IEC 61558-2-26:2013

Safety of transformers, reactors, power supply units and combinations thereof - Part 2-26: Particular requirements and tests for transformers and power supply units all for saving energy and other purposes

IEC 61558-2-26:2013 deals with the safety of transformers, power supply units and switch mode power supply units all for saving energy and other purposes in electrical installations by adjusting the output voltage and/or other electrical characteristics on the output circuits without interruption affected by the transformers, power supply unit and switch mode power supply unit. The attention of National Committees is drawn to the fact that equipment manufacturers and testing organizations may need a transitional period following publication of a new, amended or revised IEC publication in which to make products in accordance with the new requirements and to equip them for conducting new or revised tests. It is the recommendation of the committee that the content of this publication be adopted for implementation nationally not earlier than 12 months from the date of publication.
This publication is to be read in conjunction with IEC 61558-1:2005.

Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et des combinaisons de ces éléments - Partie 2-26: Règles particulières et essais pour les transformateurs et les blocs d'alimentation entièrement destinés à l'économie d'énergie et à d'autres fins

La CEI 61558-2-26:2013 traite de la sécurité des transformateurs, des blocs d'alimentation et/ou des blocs d'alimentation à découpage entièrement destinés à l'économie d'énergie et à d'autres fins dans les installations électriques, au moyen d'un réglage de la tension secondaire et/ou d'autres caractéristiques électriques des circuits secondaires sans interruption des transformateurs, des blocs d'alimentation et/ou des blocs d'alimentation à découpage. L'attention des Comités nationaux est attirée sur le fait que les fabricants d'appareils et les organismes d'essai peuvent avoir besoin d'une période transitoire après la publication d'une nouvelle publication CEI, ou d'une publication amendée ou révisée, pour fabriquer des produits conformes aux nouvelles exigences et pour adapter leurs équipements aux nouveaux essais ou aux essais révisés. Le comité recommande que le contenu de la présente publication soit entériné au niveau national au plus tôt 12 mois après la date de publication.
Cette publication doit être lue conjointement avec la CEI 61558-1:2005.

General Information

• Status: Published
• Publication Date: 09-Jul-2013
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 96 - Transformers and reactors
• Current Stage: PPUB - Publication issued
• Start Date: 10-Jul-2013
• Completion Date: 31-Jul-2013

Overview

IEC 61558-2-26:2013 is a critical international standard published by the International Electrotechnical Commission (IEC) focusing on the safety of transformers, power supply units, and switch mode power supply units designed for energy saving and other specialized applications. This part of the IEC 61558 series establishes particular safety requirements and testing protocols to ensure these devices safely adjust output voltage or other electrical characteristics in electrical installations without interruption.

Designed for both single-phase and three-phase equipment, IEC 61558-2-26:2013 applies to air-cooled transformers and power supply units (natural or forced ventilation) used for voltage stabilization and energy-efficient electrical supply systems. The standard complements the general safety requirements set forth in IEC 61558-1 and covers devices operating at rated supply voltages up to 1000 V AC and frequencies up to 500 Hz.

Key Topics

• Scope and Applicability
  Addresses transformers and power supply units tailored to energy-saving applications and other functions requiring precise adjustment of output voltage or electrical characteristics without power interruption.

• Safety Considerations
  Emphasizes electrical, thermal, and mechanical safety aspects, including protection against electric shock, mechanical strength, and resistance to environmental factors such as dust and moisture ingress.

• Voltage and Current Parameters
  Defines requirements related to output voltage stability under load, no-load voltage characteristics, short-circuit voltage, and current ratings to ensure consistent and safe performance.

• Testing Protocols
  Specifies particular tests to verify compliance, including dielectric strength, insulation resistance, temperature rise, short-circuit and overload protections, and routine production testing to maintain high safety standards throughout the product lifecycle.

• Marking and Documentation
  Details marking requirements for clear identification, including electrical ratings and safety instructions, aiding manufacturers and end-users in proper product application.

• Integration with Other IEC Standards
  IEC 61558-2-26:2013 is intended to be used alongside IEC 61558-1:2005 and references other parts of the IEC 61558 series covering specific transformer types (e.g., isolating, auto, variable, switch mode power supply units) to ensure comprehensive safety compliance.

