IEC TS 61200-201:2026

• Abstract:

  IEC TS 61200-201:2026 provides guidance, based on the general requirements provided in the IEC 60364 series, on the implementation of protective measures for low-voltage asynchronous motors. This document covers the control and the protection of low-voltage asynchronous motors.

• Status: Published
• Publication Date: 06-Aug-2026
• ICS: 91.140.50 - Electricity supply systems
• Technical Committee: TC 64 - Electrical installations and protection against electric shock
• Drafting Committee: WG 43 - TC 64/WG 43
• Current Stage: PPUB - Publication issued
• Start Date: 07-Aug-2026
• Completion Date: 04-Sep-2026

IEC TS 61200-201 ®
Edition 1.0 2026-08
TECHNICAL
SPECIFICATION
Application guidance based on the IEC 60364 series -
Part 201: Asynchronous motor starting and protection
ICS 91.140.50  ISBN 978-2-8327-1425-6

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CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 General information . 8
5 Presentation of the application . 8
5.1 Types of equipment . 8
5.2 Technical characteristics . 8
6 Protection . 9
6.1 Protection against electric shock . 9
6.1.1 General. 9
6.1.2 Basic protection . 9
6.1.3 Fault protection. 9
6.1.4 Isolation . 9
6.2 Protection against thermal effects . 10
6.2.1 General. 10
6.2.2 Residual current devices (RCDs) . 11
6.2.3 Thermal protector . 11
6.3 Protection against overload . 11
7 Control . 13
7.1 General . 13
7.2 Coordination between protective and control devices . 14
7.2.1 General. 14
7.2.2 Characteristics of starting current of asynchronous motor . 14
7.2.3 High efficiency electric motor characteristics . 15
7.2.4 The basics of coordination . 16
7.2.5 Different types of coordination . 17
Annex A (informative) Categories of asynchronous motor . 19
A.1 Squirrel cage rotor . 19
A.2 Wound rotor (slip-ring rotor) . 19
Annex B (informative) Motor starters . 21
B.1 General . 21
B.1.1 Functions of starters. 21
B.1.2 Categories of starter. 21
B.2 Electromechanical controlgear . 23
B.2.1 Presentation . 23
B.2.2 "Three-device" solution . 25
B.2.3 "Two-device" solution . 25
B.2.4 "All-in-one" solution . 25
B.2.5 Utilization categories . 25
B.2.6 Functional aspects of motor starters . 26
B.3 Electronic starters and variable frequency drives . 28
B.3.1 Presentation . 28
B.3.2 Functions provided . 29
B.3.3 Operating modes . 29
Annex C (informative) Other types of protection . 31
C.1 Electromechanical devices . 31
C.2 Electronic equipment. 31
Annex D (informative) Asynchronous motor starting systems . 33
D.1 Direct on-line starting . 33
D.2 Star-delta starting . 34
D.3 Part winding motor starting . 35
D.4 Resistance stator starting . 36
D.5 Auto-transformer starting . 37
D.6 Slip ring motor starting . 39
D.7 Soft-starter motor control . 40
D.8 Frequency converter starting . 42
Bibliography . 43

Figure 1 – Symbol IEC 60417-6169-1:2012-08 for device suitable for isolation . 10
Figure 2 – Operation curves of overload relays . 12
Figure 3 – Direct on-line starting current characteristics of an induction motor . 15
Figure 4 – High efficiency electric motor starting current . 16
Figure 5 – Operating characteristics of a circuit-breaker–contactor–thermal relay
combination . 17
Figure A.1 – Exploded view of a squirrel cage rotor motor . 19
Figure A.2 – Exploded view of a slip-ring rotor motor. 20
Figure B.1 – Various functions and their combinations forming a motor starter . 23
Figure B.2 – Typical variants of protected starters, combination starters, protected
switching devices and combination switching devices . 24
Figure B.3 – Functional view of motor starters . 27
Figure B.4 – Motor overload protection embedded into a circuit-breaker . 28
Figure B.5 – Block diagram for variable frequency drive controlling a motor . 28
Figure B.6 – The four possible situations of a machine in its torque-speed diagram . 29
Figure D.1 – Direct on-line starting . 33
Figure D.2 – Connections to motor windings . 34
Figure D.3 – Star-delta starting . 35
Figure D.4 – Part winding starting . 36
Figure D.5 – Resistance stator starting . 37
Figure D.6 – Auto-transformer starting . 38
Figure D.7 – Typical schematic diagrams for starting alternating-current induction
motors by means of auto-transformers . 39
Figure D.8 – Slip ring motor starting . 40
Figure D.9 – Multiple motor starting with a soft-starter . 41
Figure D.10 – Working diagram of a frequency converter . 42

