades for Method F17 . 27
Annex A (informative) Test results of the cable shrinkage study . 29
A.1 General . 29
A.2 Shrinkage test results of simplex cables . 29
A.2.1 Simplex cable types for shrinkage tests . 29
A.2.2 Shrinkage test with different aging methods and duration . 29
A.2.3 Shrinkage test with various numbers of temperature cycles . 33
A.2.4 Shrinkage test with different sample lengths . 34
A.2.5 Shrinkage test versus optical performance of two different simplex
cables . 34
A.2.6 Shrinkage test versus optical performance of different versions of a
simplex cable . 36
A.2.7 Change in length during and after climatic exposure . 36
A.3 Shrinkage test results for loose tube cables . 37
A.3.1 Loose tube cable types for shrinkage tests . 37
A.3.2 Shrinkage test (method F11 modified) of four loose tube cable types . 37
A.3.3 Shrinkage test (method F17) of four loose tube cable types . 39
A.3.4 Shrinkage test of nine unitube cable types . 43
Annex B (informative) Test method for change in length during climatic exposure . 45
B.1 General . 45
B.2 Cable samples . 45
B.3 Apparatus for determination of the change in length . 45
B.4 Procedure for determination of the change in length . 46
B.5 Test results for the change in length . 46
B.6 Procedure for determination of the change in attenuation. 47
B.7 Test results for the change in attenuation . 47
B.8 Comparison of change in length with change in attenuation . 50
B.9 Conclusion . 51
Annex C (informative) Shrinkage testing template . 52
Annex D (informative)  Recommended tests for performance evaluation of cables to
be terminated with connectors . 53
D.1 General . 53

– 4 – IEC TR 62959:2021  IEC 2021
D.2 Connector types and design . 53
D.3 Simplex and duplex cable types . 55
D.4 Termination of a cable to a connector . 56
D.5 Overview of recommended cable tests . 57
D.6 Main performance of a terminated cable . 57
D.7 Guidance for change of temperature test methods . 58
Annex E (informative) Recommended tests for performance evaluation of cables to be
terminated with hardened connectors . 59
E.1 General . 59
E.2 Connector types and design . 59
E.3 Cable types for hardened connectors . 59
E.4 Termination of a cable to a hardened connector . 59
E.5 Overview of recommended cable tests . 60
E.6 Environmental performance of a terminated cable . 60
Annex F (informative) Recommended tests for performance evaluation of cables fixed

into a module and fibres terminated with connectors . 61
F.1 General . 61
F.2 Connector types and design . 61
F.3 Cable types . 61
F.4 Termination of a cable to a module . 61
F.5 Overview of recommended cable tests . 62
F.6 Main performance of a terminated cable . 62
Annex G (informative) Recommended tests for performance evaluation of cables fixed
into a divider and fan-out cables terminated with connectors. 63
G.1 General . 63
G.2 Connector types and design . 63
G.3 Cable types . 63
G.3.1 Cables . 63
G.3.2 Fan-out cables . 63
G.4 Termination of a cable into a divider and at fan-out cables . 64
G.5 Overview of recommended cable tests . 64
G.5.1 Recommended test for cable assembly . 64
G.5.2 Recommended tests for cables . 64
G.5.3 Recommended tests for fan-out cables . 65
Annex H (informative) Recommended tests for performance evaluation of cables fixed

into a protective housing and terminated with splices . 66
H.1 General . 66
H.2 Types of protective housings. 66
H.3 Cable types . 67
H.4 Termination of a cable in a protective housing . 67
H.5 Overview of recommended cable tests . 67
H.6 Main performance of a terminated cable . 68
Annex I (informative) Recommended tests for performance evaluation of cables fixed
into a protective housing and terminated with connectors . 69
I.1 General . 69
I.2 Types of protective housings. 69
I.3 Cable types . 69
I.4 Termination of a cable into a protective housing . 69
I.5 Overview of recommended cable tests . 70

I.6 Main performance of a terminated cable . 70
Annex J (informative) Recommended test parameters for change of temperature
testing . 71
J.1 Test methods and severities . 71
J.2 Additional recommendations for the change of temperature test . 72
Annex K (informative) Cross-references of cable test methods . 73
Bibliography . 74

