IEC 60470:1999

INTERNATIONAL IEC
STANDARD
Second edition
1999-10
High-voltage alternating current contactors
and contactor-based motor-starters
Contacteurs pour courants alternatifs haute tension
et démarreurs de moteurs à contacteurs
Reference number
Numbering
As from 1 January 1997 all IEC publications are issued with a designation in the
60000 series.
Consolidated publications
Consolidated versions of some IEC publications including amendments are
available. For example, edition numbers 1.0, 1.1 and 1.2 refer, respectively, to the
base publication, the base publication incorporating amendment 1 and the base
publication incorporating amendments 1 and 2.
Validity of this publication
The technical content of IEC publications is kept under constant review by the IEC,
thus ensuring that the content reflects current technology.
Information relating to the date of the reconfirmation of the publication is available
in the IEC catalogue.
Information on the subjects under consideration and work in progress undertaken
by the technical committee which has prepared this publication, as well as the list
of publications issued, is to be found at the following IEC sources:
• IEC web site*
•
Catalogue of IEC publications
Published yearly with regular updates
(On-line catalogue)*
• IEC Bulletin
Available both at the IEC web site* and as a printed periodical
Terminology, graphical and letter symbols
For general terminology, readers are referred to IEC 60050: International
Electrotechnical Vocabulary (IEV).
For graphical symbols, and letter symbols and signs approved by the IEC for
general use, readers are referred to publications IEC 60027: Letter symbols to be
used in electrical technology, IEC 60417: Graphical symbols for use on equipment.
Index, survey and compilation of the single sheets and IEC 60617: Graphical symbols
for diagrams.
* See web site address on title page.

INTERNATIONAL IEC
STANDARD
Second edition
1999-10
High-voltage alternating current contactors
and contactor-based motor-starters
Contacteurs pour courants alternatifs haute tension
et démarreurs de moteurs à contacteurs
 IEC 1999  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland
Telefax: +41 22 919 0300 e-mail: inmail@iec.ch IEC web site http://www.iec.ch
Commission Electrotechnique Internationale
PRICE CODE
XC
International Electrotechnical Commission
For price, see current catalogue

– 2 – 60470 © IEC:1999(E)
CONTENTS
Page
FOREWORD . 5
Clause
1 General. 7
1.1 Scope and object . 7
1.2 Normative references. 9
2 Normal service conditions . 10
2.1 Special service conditions . 10
3 Definitions. 10
3.1 General terms . 10
3.2 Assemblies of switchgear and controlgear . 11
3.3 Parts of assemblies. 11
3.4 Switching devices. 11
3.5 Parts of switchgear and controlgear. 13
3.6 Operation. 14
3.7 Characteristic quantities. 16
4 Ratings . 20
4.1 Rated voltage (U ) . 22
r
4.2 Rated insulation level . 22
4.3 Rated frequency (f ) . 23
r
4.4 Rated normal current and temperature rise. 23
4.5 Rated short-time withstand current (I ) . 24
k
4.6 Rated peak withstand current (I ) . 24
p
4.7 Rated duration of short circuit (t ). 24
k
4.8 Rated supply voltage of closing and opening devices, and of auxiliary and
control circuits (U ) . 24
a
4.9 Rated supply frequency of closing and opening devices, and of auxiliary circuits. 24
4.10 Rated pressure of compressed gas supply for insulation and/or operation. 24
5 Design and construction . 33
5.1 Requirements for liquids. 33
5.2 Requirements for gases . 33
5.3 Earthing . 33
5.4 Auxiliary and control equipment. 34
5.5 Dependent power operation. 34
5.6 Stored energy operation . 34
5.7 Independent manual operation . 34
5.8 Operation of releases. 34
5.9 Low- and high-pressure interlocking and monitoring devices. 34
5.10 Nameplates. 34
5.11 Interlocking devices . 35
5.12 Position indication . 35
5.13 Degrees of protection by enclosures. 35
5.14 Creepage distances . 35

