IEC 61558-2-16:2021

IEC 61558-2-16 ®
Edition 2.0 2021-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-16: Particular requirements and tests for switch mode power supply units
and transformers for switch mode power supply units for general applications

Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et
combinaisons de ces éléments –
Partie 2-16: Exigences particulières et essais pour les blocs d'alimentation à
découpage et les transformateurs pour blocs d'alimentation à découpage pour
applications d'ordre général
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IEC 61558-2-16 ®
Edition 2.0 2021-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Safety of transformers, reactors, power supply units and combinations thereof –

Part 2-16: Particular requirements and tests for switch mode power supply units

and transformers for switch mode power supply units for general applications

Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et

combinaisons de ces éléments –

Partie 2-16: Exigences particulières et essais pour les blocs d'alimentation à

découpage et les transformateurs pour blocs d'alimentation à découpage pour

applications d'ordre général
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180 ISBN 978-2-8322-9855-8

– 2 – IEC 61558-2-16:2021 © IEC 2021
CONTENTS
FOREWORD . 4
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 10
3 Terms and definitions . 10
4 General requirements . 11
5 General notes on tests . 12
6 Ratings . 12
7 Classification . 12
8 Marking and other information . 12
9 Protection against electric shock . 14
10 Change of input voltage setting . 14
11 Output voltage and output current under load . 15
12 No-load output voltage . 15
13 Short-circuit voltage . 16
14 Heating . 16
15 Short-circuit and overload protection . 17
16 Mechanical strength . 17
17 Protection against harmful ingress of dust, solid objects and moisture . 17
18 Insulation resistance, dielectric strength and leakage current . 17
19 Construction . 17
20 Components . 18
21 Internal wiring . 18
22 Supply connection and other external flexible cable or cords . 18
23 Terminals for external conductors . 18
24 Provisions for protective earthing. 18
25 Screws and connections . 18
26 Creepage distances, clearances and distances through insulation . 18
27 Resistance to heat, fire and tracking . 32
28 Resistance to rusting . 32
Annexes . 33
Annex AA (normative) Partial discharge (PD) test . 34
Annex BB (normative) Particular requirements for associated transformers for use in
switch mode power supply units with internal frequencies > 500 Hz . 35
Annex CC (informative) Example for determination of clearances and creepage
distances for associated transformers for use in switch mode power supply units . 38
Bibliography . 40

Figure 101 – Diagram for dimensioning of clearances . 19
Figure 102 – Diagram of dimensioning creepage distances . 24
Figure 103 – Permissible electric field strength for dimensioning of solid insulation in
accordance with Formula (2) . 32

Table 101 – Symbols used on SMPS . 13
Table 102 – Output voltage ratio . 16
Table 103 – Rated impulse voltage . 20
Table 104 – Clearances to withstand transient overvoltages for inhomogeneous field . 21
Table 105 – Values of clearances for peak working voltages produced in the SMPS for
frequencies ≤ 30 kHz . 22
Table 106 – Minimum values of clearances in air for inhomogeneous electric field
conditions for frequency > 30 kHz . 23
Table 107 – Basic or supplementary insulation – Minimum values of creepage
distances for different frequency ranges (pollution degree 1) . 25
Table 108 – Basic or supplementary insulation – Minimum values of creepage
distances for different frequency ranges (pollution degree 2) . 26
Table 109 – Basic or supplementary insulation – Minimum values of creepage
distances for different frequency ranges (pollution degree 3) . 27
Table 110 – Double or reinforced insulation – Minimum values of creepage distances
for different frequency ranges (pollution degree 1) . 28
Table 111 – Double or reinforced insulation – Minimum values of creepage distances
for different frequency ranges (pollution degree 2) . 29
Table 112 – Double or reinforced insulation – Minimum values of creepage distances
for different frequency ranges (pollution degree 3) . 30
Table CC.1 – Conditions . 38

– 4 – IEC 61558-2-16:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS, POWER SUPPLY
UNITS AND COMBINATIONS THEREOF –

Part 2-16: Particular requirements and tests for switch mode power
supply units and transformers for switch mode power supply units
for general applications
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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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 61558-2-16 has been prepared by IEC technical committee 96:
Transformers, reactors, power supply units and combinations thereof.
This second edition cancels and replaces the first edition published in 2009 and
amendment 1:2013. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) adjustment of structure and references in accordance with IEC 61558-1:2017;
b) definitions of different voltage characteristics;
c) partial discharge and description of constructions moved to IEC 61558-1:2017;
d) alternative method for dimensioning of clearances;
e) removal of requirements for homogeneous field conditions.

