SIST EN IEC 60947-8:2023

Low-voltage switchgear and controlgear - Part 8: Control units for built-in thermal protection (PTC) for rotating electrical machines (IEC 60947-8:2021)

This part of IEC 60947 series specifies requirements for control units, which control a switching device in response to the PTC thermistors incorporated in rotating electrical machines and the industrial application.
It specifies requirements for that type of system comprising a positive temperature coefficient (PTC) thermistor having particular characteristics, and its associated control unit.
This document includes:
- the characteristics, construction, performance and tests of the control unit; and
- its association with a PTC thermistor designated "Mark A".
This document does not cover:
- the incorporation of thermal protections into rotating machines and their maximum winding temperature. See IEC 60034-11;
- use of the product within explosive atmospheres (see IEC 60079 (all parts));
- software and firmware requirements;
NOTE 1 Guidance on embedded software is given in IEC TR 63201.
- cyber security aspects (see IEC TS 63208).
NOTE 2 It is not possible to specify all the requirements for the operating characteristics of a control unit, as they are dependent on some aspects of the PTC thermistors. Some aspects of the requirements of the thermal protector system can only be specified when account is taken of the characteristics of the rotating machine to be protected and the method of installation of the PTC thermistor within the machine.

Niederspannungsschaltgeräte - Teil 8: Auslösegeräte für den eingebauten thermischen Schutz (PTC) von rotierenden elektrischen Maschinen (IEC 60947-8:2021)

Appareillage à basse tension - Partie 8: Unités de commande pour la protection thermique incorporée (CTP) aux machines électriques tournantes (IEC 60947-8:2021)

L'IEC 60947-8:2021 spécifie les exigences pour les unités de commande qui commandent un appareil de connexion réagissant aux thermistances CTP incorporées dans les machines électriques tournantes et l’application industrielle.
Cette deuxième édition annule et remplace la première édition parue en 2003, son Amendement 1:2006 et son Amendement 2:2011. Cette édition constitue une révision technique.
Cette édition inclut les modifications techniques majeures suivantes par rapport à l’édition précédente:

   
1. des aspects liés à la sécurité concernant:

   
• les aspects généraux;

   
• les circuits à énergie limitée;

   
• les circuits électroniques;

   
2. l’alignement avec l’IEC 60947-1:2020;

   
3. la fonction de détection de rupture de conducteur;

   
4. le terme détecteur est remplacé par thermistance;

   
5. la référence à l’IEC 60738-1-4.

Nizkonapetostne stikalne in krmilne naprave - 8. del: Krmilne enote za vgrajeno toplotno zaščito (PTC) rotacijskih električnih strojev (IEC 60947-8:2021)

Ta del skupine standardov IEC 60947 določa zahteve za krmilne enote, ki krmilijo stikalno napravo kot odziv na termistorje s pozitivnim temperaturnim koeficientom (PTC), vgrajene v rotacijske električne stroje, in industrijsko uporabo.
Določa zahteve za to vrsto sistema s termistorjem s pozitivnim temperaturnim koeficientom (PTC) s posebnimi značilnostmi in z njim povezano krmilno enoto.
Dokument vsebuje:
– lastnosti, izdelavo, učinkovitost in preskuse krmilne enote; in
– njeno povezavo s termistorjem s pozitivnim temperaturnim koeficientom z oznako »Oznaka A«.
Ta dokument ne zajema:
– vgradnje toplotnih zaščit v rotacijske stroje in njihove maksimalne temperature navitja. Glej standard IEC 60034-11;
– uporabe izdelka v eksplozivnih atmosferah (glej skupino standardov IEC 60079);
– zahtev za programsko in vdelano programsko opremo;
OPOMBA 1: Smernice o vgrajeni programski opremi so navedene v standardu IEC TR 63201.
– vidikov kibernetske varnosti (glej standard IEC TS 63208).
OPOMBA 2: Vseh zahtev za obratovalne značilnosti krmilne enote ni mogoče določiti, saj so odvisne od nekaterih vidikov termistorjev s pozitivnim temperaturnim koeficientom. Nekatere vidike zahtev toplotnega zaščitnega sistema je mogoče določiti le ob upoštevanju značilnosti rotacijskega stroja, ki bo zaščiten, in metode vgradnje termistorja s pozitivnim temperaturnim koeficientom.

