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

IEC 60947-8:2021 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.
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:  
safety aspects related to:  
general aspects;
limited energy circuits;
electronic circuits;  
alignment to IEC 60947-1:2020;
wire break detection function;
the term detector is replaced by thermistor;
reference to IEC 60738-1-4.

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

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:  
des aspects liés à la sécurité concernant:  
les aspects généraux;
les circuits à énergie limitée;
les circuits électroniques;  
l’alignement avec l’IEC 60947-1:2020;
la fonction de détection de rupture de conducteur;
le terme détecteur est remplacé par thermistance;
la référence à l’IEC 60738-1-4.

General Information

Status
Published
Publication Date
27-Jul-2021
Current Stage
PPUB - Publication issued
Completion Date
28-Jul-2021
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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
IEC 60947-8:2021-07(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
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 978-2-8322-1009-4

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 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

---------------------- Page: 4 ----------------------
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

---------------------- Page: 5 ----------------------
– 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

---------------------- Page: 6 ----------------------
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

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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;
---------------------- Page: 7 ----------------------
– 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.
---------------------- Page: 8 ----------------------
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”.
---------------------- Page: 9 ----------------------
– 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
...

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