Figure 1 – Qualitative example of force during decreasing temperature of two polymer

materials . 13
Figure 2 – Cable sample for shrinkage testing according to Method F11 . 18
Figure 3 – Cable sample for fibre protrusion testing according to Method F17 . 19
Figure A.1 – Sheath shrinkage in mm of cable type 1 with different temperatures . 31
Figure A.2 – Sheath shrinkage in mm of cable type 2 with different temperatures . 32
Figure A.3 – Sheath shrinkage in mm of cable type 3 with different temperatures . 33
Figure A.4 – Sheath shrinkage at different number of cycles . 34
Figure A.5 – Change in attenuation during temperature cycling . 35
Figure A.6 – Change in attenuation versus sheath shrinkage . 36
Figure A.7 – Preparation of sample and measured lengths . 38
Figure A.8 – Shrinkage of sheath and loose tube after different number of cycles . 39
Figure A.9 – Preparation of sample and measured or calculated protrusion lengths . 40
Figure A.10 – Protrusion length of cable type 1 . 41
Figure A.11 – Protrusion length of cable type 2 . 41
Figure A.12 – Protrusion length of cable type 3 . 42
Figure A.13 – Protrusion length of cable type 4 . 42
Figure A.14 – Change of fibre protrusion. 44
Figure B.1 – Apparatus for holding cable samples . 45
Figure B.2 – Temperature cycle with measurement points . 46
Figure B.3 – Cable sheath length measurement results . 47
Figure B.4 – Change in attenuation of orange cable samples at 1 310 nm . 48
Figure B.5 – Change in attenuation of orange cable samples at 1 550 nm . 48
Figure B.6 – Change in attenuation of orange cable samples at 1 625 nm . 49
Figure B.7 – Change in attenuation of yellow cable samples at 1 310 nm . 49
Figure B.8 – Change in attenuation of yellow cable samples at 1 550 nm . 50
Figure B.9 – Change in attenuation of yellow cable samples at 1 625 nm . 50
Figure D.1 – Cable terminated with connector plug . 53
Figure D.2 – LC connector variants . 53
Figure D.3 – Simplex cable terminated at LC simplex connector . 54
Figure D.4 – Fibre movement in spring-loaded connectors . 55
Figure D.5 – Simplex cable type . 55
Figure D.6 – Duplex cable types . 56
Figure D.7 – Test arrangement for method F12 . 58
Figure E.1 – Cable terminated with hardened connector . 59
Figure F.1 – Cable fixed into a module and terminated with connectors . 61

– 6 – IEC TR 62959:2021  IEC 2021
Figure G.1 – Cable fixed into a divider and fan-out cables terminated with connectors . 63
Figure H.1 – Cable fixed into a protective housing and terminated with splices . 66
Figure I.1 – Cable fixed into a protective housing and terminated with connectors . 69
Figure J.1 – Change of temperature test configuration . 72

Table 1 – Linear coefficients of thermal expansion of materials (informative) . 12
Table 2 – Typical characteristics of indoor and outdoor cables . 15
Table 3 – Overview of different termination cases . 21
Table 4 – Temperature cycling severities for shrinkage testing for Methods F11A and
F17 . 27
Table 5 – Recommended sheath shrinkage grades . 27
Table 6 – Recommended change of fibre protrusion ∆L grades . 28
Table 7 – Recommended change of fibre protrusion ∆L grades . 28
Table A.1 – Overview of shrinkage results . 34
Table A.2 – Overview of simplex results . 35
Table A.3 – Details of loose tube cable types . 37
Table A.4 – Details of unitube cable types . 43
Table B.1 – Comparison of change in length with change in attenuation . 51
Table C.1 – Shrinkage testing template . 52
Table D.1 – Recommended tests for cables to be terminated with connectors . 57
Table E.1 – Recommended tests for cables to be terminated with hardened

connectors . 60
Table F.1 – Recommended tests for cables fixed into module and terminated with
connectors . 62
Table G.1 – Recommended tests for cable assembly . 64
Table G.2 – Recommended tests for cables fixed into dividers . 64
Table G.3 – Recommended tests for fan-out cables . 65
Table H.1 – Recommended tests for cables fixed at protective housing and terminated
with splices . 67
Table I.1 – Recommended tests for cables fixed into a protective housing and
terminated with connectors . 70
Table J.1 – Severities for change of temperature testing . 71
Table K.1 – Cross reference table of mechanical test methods . 73
Table K.2 – Cross reference table of environmental test methods . 73

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL FIBRE CABLES –
SHRINKAGE EFFECTS ON CABLE AND CABLE
ELEMENT END TERMINATION – GUIDANCE