General Information

• Status: Published
• Publication Date: 12-Apr-2023
• ICS: 29.130.20 - Low voltage switchgear and controlgear
• Technical Committee: SKA - Switchgear and control gear
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 12-Apr-2023
• Due Date: 17-Jun-2023
• Completion Date: 13-Apr-2023
• Directive: 2014/30/EU - Directive 2014/30/EU of the European Parliament and of the Council of 26 February 2014 on the harmonisation of the laws of the Member States relating to electromagnetic compatibility (recast)
• Directive: 2014/35/EU - Directive 2014/35/EU of the European Parliament and of the Council of 26 February 2014 on the harmonisation of the laws of the Member States relating to the making available on the market of electrical equipment designed for use within certain voltage limits
• Mandate: M/511 - Mandate to CEN, CENELEC and ETSI relating to harmonised standards in the field of the Low Voltage Directive
• Mandate: M/552 - [C(2016) 7641 final] Standardisation request as regards harmonised standards in support of Directive 2014/30/EU of the European Parliament and of the Council of 26 February 2014 on the harmonisation of the laws of the Member States relating to electromagnetic compatibility
• Ref Project: EN IEC 60947-8:2023 - Low-voltage switchgear and controlgear - Part 8: Control units for built-in thermal protection (PTC) for rotating electrical machines

Relations

• Replaces: SIST EN 60947-8:2003 - Low-voltage switchgear and controlgear -- Part 8: Control units for built-in thermal protection (PTC) for rotating electrical machines
• Effective Date: 01-Jun-2023
• Replaces: SIST EN 60947-8:2003/A1:2007 - Low-voltage switchgear and controlgear -- Part 8: Control units for built-in thermal protection (PTC) for rotating electrical machines
• Effective Date: 01-Jun-2023
• Replaces: SIST EN 60947-8:2003/A2:2012 - Low-voltage switchgear and controlgear - Part 8: Control units for built-in thermal protection (PTC) for rotating electrical machines (IEC 60947-8:2003/A2:2011)
• Effective Date: 01-Jun-2023

Standards Content (Sample)

SLOVENSKI STANDARD
01-junij-2023
Nizkonapetostne stikalne in krmilne naprave - 8. del: Krmilne enote za vgrajeno
toplotno zaščito (PTC) rotacijskih električnih strojev (IEC 60947-8:2021)
Low-voltage switchgear and controlgear - Part 8: Control units for built-in thermal
protection (PTC) for rotating electrical machines (IEC 60947-8:2021)
Niederspannungsschaltgeräte - Teil 8: Auslösegeräte für den eingebauten thermischen
Schutz (PTC) von rotierenden elektrischen Maschinen (IEC 60947-8:2021)
Appareillage à basse tension - Partie 8: Unités de commande pour la protection
thermique incorporée (CTP) aux machines électriques tournantes (IEC 60947-8:2021)
Ta slovenski standard je istoveten z: EN IEC 60947-8:2023
ICS:
29.130.20 Nizkonapetostne stikalne in Low voltage switchgear and
krmilne naprave controlgear
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60947-8