60470 © IEC:1999(E) – 3 –
Clause Page
5.15 Gas and vacuum tightness . 35
5.16 Liquid tightness. 36
5.17 Flammability. 36
5.18 Electromagnetic compatibility (EMC) . 36
6 Type tests . 41
6.1 General. 41
6.2 Dielectric tests . 43
6.3 Radio interference voltage (r.i.v.) test. 43
6.4 Measurement of the resistance of circuits. 43
6.5 Temperature-rise tests . 43
6.6 Short-time withstand current and peak withstand current tests . 47
6.7 Verification of the protection. 47
6.8 Tightness tests. 47
6.9 Electromagnetic compatibility tests (EMC) . 47
7 Routine tests.59
7.1 Dielectric test on the main circuit. 59
7.2 Dielectric test on auxiliary and control circuits. 59
7.3 Measurement of the resistance of the main circuit . 59
7.4 Tightness test . 59
7.5 Design and visual checks . 60
8 Guide to the selection of contactors and motor-starters for service . 61
9 Information to be given with enquiries, tenders and orders. 65
10 Rules for transport, storage, erection, operation and maintenance . 66
11 Safety . 66
Annex A (normative) Records and reports of type tests for making, breaking
and short-time current performance . 75
Figure 1 – Examples of speed/time curves . 67
Figure 2 – Test duties A and B – preferred earth point . 68
Figure 3 – Test duties A and B – alternative earth point. 69
Figure 4 – Test duty C – preferred earth point . 70
Figure 5 – Test duty C – alternative earth point . 71
Figure 6 – Representation by two parameters of a prospective TRV of a circuit . 71
Figure 7 – Representation by four parameters of a prospective TRV of a circuit. 72
Figure 8 – Representation of the specified TRV by a two-parameter reference line
and a delay line . 72
Figure 9 – Determination of power frequency recovery voltage . 73
Figure 10 – Characteristics for determining take-over current. 74

– 4 – 60470 © IEC:1999(E)
Page
Table 1 – Ratings and characteristics – Rating/characteristic . 21
Table 2 – Utilization categories . 28
Table 3 – Characteristics dependent on starter type. 33
Table 4 – Characteristics of the opening operation of overload relays when energized
on all poles. 39
Table 5 – Characteristics of the opening operation of three-pole thermal overload relays
when energized on two poles only. 39
Table 6 – Characteristics of the opening by three-pole phase failure-sensitive thermal
overload relays when their poles are not equally energized. 40
Table 7 – Applicable type tests . 42
Table 8 – Test copper conductors for test currents up to 800 A inclusive. 44
Table 9 – Intermittent duty operating cycles . 45
Table 10 – Verification of rated making and breaking capacities – Conditions for making
and breaking corresponding to the several utilization categories at rated voltage U . 49
r
Table 11 – Relationship between current broken I and OFF time. 52
c
Table 12 – Overload current withstand requirements. 53
Table 13 – Transient recovery voltage characteristics . 58
Table 14 – Verification of the number of on-load operating cycles – Conditions for
making and breaking corresponding to the several utilization categories. 59

60470 © IEC:1999(E) – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
HIGH-VOLTAGE ALTERNATING CURRENT CONTACTORS
AND CONTACTOR-BASED MOTOR-STARTERS
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may
participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. The IEC collaborates closely with the International Organization
for Standardization (ISO) in accordance with conditions determined by agreement between the two
organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an
international consensus of opinion on the relevant subjects since each technical committee has representation
from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60470 has been prepared by subcommittee 17A: High-voltage
switchgear and controlgear, of IEC technical committee 17: Switchgear and controlgear.
This standard is to be read in conjunction with IEC 60694, second edition, published in 1996,
which is applicable unless otherwise specified in this standard. In order to simplify the
indication of corresponding requirements, the same numbering of clauses and subclauses as in
IEC 60694 is used. Amendments to these clauses and subclauses are given under the same
references whilst additional subclauses are numbered from 101.
This second edition cancels and replaces the first edition of IEC 60470 published in 1974 and
its amendment 1 (1995), as well as IEC 60632-1.
The text of this standard is based on the following documents:
FDIS Report on voting
17A/545/FDIS 17A/554/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 3.
Annex A forms an integral part of this standard.
A bilingual version of this publication may be issued at a later date.

