IEC TS 62818-1:2024

IEC TS 62818-1 ®
Edition 1.0 2024-12
TECHNICAL
SPECIFICATION
colour
inside
Conductors for overhead lines – Fiber reinforced composite core used as
supporting member material –
Part 1: Polymeric matrix composite cores

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Secretariat Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform IEC Products & Services Portal - products.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews, graphical symbols and the glossary.
committee, …). It also gives information on projects, replaced With a subscription you will always have access to up to date
and withdrawn publications. content tailored to your needs.

IEC Just Published - webstore.iec.ch/justpublished
Electropedia - www.electropedia.org
Stay up to date on all new IEC publications. Just Published
The world's leading online dictionary on electrotechnology,
details all new publications released. Available online and once
containing more than 22 500 terminological entries in English
a month by email.
and French, with equivalent terms in 25 additional languages.

Also known as the International Electrotechnical Vocabulary
IEC Customer Service Centre - webstore.iec.ch/csc
(IEV) online.
If you wish to give us your feedback on this publication or need

further assistance, please contact the Customer Service
Centre: sales@iec.ch.
IEC TS 62818-1 ®
Edition 1.0 2024-12
TECHNICAL
SPECIFICATION
colour
inside
Conductors for overhead lines – Fiber reinforced composite core used as

supporting member material –
Part 1: Polymeric matrix composite cores

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.240.20  ISBN 978-2-8322-6983-1

– 2 – IEC TS 62818-1:2024 © IEC 2024
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 Symbols and abbreviated terms . 10
5 Requirements . 10
5.1 Composite core manufacturing . 10
5.2 Composite core sampling and tests . 10
5.2.1 General . 10
5.2.2 Type tests . 11
5.2.3 Sample tests . 11
5.2.4 Routine tests . 11
5.3 Composite core traceability and packaging . 11
6 Composite core thermal performance . 11
6.1 General . 11
6.2 Maximum continuous temperature of the composite core: T . 12
C,CORE
6.3 Temperature limit for use in peak load of the composite core: T . 12
P,CORE
7 Tests for the composite core characterization . 12
7.1 Appearance . 12
7.2 Diameter . 12
7.2.1 Diameter measurement for single wire composite core . 12
7.2.2 Diameter measurement for multi-wires composite core . 13
7.3 Lay length measurement for multi-wires composite core . 14
7.4 Protective layer thickness . 15
7.5 DC electrical resistance . 15
7.6 Mass per unit length . 15
7.7 Tensile test . 15
7.8 Bending test . 16
7.8.1 General . 16
7.8.2 Mandrel test . 16
7.8.3 Coiling test . 17
7.9 Measurement of Glass transition temperature (by DMA). 18
7.10 Coefficient of thermal expansion . 19
7.10.1 Sample preparation . 19
7.10.2 Procedure . 19
7.11 T determination . 20
onset Thermolysis
7.12 Isothermal ageing . 21
7.12.1 General . 21
7.12.2 Product stability at T . 21
C,CORE
7.12.3 Product stability at T . 22
P,CORE
8 Optional tests . 22
8.1 Twisting test . 22
8.2 Crushing test . 23
8.3 Salt fog test . 24

8.4 Fiber volume ratio . 24
8.4.1 General . 24
8.4.2 TGA method . 24
8.4.3 Calculated method . 26
8.5 Porosity . 26
8.6 UV ageing . 27
Annex A (normative) Testing table . 28
Annex B (normative) Arrhenius thermal ageing test . 29
B.1 General . 29
B.2 Ageing temperatures, number of samples and picking frequency . 29
B.2.1 Overview . 29
B.2.2 Definition of the testing plan . 29
B.3 Test method . 30
Annex C (informative) For more info on composite core T . 34
g
Bibliography . 35

Figure 1 – Measurement of multi-wire core diameter . 13
Figure 2 – Illustration of the mandrel test . 17
Figure 3 – Illustration of the coiling test . 18
Figure 4 – CTE test setup . 19
Figure 5 – Illustration for T determination . 20
onset thermolysis
Figure 6 – Illustration of the twisting test . 23
Figure 7 – Illustration of the crushing test . 24
Figure 8 – TGA curve for the measurement of weight loss versus temperature . 25
Figure B.1 – Example of decay curves . 31
Figure B.2 – Example of decay curves and identification of times to end-point
according to method A . 31
Figure B.3 – Example of decay curves and identification of times to end-point
according to method B . 32
Figure B.4 – Example of Arrhenius curve with the long-term extrapolation to 40 years . 32
Figure C.1 – Example of storage modulus and loss modulus curves and Tg point

determination . 34

Table 1 – Testing table for core diameter measurement by core type . 14
Table 2 – DMA testing specification . 18
Table A.1 – Tests on composite core . 28