Table 1 – Comparison between the different methods of starting low-voltage (LV)
asynchronous motors . 8
Table 2 – Main tripping classes of overload relays as specified in IEC 60947-4-1 . 12
Table 3 – Comparison of starting current and time characteristics according to the
various motor control solutions . 15
Table B.1 – Comparison of different motor control solutions . 21
Table B.2 – Comparison of the main characteristics of the different types of motor
starter . 22
Table B.3 – Contactor utilization categories based on the purposes they are designed
for, as specified in IEC 60947-1 [23] . 26
Table B.4 – The four possible situations of a machine in its torque-speed diagram . 30
Table C.1 – Classification of protective functions . 31

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Application guidance based on the IEC 60364 series -
Part 201: Asynchronous motor starting and protection

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for
standardization comprising all national electrotechnical committees (IEC National Committees).
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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) IEC draws attention to the possibility that the implementation of this document may involve
the use of (a) patent(s). IEC takes no position concerning the evidence, validity or applicability
of any claimed patent rights in respect thereof. As of the date of publication of this document,
IEC had not received notice of (a) patent(s), which may be required to implement this document.
However, implementers are cautioned that this may not represent the latest information, which
may be obtained from the patent database available at https://patents.iec.ch. IEC shall not be
held responsible for identifying any or all such patent rights.
IEC TS 61200-201 has been prepared by IEC technical committee 64: Electrical installations
and protection against electric shock. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
64/2860/DTS 64/2871/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
INTRODUCTION
Asynchronous motors are used in a wide variety of applications. The following are examples of
driven machines:
– centrifugal pumps;
– fans and blowers;
– compressors;
– crushers;
– conveyors;
– lifts and cranes.
The consequences of a motor failure due to incorrect protection or the inability of control circuits
to operate can include the following.
– For persons:
• lack of fresh air due to the blockage of motor ventilation;
• electrocution or electric shock due to insulation failure in the motor;
• accident due to non-stopping of the motor.
– For the driven machine and the process:
• shaft couplings, axles, driving belts, etc. damaged due to a stalled rotor;
• loss of production;
• delayed manufacturing.
– For the motor itself:
• motor winding burnt out due to stalled rotor;
• economical aspects of repair;
• economical aspects of replacement.
Therefore, safety of persons and properties, as well as reliability and availability levels, are
highly dependent on the selection of protective devices.
In economic terms, it is important to consider the overall cost of failure. This is linked with the
size of the motor and with the difficulties of access and replacement. Loss of production is a
further and evidently important factor.
Specific features of motor performance influence the power supply circuits that are needed for
satisfactory operation.
A motor power-supply circuit presents certain constraints not normally encountered in other
(common) final circuits. These are due to the particular characteristics of motors directly
connected to the line, such as the following:
– high start-up current, which is mostly reactive, and can therefore be the cause of significant
voltage drop;
– high number and frequency of start-up operations;
– because of the high start-up current, motor overload protective devices must have operating
characteristics which avoid tripping during the starting period;
– some safety application requiring exemption of protection against overload;
– specificities due to application, e.g. lifts, cranes, motor with strong inertia.
All guidance in this document is based on the IEC 60364 series [1].
1 Scope
This part of IEC 61200 provides guidance, based on the general requirements provided in the
IEC 60364 series, on the implementation of protective measures for low-voltage asynchronous
motors. This document covers the control and the protection of low-voltage asynchronous
motors.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60364-1, Low-voltage electrical installations - Part 1: Fundamental principles, assessment
of general characteristics, and definitions
IEC 60364-4-41, Low-voltage electrical installations - Part 4-41: Protection for safety -
Protection against electric shock
IEC 60364-4-43, Low-voltage electrical installations - Part 4-43: Protection for safety -
Protection against overcurrent
IEC 60364-5-53:2019, Low-voltage electrical installations - Part 5-53: Selection and erection of
electrical equipment - Devices for protection for safety, isolation, switching, control and
monitoring
IEC 60947-4-1, Low-voltage switchgear and controlgear - Part 4-1: Contactors and motor-
starters - Electromechanical contactors and motor-starters
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60364-1 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.1
asynchronous motor
alternating current motor in which the speed of the motor is not in a fixed ratio with the frequency
of the current supplied
Note 1 to entry: For more details and information on various categories of asynchronous motor, refer to Annex A.
[SOURCE: IEC 60050-811:2017 [2], 811-12-25, modified – Note 1to entry has been added.]
3.2
starter
combination of all the switching means necessary to start and stop a motor in combination with
suitable overload protection
Note 1 to entry: Starters may be designated according to the method by which the force for closing the main contacts
is provided.
Note 2 to entry: For more details and information on various motor starters, refer to Annex B.
[SOURCE: IEC 60050-441:1984 [3], 441-14-38, modified – Note 2 to entry has been added.]
3.3
direct-on-line starter
starter which connects the line voltage across the motor terminals in one step