The text of this International Standard is based on the following documents:
FDIS Report on voting
96/509/FDIS 96/513/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
It has the status of a group safety publication in accordance with IEC Guide 104.
This International Standard is to be used in conjunction with IEC 61558-1:2017.
NOTE When "Part 1" is mentioned in this standard, it refers to IEC 61558-1:2017.
This document supplements or modifies the corresponding clauses in IEC 61558-1:2017, so as
to convert that publication into the IEC standard: Particular requirements and tests for switch
mode power supply units and transformers for switch mode power supply units for general
applications.
A list of all parts in the IEC 61558 series, published under the general title Safety of
transformers, reactors, power supply units and combinations thereof, can be found on the IEC
website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
Where this document states "addition", "modification" or "replacement", the relevant text of
IEC 61558-1:2017 is to be adapted accordingly.
In this document, the following print types are used:
• requirements proper: in roman type;
• test specifications: in italic type;
• explanatory matter: in smaller roman type.
In the text of this document, the words in bold are defined in Clause 3.
Subclauses, notes, figures and tables additional to those in IEC 61558-1:2017 are numbered
starting from 101; supplementary annexes are entitled AA, BB, etc.

– 6 – IEC 61558-2-16:2021 © IEC 2021
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
INTRODUCTION
IEC TC 96 has a group safety function in accordance with IEC Guide 104 for transformers other
than those intended to supply distribution networks, in particular transformers and power supply
units intended to allow the application of protective measures against electric shock as defined
by TC 64, but in certain cases including the limitation of voltage and horizontal safety function
for SELV, in accordance with IEC 60364-4-41.
The group safety function (GSF) is necessary because of responsibility for safety extra-low
voltage (SELV) in accordance with IEC 61140:2016, 5.2.6 and IEC 60364-4-41:2017, 414.3.1
or control circuits in accordance with IEC 60204-1:2016, 7.2.4.
The group safety function is needed for each part of IEC 61558-2 because different standards
of the IEC 61558 series can be combined in one construction but in certain cases with no
limitation of rated output power.
For example, an auto-transformer in accordance with IEC 61558-2-13 can be designed with a
separate SELV-circuit in accordance with the particular requirements for IEC 61558-2-6 relating
to the general requirements of IEC 61558-1.

– 8 – IEC 61558-2-16:2021 © IEC 2021
SAFETY OF TRANSFORMERS, REACTORS, POWER SUPPLY
UNITS AND COMBINATIONS THEREOF –

Part 2-16: Particular requirements and tests for switch mode power
supply units and transformers for switch mode power supply units
for general applications
1 Scope
Replacement
This part of IEC 61558 deals with the safety of switch mode power supply units and
transformers for switch mode power supply units.
NOTE 1 Safety includes electrical, thermal and mechanical aspects.
Unless otherwise specified, from here onward, the term SMPS covers switch mode power
supply units for general applications.
SMPS covered by this document are air cooled (natural or forced) independent, associated,
stationary, portable, single-phase or polyphase with the rated supply voltage not exceeding
1 000 V AC, the rated supply frequency not exceeding 500 Hz, the rated internal operating
frequency exceeding 500 Hz, but not exceeding 100 MHz, and the rated output not exceeding
1 kVA or 1 kW, incorporating dry-type transformers with encapsulated or non-encapsulated
windings.
NOTE 2 As the maximum rated supply voltage of the internal transformer is 1 000 V AC, the maximum rated
supply voltage of the switch mode power supply unit can be lower due to the type of rectification.
NOTE 3 For higher frequencies, additional requirements can be necessary. However, this document can be used
for guidance.
This document is applicable to SMPS, converters and inverters without limitation of the rated
output subject to an agreement between the purchaser and the manufacturer.
NOTE 4 In the context of this document, converters and inverters are considered to be SMPS.
This document applies to:
a) SMPS incorporating safety isolating transformers providing SELV, PELV, AC or DC
output voltage(s) or a combination thereof in accordance with IEC 61140 and IEC 60364-
4-41 for use with household and other consumer products,
b) SMPS with a maximum output voltage not exceeding 1 000 V AC or 1 415 V ripple-free DC
for use with household and other consumer products, except for products covered in a),
c) This document can be used for transformers for use in SMPS (see Annex BB).
This document does not apply to:
• motor-generator sets;
• uninterruptible power supplies (UPS) in accordance with the IEC 62040 series;
• SMPS covered by IEC 61204-7 (i.e. low-voltage power supply devices DC output,
performance characteristics) and DC power and distribution equipment and SMPS for use
in applications covered by IEC 61010-1 and IEC 60601-1;
• lamp control gear covered by the IEC 61347 series;