NORME EUROPÉENNE
EUROPÄISCHE NORM April 2023
ICS 29.130.20 Supersedes EN 60947-8:2003; EN 60947-
8:2003/A1:2006; EN 60947-8:2003/A2:2012
English Version
Low-voltage switchgear and controlgear - Part 8: Control units
for built-in thermal protection (PTC) for rotating electrical
machines
(IEC 60947-8:2021)
Appareillage à basse tension - Partie 8: Unités de Niederspannungsschaltgeräte - Teil 8: Auslösegeräte für
commande pour la protection thermique incorporée (CTP) den eingebauten thermischen Schutz (PTC) von
aux machines électriques tournantes rotierenden elektrischen Maschinen
(IEC 60947-8:2021) (IEC 60947-8:2021)
This European Standard was approved by CENELEC on 2023-01-11. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60947-8:2023 E

European foreword
The text of document 121A/424/FDIS, future edition 2 of IEC 60947-8, prepared by SC 121A "Low-
voltage switchgear and controlgear" of IEC/TC 121 "Switchgear and controlgear and their assemblies
for low voltage" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2023-10-11
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2026-01-11
document have to be withdrawn
This document supersedes EN 60947-8:2003 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
This document has been prepared under a Standardization Request given to CENELEC by the
European Commission and the European Free Trade Association, and supports essential
requirements of EU Directive(s) / Regulation(s).
For the relationship with EU Directive(s) / Regulation(s), see informative Annex ZZ, which is an
integral part of this document.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 60947-8:2021 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 60034-11:2020 NOTE Approved as EN IEC 60034-11:20201 (not modified)
IEC 60990:2016 NOTE Approved as EN 60990:2016 (not modified)
IEC 62477-1:2012 NOTE Approved as EN 62477-1:2012 (not modified) + A11:2014
IEC 62477-1:2012/A1:2016 NOTE Approved as EN 62477-1:2012/A1:2017 (not modified)
IEC/TR 63201 NOTE Approved as CLC IEC/TR 63201
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
CISPR 11 (mod) 2015 Industrial, scientific and medical equipment EN 55011 2016
- Radio-frequency disturbance
characteristics - Limits and methods of
measurement
+ A1 2016 + A1 2017
+ A11 2020
IEC 60068-2-6 2007 Environmental testing – Part 2-14: Tests – EN 60068-2-6 2008
Test Fc: Vibration (sinusoidal)
IEC 60068-2-27 2008 Environmental testing – Part 2: Tests – EN 60068-2-27 2009
Test Ea and guidance: Shock
IEC 60417 - Graphical symbols for use on equipment - -
IEC 60445 - Basic and safety principles for man- EN 60445 2017
machine interface, marking and
identification - Identification of equipment
terminals, conductor terminations and
conductors
IEC 60730-1 (mod) - Automatic electrical controls - Part 1: EN 60730-1 2016
General requirements
+ A1 2019
IEC 60738-1 2006 Thermistors – Directly heated positive step- EN 60738-1 2006
function temperature coefficient – Part 1:
Generic specification
+ A1 2009 + A1 2009
IEC 60738-1-4 2008 Thermistors - Directly heated positive step- EN 60738-1-4 2008
function temperature coefficient - Part 1-4:
Blank detail specification - Sensing
application - Assessment level EZ
IEC 60947-1 2020 Low-voltage switchgear and controlgear - EN IEC 60947-1 2021
Part 1: General rules
Publication Year Title EN/HD Year
IEC 60947-5-1 2016 Low-voltage switchgear and controlgear - EN 60947-5-1 2017
Part 5-1: Control circuit devices and
switching elements - Electromechanical
control circuit devices
+ AC 2020-
IEC 61140 2016 Protection against electric shock – EN 61140 2016
Common aspects for installation and
equipment
ISO 2859-1 1999 Sampling procedures for inspection by - -
attributes - Part 1: Sampling schemes
indexed by acceptance quality limit (AQL)
for lot-by-lot inspection
+ A1 2011 - -
Annex ZZ
(informative)
Relationship between this European standard and the safety
objectives of Directive 2014/35/EU [2014 OJ L96] aimed to be
covered
This European standard has been prepared under a Commission’s standardisation request relating to
