IEC 60947-8:2003+AMD1:2006+AMD2:2011 CSV

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

IEC 60947-8:2003+A1:2006+A2:2011 specifies rules for control units, which perform the switching functions in response to the thermal detectors incorporated in rotating electrical machines according to IEC 60034-11, and the industrial application. It specifies rules for that type of system comprising a positive temperature coefficient (PTC) thermistor detector having particular characteristics, and its associated control unit. The PT100 detectors are covered by IEC 60751, where the resistor values are given according to the temperatures of the detector. The present rules lay down the characteristics of association of this particular positive temperature coefficient thermistor detector and its associated control unit (designated "Mark A detector" and "Mark A control unit"), when they are used in thermal protection systems. The technical content is therefore identical to the base edition and its amendments and has been prepared for user convenience. It bears the edition number 1.2. A vertical line in the margin shows where the base publication has been modified by amendments 1 and 2.
This publication is to be read in conjunction with  IEC 60947-1:2007
This consolidated version consists of the first edition (2003), its amendment 1 (2006) and its amendment 2 (2011). Therefore, no need to order amendments in addition to this publication.

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

La CEI 60947-8:2003+A1:2006+A2:2011 spécifie les règles pour les unités de commande, qui réalisent les fonctions de commutation en réponse aux détecteurs thermiques incorporés aux machines électriques tournantes selon la CEI 60034-11, et l'application industrielle. Elle spécifie les règles pour ce type de dispositif comprenant un détecteur à thermistance à coefficient de température positif (CTP) ayant des caractéristiques particulières, et son unité de commande associée. Les détecteurs PT100 sont couverts par la CEI 60751, où les valeurs de résistance sont données selon les températures du détecteur. Les présentes règles fixent les caractéristiques de l'association de ce détecteur à thermistance à coefficient de température positif particulier et de son unité de commande associée (désignés par "Détecteur A" et "Unité de commande A"), lorsqu'ils sont utilisés dans des dispositifs de protection thermique. Le contenu technique de cette version consolidée est donc identique à celui de l'édition de base et à ses amendements; cette version a été préparée par commodité pour l'utilisateur. Elle porte le numéro d'édition 1.2. Une ligne verticale dans la marge indique où la publication de base a été modifiée par les amendements 1 et 2.
Cette publication doit être lue conjointement avec la  CEI 60947-1:2007
Cette version consolidée comprend la première édition (2003), son amendement 1 (2006) et son amendement 2 (2011). Il n'est donc pas nécessaire de commander les amendements avec cette publication.

General Information

• Status: Published
• Publication Date: 17-Oct-2011
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 29.130.20 - Low voltage switchgear and controlgear
• Technical Committee: SC 121A - Low-voltage switchgear and controlgear
• Current Stage: DELPUB - Deleted Publication
• Completion Date: 28-Jul-2021

Standards Content (Sample)

IEC 60947-8 ®
Edition 1.2 2011-10
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 60947-8:2003+A1:2006+A2:2011

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IEC 60947-8 ®
Edition 1.2 2011-10
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
PRICE CODE
INTERNATIONALE
CODE PRIX CP
ICS 29.130.20 ISBN 978-2-88912-722-1

– 2 – 60947-8  IEC:2003+A1:2006+A2:2011
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, symbols and abbreviations . 8
3.1 Terms and definitions . 8
3.2 Symbols and abbreviations . 11
4 Classification . 12
5 Characteristics . 12
5.1 General . 12
5.2 Type of equipment . 12
5.3 Rated electrical values of protection systems . 14
5.4 Rated electrical values of characteristic variation thermal detectors . 15
5.5 Rated voltage of the detector circuit of the control unit . 15
6 Product information . 15
6.1 Nature of information . 15
6.2 Marking . 16
6.3 Instructions for installation, operation and maintenance . 16
7 Normal service, mounting and transport conditions . 16
8 Constructional and performance requirements . 16
8.1 Constructional requirements . 16
8.2 Performance requirements . 17
8.3 Electromagnetic compatibility (EMC) . 19
8.3.1 General . 19
8.3.2 Immunity . 19
8.3.3 Emission . 20
9 Tests . 21
9.1 Kinds of tests . 21
9.2 Compliance with constructional requirements . 22
9.3 Compliance with performance requirements . 22
9.4 EMC tests . 28
9.5 Routine and sampling tests . 30