– 6 – 60470 © IEC:1999(E)
The committee has decided that this publication remains valid until 2011. At this date, in
accordance with the committee's decision, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
60470 © IEC:1999(E) – 7 –
HIGH-VOLTAGE ALTERNATING CURRENT CONTACTORS
AND CONTACTOR-BASED MOTOR-STARTERS
1 General
1.1 Scope and object
This International Standard is applicable to a.c. contactors and/or contactor-based motor-
starters designed for indoor installation and operation at frequencies up to and including 60 Hz
on systems having voltages above 1 000 V but not exceeding 12 000 V.
It is applicable only to three-pole contactors and starters for use in three-phase systems,
and single-pole contactors and starters for use in single-phase systems. Two-pole contactors and
starters for use in single-phase systems are subject to agreement between manufacturer
and user.
Contactors and/or starters dealt with in this standard are not normally designed to interrupt
short-circuit currents. Therefore, suitable short-circuit protection (see 3.4.110.12 and note 2
below) forms part of the installation, but not necessarily of the contactor or the starter.
In this context, this standard gives requirements for
– contactors associated with overload and/or short-circuit protective devices (SCPD);
– starters associated with separate short-circuit protective devices and/or with separate
short-circuit and integrated overload protective devices;
– contactors or starters combined, under specified conditions, with their own short-circuit
protective devices. Such combinations, for example combination starters (see 3.4.110.9),
are rated as units.
Contactors intended for closing and opening electric circuits and, if combined with suitable
relays, for protecting these circuits against operating overloads which may occur therein, are
covered in this standard.
This standard is also applicable to the operating devices of contactors and to their auxiliary
equipment.
Motor-starters intended to start and accelerate motors to normal speed, to ensure continuous
operation of motors, to switch off the supply from the motor and to provide means for the
protection of motors and associated circuits against operating overloads are dealt with.
Motor-starter types included are
– direct-on-line starters;
– reversing starters;
– two-direction starters;
– reduced kVA (voltage) starters;

– 8 – 60470 © IEC:1999(E)
– auto-transformer starters;
– rheostatic starters;
– reactor starters.
Starters, the operation of which depends on thermal electrical relays for motor protection
complying with IEC 60255-8, or motor-incorporated thermal protective devices dealt with in
IEC 60034-11, do not necessarily meet all the relevant requirements of this standard.
Overload relays for starters, including those based on solid-state technology, are covered by
this standard.
This standard does not apply to
– circuit-breaker-based motor-starters;
– single-pole operation of multi-pole contactors or starters;
– two-step auto-transformer starters designed for continuous operation in the starting
position;
– unbalanced rheostatic rotor starters, i.e. where the resistances do not have the same value
in all phases;
– equipment designed not only for starting, but also for adjustment of speed;
– liquid starters and those of the "liquid-vapour" type;
– semiconductor contactors and starters making use of semiconductor contactors in the
main circuit;
– rheostatic stator starters;
– contactors or starters designed for special applications.
This standard does not deal with components contained in contactors and contactor-based
motor-starters, for which individual specifications exist.
NOTE 1 Thermal electrical relays are covered by IEC 60255-8.
NOTE 2 High-voltage current-limiting fuses are covered by IEC 60282-1 and IEC 60644.
NOTE 3 Metal-enclosed switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV
are covered by IEC 60298.
NOTE 4 Disconnectors and earthing switches are covered by IEC 60129.
NOTE 5 High-voltage switches above 1 kV and less than 52 kV are covered by IEC 60265-1.
The object of this standard is to state
a) the characteristics of contactors and starters and associated equipment;
b) the conditions with which contactors or starters shall comply with reference to:
1) their operation and behaviour,
2) their dielectric properties,
3) the degrees of protection provided by their enclosures, where applicable,
4) their construction,
5) for combinations, interactions between the various components, for example SCPD
co-ordination;
c) the tests intended for confirming that these conditions have been met, and the methods to
be adopted for these tests;
d) the information to be given with the equipment or in the manufacturer's literature.