harmonised standards in the field of the Low Voltage Directive, M/511, to provide one voluntary means
of conforming to safety objectives of Directive 2014/35/EU of the European Parliament and of the
Council of 26 February 2014 on the harmonisation of the laws of the Member States relating to the
making available on the market of electrical equipment designed for use within certain voltage limits
[2014 OJ L96].
Once this standard is cited in the Official Journal of the European Union under that Directive,
compliance with the normative clauses of this standard given in Table ZZB.1 confers, within the limits
of the scope of this standard, a presumption of conformity with the corresponding safety objectives of
that Directive, and associated EFTA regulations.
Table ZZB.1 — Correspondence between this European standard and Annex I of Directive
2014/35/EU [2014 OJ L96]
Safety objectives of Clause(s) / sub-clause(s) of Remarks/note
Directive 2014/35/EU this EN
1 a) 5, 6, 8, Annex A
1 b) 5, 6, 7, 8, 9, Annex A, Annex B
1 c) 5, 6, 7, 8, 9, Annex A
2 a) 5, 6, 8, 9, Annex B
2 b) 5, 6, 8, 9, Annex A
2 c) 5, 6, 7, 8, Annex A
2 d) 5, 6, 7, 8, 9, Annex B
3 a) 5, 6, 7, 8, 9
3 b) 5, 6, 7, 8, 9, Annex A
3 c) 5, 6, 8, 9
WARNING 1 — Presumption of conformity stays valid only as long as a reference to this European
standard is maintained in the list published in the Official Journal of the European Union. Users of this
standard should consult frequently the latest list published in the Official Journal of the European
Union.
WARNING 2 — Other Union legislation may be applicable to the product(s) falling within the scope of
this standard.
IEC 60947-8 ®
Edition 2.0 2021-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Low-voltage switchgear and controlgear –
Part 8: Control units for built-in thermal protection (PTC) for rotating electrical
machines
Appareillage à basse tension –
Partie 8: Unités de commande pour la protection thermique incorporée (CTP)
aux machines électriques tournantes
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.130.20 ISBN 978-2-8322-4715-0
– 2 – IEC 60947-8:2021 © IEC 2021
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions, symbols and abbreviated terms . 9
3.1 Terms and definitions . 9
3.2 Symbols and abbreviated terms . 11
4 Void . 11
5 Characteristics of control units for built-in thermal protection (PTC) . 11
5.1 Summary of characteristics . 11
5.2 Type of equipment . 11
5.2.1 Operating temperatures of protection systems . 11
5.2.2 Rated PTC thermistor operating temperature . 11
5.2.3 Rated system operating temperature . 12
5.2.4 Maximum permissible rated operating temperature for the system . 12
5.2.5 Control unit with reset temperature . 12
5.2.6 Control unit with sensor short-circuit detection . 12
5.2.7 Control unit with sensor wire break detection . 12
5.3 Rated electrical values of the switching device of the control unit . 13
5.3.1 Rated electrical values of switching devices . 13
5.3.2 Rated voltages of a control unit . 13
5.3.3 Rated currents of a control unit . 13
5.3.4 Rated making and breaking capacities of a control unit . 13
5.4 Rated electrical values of characteristic variation related to PTC thermistors . 13
5.4.1 General . 13
5.4.2 Electrical data/ratings and characteristics related to the PTC thermistor . 13
5.4.3 Rated voltage of the PTC thermistor circuit of the control unit . 14
5.5 Control supply circuit . 14
5.6 Auxiliary circuits . 14
6 Product information . 14
6.1 Nature of information . 14
6.2 Marking . 15
6.3 Instructions for installation, operation and maintenance, decommissioning
and dismantling. 15
6.4 Environmental information . 15
7 Normal service, mounting and transport conditions . 15
8 Constructional and performance requirements . 16
8.1 Constructional requirements . 16
8.1.1 General . 16
8.1.2 Materials . 17
8.1.3 Current-carrying parts and their connections . 17
8.1.4 Clearances and creepage distances . 17
8.1.5 Vacant . 17
8.1.6 Vacant . 17
8.1.7 Vacant . 17
8.1.8 Terminals . 17