– 4 – IEC TS 62818-1:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CONDUCTORS FOR OVERHEAD LINES – FIBER REINFORCED
COMPOSITE CORE USED AS SUPPORTING MEMBER MATERIAL –

Part 1: Polymeric matrix composite cores

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 in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
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
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC TS 62818-1 has been prepared by IEC technical committee 7: OVERHEAD ELECTRICAL
CONDUCTORS. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
7/752/DTS 7/754/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.

A list of all parts in the IEC 62818 series, published under the general title Conductors for
overhead lines – Fiber reinforced composite core used as supporting member material, can be
found on the IEC website.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
IMPORTANT – The "colour inside" logo on the cover page of this document 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.

– 6 – IEC TS 62818-1:2024 © IEC 2024
INTRODUCTION
The first conductors using a composite core were installed in the early 2000s. Since then, they
have been increasingly used by utilities worldwide. As a result, there is a need for an IEC
publication to agree on tests methods to qualify these cores.
Because of the variety of products used for this purpose, this document does not set minima or
maxima (usually provided by the manufacturer), but rather standardizes testing methods to
ascertain the numerical values of the basic properties needed by the purchaser to choose the
right supporting member material according to the properties of the overhead lines conductors.
Future discussion items for review may include performance level and acceptance criteria, other
ageing tests and criteria or other relevant tests.
In a future document, tests on the complete conductor which include the composite core will be
covered in detail (for example salt fog, corrosion test, mechanical tests, thermal tests, flexural
under tension, etc.).
CONDUCTORS FOR OVERHEAD LINES – FIBER REINFORCED
COMPOSITE CORE USED AS SUPPORTING MEMBER MATERIAL –

Part 1: Polymeric matrix composite cores

1 Scope
This part of IEC 62818, which is a Technical Specification, establishes a system of fiber
reinforced composite core used as supporting member material in conductors for overhead lines
which may be used as the basis for specifications. This document is applicable to fiber
reinforced composite core, with polymeric matrix, used as supporting member material in
conductors for overhead lines.
This document gives guidance on:
– defining the common terms used for fiber reinforced composite core with polymeric matrix,
– prescribing common methods and recommendations to characterize the properties of fiber
reinforced composite core based on single or multi-wires with PMC (Polymeric Matrix
Composite) used as supporting member material in conductors,
– prescribing or recommending acceptance or failure criteria when applicable.
These tests, criteria and recommendations are intended to ensure a satisfactory use and quality
under normal operating and environmental conditions.
This document does not apply to compliance criteria which may be required but indicative
values could be given in Annexes for guidance.
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 60068-2-11:2021, Environmental testing – Part 2-11: Tests – Test Ka: Salt mist
IEC 60216-1:2013, Electrical insulating materials – Thermal endurance properties – Part 1:
Ageing procedures and evaluation of test results
IEC 60468:1974, Method of measurement of resistivity of metallic materials
ISO 527-5:2021, Plastics: Determination of tensile properties – Part 5: Test conditions for
unidirectional fiber-reinforced plastic composites
ISO 4892-2:2013, Plastics: Methods of exposure to laboratory light sources – Part 2: Xenon-
arc lamps
ISO 11358-1:2022, Plastics – Thermogravimetry (TG) of polymers – Part 1: General principles