60470 © IEC:1999(E) – 9 –
1.2 Normative references
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this International Standard. For dated references, subsequent
amendments to, or revisions of, any of these publications do not apply. However, parties to
agreements based on this International Standard are encouraged to investigate the possibility
of applying the most recent editions of the normative documents indicated below. For undated
references, the latest edition of the normative document referred to applies. Members of IEC
and ISO maintain registers of currently valid International Standards.
IEC 60034-11:1978, Rotating electrical machines – Part 11: Built-in thermal protection –
Chapter 1: Rules for protection of rotating electrical machines
IEC 60050(441):1984, International Electrotechnical Vocabulary (IEV) – Chapter 441:
Switchgear, controlgear and fuses
IEC 60056:1987, High-voltage alternating-current circuit-breakers
IEC 60076-2:1993, Power transformers – Part 2: Temperature rise
IEC 60129:1984, Alternating current disconnectors and earthing switches
IEC 60255-8:1990, Electrical relays – Part 8: Thermal electrical relays
IEC 60265-1:1983, High-voltage switches – Part 1: High-voltage switches for rated voltages
above 1 kV and less than 52 kV
IEC 60282-1:1994, High-voltage fuses – Part 1: Current-limiting fuses
IEC 60298:1990, A.C. metal-enclosed switchgear and controlgear for rated voltages above
1 kV and up to and including 52 kV
Amendment 1 (1994)
IEC 60417, (all parts) Graphical symbols for use on equipment – Index, survey and compilation
of the single sheets
IEC 60644:1979, Specification for high-voltage fuse-links for motor circuit applications
IEC 60694:1996, Common specifications for high-voltage switchgear and controlgear standards
IEC 60726:1982, Dry-type power transformers
IEC 60947-5-1:1997, Low-voltage switchgear and controlgear – Part 5: Control circuit devices
and switching elements – Section one: Electromechanical control circuit devices
IEC 61233:1994, High-voltage alternating current circuit-breakers – Inductive load switching
IEC 61812-1:1996, Specified time relays for industrial use – Part 1: Requirements and tests

– 10 – 60470 © IEC:1999(E)
2 Normal and special service conditions
2.1 Normal service conditions
Subclause 2.1 of IEC 60694 is applicable with the following modification.
For outdoor installations refer to 8.102.6.
2.2 Special service conditions
Subclause 2.2 of IEC 60694 is applicable with the following modification.
2.2.1 Altitude
Altitude classes of 1 000 m, 2 000 m and 3 000 m are recognized. See 8.102.7.
NOTE These classes are necessary for some types of operating mechanism.
3 Definitions
For the purpose of this International Standard, clause 3 of IEC 60694 applies with the following
additional definitions.
3.1 General terms
3.1.101
controlgear
a general term covering switching devices and their combination with associated control,
measuring, protective and regulating equipment, also assemblies of such devices and equip-
ment with associated interconnections, accessories, enclosures and supporting structures,
intended in principle for the control of electric energy consuming equipment [IEV 441-11-03]
3.1.102
over-current
a current exceeding the rated current [IEV 441-11-06]
3.1.103
short-circuit current
an over-current resulting from a short circuit due to a fault or an incorrect connection in an
electric circuit [IEV 441-11-07]
3.1.104
overload
operating conditions in an electrically undamaged circuit, which cause an over-current
[IEV 441-11-08]
3.1.105
conductive part
a part which is capable of conducting current although it may not necessarily be used for
carrying service current [IEV 441-11-09]
3.1.106
ambient air temperature
the temperature, determined under prescribed conditions, of the air surrounding the complete
switching device or fuse [IEV 441-11-13]
NOTE For switching devices or fuses installed inside an enclosure, it is the temperature of the air outside the enclosure.

60470 © IEC:1999(E) – 11 –
3.2 Assemblies of switchgear and controlgear
No particular definitions.
3.3 Parts of assemblies
No particular definitions.
3.4 Switching devices
3.4.101
switching device
a device designed to make or break the current in one or more electric circuits [IEV 441-14-01]
3.4.102
mechanical switching device
a switching device designed to close and open one or more electric circuits by means of
separable contacts [IEV 441-14-02]
NOTE Any mechanical switching device may be designated according to the medium in which its contacts open
and close, e.g. air, SF , oil.
3.4.103
disconnector
a mechanical switching device which provides, in the open position, an isolating distance in
accordance with specified requirements [IEV 441-14-05]
NOTE A disconnector is capable of opening and closing a circuit either when negligible current is broken or made,
or when no significant change in the voltage across the terminals of each of the poles of the disconnector occurs. It
is also capable of carrying currents under normal circuit conditions and carrying for a specified time currents under
abnormal conditions such as those of short circuit.
3.4.104
earthing switch
a mechanical switching device for earthing parts of a circuit, capable of withstanding for a
specified time currents under abnormal conditions such as those of short circuit, but not
required to carry current under normal conditions of the circuit [IEV 441-14-11]
NOTE An earthing switch may have a short-circuit making capacity.
3.4.105
contactor (mechanical)
a mechanical switching device having only one position of rest, operated otherwise than by
hand, capable of making, carrying and breaking currents under normal circuit conditions
including operating overload conditions [IEV 441-14-33]
NOTE 1 A contactor may also be capable of making and breaking short-circuit currents.
NOTE 2 A contactor is usually intended to operate frequently.
3.4.106
electromagnetic contactor
a contactor in which the force for closing the normally open main contacts or for opening the
normally closed main contacts is provided by an electromagnet
3.4.107
vacuum contactor
a contactor in which the main contacts open and close within a highly evacuated envelope