Applications

IEC 61558-2-26:2013 plays a vital role in industries and settings where energy efficiency and electrical safety are paramount. Typical applications include:

• Lighting Systems
  Voltage stabilization transformers for indoor and outdoor lighting installations, improving energy consumption without compromising safety or performance.

• Industrial Electrical Installations
  Power supply units designed to regulate output voltage and optimize energy use in manufacturing and production environments.

• Renewable Energy Systems
  Transformers and power units that support energy-saving initiatives in sustainable energy setups by controlling voltage fluctuations and ensuring safe operation.

• Consumer and Commercial Electronics
  Switch mode power supplies and transformers used in devices and systems requiring precise voltage adjustments to enhance energy efficiency.

By ensuring stringent safety requirements, this standard assists manufacturers in designing products that comply with international safety norms, safeguards end-users, and promotes energy conservation.

Related Standards

IEC 61558-2-26:2013 is part of the broader IEC 61558 series focusing on the safety of transformers, reactors, power supply units, and combinations thereof. Related standards include:

• IEC 61558-1:2005 - General safety requirements for transformers and power supply units.
• IEC 61558-2-1 - Requirements for separating transformers.
• IEC 61558-2-4 - Requirements for isolating transformers.
• IEC 61558-2-6 - Requirements for safety isolating transformers.
• IEC 61558-2-13 - Auto transformers.
• IEC 61558-2-14 - Variable transformers.
• IEC 61558-2-16 - Switch mode power supply units and transformers.

These complementary standards enable a comprehensive safety framework for various transformer and power supply unit types, ensuring consistent international safety practices and facilitating easier product certification and market access.

---

Adopting IEC 61558-2-26:2013 supports manufacturers, testing organizations, and regulatory bodies in implementing effective safety measures for energy-saving transformers and power supply units, fostering energy efficiency alongside reliable electrical safety worldwide.

Standards Content (Sample)

IEC 61558-2-26 ®
Edition 1.0 2013-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-26: Particular requirements and tests for transformers and power supply
units all for saving energy and other purposes

Sécurité des transformateurs, bobines d’inductance, blocs d’alimentation et des
combinaisons de ces éléments –
Partie 2-26: Règles particulières et essais pour les transformateurs et les blocs
d’alimentation entièrement destinés à l’économie d’énergie et à d’autres fins

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IEC 61558-2-26 ®
Edition 1.0 2013-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Safety of transformers, reactors, power supply units and combinations thereof –

Part 2-26: Particular requirements and tests for transformers and power supply

units all for saving energy and other purposes

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

combinaisons de ces éléments –

Partie 2-26: Règles particulières et essais pour les transformateurs et les blocs

d’alimentation entièrement destinés à l’économie d’énergie et à d’autres fins

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX R
ICS 29.180 ISBN 978-2-8322-0913-4

– 2 – 61558-2-26 © IEC:2013
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 6
3 Terms and definitions . 7
4 General requirements . 8
5 General notes on test . 8
6 Ratings . 9
7 Classification . 9
8 Marking and other information . 9
9 Protection against electric shock . 10
10 Change of input voltage setting . 11
11 Output voltage and output current under load . 11
12 No-load output voltage . 12
13 Short-circuit voltage . 12
14 Heating. 12
15 Short circuit and overload protection . 13
16 Mechanical strength . 13
17 Protection against harmful ingress of dust, solid objects and moisture . 13
18 Insulation resistance, dielectric strength and leakage current . 13
19 Construction . 13
20 Components . 15
21 Internal wiring . 15
22 Supply connection and other external flexible cables or cords . 15
23 Terminals for external conductors . 15
24 Provisions for protective earthing . 15
25 Screws and connections . 15
26 Creepage distances, clearances and distances through insulation . 15
27 Resistance to heat, fire and tracking . 15
28 Resistance to rusting . 15
Annexes . 16
Annex B (normative) Testing a series of transformers . 16
Annex L (normative) Routine tests (production test) . 16
Annex AA (informative) Saving energy . 17
Annex BB (informative) Incorporated transformers . 18
Bibliography . 19

Table 101 – Output voltage difference . 12

61558-2-26 © IEC:2013 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-26: Particular requirements and tests for transformers and
power supply units all for saving energy and other purposes

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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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 61558-2-26 has been prepared by IEC technical committee 96:
Transformers, reactors, power supply units and combinations thereof.
The text of this standard is based on the following documents:
FDIS Report on voting
96/400/FDIS 96/404/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 2.