IEC 60947-8:2021 © IEC 2021 – 3 –
8.1.9 Vacant . 18
8.1.10 Provisions for protective earthing . 18
8.1.11 Dedicated enclosures for equipment . 18
8.1.12 Degrees of protection of enclosed equipment . 18
8.1.13 Conduit pull-out, torque and bending with metallic conduits . 18
8.1.14 Limited energy source . 18
8.1.15 Stored charge energy circuit . 20
8.1.16 Fault and abnormal conditions . 20
8.1.17 Short-circuit and overload protection of ports . 21
8.2 Performance requirements . 21
8.2.1 Operating conditions . 21
8.2.2 Abnormal conditions of service . 22
8.2.3 Dielectric properties . 22
8.2.4 Temperature rise . 22
8.2.5 Conditional short-circuit current . 22
8.2.6 Making and breaking capacities for control and auxiliary circuits . 22
8.2.7 Additional requirements and tests for equipment with protective

separation . 22
8.2.8 Operating temperature variation . 22
8.2.9 Damp heat . 22
8.2.10 Shock and vibration . 22
8.2.11 Requirements for short-circuit detection within the PTC thermistor
circuit . 23
8.2.12 Requirements for wire break detection within the PTC thermistor circuit . 23
8.3 Electromagnetic compatibility (EMC) . 23
8.3.1 General . 23
8.3.2 Immunity . 23
8.3.3 Emission . 24
9 Tests . 24
9.1 Kinds of tests . 24
9.1.1 General . 24
9.1.2 Type tests . 24
9.1.3 Routine tests . 24
9.1.4 Sampling tests . 25
9.1.5 Special tests . 25
9.2 Compliance with constructional requirements . 25
9.2.1 General . 25
9.2.2 Electrical performance of screwless-type clamping units . 25
9.2.3 Ageing test for screwless-type clamping units . 25
9.2.4 Limited energy source test . 25
9.2.5 Breakdown of components . 26
9.3 Compliance with performance requirements . 27
9.3.1 Test sequences . 27
9.3.2 General test conditions . 28
9.3.3 Performance . 28
9.3.4 Performance under conditional short-circuit current . 32
9.4 EMC tests . 32
9.4.1 General . 32
9.4.2 Immunity . 32

– 4 – IEC 60947-8:2021 © IEC 2021
9.4.3 Emission . 33
9.5 Routine and sampling tests . 34
9.5.1 General . 34
9.5.2 Operating tests on control units . 34
9.5.3 Dielectric tests . 34
9.5.4 Routine verification of switch on and switch off of Mark A control units . 34
Annex A (normative) PTC thermistors used in thermal protection systems . 35
A.1 Characteristics of association of Mark A thermistors . 35
A.2 Verification of interchangeability characteristics . 35
A.2.1 Type tests on Mark A thermistors. 35
A.2.2 Routine tests on Mark A thermistors . 36
Annex B (normative) Additional requirements and tests for equipment with protective
separation . 37
B.1 General . 37
B.2 Definitions. 37
B.3 Requirements . 37
B.3.1 Test method for implementing protective impedance . 37
B.3.2 Touch current measurement . 38
Bibliography . 40

Figure 1 – Measurement of wire break detection . 31
Figure A.1 – Characteristic curve of a typical Mark A thermistor. 36
Figure B.1 – Protection by means of protective impedance . 38
Figure B.2 – Measuring instrument . 39

Table 1 – Limits for limited energy sources without an over-current protective device . 19
Table 2 – Limits for limited energy sources with an over-current protective device . 19
Table 3 – Limits for limited energy source with current limiting impedance . 20
Table 4 – Terminal disturbance voltage limits for conducted radio-frequency emission