– 12 – 60470 © IEC:1999(E)
3.4.108
SF contactor
a contactor in which the main contacts open and close within an SF gas-filled compartment
3.4.109
latched contactor
a contactor, the moving elements of which are prevented by means of a latching arrangement from
returning to the position of rest when the operating means are de-energized [IEV 441-14-34]
NOTE The latching, and the release of the latching, may be mechanical, electromagnetic, pneumatic, etc.
3.4.110
starter
the combination of all the switching means necessary to start and stop a motor in combination
with suitable overload protection [IEV 441-14-38]
NOTE Starters may be designated according to the method by which the force for closing the main contacts is
provided.
3.4.110.1
direct-on-line starter
a starter which connects the line voltage across the motor terminals in one step [IEV 441-14-40]
3.4.110.2
reversing starter
a starter intended to cause the motor to reverse the direction of rotation by reversing the motor
primary connections even when the motor is running
3.4.110.3
two-direction starter
a starter intended to cause the motor to reverse the direction of rotation by reversing the motor
primary connections only when the motor is not running
3.4.110.4
reduced kVA (voltage) starter
a starter which reduces the starting kVA of the motor
NOTE Reduced kVA starters may include auto-transformer, reactor, rheostatic starters.
3.4.110.5
auto-transformer starter
a starter which uses one or more reduced voltages derived from an auto-transformer
3.4.110.6
rheostatic starter
a starter utilizing one or several resistors for obtaining, during starting, stated motor torque
characteristics and for limiting the current [IEV 441-14-42]
NOTE A rheostatic starter generally consists of three basic parts, which may be supplied either as a composite
unit or as separate units to be connected at the place of utilization:
– the mechanical switching devices for supplying the stator (generally associated with an overload protective device);
– the resistor(s) inserted in the rotor circuit;
– the mechanical switching devices for cutting out the resistor(s) successively.

60470 © IEC:1999(E) – 13 –
3.4.110.7
rheostatic rotor starter
a rheostatic starter for an asynchronous wound-rotor motor which, during the starting period,
cuts out successively one or several resistors previously provided in the rotor circuit [IEV
441-14-43]
3.4.110.8
reactor starter
a starter that includes a reactor connected in series with the stator winding of an alternating
current motor to furnish reduced voltage for starting
3.4.110.9
combination starter (often referred to as a controller)
equipment consisting of a contactor, overload protection, a manual externally operated
disconnector and a short-circuit protective device, mounted and wired in a dedicated enclosure
NOTE 1 A dedicated enclosure is an enclosure specifically designed and dimensioned for its application in which
all tests are conducted, and which may also include an earthing function.
NOTE 2 A combination starter may be used for functions other than motor starting, for example transformer
control and protection.
3.4.110.10
electromagnetic starter
starter in which the force for closing the main contacts is provided by an electromagnet
3.4.110.11
n-step starter
a starter in which there are (n – 1) intermediate accelerating positions between the off and full
on positions [IEV 441-14-41]
NOTE 1 A starter in which there is no intermediate accelerating position between the OFF and ON positions is a
single step or direct-on-line starter (see 3.4.110.1).
NOTE 2 A starter in which there is only one intermediate accelerating position between the OFF and ON positions
is known as a two-step starter.
NOTE 3 A three-step rheostatic starter has two sections of resistors used for starting.
3.4.110.12
short-circuit protective device (SCPD)
a device intended to protect a circuit or parts of a circuit against short-circuit currents by
interrupting them
3.5 Parts of switchgear and controlgear
3.5.101
pole of a switching device
the portion of a switching device associated exclusively with one electrically separated
conducting path of its main circuit and excluding those portions which provide a means for
mounting and operating all poles together [IEV 441-15-01]
NOTE A switching device is called single-pole if it has only one pole. If it has more than one pole, it may be called
multipole (two-pole, three-pole, etc.) provided the poles are or can be coupled in such a manner as to operate
together.
3.5.102
main circuit (of a switching device)
all the conductive parts of a switching device included in the circuit which it is designed to close
or open [IEV 441-15-02]
– 14 – 60470 © IEC:1999(E)
3.5.103
control circuit (of a switching device)
all the conductive parts (other than the main circuit) of a switching device which are included in a
circuit used for the closing operation or opening operation, or both, of the device [IEV 441-15-03]
3.5.104
auxiliary circuit (of a switching device)
all the conductive parts of a switching device which are intended to be included in a circuit
other than the main circuit and the control circuits of the device [IEV 441-15-04]
NOTE Some auxiliary circuits fulfil supplementary functions such as signalling, interlocking, etc., and, as such,
they may be part of the control circuit of another switching device.
3.5.105
main contact
a contact included in the main circuit of a mechanical switching device, intended to carry, in the
closed position, the current of the main circuit [IEV 441-15-07]
3.5.106
control contact
a contact included in a control circuit of a mechanical switching device and mechanically
operated by this device [IEV 441-15-09]
3.5.107
auxiliary contact
a contact included in an auxiliary circuit and mechanically operated by the switching device
[IEV 441-15-10]
3.5.108
"a" contact; make contact
a control or auxiliary contact which is closed when the main contacts of the mechanical
switching device are closed and open when they are open [IEV 441-15-12]
3.5.109
"b" contact; break contact
a control or auxiliary contact which is open when the main contacts of a mechanical switching
device are closed and closed when they are open [IEV 441-15-13]
3.6 Operation
3.6.101
operation (of a mechanical switching device)
the transfer of the moving contact(s) from one position to an adjacent position [IEV 441-16-01]
NOTE 1 For a circuit-breaker, this may be a closing operation or an opening operation.
NOTE 2 If distinction is necessary, an operation in the electrical sense, e.g. make or break, is referred to as a
switching operation, and an operation in the mechanical sense, e.g. close or open, is referred to as a mechanical
operation.
3.6.102
operating cycle (of a mechanical switching device)
a succession of operations from one position to another and back to the first position through
all other positions, if any [IEV 441-16-02]
NOTE 1 This may be a closing operation followed by an opening operation.
NOTE 2 A succession of operations not forming an operating cycle is referred to as an operating series.