– 8 – IEC TS 62818-1:2024 © IEC 2024
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
polymer matrix composite
PMC
assembly of continuous fibers (such as carbon or glass fibers) embedded longitudinally in a
polymer matrix (such as epoxy resin)
3.2
composite core
PMC single or multi-wires, including additional protection (metallic or non-metallic), if existing
in the final application
3.3
external protective layer
outer layer made of metallic or non-metallic material applied onto the PMC for the purpose of
protecting it against external aggressions (such as corrosion, oxidation, etc.) and also acting
as a protection against galvanic corrosion, if any
Note 1 to entry: In case of a core based on an assembly of composite wires, this protective layer could be applied
to:
- each individual wire,
- the assembly of wires.
Note 2 to entry: Individual wires could be protected with different materials. In this case, testing protocols shall be
adapted in relation to the specific material.
3.4
fiber reinforcement
incorporation of continuous fibers within a polymeric matrix in order to increase its performance
Note 1 to entry: It is achieved through specific processes such as winding, moulding or pultrusion.
3.5
fiber
organic or inorganic bundle of filaments that is essentially continuous
3.6
resin
matrix component of PMC
Note 1 to entry: There are two types of resin, namely thermosetting resin and thermoplastic resin.
3.7
thermoplastic resin
type of resin made of long polymer chains with weak bonding between them, which, when the
resin is heated, break in a reversible way and make the material shapeable
Note 1 to entry: This is classified into two types by array of polymer chain. One is semi-crystalline resin and the
other is amorphous resin.
3.8
thermosetting resin
type of resin made of a network of cross linked polymer chains
Note 1 to entry: The network is created by heating monomers which polymerized under high temperature.

3.9
porosity
measurement of the void fraction in the material over the total volume
Note 1 to entry: It results from a lack of matrix impregnation or from matrix degradation. It distinguishes itself from
composite crack or fracture by that it's a lack of matrix or matrix deficiency but not a matrix mechanical fracture.
3.10
glass transition temperature
T
g
temperature where the PMC properties transition from a hard, glassy state to a rubbery state
Note 1 to entry: T of PMC is related to T of the polymer matrix but it can be different, depending on each
g g
technology and specific product design.
3.11
glass transition temperature onset
T
g,onset
temperature corresponding to the onset of the transition from the glassy state as defined by the
intercept of the two tangent of the storage (E') modulus curve (see Annex C)
3.12
glass transition temperature loss modulus
T
g,LossModulus
temperature corresponding to the peak (maximum) in the loss (E'') modulus curve (see Annex C)
3.13
thermolysis temperature
T
onset thermolysis
temperature corresponding to the start of the polymeric matrix thermolysis, an irreversible
reaction that breaks structures of resin (e.g. main chain, cross-link, etc.) and affects the lifetime
of PMC
3.14
lot
group of production units of one type and size of wire, which was manufactured by the same
manufacturer during the same time period under similar conditions of production. A lot may
consist of part or all of a purchased quantity
Note 1 to entry: A lot may consist of part or all of a purchased quantity.
Note 2 to entry: If agreed between the manufacturer and the purchaser, for example for the Type tests, a Lot could
be composed by only one Production unit.
3.15
production unit
coil, reel, spool or other package of individual composite core that represents a single usable
length
3.16
sample
specimen(s) removed from a production unit(s) which is considered to have properties
representative of a lot
3.17
specimen
length of composite core removed for test purposes
3.18
equivalent diameter
diameter of a circle which would have the same cross-sectional area as a given formed wire

– 10 – IEC TS 62818-1:2024 © IEC 2024
4 Symbols and abbreviated terms
-1
CTE coefficient of thermal expansion (°C )
DC direct current (A)
DMA dynamic mechanical analysis
E tensile modulus (GPa)
t
F compressive load at break (N)
c
F tensile load at break (N)
t
K compressive stiffness (K = F /ε ) (N)
c c c c
RTS rated tensile strength (kN)
SEM scanning electron microscope
TGA thermo-gravimetric analysis
TMA thermo-mechanical analysis
T maximum continuous temperature (°C) of the composite core
C,CORE
T maximum peak-load temperature (°C) of the composite core
P,CORE
ε compressive strain at break (%)
c
ε elongation at break (%)
t
σ tensile stress at break (MPa)
t
5 Requirements
5.1 Composite core manufacturing
Composite core shall be produced according to the dimensional, mechanical and thermal
properties agreed between purchaser and manufacturer, respecting the acceptance values and
tolerances. These properties shall be uniform along the lot and every production unit shall be
free of internal or external imperfections (e.g. high porosity, inclusions, scratches, scrape, notch,
holes, cracks). Each composite wire shall be produced with a single assembly of continuous
fibers; no fiber end-to-end joint is allowed, unless clearly agreed between both parts. The fiber
splicing is accepted in the protective layer. The purchaser may be informed upon request that
splicing was used for protective layer.
5.2 Composite core sampling and tests
5.2.1 General
Tests on composite core are described in Clause 7 and shall be classified as:
– Type test (T),
– Sample test (S),
– Routine test (R).
In order to ensure a satisfactory quality of the core and to properly characterize its properties,
a list of type tests, sample tests and routine tests is provided in Table A.1, with a suggested
sampling.
For a more detailed characterization of the core, additional/optional tests are also proposed in
Table A.1 and described in Clause 8.