– 4 – 61558-2-26 © IEC:2013
This part is intended to be used in conjunction with the latest edition of IEC 61558-1 and its
amendments. It is based on the second edition (2005) of that standard.
This part supplements or modifies the corresponding clauses in IEC 61558-1, so as to convert
that publication into the IEC standard: Particular requirements and tests for transformers and
power supply units all for saving energy and other purposes.
A list of all parts of the IEC 61558 series, under the general title: Safety of transformers,
reactors, power supply units and combination 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 a particular subclause of Part 1 is not mentioned in this part that subclause applies as
far as is reasonable. Where this part states "addition", "modification" or "replacement", the
relevant text of Part 1 is to be adapted accordingly.
In this part 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 part, the words in bold are defined in Clause 3.
Subclauses, notes, figures and tables additional to those in Part 1 are numbered starting from
101; supplementary annexes are entitled AA, BB, etc.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
NOTE The attention of National Committees is drawn to the fact that equipment manufacturers and testing
organizations may need a transitional period following publication of a new, amended or revised IEC publication in
which to make products in accordance with the new requirements and to equip them for conducting new or revised
tests.
It is the recommendation of the committee that the content of this publication be adopted for implementation
nationally not earlier than 12 months from the date of publication.

61558-2-26 © IEC:2013 – 5 –
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-26: Particular requirements and tests for transformers and
power supply units all for saving energy and other purposes

1 Scope
Replacement:
This part of IEC 61558 deals with the safety of transformers, power supply units and
switch mode power supply units all for saving energy and other purposes in electrical
installations by adjusting the output voltage and/or other electrical characteristics on the
output circuits without interruption affected by the transformers, power supply unit and
switch mode power supply unit.
NOTE 1 Safety includes electrical, thermal and mechanicals aspects.
The saving of energy is obtained by voltage stabilization and/or voltage adjusting of the
electrical installation. This standard may also be used for power supply units and switch
mode power supply units intended to be used where adjusting of the voltage or other
electrical characteristics is required by the final application.
NOTE 2 An example of electrical installation is lighting installations, outdoor or indoor.
NOTE 3 In special applications the reduction of the output voltage may affect the safety and the performance of
the supplied equipment.
This part applies to single-phase or three-phase transformers, power supply units and
switch mode power supply units all for saving energy which are air-cooled (natural or
forced), independent or incorporated and containing transformers and/or power supply
units from the following parts of the IEC 61558 series:
Part 2-1: Particular requirements and tests for separating transformers and power supplies
incorporating separating transformers for general applications.
Part 2-4: Particular requirements and tests for isolating transformers and power supply units
incorporating isolating transformers.
Part 2-6: Particular requirements and tests for safety isolating transformers and power supply
units incorporating safety isolating transformers.
Part 2-13: Particular requirements and tests for auto transformers and power supply units
incorporating auto transformers.
Part 2-14: Particular requirements and tests for variable transformers and power supply units
incorporating variable transformers.
Part 2-16: Particular requirements and tests for switch mode power supply units and
transformers for switch mode power supply units.
The rated supply voltage does not exceed 1 000 V a.c., and the rated supply frequency
does not exceed 500 Hz.
– 6 – 61558-2-26 © IEC:2013
This standard is applicable to linear powers supply units with internal operational
frequency not exceeding 500 Hz.
This standard in combination with part 2-16 is also applicable to switch mode power supply
unit and transformer all for saving energy with internal operating frequency higher than 500
Hz.
For specific application corresponding to the other parts 2 of IEC 61558 series, the necessary
requirements of the relevant parts 2 are applicable. In addition, the requirements listed in this
part apply.
When two requirements are in conflict, the most severe take precedence.
The rated output does not exceed:
– 150 kVA for single-phase transformer, power supply unit and switch mode power
supply unit all for saving energy;
– 400 kVA for three-phase transformer, power supply unit and switch mode power
supply unit all for saving energy.
This part is also applicable to transformer, power supply unit and switch mode power
supply unit all for saving energy without limitation of the rated output subject to an
agreement between the purchaser and the manufacturer.
The standard is also not applicable to external circuits and their components intended to be
connected to the input terminals and/or output terminals of the transformer, power supply
unit and switch mode power supply unit all for saving energy.
This standard is not applicable to other devices having similar functions, for example double
level control gears, electronic control gears and specific dimmers covered by other standards.
Measures to protect the enclosure and components inside the enclosure against external
influences such as fungus, vermin, termites, solar-radiation, and icing shall also be
considered.
The different conditions for transportation, storage, and operation of the transformer, power
supply unit and switch mode power supply unit all for saving energy shall also be
considered.
Additional requirements in accordance with other appropriate standards and national rules
may be applicable to transformer, power supply unit and switch mode power supply unit
all for saving energy intended for use in special environments, such as tropical environment.
2 Normative references
This clause of Part 1 is applicable, except as follows.
Addition:
IEC 61558-1:2005, Safety of power transformers, power supplies, reactors and similar
products – Part 1: General requirements and tests
IEC 61558-2-13, Safety of transformers, reactors, power supply units and similar products for
supply voltages up to 1 100 V – Part 2-13: Particular requirements and tests for auto
transformers and power supply units incorporating auto transformers