• external circuits and their components intended to be connected to the input terminals and
output terminals of the SMPS;
• equipment in accordance with IEC 60065, IEC 60950-1 and IEC 62368-1.
This document can also be used for guidance for products not covered by the scope of this
document, the scope of IEC 61204-7 or the scope of the IEC 61347 series.
This document covers the safety requirements for:
• SMPS incorporating separating transformers for general use corresponding to
IEC 61558-2-1;
• SMPS incorporating isolating transformers for general use corresponding to
IEC 61558-2-4;
• SMPS incorporating safety isolating transformers for general use corresponding to
IEC 61558-2-6;
• SMPS incorporating auto-transformers for general use corresponding to IEC 61558-2-13.
For SMPS for specific applications corresponding to the other documents of the IEC 61558-2
series, the necessary requirements of the relevant documents of the IEC 61558-2 series are
applicable. In addition, the requirements listed in this document apply. Where two requirements
are in conflict, the more severe takes precedence.
The no-load output voltage or the rated output voltage of SMPS does not exceed:
• 1 000 V AC or 1 415 V ripple-free DC when SMPS incorporating separating transformers
or auto-transformers are used;
• 500 V AC or 708 V ripple-free DC when SMPS incorporating isolating transformers are
used;
• 50 V AC or 120 V ripple-free DC when SMPS incorporating safety isolating transformers
is used.
The no-load output voltage or the rated output voltage of independent SMPS is not less
than:
• 50 V AC or 120 V ripple-free DC when separating transformers, isolating transformers
or auto-transformers are used.
Attention is drawn to the following:
• additional requirements for SMPS intended to be used in vehicles, on board ships and
aircraft (from other applicable standards, national rules, etc.);
• measures to protect the enclosure and the components inside the enclosure against
external influences such as fungus, vermin, termites, solar-radiation and icing;
• the different conditions for transportation, storage and operation of the SMPS;
• additional requirements in accordance with other appropriate standards and national rules
can be applicable to SMPS intended for use in special environments.
Future technological development of SMPS can necessitate a need to increase the upper limit
of the frequencies. Until then, this document can be used as a guidance document.
This group safety publication focusing on safety guidance is primarily intended to be used as a
product safety standard for the products mentioned in the scope, but is also intended to be used
by TCs in the preparation of publications for products similar to those mentioned in the scope
of this group safety publication, in accordance with the principles laid down in IEC Guide 104
and lSO/lEC Guide 51.
– 10 – IEC 61558-2-16:2021 © IEC 2021
One of the responsibilities of a TC is, wherever applicable, to make use of BSPs and/or GSPs
in the preparation of its publications.
2 Normative references
This clause of Part 1 is applicable except as follows:
Addition:
IEC 60664-4:2005, Insulation coordination for equipment within low-voltage systems – Part 4:
Consideration of high-frequency voltage stress
IEC 61558-1:2017, Safety of transformers, reactors, power supply units and combinations
thereof – Part 1: General requirements and tests
IEC 61558-2-1, Safety of power transformers, power supplies, reactors and combinations
thereof – Part 2-1: Particular requirements and tests for separating transformers and power
supplies incorporating separating transformers for general applications
IEC 61558-2-4, Safety of transformers, reactors, power supply units and combinations thereof
– Part 2-4: Particular requirements and tests for isolating transformers and power supply units
incorporating isolating transformers for general applications
IEC 61558-2-6, Safety of transformers, reactors, power supply units and combinations thereof
– Part 2-6: Particular requirements and tests for safety isolating transformers and power supply
units incorporating safety isolating transformers for general applications
IEC 61558-2-13, Safety of transformers, reactors, power supply units and combinations thereof
– Part 2-13: Particular requirements and tests for auto transformers and power supply units
incorporating auto transformers
3 Terms and definitions
This clause of Part 1 is applicable except as follows:
Replacement:
For the purposes of this document, the terms and definitions given in Part 1 apply.
The term transformer in Part 1 also designates an SMPS as defined in this document.
In Annex BB, the term transformer applies to a transformer for SMPS.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp

Replacement:
3.3.8
working voltage
highest RMS value of the AC or DC voltage that can occur (locally) across any insulation at
rated supply voltage under no-load or normal operating conditions, transients being
disregarded
Note 1 to entry: The working voltage between any point in the circuit supplied by electrical power sources and
other isolated parts shall be assumed to be:
• the rated supply voltage, or
• the measured working voltage
whichever is greater.
Note 2 to entry: When considering the insulation system between windings not intended to be connected together,
the working voltage is considered to be the highest voltage occurring on any of these windings.
Note 3 to entry: On three-phase systems, the working voltage can be different from the nominal voltage.
3.5.101
peak working voltage
peak value of the working voltage, including any DC component and any repetitive peak
impulses generated in the SMPS
Note 1 to entry: Details about peak working voltages can be found in IEC 60664-1:2007, Figure 1.
[SOURCE: IEC 60050-903:2014, 903-04-02, modified – "equipment" replaced by "SMPS" and
Note 1 to entry has been added]
3.5.102
rated impulse voltage
impulse withstand voltage value assigned by the manufacturer to the equipment or to a part of
it, characterizing the specified withstand capability of its insulation against transient
overvoltages
[SOURCE: IEC 60664-1:2007, 3.9.2]
3.7.101
inhomogeneous electric field
electric field which does not have an essentially constant voltage gradient between electrodes
(non-uniform field)
Note 1 to entry: The inhomogeneous field condition of a point-plane electrode configuration is the worst case with
regard to voltage withstand capability and is referred to as case A in IEC 60664-1 It is represented by a point
electrode having a 30 μm radius and a plane of 1 m × 1 m.
Note 2 to entry: For frequencies exceeding 30 kHz, the field is considered to be inhomogeneous when the radius
of curvature of the conductive parts is less than 20% of the clearance
[SOURCE: IEC 60050-442:2014, 442-09-03, modified – The term "non-uniform electric field"
has been omitted, and "(non-uniform field)" has been added to the definition.]
4 General requirements
This clause of Part 1 is applicable.

– 12 – IEC 61558-2-16:2021 © IEC 2021
5 General notes on tests
This clause of Part 1 is applicable.
6 Ratings
This clause of Part 1 is applicable, except as follows:
Addition
6.101 The rated output voltage shall not exceed:
– 1 000 V AC or 1 415 V ripple-free DC for SMPS incorporating separating transformers
or auto-transformers;
– 500 V AC or 708 V ripple-free DC for SMPS incorporating isolating transformers;
– 50 V AC or 120 V ripple-free DC for SMPS incorporating safety isolating transformers.
For independent SMPS incorporating separating transformers, isolating transformers or
auto-transformers, the rated output voltage shall exceed 50 V AC or 120 V ripple-free DC.
6.102 The rated output of the SMPS shall not exceed 1 kVA or 1 kW.
SMPS without limitation of the rated output shall be subject to agreement between the
purchaser and the manufacturer.
NOTE See Annex BB for a transformer incorporated in an SMPS.
6.103 The rated supply frequency shall not exceed 500 Hz.
6.104 The rated internal operating frequency shall not exceed 100 MHz.
6.105 The rated supply voltage shall not exceed 1 000 V AC.
Compliance with 6.101 to 6.105 is checked by inspection of the marking.
7 Classification
This clause of Part 1 is applicable.
8 Marking and other information
This clause of Part 1 is applicable except as follows:
8.1 h)
Replacement
relevant graphical symbols shown in Table 101 that indicate the kind of transformer in addition
with the symbol for SMPS. If an IP00 transformer or and associated transformers have
circuits corresponding to different documents of the IEC 61558-2 series in the same
construction (e.g. SELV output circuit in accordance with IEC 61558-2-6 and 230 V output
circuit in accordance with IEC 61558-2-4), the relevant symbols have to be used. The term
transformer shall be replaced by SMPS, except for the marking that applies to incorporated
transformers and incorporated SMPS;
8.11
Addition
The symbol for SMPS shall be used in conjunction with the symbol to indicate the type of
transformer(s) that is/are incorporated.
Table 101 covers the symbols for transformers corresponding to the basic kinds of
transformers.
Table 101 – Symbols used on SMPS
Symbol or Explanation or title Identification
graphical symbol
SMPS (Switch mode power supply unit) IEC 60417-6190:2013-10
S
SMPS incorporating a IEC 60417-5156:2003-08
fail-safe separating transformer