Annex A (normative) Thermal detectors used in thermal protection systems . 31
Annex B (normative) Special tests . 33

Figure A.1 – Characteristic curve of a typical Mark A detector . 32

Table 1 – Tests for EMC – Immunity . 29
Table 2 – Vibration test parameters . 19

60947-8  IEC:2003+A1:2006+A2:2011 – 3 –
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
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
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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.
International Standard IEC 60947-8 has been prepared by subcommittee 17B: Low-voltage
switchgear and controlgear, of IEC technical committee 17: Switchgear and controlgear.
This consolidated version of IEC 60947-8 consists of the first edition (2003) [documents
17B/1276/FDIS and 17B/1282/RVD], its amendment 1 (2006) [documents 17B/1477/FDIS and
17B/1504/RVD] and its amendment 2 (2011) [documents 17B/1732/FDIS and 17B/1739/RVD].
The technical content is therefore identical to the base edition and its amendments and has
been prepared for user convenience.
It bears the edition number 1.2.
A vertical line in the margin shows where the base publication has been modified by
amendments 1 and 2.
This standard shall be used in conjunction with IEC 60947-1: General rules.

– 4 – 60947-8  IEC:2003+A1:2006+A2:2011
The provisions of the general rules dealt with in IEC 60947-1 are applicable to this standard,
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 (e.g. 1.2.3 of
IEC 60947-1, Table 4 of IEC 60947-1 or Annex A of IEC 60947-1, etc.).
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of the base publication and its amendments will
remain unchanged until the stability date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The “colour inside” logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this publication using a colour printer.

60947-8  IEC:2003+A1:2006+A2:2011 – 5 –
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 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 may not ensure this type of protection.
Since the operating temperature and response times of thermal protection systems are fixed
in advance, they may not be adjusted in relation to the conditions of use of the machine and
they may not be completely effective for all fault conditions or improper use of the machine.
A thermal protection system in accordance with this standard may 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 necessary 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 standard, but in some fields the
practice is likely to be that this interchangeable system will be used, as indicated by
the designation “Mark A”.
– 6 – 60947-8  IEC:2003+A1:2006+A2:2011
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 specifies rules for control units, which perform the switching functions
in response to the thermal detectors incorporated in rotating electrical machines according to
IEC 60034-11, and the industrial application.
It specifies rules for that type of system comprising a positive temperature coefficient (PTC)
thermistor detector having particular characteristics, and its associated control unit.
The PT100 detectors are covered by IEC 60751, where the resistor values are given
according to the temperatures of the detector.
The present rules lay down the characteristics of association of this particular positive
temperature coefficient thermistor detector and its associated control unit (designated “Mark A
detector” and “Mark A control unit”), when they are used in thermal protection systems.
NOTE 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 thermal detectors. 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 detector within the machine.
For these reasons, for each characteristic it is necessary to specify who is responsible for stating the required
values and who is responsible for compliance with the requirement and for carrying out any confirmatory test.
2 Normative references
The following referenced documents are indispensable for the application 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 60034-11:2004, Rotating electrical machines – Part 11: Thermal protection
IEC 60068-2-1, Environmental testing – Part 2-1: Tests – Test A: Cold
IEC 60068-2-6:1995, Environmental testing – Part 2: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-27:1987, Environmental testing – Part 2: Tests – Test Ea and guidance: Shock
IEC 60410:1973, Sampling plans and procedures for inspection by attributes
IEC 60417:2002, Graphical symbols for use on equipment
IEC 60738-1:1998, Thermistors – Directly heated positive step-function temperature
coefficient – Part 1: Generic specification