[SOURCE: IEC 60050-441:1984 [3], 441-14-40]
3.4
star-delta starter
starter for a three-phase induction motor such that in the starting position the stator windings
are connected in star and in the final running position they are connected in delta
[SOURCE: IEC 60050-441:1984 [3], 441-14-44]
4 General information
This document provides application guidance for low-voltage asynchronous motor starting and
protection systems. Statements and guidance are based on technology known at the date of
development of this document. As technology evolves quickly, this document will need frequent
updates in order to follow evolution and improvement of technologies as described in its content.
Users of this document should therefore pay attention to the latest technology available for this
application and verify the appropriateness of the requirements, recommendations and
statements given in this document.
5 Presentation of the application
5.1 Types of equipment
This document covers the following alternating asynchronous motors:
– squirrel cage rotor (see Clause A.1);
– wound rotor (slip-ring rotor) (see Clause A.2).
5.2 Technical characteristics
Table 1 gives a quick overview of available electric asynchronous motor starting methods,
together with their main characteristics and the areas in which they are used.
The importance of three-phase squirrel cage asynchronous motors is emphasized. The term
"standard" applied to this type of motor is now even more appropriate since they are ideal for
uses that have arisen from the development of electronic devices for variable frequency drives.
Table 1 – Comparison between the different methods of starting low-voltage (LV)
asynchronous motors
Methods of starting LV asynchronous Squirrel cage asynchronous Slip-ring asynchronous
motors
three-phase single-phase
Direct on-line Adopted Adopted Special starting device
Variable frequency drive Adopted Very rare Possible
Rheostatic or auto-transformer Adopted Not well adopted Adopted
Soft-starter Adopted Adopted Adopted
6 Protection
6.1 Protection against electric shock
6.1.1 General
Protection against electric shock is given by a combination of basic protection, fault protection
and, in specific cases, additional protection. For more details and information on other
additional types of protection, refer to Annex C.
6.1.2 Basic protection
Under normal conditions, basic protection consists of at least one provision that prevents direct
contact with hazardous-live-parts.
Basic protection is usually provided by using insulating material or by barriers or enclosures
(IEC 60364-4-41:2005 [4], Annex A).
In electrical installations which are controlled or supervised by skilled or instructed persons,
obstacles and placing out of reach provide basic protection as well (IEC 60364-4-41:2005 [4],
Annex B).
Except where safety extra-low voltage (SELV) or protective extra-low voltage (PELV) is used
as protective measure, basic protection is usually provided by using enclosures. A minimum
ingress protection rating of IP 2X or IP XXB as specified in IEC 60529:1989 [5] should be
applied.
6.1.3 Fault protection
The most common protective provision for fault protection corresponds to automatic
disconnection of supply. Requirements concerning this protective measure are specified in IEC
60364-4-41 and are not specific to motors.
When electromechanical devices are used, overcurrent protective devices used for protection
of motors against overcurrent can also be used jointly for automatic disconnection of supply
provided that both types of requirements are simultaneously fulfilled. Only some specified
protective devices are recognized by IEC 60364-4-41 [6] and IEC 60364-5-53 [7] as appropriate
for fault protection such as:
– overcurrent protective devices (OCPD) in accordance with IEC 60898-1:2015 [8] or IEC
60898-2:2016 [9] or IEC 60947-2:2016 [10] or IEC 60269-2:2013 [11] or IEC 60269-3:2010
[12] or IEC 60269-4:2009 [13];
– control and protective switching devices (CPS) in accordance with IEC 60947-6-2 [14];
– residual current devices (RCDs) in accordance with IEC 60947-2:2016 [10] or the IEC 61008
series [15] or the IEC 61009 series [16] or IEC 62423:2009 [17].
These protective devices are suitable for isolation.
Some soft-starters or variable frequency drives can provide protective functions against electric
shock, as indicated in IEC 60364-4-41 [6].
6.1.4 Isolation
Devices for isolation should be installed at or near the origin of circuits (see IEC 60364-5-53
[7]). Devices for isolation should be installed for each circuit supplying a motor starter unit.
Their role is to isolate circuits safely from their energy source (main power supply) to ensure
the protection of persons in case of maintenance, repair, or modification of downstream electric
circuit(s).
Devices for isolation shall comply with the requirements as specified in IEC 60364-5-53:2019,
Clause 536, which require:
– isolation of all live conductors;
– the ability to withstand minimum impulse voltages depending on the nominal voltage and on
risk assessment (see IEC 60364-4-44:2007 [18], Table 443.2);
– the prevention of unintentional or unauthorized operation (e.g. padlocking);
– position of contacts be either externally visible or clearly and reliably indicated (e.g. visible
or apparent break).
NOTE A visible break means that the opening of the poles is completely visible for an operator. An apparent break
can be identified either by the position of the working gear, or by the position indicator that can only indicate the de-
energized position if the contacts are actually separated by an adequate distance as specified in the standards.
Manufacturers offer a number of devices with these functions. Often one device can handle the functions of isolating
contacts and protection against short-circuits (e.g. fuse holder or disconnector device). In the case of some basic
devices, it is important to add an additional connection boosting device.
When electromechanical devices, for example, circuit-breakers, or fuse holders are used, they
may be used for isolation provided they are declared as such by the manufacturer in accordance
with the relevant product standard. In this case, the symbol IEC 60417-6169-1:2012-08 (see
IEC 60417:2025 DB [19]) in Figure 1 shall be found on the front label of the device.