SMPS incorporating a IEC 60417-5223:2002-10
non-short-circuit-proof separating transformer

SMPS incorporating a IEC 60417-5220:2002-10
short-circuit-proof separating transformer
(inherently or non-inherently)

SMPS incorporating a IEC 60417-5221:2002-10
fail-safe isolating transformer

SMPS incorporating a IEC 60417-5944:2013-06
non-short-circuit-proof isolating transformer

– 14 – IEC 61558-2-16:2021 © IEC 2021
Symbol or Explanation or title Identification
graphical symbol
SMPS incorporating a IEC 60417-5945:2013-06
short-circuit-proof isolating transformer
(inherently or non-inherently)

SMPS incorporating a IEC 60417-5222:2002-10
fail-safe safety isolating transformer

SMPS incorporating a IEC 60417-5946:2002-10
non-short-circuit-proof safety isolating transformer

SMPS incorporating a IEC 60417-5947:2002-10
short-circuit-proof safety isolating transformer
(inherently or non-inherently)

SMPS incorporating a IEC 60417-5941:2002-10
fail-safe auto-transformer
SMPS incorporating a IEC 60417-5942:2002-10
non-short-circuit proof auto-transformer

SMPS incorporating a IEC 60417-5943:2002-10
short-circuit proof auto-transformer (inherently or non-
inherently)
9 Protection against electric shock
This clause of Part 1 is applicable.
10 Change of input voltage setting
This clause of Part 1 is applicable except as follows:
Addition
10.101 A wide range (e.g. 100 V AC to 240 V AC) of supply voltage is allowed if the output
voltage does not exceed the rated output voltage and the no-load output voltage does not
exceed the limits of the output voltage deviation in accordance with the type of transformer
feeding the appropriate output circuit.

11 Output voltage and output current under load
This clause of Part 1 is applicable.
12 No-load output voltage
This clause of Part 1 is applicable except as follows:
Addition
The no-load output voltage is measured when the SMPS is connected to the rated supply
voltage at the rated supply frequency at ambient temperature.
12.101 The no-load output voltage shall not exceed:
• 1 000 V AC or 1 415 V ripple-free DC for SMPS incorporating separating transformers or
auto-transformers;
• 500 V AC or 708 V ripple-free DC for SMPS incorporating isolating transformers;
• 50 V AC or 120 V ripple-free DC for SMPS incorporating safety isolating transformers.
For independent SMPS incorporating separating transformers, isolating transformers or
auto-transformers, the no-load output voltage shall exceed 50 V AC or 120 V ripple-free DC.
For independent SMPS this output voltage limitation applies even when output windings,
not intended for interconnection, are connected in series.
The requirement for series connection does not apply to associated or IP 00 SMPS.
12.102 The difference between the no-load output voltage and the output voltage under
rated load shall not be excessive.
The ratio between the no-load output voltage measured in Clause 12 and the output voltage
under load measured during the test of Clause 11, expressed as a percentage of the latter
voltage, shall not exceed the values shown in Table 102.
The ratio is determined by Formula (1):
UU−
no-load load
×100 %
( )
(1)
U
load
where
U is the no-load output voltage, expressed in V
no-load
is the output voltage under load, expressed in V
U
load
– 16 – IEC 61558-2-16:2021 © IEC 2021
Table 102 – Output voltage ratio
Rated output Ratio between no-load output voltage
and output voltage under load
VA %
up to and including 63 20
over 63 up to and including 250 15
over 250 up to and including 630 10
over 630 5
Compliance with the requirements of 12.101 and 12.102 is checked by measuring the no-load
output voltage at the ambient temperature when the SMPS is connected to the rated supply
voltage at the rated supply frequency.
The ratio shall not exceed the values shown in Table 102.
NOTE The values of Table 102 are based on the values of IEC 61558-2-4 and are also applicable to SMPS in
accordance with IEC 61558-2-1, IEC 61558-2-6, and IEC 61558-2-13.
12.103 Unless otherwise specified by the manufacturer, SMPS shall be tested with a length of
20 cm and 200 cm of wire connected to the output terminals under the most unfavourable
conditions. Twisted wires or cables rated in accordance with IEC 60227-5:2011 (type
60227 IEC 53) may be used. The cross-sectional area of the conductors shall be determined in
accordance with the rated output current of the SMPS and the current density shall not exceed
5 A/mm2 in normal use.
NOTE The current density for 12.103 is only required for the external connecting wire of the test.
13 Short-circuit voltage
This clause of Part 1 is applicable.
14 Heating
This clause of Part 1 is applicable, except as follows:
Addition
14.101 For SMPS incorporating transformers with internal frequencies higher than 500 Hz,
thermocouples or equivalent means of measuring the temperatures may be used to determine
the temperature of the windings and the insulating materials.
The maximum values of Table 2 in IEC 61558-1:2017 for winding temperatures shall be reduced
by 10°C for the thermocouple measurements. The thermocouples shall be mounted only on
accessible surfaces of the incorporated transformers.
The thermocouples should not be integrated in the windings.
14.102 SMPS shall be tested at 0,9 times and 1,1 times the rated supply voltage.