60947-8  IEC:2003+A1:2006+A2:2011 – 7 –
IEC 60751:1983, Industrial platinum resistance thermometer sensors
Amendment 1 (1986)
Amendment 2 (1995)
IEC 60947-1:2007, Low-voltage switchgear and controlgear – Part 1: General rules
IEC 60947-5-1:2003, Low-voltage switchgear and controlgear – Part 5-1: Control circuit
devices and switching elements – Electromechanical control circuit devices
IEC 61000-4-2:2008, Electromagnetic compatibility (EMC) – Part 4-2: Testing and
measurement techniques – Electrostatic discharge immunity test
IEC 61000-4-3:2006, Electromagnetic compatibility (EMC) - Part 4-3: Testing and
measurement techniques - Radiated, radio-frequency, electromagnetic field immunity test
Amendment 1 (2007)
Amendment 2 (2010)
IEC 61000-4-4:2004, Electromagnetic compatibility (EMC) – Part 4-4: Testing and
measurement techniques – Electrical fast transient/burst immunity test
Amendment 1 (2010)
IEC 61000-4-5:2005, Electromagnetic compatibility (EMC) – Part 4-5: Testing and
measurement techniques – Surge immunity test
Corrigendum 1 (2009)
IEC 61000-4-6:2008, Electromagnetic compatibility (EMC) – Part 4-6: Testing and
measurement techniques – Immunity to conducted disturbances, induced by radio-frequency
fields
IEC 61000-4-8:2009, Electromagnetic compatibility (EMC) – Part 4-8: Testing and
measurement techniques – Power frequency magnetic field immunity test
IEC 61000-4-11:2004, Electromagnetic compatibility (EMC) – Part 4-11: Testing and
measurement techniques – Voltage dips, short interruptions and voltage variations immunity
tests
IEC 61000-4-13:2002, Electromagnetic compatibility (EMC) – Part 4-13: Testing and
measurement techniques – Harmonics and interharmonics including mains signalling at a.c.
power port, low-frequency immunity tests
Amendment 1 (2009)
CISPR 11:2009, Industrial, scientific and medical equipment – Radio-frequency disturbance
characteristics – Limits and methods of measurement
Amendment 1 (2010)
CISPR 22:2008, Information technology equipment – Radio disturbance characteristics –
Limits and methods of measurement

– 8 – 60947-8  IEC:2003+A1:2006+A2:2011
3 Terms, definitions, symbols and abbreviations
For the purposes of this document, relevant definitions of IEC 60947-1, together with the
following definitions, apply.
3.1 Terms and definitions
Reference
A
Abrupt characteristic change thermal detector . 3.1.14

B
Built-in thermal protection . 3.1.1

C
Category of thermal protection . 3.1.12
Characteristic variation thermal detector . 3.1.13
Control circuit . 3.1.16
Control system . 3.1.5
Control unit . 3.1.15
Control unit with dynamic wire break detection. 3.1.25
Control unit with short-circuit detection within the thermal detector circuit . 3.1.24

D
Detector operating temperature (TNF) . 3.1.17

E
Electrically separated contact elements . 3.1.20

M
Mark A control unit . 3.1.23
Mark A detector . 3.1.22
Maximum temperature after tripping . 3.1.11

P
Protected part . 3.1.6
PTC thermistor detector . 3.1.21

R
Reset temperature . 3.1.19

S
Switching type thermal detector . 3.1.4
System operating temperature (TFS) . 3.1.18

T
Thermal detector. 3.1.3
Thermal overload with rapid variation . 3.1.8
Thermal overload with slow variation . 3.1.7
Thermal protection system . 3.1.2
Thermal protection with detector . 3.1.10
Thermally critical part of a machine . 3.1.9
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

60947-8  IEC:2003+A1:2006+A2:2011 – 9 –
3.1.2
thermal protection system
system intended to ensure the thermal protection of a rotating electrical machine by means of
a built-in thermal detector together with a control unit
3.1.3
thermal detector
electrical insulated device (component), sensitive to temperature only, which will initiate a
switching function in the control system when its temperature reaches a predetermined level
3.1.4
switching type thermal detector
thermal detector which causes a direct operation of a switching element
NOTE The combination of the thermal detector and the switching element is rated as a unit and mounted in the
rotating electrical machine.
3.1.5
control system
system to translate a particular point on the characteristic of a thermal detector to a switching
function on the supply to the rotating electrical machine
NOTE The system is capable of being reset (either manually or automatically) when the temperature falls to the
reset value.
3.1.6
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
3.1.7
thermal overload with slow variation
slow temperature rise above the normal operating temperature
NOTE 1 The variation of the temperature of the protected part is sufficiently slow for the temperature of the
thermal detector to follow without appreciable delay.
NOTE 2 A thermal overload with slow variation may be caused, for instance, by:
− defects in ventilation or in the ventilation system, for example partial blocking of the ventilation ducts,
excessive dust, dirt on the windings or on the cooling ribs of the frame;
− an excessive rise in the ambient temperature or in the temperature of the cooling medium;
− gradually increasing mechanical overload;
− prolonged voltage drop or over-voltage in the machine supply;
− excessive duty in a machine.
3.1.8
thermal overload with rapid variation
rapid rise of temperature above the normal operating temperature
NOTE 1 The variation of the temperature of the protected part may be too rapid for the temperature of the thermal
detector to follow without delay. This may result in a significant temperature difference between the thermal
detector and the protected part.
NOTE 2 A thermal overload with rapid variation may be caused, for instance, by stalling the machine or in certain
circumstances, by phase failure or by starting under abnormal conditions (inertia too high, voltage too low, load
torque abnormally high).
3.1.9
thermally critical part of a machine
part of a machine in which the temperature most rapidly reaches its dangerous value
NOTE A part of a machine which is thermally critical in the case of thermal overload with slow variation may not
be so for a thermal overload with rapid variation.