Figure 1 – Symbol IEC 60417-6169-1:2012-08 for device suitable for isolation
This symbol may be combined with other symbols, for instance, IEC 60417-6169-2:2012-08,
disconnecting circuit-breaker.
Electronic devices cannot be used as devices for isolation. Therefore, a dedicated device for
isolation can be installed in series with an electronic starter (soft-starter or variable frequency
drives). This device for isolation may be directly installed upstream of the electronic starter.
6.2 Protection against thermal effects
6.2.1 General
Protection against thermal effects is essential. Thermal effects can result from frequent starting,
motor overload, or internal faults. A combination of protection by analysing the current and
thermal protector within the motor could be used to protect against thermal effects.

Protection against thermal effects is provided by:
– application of measures for protection against overcurrent (see 6.3);
– use of RCDs with a rated residual operating current not exceeding 300 mA;
– thermal protector.
6.2.2 Residual current devices (RCDs)
The installation of an RCD with a rated residual operating current not exceeding 300 mA
provides protection against earth leakage or insulation failure in motor stators.
6.2.3 Thermal protector
This solution can provide complementary protection against thermal effects in place or in
addition to overload protection described in 6.3.
6.3 Protection against overload
The principles and requirements specified in IEC 60364-4-43 apply for the protection of wiring
systems. Nevertheless, dedicated protection of motors against overload is used in industry.
Where electromechanical devices are used, dedicated overload relays (thermal or electronic)
as described in Table 2 protect motors against overloads, but they should allow the temporary
overload caused by starting and should also not operate unless the starting time is abnormally
long.
Depending on the application, the motor starting time can vary from a few seconds (for no-load
starting, low resistive torque, etc.) to several tens of seconds (for high resistive torque, high-
inertia load, etc.). Therefore, relays appropriate to the starting time shall be selected.
To meet this requirement, IEC 60947-4-1 [20] defines several classes of overload relays, each
characterized by its operating curve (see Figure 2).
The relay rating is chosen according to the nominal motor current and the calculated starting
time.
a) Trip class 10 is adapted to normal duty.
b) Trip class 20 is recommended for heavy-duty motors.
c) Trip class 30 is necessary for very long motor starting.
Figure 2 – Operation curves of overload relays
Table 2 – Main tripping classes of overload relays as specified in IEC 60947-4-1
Class Tripping time as from state
Cold Hot Hot Cold Tighter tolerance
(band E)
at 1,05 × I at 1,2 × I at 1,5 × I at 7,2 × I
r r r r
10 A > 2 h < 2 h < 2 min -
2 s < t < 10 s
p
10 > 2 h < 2 h < 4 min
4 s < t < 10 s 5 s < t < 10 s
p p
20 > 2 h < 2 h < 8 min
6 s < t < 20 s 10 s < t < 20 s
p p
30 > 2 h < 2 h < 12 min
9 s < t < 30 s 20 s < t < 30 s
p p
Cold state: Initial state without load
Hot state: Thermal stability reached at I
r
I : Setting current of the overload relay
r
Where electronic equipment is used, the current through these types of drives has a harmonic
current content due to the presence of electronic switches (e.g. thyristors). The estimation of
the rated current of the overload protective devices should therefore consider the harmonic
current content.
It is calculated based on:
– the motor nominal mechanical power;
– the nominal supply voltage;
– the efficiency of the motor and the drive;
– a permissible continuous overload of 1,1 × T at constant torque and 1,05 × T at variable
n n
torque, where T is the normal operating torque;
n
NOTE This torque is for selection, based on the motor starting torque, and is different from the normal operating
operating torque.
– harmonics, since the current is not sinusoidal.