60470 © IEC:1999(E) – 15 –
3.6.103
closing operation (of a mechanical switching device)
an operation by which the device is brought from the open position to the closed position
[IEV 441-16-08]
3.6.104
opening operation (of a mechanical switching device)
an operation by which the device is brought from the closed position to the open position
[IEV 441-16-09]
3.6.105
closed position (of a mechanical switching device)
the position in which the predetermined continuity of the main circuit of the device is secured
[IEV 441-16-22]
3.6.106
open position (of a mechanical switching device)
the position in which the predetermined clearance between open contacts in the main circuit of
the device is secured [IEV 441-16-23]
3.6.107
position of rest (of a contactor)
the position which the moving elements of the contactor take up when its electromagnet or its
compressed-air device is not energized [IEV 441-16-24]
3.6.108
overload relay or release
an over-current relay or release intended for protection against overloads (including, where
applicable, operating transformer(s) and interconnections)
3.6.109
thermal overload relay or release
an inverse time-delay overload relay or release depending for its operation (including its time
delay) on the thermal action of the current flowing in the relay or release
3.6.110
current setting of an overload relay or release
the value of current for which the relay or release is adjusted and in accordance with which its
operating conditions are defined
3.6.111
current setting range of an overload relay or release
the range between the minimum and maximum values over which the current setting of the
relay or release can be adjusted
3.6.112
phase failure sensitive overload relay or release
a multi-pole overload relay or release which, in accordance with specified requirements,
operates at a current value lower than its current setting in the case of current unbalance
3.6.113
under-current (under-voltage) relay or release
a measuring relay or release which operates automatically when the current through it (or the
voltage applied to it) is reduced below a pre-determined value