– 10 – 60947-8  IEC:2003+A1:2006+A2:2011
3.1.10
thermal protection with detector
form of protection where the part of the machine in which the thermal detector(s) is (are)
incorporated is the thermally critical part
3.1.11
maximum temperature after tripping
maximum value of the temperature which is reached by the protected part of the machine
during the period which follows tripping by the thermal protection system, for thermal overload
with rapid variation
3.1.12
category of thermal protection
indication of the permissible temperature levels on the windings of a machine when subjected
to the thermal overload
3.1.13
characteristic variation thermal detector
thermal detector which has a characteristic the variation of which, related to the temperature,
is able to initiate a switching function in the control system for one temperature fixed in
advance during manufacture or by initial adjustment of the control unit
NOTE For example, a resistor detector, thermocouple detector, negative temperature coefficient thermistor
detector, positive temperature coefficient thermistor detector.
3.1.14
abrupt characteristic change thermal detector
thermal detector which has a characteristic, the abrupt change of which for one temperature
fixed in advance during manufacture is able to initiate a switching operation in the control
system
3.1.15
control unit
device which converts into a switching function the variation of the characteristic of a thermal
detector
NOTE The control unit may be part of other devices or systems.
3.1.16
control circuit
circuit controlling the switching device which makes and breaks the power supply
3.1.17
detector operating temperature (TNF)
detector temperature at which detector switching occurs during an increase of temperature, or
at which the variation of the characteristic related to the temperature is such as to cause
operation of the associated control unit
3.1.18
system operating temperature (TFS)
detector temperature at which, during an increase of temperature, the detector and control
unit together cause the operation of the control unit

60947-8  IEC:2003+A1:2006+A2:2011 – 11 –
3.1.19
reset temperature
detector temperature at which, during a decrease of temperature, detector switching occurs
or at which the variation of the characteristic related to the temperature is such that in
conjunction with the control unit it permits the resetting of the control unit
3.1.20
electrically separated contact elements
contact elements belonging to the same control unit, but adequately insulated from each other
so that they can be connected into electrically separated circuits
3.1.21
PTC thermistor detector
abrupt characteristic change thermal detector made by a PTC thermistor, having on part of its
resistance-temperature characteristic, known as the PTC part, a considerable increase in
its electrical resistance with negligible power dissipation as soon as its temperature exceeds
a given value
3.1.22
mark A detector
PTC thermistor detector having the particular characteristics described in Annex A
3.1.23
mark A control unit
control unit having the particular characteristics specified in this standard and intended for
operation in conjunction with a mark A detector
3.1.24
control unit with short-circuit detection within the thermal detector circuit
control unit capable of detecting short-circuited thermal detector circuits
3.1.25
control unit with dynamic wire break detection
control unit capable of indicating wire breaks within the thermal detector circuits
3.2 Symbols and abbreviations
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 (9.3.3.13.3)
TFS System operating temperature (3.1.18)
TNF Detector operating temperature (3.1.17)
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 detector circuit (6.1)
r
U Rated control supply voltage (6.1)
s
– 12 – 60947-8  IEC:2003+A1:2006+A2:2011
4 Classification
Under consideration.
5 Characteristics
5.1 General
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 protection systems (see 5.3);
− rated electrical values of characteristic variation thermal detectors (see 5.4);
− rated voltage of the detector circuit of the control unit (see 5.5).
5.2 Type of equipment
5.2.1 Operating temperatures of protection systems
Each detector, or detector 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. For example:
a) Switching type thermal detector: TNF shall be declared.
b) Abrupt characteristic change thermal detector: TNF shall be declared; TFS is not
applicable.
c) Abrupt characteristic change thermal detector with its control unit: TFS shall be declared.
In this case, the value of TFS may coincide with the value of TNF for the detector itself.
d) Characteristic variation thermal detector with its control unit: TFS shall be declared. In this
case, the detector may not have a definable value of TNF.
5.2.2 Rated detector operating temperature
In the case of an abrupt characteristic change thermal detector, the value of the TNF shall be
declared by the detector manufacturer.
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.
It shall be the responsibility of the detector manufacturer to verify the detector operating
temperature.
5.2.3 Rated system operating temperature
If the protection system of detector and the control unit are supplied through a single supplier
then that supplier shall declare the value of the TFS.
In all other cases, the control unit manufacturer shall declare the value of the TFS.