(for control supply input) . 33
Table 5 – Radiated emission test limits . 33

IEC 60947-8:2021 © IEC 2021 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
LOW-VOLTAGE SWITCHGEAR AND CONTROLGEAR –

Part 8: Control units for built-in thermal protection (PTC)
for rotating electrical machines

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
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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.
IEC 60947-8 has been prepared by subcommittee 121A: Low voltage switchgear and
controlgear, of IEC technical committee 121: Switchgear and controlgear and their assemblies
for low voltage. It is an International Standard.
This second edition cancels and replaces the first edition published in 2003, Amendment 1:2006
and Amendment 2:2011. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) safety aspects related to:
• general aspects;
• limited energy circuits;
• electronic circuits;
b) alignment to IEC 60947-1:2020;

– 6 – IEC 60947-8:2021 © IEC 2021
c) wire break detection function;
d) the term detector is replaced by thermistor;
e) reference to IEC 60738-1-4.
The provisions of the general rules dealt with IEC 60947-1 are applicable to this part of
IEC 60947 series where specifically called for. Clauses and subclauses, tables, figures and
annexes of the general rules thus applicable are identified by reference to IEC 60947‑1:2020.
The text of this International Standard is based on the following documents:
FDIS Report on voting
121A/424/FDIS 121A/436/RVD
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 International Standard is English.
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/standardsdev/publications.
A list of all the parts in the IEC 60947 series, under the general title Low-voltage switchgear
and controlgear, can be found on the IEC website.
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,
• replaced by a revised edition, or
• amended.
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.

IEC 60947-8:2021 © IEC 2021 – 7 –
INTRODUCTION
Thermal protection systems which are based on the principle of monitoring the temperature of
the protected parts constitute a simple and effective means of protecting rotating electrical
machines, called also electric motors, against excessive temperature rises, including those
caused by faults in the cooling system, or excessively high ambient temperature, whereas
systems of protection based only on monitoring the current absorbed do not ensure this type of
protection in every circumstances.
Since the operating temperature and response times of thermal protection systems are fixed in
advance, they are not often adjusted in relation to the conditions of use of the machine and,
hence, they are not completely effective for all fault conditions, or improper use of the machine.
A thermal protection system in accordance with this document can consist of a characteristic
change thermal detector which has an associated control unit to convert a point on the
characteristic of the detector to a switching function. A very large number of thermal protection
systems are in use and, in all cases, the machine manufacturer will fit the detectors in the
machine. The machine manufacturer will either supply the control unit with the machine or
specify particulars of the control unit to be used.
It is also customary for the control units to be considered as part of the control system and not
necessarily supplied with the machine. For this reason, it is considered useful to have an
interchangeable system, where the characteristics of association between the detector and the
control unit are specified. This particular system is not considered superior in any way to other
systems complying with the requirements of this document, but in some fields the practice is
likely to be that this interchangeable system will be used, as indicated by the designation
“Mark A”.
– 8 – IEC 60947-8:2021 © IEC 2021
LOW-VOLTAGE SWITCHGEAR AND CONTROLGEAR –

Part 8: Control units for built-in thermal protection (PTC)
for rotating electrical machines