Laboratories and scheduling of tests shall be previously agreed between the purchaser and
manufacturer. The ageing test being very long, a manufacturer's laboratory may be used under
the supervision of an independent third party.
5.2.2 Type tests
Type tests are intended to establish design characteristics. They are normally made once on a
prototype and repeated only in case of a change of materials or design (for example, fiber type,
matrix type, fiber volume ratio, ratio of carbon fiber composite to galvanic layer or shape). The
type tests performed for a given diameter may qualify a range of diameters to be agreed
between the purchaser and manufacturer. The results of type tests are recorded as evidence
of compliance with design requirements.
5.2.3 Sample tests
Sample tests are intended to verify the quality of materials and workmanship. They are
performed on samples taken from the produced drums of finished core in order to verify the
compliance with design specifications and type tests results.
The sampling of the sample tests is suggested in Table A.1.
5.2.4 Routine tests
Routine tests are intended to verify compliance and stability of core characteristics during the
production of a lot. Sampling for routine tests depends on the characteristics and monitoring
system of each production process.
5.3 Composite core traceability and packaging
In order to ensure composite core traceability, orders shall include at least the following
information:
a) lot identification number;
b) number of production units per lot;
c) core size (diameter in mm, if applicable number of wires, sizes of wires, lay length and
direction);
d) length of each type of core;
e) type and size of package and method of packing;
f) special package marking;
g) test report with quantitative results (if required).
The core shall be suitably protected against damage and deterioration which could occur in
ordinary handling, shipping and storage.
Package marking shall not be easily removable during ordinary handling.
The manufacturer shall have raw material traceability for production units and lots.
6 Composite core thermal performance
6.1 General
Composite materials can experience a change in their composition and a deterioration of their
mechanical performance after a long-term exposure to high temperatures. Thus, it is necessary
to experimentally assess their inner resistance to thermal degradation in order to define the
maximum temperatures to be respected for a safe use of the complete conductor during the
lifetime of the overhead line.

– 12 – IEC TS 62818-1:2024 © IEC 2024
The composite core thermal performance is defined by the two temperatures below:
a) Maximum continuous temperature of the composite core: T
C,CORE
b) Temperature limit for use in peak load of the composite core: T
P,CORE
These temperatures are intended as measured at the external surface of the composite core.
T and T shall be determined from the experimental result of the test described in
C,CORE P,CORE
7.12.
A lower T and T value may be utilized if agreed upon between purchaser and
C,CORE P,CORE
manufacturer.
6.2 Maximum continuous temperature of the composite core: T
C,CORE
This temperature is the maximum continuous temperature at which the composite core can be
exposed, with deterioration acceptable in accordance with Annex B, for a duration equal (by
definition) to its lifetime. The intended life expectancy of the core is typically 40 or 50 years.
6.3 Temperature limit for use in peak load of the composite core: T
P,CORE
This temperature is the maximum peak load temperature at which the composite core can be
exposed, with deterioration acceptable in accordance with Annex B, for a maximum cumulative
time during its lifespan.
The duration of this maximum time of exposure at high temperature is typically 400 to 1000
cumulative hours during the life expectancy of the core.
As this temperature is related to the final use of the conductor for which the core will be used,
a longer time can be specified by the purchaser, if needed.
7 Tests for the composite core characterization
7.1 Appearance
All the elements composing the core (composite wire(s), external protective layer(s), etc.) shall
be free from any defect (ex: scratch, scrape notch hole, crack) significantly visible with the
naked eye, normal or corrected. When removable external protective layer(s) is(are) present, it
(they) shall be removed to allow the inspection of composite wire(s). A representative picture
of a normal surface may be attached to official test report under purchaser request.
7.2 Diameter
7.2.1 Diameter measurement for single wire composite core
The diameter of the single wire (with the external protective layer) shall be measured with a
device with an accuracy of at least 0,01 mm. Diameter(s) shall be expressed in millimeters to
two decimal places.
Diameter(s) shall be measured by one of the following methods:
a) a continuous/online process measurement (online measurement), performed using a 2- or
3-axis caliper (laser or mechanical) with equal phase shifts in the same straight section.
Minimum, maximum and average values shall be reported.