60947-8  IEC:2003+A1:2006+A2:2011 – 13 –
The tolerance on the declared value of the TFS shall be ±6 K unless otherwise agreed
between the manufacturers.
NOTE The tolerance is the sum of the tolerances of the detector and the control unit.
It shall be the responsibility of the manufacturer, or supplier who declares the value of the
TFS, to ensure that this value is verified, but the test may be carried out by the detector
manufacturer or the control unit manufacturer by agreement.
Routine tests shall be carried out by the control unit manufacturer to verify correct operation
under normal operating conditions in accordance with 8.2.1.
5.2.4 Maximum permissible rated operating temperature for the system
The maximum permissible value of the TFS for a particular detector or a particular control unit
shall be declared by the detector manufacturer or by the control unit manufacturer
respectively.
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 detector, or by the limits on the characteristics of the detector which can
be modified by the range of settings available with the control unit design.
5.2.5 Reset temperature
The reset temperature value and tolerances may be declared by the manufacturer of the
detector or, in cases where this depends upon the combination of the detector and its control
unit, by the control unit manufacturer.
It shall be the responsibility of the detector manufacturer or the control unit manufacturer,
depending on which of them has declared the reset temperature, to ensure that this is verified
in accordance with 9.3.3.8, but the test may be carried out by either manufacturer by
agreement.
NOTE To restart the machine after the tripping of the control system, it is important for the machine winding and
the thermal detector to cool sufficiently to permit normal machine acceleration without nuisance tripping, especially
with a high inertia load. The temperature value for restarting depends on installation and service conditions. The
control system may be designed in order to permit a selection of different temperature values.
For a manual restarting system, the maximum temperature shall be considered. For automatic
restarting systems, the machine manufacturer should consider the minimum and maximum
differential temperatures which result from choices of TNF or TFS and rest temperature with
the declared tolerance values. Differential values which are too narrow may not permit
sufficient cool-down for restarting without nuisance tripping. Differential temperatures that are
too wide may result in an excessively long machine cooling down time or resetting may be
prevented in high ambient temperatures.
5.2.6 Characteristics of Mark A control units
When the control unit operates under the normal conditions of service and the detector circuit
is connected to the terminals of the control unit, the following conditions shall be met.
Compliance shall be verified by the tests specified in 9.3.3.10.
a) The control unit shall switch on, or be able to be reset, when the resistance of the detector
circuit is 750 Ω or less.
b) The control unit shall switch off when the resistance of the thermistor detector circuit is
increased from 1 650 Ω to 4 000 Ω.