FOREWORD
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The main task of IEC technical committees is to prepare International Standards. However, a
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example "state of the art".
IEC TR 62959, 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/2032/DTR 86A/2058/RVDTR
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.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 8 – IEC TR 62959:2021  IEC 2021
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IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
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INTRODUCTION
Cable shrinkage is sometimes used as a part of the performance criteria for optical fibre cables,
including standard glass optical fibres for telecommunication application. However, there is only
a partial correlation between shrinkage and other important cable parameters such as
temperature performance and optical transmission characteristics, particularly during
mechanical and environmental stress, since shrinkage strongly depends on the cable materials,
the cable construction and the manufacturing processes.
The environmental performance of optical fibre cables is mainly determined using a suitable
temperature cycling test while continuously measuring the change in attenuation during and
after the test. Low shrinkage performance is not guaranteed by such a test method, so any
cable shrinkage observed during and/or after the temperature cycle test can be used as an
additional indicator for the characterisation of cables.
Cable shrinkage should be understood to include shrinkage of the entire cable, shrinkage of
cable sub-assemblies such as units, and shrinkage of cable elements. It should also be
understood that shrinkage of portions of the cable might be expressed as "growth" of other
elements, such as fibres, strength members. Specific issues of cable shrinkage – buffer
shrinkage, strength member growth, sheath shrinkage, etc. – should be carefully addressed
when applying the principles of this document.
A combination of the passive component design (connectors, passive components, protective
housings or cable management components) and cable shrinkage influences the
cable/component performance. Excessive shrinkage at the cable/device interface can cause
extra process steps and/or extra precautions to be taken at the interface and can cause
degradation of the interface in service, for example the failure of strain relief effectiveness at a
connector as the sheath shrinks back in use compromising the continuously optimal optical
transmission parameters. Component manufacturers use a number of compensations for cable
shrinkage in the design or assembly process of their components and will often select cables
used in finished components for their low shrinkage performance. On the other hand, shrinkage
can be compensated by installation technique.
To cover all relevant aspects of cables to be terminated, the recommended tests for
performance evaluation of cables for different termination cases in addition to the optional tests
for evaluation of shrinkage effects are included in this document.
This study into cable shrinkage was triggered by a CENELEC/TC86 BXA liaison letter sent to
IEC/SC 86A in April 2016. The letter pointed out observed inconsistencies in indoor cable
standards from a user point of view and asked for their concerns and recommendations to be
addressed. The main subject was that jacket shrinkage should be a specified parameter for all
indoor cables that are normally terminated by connectors, passive components or
closures/enclosures.
A correspondence group in IEC/SC 86A/WG 3 was formed in 2016 to address issues about
cable shrinkage. After discussion about relevant issues, cable shrinkage tests were performed,
and the test results were collected and recorded. Annex A shows these test results and
Clause 7 gives the conclusions of the cable shrinkage study. Generally, optical fibre cable types
with a small outer diameter were involved in shrinkage testing. The results of different cable
types from only a few cable manufactures were included, hence the number of cable types was
limited and does not represent all cable types in the worldwide market. Subsequent work was
done on recommendations for performance evaluation of cables to be terminated with
connectors.
– 10 – IEC TR 62959:2021  IEC 2021
OPTICAL FIBRE CABLES –
SHRINKAGE EFFECTS ON CABLE AND CABLE
ELEMENT END TERMINATION – GUIDANCE