– 16 – 60470 © IEC:1999(E)
3.6.114
starting time (of a rheostatic starter)
the period of time during which the starting resistors or parts of them carry current
NOTE The starting time of a starter is shorter than the total starting time of the motor, which takes into account
the last period of acceleration following the switching operation ON position.
3.6.115
starting time (of an auto-transformer starter)
the period of time during which the auto-transformer carries current
NOTE The starting time of a starter is shorter than the total starting time of the motor, which takes into account
the last period of acceleration following the switching operation ON position.
3.6.116
open transition (with an auto-transformer starter)
a circuit arrangement so that the supply to the motor is interrupted and reconnected when
changing over from one step to another
NOTE The transition stage is not considered an additional step.
3.6.117
closed transition (with an auto-transformer starter)
a circuit arrangement so that the supply to the motor is not interrupted (even momentarily)
when changing over from one step to another
NOTE The transition stage is not considered an additional step.
3.6.118
inching (jogging)
energizing a motor or solenoid repeatedly for short periods to obtain small movements of the
driven mechanism
3.6.119
plugging
stopping or reversing a motor rapidly by reversing the motor primary connections while the
motor is running
3.7 Characteristic quantities
3.7.101
breaking current (of a switching device or a fuse)
the current in a pole of a switching device or in a fuse at the instant of initiation of the arc
during a breaking process [IEV 441-17-07]
3.7.102
breaking capacity (of a switching device or a fuse)
a value of prospective current that a switching device or a fuse is capable of breaking at a
stated voltage under prescribed conditions of use and behaviour [IEV 441-17-08]
NOTE 1 The voltage to be stated and the conditions to be prescribed are dealt with in the relevant publications.
NOTE 2 For switching devices, the breaking capacity may be termed according to the kind of current included in
the prescribed conditions, e.g. line charging breaking capacity, cable charging breaking capacity, single capacitor
bank breaking capacity, etc.
60470 © IEC:1999(E) – 17 –
3.7.103
making capacity (of a switching device)
a value of prospective making current that a switching device is capable of making at a stated
voltage under prescribed conditions of use and behaviour [IEV 441-17-09]
NOTE The voltage to be stated and the conditions to be prescribed are dealt with in the relevant specifications.
3.7.104
take-over current
the current coordinate of the intersection between the time-current characteristics of two over-
current protective devices [IEV 441-17-16]
3.7.105
short-time withstand current
the current that a circuit or a switching device in the closed position can carry during a
specified short time under prescribed conditions of use and behaviour [IEV 441-17-17]
3.7.106
recovery voltage
the voltage which appears across the terminals of a pole of a switching device or a fuse after
the breaking of the current [IEV 441-17-25]
NOTE This voltage may be considered in two successive intervals of time, one during which a transient voltage
exists, followed by a second one during which the power frequency or the steady-state recovery voltage alone exists.
3.7.107
transient recovery voltage (TRV)
the recovery voltage during the time in which it has a significant transient character [IEV 441-17-26]
NOTE 1 The transient recovery voltage may be oscillatory or non-oscillatory, or a combination of these, depending on
the characteristics of the circuit and the switching device. It includes the voltage shift of the neutral of a polyphase circuit.
NOTE 2 The transient recovery voltage in three-phase circuits is, unless otherwise stated, that across the first
pole to clear, because this voltage is generally higher than that which appears across each of the other two poles.
3.7.108
power frequency recovery voltage
the recovery voltage after the transient voltage phenomena have subsided [IEV 441-17-27]
3.7.109
prospective current (of a circuit and with respect to a combination situated therein)
the current that would flow in the circuit if each pole of the combination were replaced by a
conductor of negligible impedance [IEV 441-17-01, modified]
3.7.110
prospective peak current
the peak value of a prospective current during the transient period following initiation
[IEV 441-17-02]
NOTE The definition assumes that the current is made by an ideal switching device, i.e. with instantaneous transition
from infinite to zero impedance. For circuits where the current can follow several different paths, e.g. polyphase circuits, it
further assumes that the current is made simultaneously in all poles, even if only the current in one pole is considered.
3.7.111
maximum prospective peak current (of an a.c. circuit)
the prospective peak current when initiation of the current takes place at the instant which
leads to the highest possible value [IEV 441-17-04]
NOTE For a multiple device in a polyphase circuit, the maximum prospective peak current refers to a single pole only.

– 18 – 60470 © IEC:1999(E)
3.7.112
prospective breaking current (for a pole of a switching device or a fuse)
the prospective current evaluated at a time corresponding to the instant of the initiation of the
breaking process [IEV 441-17-06]
NOTE Specifications concerning the instant of the initiation of the breaking process are to be found in the relevant
publications. For mechanical switching devices or fuses, it is usually defined as the moment of initiation of the arc
during the breaking process.
3.7.113
minimum breaking current
a minimum value of prospective current that a fuse-link is capable of breaking at a stated
voltage under prescribed conditions of use and behaviour [IEV 441-18-29]
3.7
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