1 Scope
This part of IEC 60947 series specifies requirements for control units, which control a switching
device in response to the PTC thermistors incorporated in rotating electrical machines and the
industrial application.
It specifies requirements for that type of system comprising a positive temperature coefficient
(PTC) thermistor having particular characteristics, and its associated control unit.
This document includes:
– the characteristics, construction, performance and tests of the control unit; and
– its association with a PTC thermistor designated “Mark A”.
This document does not cover:
– the incorporation of thermal protections into rotating machines and their maximum winding
temperature. See IEC 60034-11;
– use of the product within explosive atmospheres (see IEC 60079 (all parts));
– software and firmware requirements;
NOTE 1 Guidance on embedded software is given in IEC TR 63201.
– cyber security aspects (see IEC TS 63208).
NOTE 2 It is not possible to specify all the requirements for the operating characteristics of a control unit, as they
are dependent on some aspects of the PTC thermistors. Some aspects of the requirements of the thermal protector
system can only be specified when account is taken of the characteristics of the rotating machine to be protected
and the method of installation of the PTC thermistor within the machine.
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.
CISPR 11:2015, Industrial, scientific and medical equipment – Radio-frequency disturbance
characteristics – Limits and methods of measurement
CISPR 11:2015/AMD1:2016
IEC 60068-2-6:2007, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-27:2008, Environmental testing – Part 2-27: Tests – Test Ea and guidance: Shock
IEC 60417, Graphical symbols for use on equipment (available at http://www.graphical-
symbols.info/equipment)
IEC 60445, Basic and safety principles for man-machine interface, marking and identification –
Identification of equipment terminals, conductor terminations and conductors

IEC 60947-8:2021 © IEC 2021 – 9 –
IEC 60730-1, Automatic electrical controls – Part 1: General requirements
IEC 60738-1:2006, Thermistors – Directly heated positive temperature coefficient – Part 1:
Generic specification
IEC 60738-1:2006/AMD1:2009
IEC 60738-1-4:2008, Thermistors – Directly heated positive step-function temperature
coefficient – Part 1-4: Blank detail specification – Sensing application – Assessment level EZ
IEC 60947-1:2020, Low-voltage switchgear and controlgear – Part 1: General rules
IEC 60947-5-1:2016, Low-voltage switchgear and controlgear – Part 5-1: Control circuit devices
and switching elements – Electromechanical control circuit devices
IEC 61140:2016, Protection against electric shock – Common aspects for installation and
equipment
ISO 2859-1:1999, Sampling procedures for inspection by attributes – Part 1: Sampling schemes
indexed by acceptance quality limit (AQL) for lot-by-lot inspection
ISO 2859-1:1999/AMD1:2011
3 Terms and definitions, symbols and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60947-1:2020, as
well as the following terms and definitions, 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
3.1.1
built-in thermal protection
protection of certain parts (called protected parts) of a rotating electrical machine against
excessive temperatures resulting from certain conditions of thermal overload, achieved by
means of a thermal protection system, the whole or part of which is a thermally sensitive device
incorporated within the machine
3.1.2
thermal protection system
system intended to ensure the thermal protection of a rotating electrical machine by means of
a built-in PTC thermistor together with a control unit
3.1.3
control system
system to translate a particular point on the characteristic of a PTC thermistor to a switching
function on the supply to the rotating electrical machine
Note 1 to entry: The system is capable of being reset (either manually or automatically) when the temperature falls
to the reset value.
3.1.4
protected part
part of a rotating electrical machine, the temperature of which is limited to a predetermined
value by the action of the thermal protection system

– 10 – IEC 60947-8:2021 © IEC 2021
3.1.5
abrupt characteristic change PTC thermistor
PTC thermistor for which the abrupt change in resistance for one fixed temperature is able to
initiate a switching operation in the control system
3.1.6
control unit
device which converts into a switching function the variation of the characteristic of a PTC
thermistor
Note 1 to entry: The control unit can be part of other devices or systems.
3.1.7
control circuit
circuit controlling the switching device which makes and breaks the power supply
3.1.8
PTC thermistor operating temperature
thermistor temperature at which, during an increase variation of the characteristic
related to the temperature is such as to cause operation of the associated control unit
3.1.9
system operating temperature
thermistor temperature at which, during an increase of temperature, the thermistor and
control unit together cause the operation of the control unit
3.1.10
reset temperature
thermistor temperature at which, during a decrease variation of the characteristic related to the
temperature is such that it permits the resetting of the control unit
3.1.11
positive temperature coefficient thermistor
PTC thermistor
thermistor, the resistance of which increases with its increasing temperature throughout the
useful part of its characteristic
[SOURCE: IEC 60738-1:2006, 3.4, modified – Addition of alternative term.]
3.1.12
mark A thermistor
PTC thermistor having the particular characteristics described in Annex A
3.1.13
mark A control unit
control unit having the particular characteristics specified in this document and intended for
operation in conjunction with a mark A thermistor
3.1.14
short-circuit detection
control unit capable of detecting short-circuited thermistor circuits
3.1.15
wire break detection
control unit capable of detecting wire breaks within the PTC thermistor circuits