15 Short-circuit and overload protection
This clause of Part 1 is applicable, except as follows:
Addition
15.101 Electronic circuits shall be so designed and applied that a fault condition within the
SMPS will not cause electric shock, or fire hazard, and unintentional operation of the appliance
will not impair safety.
Compliance is checked by evaluation of the fault condition specified in Annex H of Part 1.
16 Mechanical strength
This clause of Part 1 is applicable.
17 Protection against harmful ingress of dust, solid objects and moisture
This clause of Part 1 is applicable.
18 Insulation resistance, dielectric strength and leakage current
This clause of Part 1 is applicable, except as follows.
Addition
18.3.1.101 For transformers incorporated in an SMPS in accordance with Annex BB, a
partial discharge type test in accordance with Annex AA shall be performed.
18.4 does not apply.
Addition
18.101 SMPS shall fulfil the impulse dielectric test in accordance with Annex R of
IEC 61558-1:2017.
After the test of 18.3, the SMPS shall be connected to the impulse test equipment. The impulse
dielectric test shall be carried out in accordance with Annex R of IEC 61558-1:2017 between
the input and output terminals of the SMPS. The interval between the impulses shall be at least
1 s if the impulses are produced inside the SMPS.
During the test, there shall be no breakdown of the insulation between turns of a winding,
between input and output circuits, between adjacent input or output circuits, or between
the windings and any conductive core.
19 Construction
This clause of Part 1 is applicable and general requirements for SMPS incorporating separating-,
isolating-, safety isolating- or auto-transformers are defined in 19.1 of Part 1.

– 18 – IEC 61558-2-16:2021 © IEC 2021
20 Components
This clause of Part 1 is applicable.
21 Internal wiring
This clause of Part 1 is applicable.
22 Supply connection and other external flexible cable or cords
This clause of Part 1 is applicable.
23 Terminals for external conductors
This clause of Part 1 is applicable.
24 Provisions for protective earthing
This clause of Part 1 is applicable.
25 Screws and connections
This clause of Part 1 is applicable.
26 Creepage distances, clearances and distances through insulation
This clause of Part 1 is applicable, except as follows:
Addition
Creepage distances and clearances between tracks of electronic circuits shall be checked
in accordance with the tests described in H.4 of IEC 61558-1:2017.
SMPS shall comply with the requirements of 26.101 to 26.106.
NOTE Some practical examples for the determination of clearances and creepage distances for associated
transformers incorporated in an SMPS can be found in Annex CC.
26.101 Creepage distances and distances through insulation given in Table 21, Table 22 and
Table 23 of IEC 61558-1:2017 are generally applicable.
26.102 In compliance with IEC 60664-4:2005, the requirements of 26.103 to 26.106 for
creepage distances, clearances and solid insulation are required above 30 kHz and up to the
frequency of 3 MHz. For frequencies above 3 MHz, the tests in accordance with 7.4 and 7.5 of
IEC 60664-4:2005, high-frequency testing (high-frequency high-voltage test and high-frequency
partial discharge test) shall be carried out.

26.103 Clearance
Dimensioning diagram
Figure 101 and Figure 102 show the relationships between the factors influencing the
dimensioning of clearances and creepage distances for insulation coordination. The diagrams
highlight the major factors and are not intended to substitute for a full review of the relevant
subclauses. In particular they do not take into account the homogeneous electric field situation
(case B values), more precise dimensioning of clearances for frequencies between f and
crit
f and dimen
...