– 14 – 60947-8  IEC:2003+A1:2006+A2:2011
c) The control unit shall switch on, or be able to be reset, when the resistance of the
thermistor detector circuit falls from 1 650 Ω to 750 Ω.
d) When a resistance of 4 000 Ω is connected between each pair of terminals intended for
the connection of a thermistor detector circuit, and when the control unit operates at its
rated voltage, the voltage per pair of terminals shall not exceed 7,5 V (direct or alternating
peak voltage).
e) There shall be no significant modification in the operation of the control unit when the
capacitance of the detector circuit is not greater than 0,2 µF.
5.2.7 Short-circuit detection within the sensor circuit
Thermal detectors have a low resistance and therefore a special measure is necessary to
recognize a reduction of the resistance to nearly zero by a short-circuit. For safety
applications, or to increase the lifetime of a rotating electrical machine, it is useful to establish
a short-circuit detection system within the sensor circuit. The safety of the thermal protection,
in particular, is increased by such a short-circuit detection.
Such a short-circuit detection only identifies a short-circuit but it does not automatically cover
a defined action. All following actions depend on the configuration of the control unit and the
manufacturers application.
5.3 Rated electrical values of protection systems
5.3.1 Rated electrical values of switching devices (i.e. control units and switching
type thermal detectors)
The rated electrical values of the switching devices of control units and switching type thermal
detectors shall be declared by the control unit manufacturer in accordance with 5.3.2 to 5.3.4,
as appropriate.
5.3.2 Rated voltages of a control unit
The rated voltages of a control unit are the rated insulation voltage (U) and the rated
i
operational voltage (U ) as defined in 4.3.1.2 and 4.3.1.1 of IEC 60947-1.
e
5.3.3 Rated currents of a control unit
The rated currents of a control unit are the conventional free air thermal current (I ) and the
th
rated operational current (I ) as defined in 4.3.2.1 and 4.3.2.3 of IEC 60947-1.
e
NOTE A control unit may be assigned a number of combinations of rated operational voltage and rated
operational current.
5.3.4 Rated making and breaking capacities of a control unit
For a control unit or a switching type thermal detector to which an utilization category is
assigned, the utilization category shall be declared according to 4.4 of IEC 60947-5-1 and it is
unnecessary to specify rated making and breaking capacities, since these values depend
directly on the utilization category and on the rated operational voltages and currents.

60947-8  IEC:2003+A1:2006+A2:2011 – 15 –
5.4 Rated electrical values of characteristic variation thermal detectors
5.4.1 General
The rated electrical values of characteristic variation thermal detectors shall be declared by
the manufacturer.
5.4.2 Rated insulation voltage
The rated insulation voltage (U) is the value of voltage to which the dielectric tests are
i
referred.
5.4.3 Rated operational voltage of the detector
For a detector for which the operation is dependent on the applied voltage, the rated
operational voltage (U ) is the value of voltage by which the detector is designated and which
e
may be applied to the detector.
NOTE For detectors used with alternating current, the rated operational voltage is the peak value of the voltage,
indicated by Û .
e
5.5 Rated voltage of the detector circuit of the control unit
The rated voltage of the detector circuit (U ) intended to be used with characteristic variation
r
thermal detectors having a defined rated operational voltage shall be declared by the
manufacturer of the control unit.
The voltage U is the maximum value of voltage which appears between each pair of terminals
r
intended for the connection of a detector circuit when a resistance, determined as below, is
connected between these terminals and when the control unit is supplied at its rated voltage.
The resistance to be used corresponds to the value of the characteristic curve when the
control unit is switched off and takes into account the number of detectors in the circuit. This
may be a maximum or minimum value depending upon the shape of the characteristic curve.
NOTE If the circuit is an a.c. circuit, the rated voltage is the peak value of voltage, indicated by Û .
r
6 Product information
6.1 Nature of information
The following information shall be given by the manufacturer:
Identification
a) manufacturer’s name or trade mark;
b) type designation or serial number;
c) 60947-8.
The Mark A control units shall be additionally marked “Mark A control unit”.
Additional marking of Mark A control units:
The control unit shall be marked with the letter “A” additional to the number of this
standard.
– 16 – 60947-8  IEC:2003+A1:2006+A2:2011
Characteristics, basic rated values and utilization
d) rated control supply voltage (U );
s
e) rated frequency of control supply voltage;
f) rated operational voltage (U ) of the control unit;
e
g) rated operational current (I ) of the control unit;
e
h) utilization category, or making and breaking capacities;
i) a circuit diagram which specifies the terminal marking and the connections of the
detectors, the control unit and the supply;
) of the control circuit;
j) rated insulation voltage (U
i
k) type of thermal detectors with which the control unit is to be used and, if applicable, the
rated voltage (U ) of the detector circuit;
r
l) IP code in case of an enclosed equipment;
m) the equipment class according to the EMC emission levels and the specific requirements
necessary to maintain compliance;
n) the immunity levels attained and the specific requirements necessary to maintain
compliance;
o) rated impulse withstand v
...