The RMS value of the current, I , depending on the harmonic distortion, is obtained using
RMS
Formula (1).
� (1)
𝐼𝐼 =𝐼𝐼 1+ THDi
RMS 1
where
I
is the fundamental current;
THDi is the total harmonic distortion (current).
thus, when THDi = 40 %, I = 1,08 × I .
RMS 1
Since the fundamental current, I , is practically in phase with the voltage, the typical value of
the current drawn by the drive, when it supplies a motor operating at its nominal point (constant
torque application), is calculated using Formula (2).
𝑃𝑃 1 1
mot
𝐼𝐼 =1,08×𝐼𝐼 ≈1,08×1,1 (2)
RMS 1
𝜂𝜂 𝜂𝜂
√3𝑈𝑈
mot drive
where
P
is the motor nominal power (kW);
mot
U
is the line-to-line voltage (V);
η
is the motor efficiency;
mot
η
is the drive efficiency.
driv e
EXAMPLE Where the motor rating is 15 kW, supplied by a line voltage at 400 V and with η = 0,95 and η = 0,97,
mot driv e
the rated current is calculated as I = 27,9 A.
RMS
7 Control
7.1 General
The word "control" means switching on and off an electrical circuit under load. The control
function can be performed by a switching device, a motor starter device, a soft-starter or by a
variable frequency drive. A contactor is typically used to perform this function because it
enables remote control. With motors, this control device should allow for a large number of
operations (electrical durability) and should comply with IEC 60947-4-1 [20].
The following parameters should be considered when selecting electrical equipment for
controlling a motor.
a) Control circuit:
1) type of control current and its frequency, in case of alternating current;
2) rated control circuit voltage (U ) or supply voltage control (U ).
c s
b) Power circuit:
1) rated operating voltage (U ): generally shown by line to line voltage. It determines the
e
utilization of the circuits contributing to the making and breaking capacity, the type of
service and the starting characteristics;
2) rated operating current (I ) or rated operational power (P ): either characteristic is
e e
defined by the manufacturer based on the nominal operational conditions and especially
taking into account the rated operational voltage and the conventional thermal current.
In the case of equipment for direct control of one motor, the indication of the rated
operational voltage can be replaced or determined by the assigned available power.
This information can, in some cases, be completed by:
– the assigned service, mentioning the intermittent service class, if there is one. The classes
define different operational cycles;
– the assigned power of the motor circuit during making or breaking operations, or both. These
are used to determine the maximum current values that the control device must reliably
make (closing) or break (opening). Control device manufacturers set the maximum current
values of the device in specific conditions. The assigned powers of making and breaking
are not necessarily specified by the manufacturer, but the minimum value for each utilization
category shall be provided.
7.2 Coordination between protective and control devices
7.2.1 General
The efficiency of the motors has been improved by reducing the internal losses using better
materials and improving the motor design. The high efficiency motor electrical model is
becoming more inductive because the resistive losses are being reduced, and the magnetic
saturation effect is decreased. Therefore, the starting direct-on-line current is significantly
higher because of the lower rotor resistance. IEC 60034-12:2016 [21] introduces motor designs
NE (normal starting torque, extended efficiency) and HE (high starting torque, extended
efficiency), which have higher locked rotor apparent power than design N (normal starting
torque) or H (high starting torque).
7.2.2 Characteristics of starting current of asynchronous motor
An example of starting current of motor is provided in Figure 3. A high inrush current is expected
at the beginning of the starting phase (I''), then a starting phase occurs with a lower current but
for a longer period (I ), then the nominal current corresponding to the normal operation of the
s
motor (I ).
n
Key
is the rated current of the motor
I
n
I is in the range 5 × I to 8 × I
s n n
I" is in the range 8 × I to 12 × I
n n
is in the range 1 s to 10 s
t
s
is in the range 20 ms to 30 ms
t"
Figure 3 – Direct on-line starting current characteristics of an induction motor
I" and I mainly depend on the motor, whereas I depends on the starter used. As an example,
n s
a comparison between the various starting methods is provided in Table 3.
Table 3 – Comparison of starting current and time characteristics according to the
various motor control solutions
Starter
I / I
s n
Direct on-line 5 to 8
Star-delta 2 to 3
Auto-transformer 2 to 3
Soft-starter 1,5 to 6
variable frequency drive 1
7.2.3 High efficiency electric motor characteristics
7.2.3.1 General
Figure 4 illustrates the main characteristics of an electric motor: inrush current associated with
the kappa factor, locked-rotor current (I ) and motor rated current.
LR
Figure 4 – High efficiency electric motor starting current
7.2.3.2 Efficiency motor analysis
The main outcomes of the analysis of measurement data of more than 4 500 high efficiency
motors performed between 2013 and 2015 are as follows.
– The rated current of the motors decreases by approximately 1 % to 2 % from one efficiency
class to the next higher one.
– The locked-rotor current (I ) increases by approximately 6 % to 10 % from one efficiency
LR
class to next higher one.
– The inrush currents increase from one efficiency class to the next higher one.
7.2.3.3 Impacts on the selection of switchgear and controlgear
Because the inrush current is higher with high efficiency motors, the tripping current of the
associated SCPD should be increased in order to avoid nuisance tripping.
This can result in an increased current value of the crossover point of the overload and short-
circuit protections. As specified in IEC 60947-4-1 [20], the simulated fault test with the current
I verifies the breaking performance of the contactor in the case of a short-circuit of fault
cd
currents below the tripping current of the SCPD.
For the above reasons, the utilization category AC-3e defined by IEC 60947-4-1 [20] is
appropriate for withstanding the effects of higher inrush currents and higher locked rotor
currents.
7.2.4 The basics of coordination
For a motor starter to operate correctly, coordination among all devices is required (see
Figure 5).
a) The overload relay should protect the magnetic circuit breaker in the overload zone: its
curve should be under the circuit breaker thermal resistance curve.
b) By contrast, in order to protect the thermal relay in short-circuit zones, the trip short-circuit
curve should drop below the relay thermal resistance curve.
c) Finally, to make sure that the contactor is protected, its thermal resistance curve should be
above the curves for both circuit breakers: thermal and magnetic.
Coordination offers the additional advantage of reducing equipment and maintenance costs,
because the different protections complement each other, with no overlapping range of
functionality.
NOTE Short-circuit protection can also be provided by gG or aM fuses.