b) a direct/manual measurement, performed measuring the diameter on the cross-section of a
cut sample in at least two directions, equally phase shifted. In this case, at least 2 samples
shall be taken and tested from each length: one at the start and one at the end of the
production unit. Each sample shall be at least 1 m long and shall be measured in the middle.
Minimum, maximum and average values of diameter shall be reported for each sample.
The manufacturer shall provide a specification for the required wire diameter and the permitted
tolerance.
7.2.2 Diameter measurement for multi-wires composite core
Core diameter shall be measured by one of the following methods:
a) a continuous/online process measurement (online measurement), performed using a 2- or
3-axis caliper (laser or mechanical) with equal phase shifts in the same straight section.
Minimum, maximum, and average values need to be reported.
b) a direct/manual measurement, performed measuring the diameter of a circumscribed circle
(see Figure 1), and at least three directions within the same cross section shall be measured
(with the external protective layer). At least 2 samples shall be taken and tested from each
length: one at the start and one at the end of the production unit. All the above-mentioned
dimensions of the complete core shall be verified on 1 sample at least 1 m long in the middle.
Minimum, maximum and average values of diameter shall be reported for each sample.

Figure 1 – Measurement of multi-wire core diameter
For non-circular wires (formed wires):
a) the wire shall be cut at 90° and polished in order to verify the compliance of the shape of
the cross section with the designed shape. The measures shall be performed with a device
(optical method system) with an accuracy of at least 0,01 mm,
b) for information, the section of the wire can be measured and the equivalent diameter
calculated as the diameter of a round wire with the same cross-sectional area of the given
formed wire.
In a multi-wire composite core, the diameter of each individual wire shall be measured as in
7.2.1 for type testing only. For cores with overall protective layer it is allowed to perform the
Sample Test on samples of the stranded core picked before the application of the layer
The manufacturer shall provide a specification for the required stranded core diameter and the
permitted tolerance. Table 1 defines the different diameter measurements for single and multi-
wire cores.
– 14 – IEC TS 62818-1:2024 © IEC 2024
Table 1 – Testing table for core diameter measurement by core type
Composite core Protective layer Test on
Unremovable (e.g. pultruded)
Complete core, d1
or absent
Single wire
Complete core, d1
Removable (e.g. pultruded)
Core without layer, d2
Complete core, d1
Unremovable (e.g. pultruded)
on each wire or absent
Wire (each type), d2
Complete core, d1
Multi wire
Removable (e.g. extruded) on Wire (each type), d2
each wire
Wire (each type)
without layer, d3
Complete core, d1
Removable (e.g. extruded) on
Core without layer, d2
complete core
Wire (each type), d3
7.3 Lay length measurement for multi-wires composite core
The lay length of every layer of multi-wires composite core shall be measured and lay ratio
calculated. The lay ratio of each layer shall be obtained through the ratio of the measured lay
length to the external diameter of layer itself (7.2.2).

The manufacturer shall provide a specification for the required lay length for each respective
layer as it applies.
7.4 Protective layer thickness
The protection layer thickness shall be expressed in millimeters to two decimal places. Minimum
thickness value shall be measured by an apparatus (micrometric caliper or optical system) with
an accuracy of at least 0,01 mm.
The manufacturer shall provide a specification for the required minimum protective layer
thickness.
7.5 DC electrical resistance
DC electrical resistance shall be measured only on PMC with metallic layer, according to the
method of IEC 60468:1974 (applying a 4-point method). The value of resistance shall be
calculated as the average value of the measures taken on at least 1 sample. The length of each
tested sample shall be at least 1 m.
The report shall include the mean value of resistance at 20 °C (Ω / m).
NOTE DC electrical resistance is not mandatory if the DC resistance value is not used in the calculation of conductor
resistance.
7.6 Mass per unit length
Mass per unit length shall be tested using an apparatus with an accuracy of ±0,1 % on the
composite core.
The value of mass per unit length shall be taken on a minimum number of 1 sample. The length
of each tested sample shall be at least 1 m.
The report shall include the mean value of mass per unit length in g/m.
The manufacturer shall provide a specification for the required mass per unit length and the
permitted tolerance.
7.7 Tensile test
The tensile test shall be performed, in accordance with ISO 527-5:2021, in order to define
mechanical characteristics of composite core and single wires (for stranded cores, if possible,
when the wires are straight not in a preformed shape) under tensile load:
– Ft: tensile load at break (N),
– εt: elongation at break (%),
– σt: tensile stress at break (MPa),
– E tensile modulus (GPa).
t:
Clamping jaws for the tensile test (e.g. epoxy inclusions, conic clamps, bolted clamp) shall be
correctly designed in order to minimize local flections, torsions or incisions, and stress
concentrations on the sample and reach the right failure mode.