1 Scope
This document, which is a Technical Report, provides information on cable shrinkage
characterisation of optical fibre cables that consist of standard glass optical fibres for
telecommunication application. The characterisation is directed to the effects of cable shrinkage
or cable element shrinkage on the termination of cables. Shrinkage can or cannot be a concern
depending on the method of termination. Examples of different cable termination cases are
included and described. Tests for the evaluation of cable shrinkage are recommended that can
be used as indicators, and shrinkage classification by several grades are given.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60794-1-1, Optical fibre cables – Part 1-1: Generic specification – General
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60794-1-1 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
shrinkage
irreversible contraction after extrusion of plastic materials caused by heating or over time at
ambient temperature
Note 1 to entry: The irreversible contraction in the direction of the cable axis is usually called "cable shrinkage".
Note 2 to entry: This behaviour is also called "shrinkback".
3.2
thermal contraction
decrease in length of an element or assembly when subjected to a temperature increase or
decrease
3.3
thermal expansion
increase in length of an element or assembly when subjected to a temperature increase or
decrease
3.4
cable end effect
effect that occurs at the cable's ends
Note 1 to entry: End effects can take different forms. For example, during winding/unwinding or over time, the cable
elements can move at the ends relative to the sheath.
4 Abbreviated terms
CTE coefficient of thermal expansion
FMC field mountable connector
FMS fibre management system
HFFR halogen free flame retardant
LSZH low smoke zero halogen
ODFM optical distribution frame module
5 Characteristics of optical fibre cables
5.1 General
For continuously good optical cable performance, the materials, design and manufacturing of
the cable should be optimised. Subclauses 5.1 to 5.5 give detailed information about these
factors.
5.2 Cable materials
5.2.1 Plastic materials
Many different plastic materials, primarily thermoplastics, are optimised for commercially
available extrusion processes. Some are specifically promoted as having a low post-extrusion
shrinkage. Nonetheless, all extruded plastic materials expand and contract reversibly and
shrink irreversibly.
It should be noted that plastic materials used for optical fibre cables have to meet many more
requirements beyond shrinkage, depending on customer technical requirements and local
market conditions and regulations. This can include, but is not limited to: free of hazardous
substances and halogens, high tensile strength, good UV resistance, good weathering and
abrasion resistance, high flame retardancy, high thermal stability, good bend behaviour, easy
strippability of the cable sheath and fibre buffer and several other attributes.
5.2.2 Reversible thermal expansion and contraction
Temperature changes cause thermal expansion or contraction of materials. Each material has
a certain linear coefficient of thermal expansion (CTE). Typical coefficients of ten materials are
listed in Table 1.
– 12 – IEC TR 62959:2021  IEC 2021
Table 1 – Linear coefficients of thermal expansion of materials (informative)
Material Linear Reference of Typical application in cables
coefficient of data (see
thermal Bibliography)
expansion
–6 –1 a
×10 K
b
−5 [1] Strength member for optical fibre cables
Aramid
Copper +17 [2] Power conductor in power and hybrid cables
c
+5,5 [2] Central strength member for optical fibre
E glass
cables
Glass (fused silica) +0,5 [2] Optical fibre
Polybutylenterephthalate +108 to +144 [3] Tube for fibres in optical fibre cables
(PBT)
Polyethylene (PE) +100 to +200 [2] Sheath
Polypropylene(PP) +58 to +100 [2] Tube for fibres in optical fibre cables
Polyvinylchloride (PVC) +70 to +210 [4] Sheath
d
+9,9 [5] Strength member for optical fibre cables
Low-carbon steel
Stainless steel (18-8) +17 [2] Armour
a
To +20 °C reference.
b
Longitudinal to the fibres.
c
Same coefficient for glass-reinforced strength member with thermosetting resin coating (glass > 80 % weight).
d
Ferritic – 410.
Because different materials are used within cables, when the temperature changes, the cable
elements and the sheath expand or contract differentially. If the elements cannot move freely,
forces are generated within the cable. If the fibre is stressed by such forces, then optical
performance can degrade temporarily. After the temperature reverts to its original value, cable
elements return to or close to their original lengths, unless they have undergone shrinkage or
are restrained by internal coupling. This reversible thermal material dimension change is seldom
independently addressed as a cable characteristic.
Annex B describes a suitable test method for determination changes in cable sheath length,
and optionally cable’s elements, on short cable samples during a climatic exposure test.
Information about the thermal expansion and contraction can be helpful when classifying a cable
and to understand the higher attenuation observed during climatic tests.
5.2.3 Irreversible thermal contraction (shrinkage)
Irreversible thermal contraction is specifically relevant for extruded plastic materials in optical
fibre cables. During the cooling stage of an extrusion process, the polymer orientation is
"frozen". If the extruded material is exposed to a high temperature, or kept for a long time at
room temperature, the frozen-in polymer orientation can relax, and the extruded plastic material
can shrink in direction of the extrusion in an irreversible way [6] . The amount and speed of
post-extrusion shrinkage can be influenced significantly by the process parameters during
extrusion and by the choice of the base material. Zero or negligible shrinkage can be achievable
in some cases.
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Numbers in square brackets refer to the Bibliography.

This post-extrusion shrinkage can be reduced by the inclusion of strength members coupled to
the plastic. The more rigid the strength members are and the more tightly the plastic materials
are extruded onto them or otherwise coupled, the more the force caused by shrinkage is
compensated for by the strength member
...