Key
A
1,05 × I to 1,20 × I
n n
B operating curve of thermal relay
C cable thermal withstand limit
D limit of thermal relay constraint
E operating curve of the MA type circuit-breaker
NOTE MA is a magnetic-only type overcurrent protective device.
F short-circuit current breaking capacity of the combination of the two switching devices (circuit-breaker and
contactor)
G short-circuit current breaking capacity of the circuit-breaker
H end of start-up period
Figure 5 – Operating characteristics of a circuit-breaker–contactor–thermal relay
combination
7.2.5 Different types of coordination
It is important for users to identify all the features of the devices to be able to coordinate these
devices. Two types of coordination are defined in IEC 60947-4-1:2023 [22], 8.2.5.1.
a) Type 1 coordination requires that, under short-circuit condition, the contactor or starter shall
cause no danger to persons or installation, but it is possible that it is not suitable for further
service without repair and replacement of parts.
This is a basic solution, as
1) switchgear cost is reduced; and
2) continuity of supply is not required.
Before restarting, it can be necessary to repair the motor starter unit.
Consequences:
3) non negligible machine downtime;
4) qualified maintenance personnel to repair, check and supply.
EXAMPLE 1 Air conditioning in the tertiary sector.
b) Type 2 coordination requires that, under short-circuit condition, the contactor or starter shall
cause no danger to persons or installation and shall be suitable for further use. The risk of
contact welding is recognized, in which case the manufacturer should indicate the measures
to be taken as regards the maintenance of the equipment.
This solution allows enhancement of continuity of supply.
Benefits:
1) reduced machine downtim
...