– 16 – IEC TS 62818-1:2024 © IEC 2024
The minimum length of each sample shall be appropriate to avoid end effects to the extent that
it is practically possible. For multi wires, sample length is linked to lay length; the longer the lay
length, the longer the sample length. Load shall be gradually increased at a ramp of 1 mm/min
to 10 mm/min, measuring the elongation with an extensometer or another equivalent device. As
composite materials show an elastic behaviour, if the elongation measurement device risks
being damaged at the break of the sample, elongation at break can be extrapolated by a linear
interpolation of the load-elongation curve.
As measured breaking load values on composite wires are usually less repeatable than on
metallic wires, at least 5 samples of complete core shall be tested in order to have a reliable
mean value for type test. A single tensile test shall be applied on each wire of a stranded core
(if not preformed).
For each sample, stress at break shall be calculated as the ratio between breaking load and
section and tensile modulus as the ratio from the slope of the load-elongation curve. It is
important to mention that the selected elongation range has an influence on tensile modulus
final value. Tensile modulus is optional for the sample test.
The type test report shall include pictures of test setting, load-elongation curves, measured
values and mean values of the characteristics above mentioned. For sample and routine tests,
only the mean values of the characteristics mentioned above are to be reported. For multi wire
composite core, tensile tests on each wires are optional depending on the design.
NOTE Composite wires are non-homogeneous materials with anisotropic properties, and the stress at break is
understood as the nominal values of the whole composite core.
All composite cores shall have a tensile breaking load meeting at least the minimum specified
RTS provided by the manufacturer.
7.8 Bending test
7.8.1 General
In order to assess bendability of the core during storage, transport, and installation, one of the
following two tests shall be performed:
7.8.2 Mandrel test
The specimen of composite core (with external protective layer, if present) shall be wrapped
around a cylindrical mandrel at 180°, as shown in Figure 2; and a mechanical load shall be
applied for 1 min.
Minimum mandrel diameter and applied load shall be agreed by the purchaser and manufacturer
in accordance with the core working conditions and core specifications. A testing load
corresponding to 7,5 % RTS of the core is suggested.
After completion of the test, the composite core part in contact with the mandrel shall be tensile
tested according to 7.7.
This test requires a special equipment. The device shall comprise a mandrel and a device to
apply a mechanical load following the direction of the two arrows.

NOTE 7,5 % of RTS is a representative tension that can be seen during stringing; it is low enough to have a
representative compression load during bending. It is also to ensure that the core will be in contact with the mandrel
during the bending test.
Figure 2 – Illustration of the mandrel test
7.8.3 Coiling test
The specimen shall be reeled around a cylindrical coiling reel as described in Figure 3. The
minimum coiling reel diameter and the coiling speed shall be defined by the manufacturer in
accordance with the core operating conditions and core specifications. Before starting the test,
both the guide device and fastening device shall be tangent to the reel as shown in Figure 3.
After a minimum of half a turn (core wrapped around reel 180°), the rotation is stopped for 1 min
and the specimen is rewound at the same speed to the initial location. A testing load
corresponding to 7,5 % RTS of the core is suggested. The composite core part in contact with
the coiling reel is analysed.
After completion of the test, the specimen shall be tensile tested according to 7.7.
This test requires a special equipment. The device shall comprise a two-way tension gear (1),
a fastening device (2) and a coiling reel (3).

– 18 – IEC TS 62818-1:2024 © IEC 2024

NOTE 7,5 % of RTS is a representative tension that can be seen during stringing; it is low enough to have a
representative compression load during bending. It is also to ensure that the core will be in contact with the mandrel
during the coiling test.
Figure 3 – Illustration of the coiling test
7.9 Measurement of Glass transition temperature (by DMA)
The glass transition temperature (T ) is measured in order to characterize the loss of PMC
g
modulus versus temperature for PMC wires (Annex C). External protective layer may be
r
...