IEC 60947-8:2021 © IEC 2021 – 11 –
3.2 Symbols and abbreviated terms
EMC Electromagnetic compatibility
I Rated operational current (5.3.3)
e
I Conventional free air thermal current (5.3.3)
th
PTC Positive temperature coefficient
Q Amplification factor (9.3.3.14.3)
TFS System operating temperature (3.1.9)
TNF PTC thermistor operating temperature (3.1.8)
U Rated operational voltage (5.3.2)
e
U Rated insulation voltage (5.3.2)
i
U Rated impulse withstand voltage (6.1)
imp
U Rated voltage of the thermistor circuit (6.1)
r
Rated control circuit supply voltage (6.1)
U
s
4 Void
5 Characteristics of control units for built-in thermal protection (PTC)
5.1 Summary of characteristics
The characteristics of a control unit shall be stated in the following terms, where such terms are
applicable:
– type of equipment (see 5.2);
– rated electrical values of the control unit (see 5.3);
– rated electrical values of the characteristic of the PTC thermistors and its circuit (see 5.4);
– rated electrical values of the control supply circuit (see 5.5).
5.2 Type of equipment
5.2.1 Operating temperatures of protection systems
Each PTC thermistor, or PTC thermistor with control unit, shall have either a declared rated
operating temperature in accordance with 5.2.2 (TNF), or a declared rated system operating
temperature in accordance with 5.2.3 (TFS), or both.
EXAMPLE
a) Abrupt characteristic change PTC thermistor: TNF to be declared; TFS is not applicable.
b) Abrupt characteristic change PTC thermistor with its control unit: TFS can be declared. For such systems the
value of TFS can coincide with the value of TNF for the PTC thermistor itself.
5.2.2 Rated PTC thermistor operating temperature
In the case of an abrupt characteristic change PTC thermistor, the value of the TNF shall be
declared under item o) of 6.1.
It is recommended that the normal value of TNF, expressed in degrees Celsius, be selected
from the series of numbers which are multiples of five.

– 12 – IEC 60947-8:2021 © IEC 2021
5.2.3 Rated system operating temperature
When the PTC thermistor and the control unit are supplied as a combined unit, the TFS shall
be declared under item o) of 6.1.
The tolerance on the declared value of the TFS shall be ±6 K unless otherwise specified.
NOTE The tolerance is the sum of the tolerances of the PTC thermistor and the control unit.
Routine tests shall be carried out to verify correct operation under normal operating conditions
in accordance with 8.2.1.1.
5.2.4 Maximum permissible rated operating temperature for the system
The maximum permissible value of the TFS depends on both the particular PTC thermistor and
the control unit. It shall be declared under item o) of 6.1.
NOTE For any particular device, the maximum value of the TFS will be dependent on the characteristics and the
materials used in the manufacture of the PTC thermistor, or by the limits on the characteristics of the PTC thermistor
which can be modified by the range of settings available with the control unit design.
5.2.5 Control unit with reset temperature
When the reset function is provided, the reset temperature value and tolerances shall be
provided under item o) of 6.1.
The reset temperature is verified in accordance with 9.3.3.8.
To restart the machine (electric motor) after the tripping of the control unit (switched off), it is
important for the machine winding and the PTC thermistor to cool sufficiently to permit normal
machine accelera
...