61558-2-26 © IEC:2013 – 7 –
IEC 61558-2-14, Safety of transformers, reactors, power supply units and combinations
thereof – Part 2-14: Particular requirements and tests for variable transformers and power
supply units incorporating variable transformers
IEC 61558-2-16, Safety of transformers, reactors, power supply units and similar products for
voltages up to 1 100 V – Part 2-16: Particular requirements and tests for switch mode power
supply units and transformers for switch mode power supply units
3 Terms and definitions
This clause of Part 1 is applicable except as follows:
When the term transformer is used it covers transformer, power supply unit and/or switch
mode power supply unit all for saving energy as defined in this part.
3.1 Transformers
Addition:
3.1.101
transformer, power supply unit and switch mode power supply unit all for saving
energy
devices including multiple components which together adjust the output voltage and/or
electrical characteristics on the output circuits and thereby saving energy in end-products like
streetlights
3.4 Circuits and windings
Addition:
3.4.5.101
internal by-pass
electronic or electromechanical by-pass system included in the transformer, which in case of
malfunction connects the input supply and the output line
Note 1 to entry: The internal by-pass can operate automatically and/or manually.
Note 2 to entry: Switch-off devices for maintenance tasks or protective devices are not considered internal by-
pass systems.
3.5 Ratings
Addition:
3.5.1.101
operation rated supply voltage range
supply voltage range assigned by the manufacturer to the transformer, power supply unit
and switch mode power supply unit all for saving energy, within which the output voltage
and/or other electrical characteristics on the output circuits is stabilized during operation
Note 1 to entry: This range shall be not lower than ± 10 % from the rated supply voltage, and it will be the one
used to calculate the rated supply voltage range required for output voltage test.
3.5.4.101
rated minimum output current
output current assigned by the manufacturer to guarantee the correct operating conditions of
the transformer, power supply unit and switch mode power supply unit all for saving
energy
– 8 – 61558-2-26 © IEC:2013
Note 1 to entry: For the definition of rated output current see 3.5.4 of Part 1.
3.5.7.101
rated minimum output
rated output assigned by the manufacturer to guarantee the correct operating conditions of
the transformer, power supply unit and switch mode power supply unit all for saving
energy
Note 1 to entry: For the definition of rated output see 3.5.7 of Part 1.
3.5.7.102
output level
level expressed as a voltage or an output that supplies the load and ensure that all the
devices connected continue to operate properly assigned by the manufacturer and expressed
in volts or as percentage of the rated output
Note 1 to entry: When the voltage stabilization and power reduction is performed by adjusting the voltage, the
output level is expressed in volt. In other cases the output level is expressed as a percentage of rated output.
3.5.7.102.1
nominal output level
output level assigned by the manufacturer for supplying the load with its rated voltage and
100 % of the output
3.5.7.102.2
start output level
output level assigned by the manufacturer ensuring that all devices connected will start
properly
3.5.7.103.3
minimum output level
output level assigned by the manufacturer ensuring that all the devices connected continue
to operate properly
3.5.7.103
output level change speed
speed assigned by the manufacturer for changes from one output level to another
Note 1 to entry: Depending on how the reduction output is set, the output levels change speed is expressed in
volt/minute or in percentage % rated output/minute.
Note 2 to entry: The output level change speed is assigned by the manufacturer.
Note 3 to entry: Output level change speed depends of the characteristics of the components to the installation
(type of lamps, minimum voltage change speed, etc.).
3.5.7.104
stabilization time
time to return to the output voltage for each output level when the rated supply voltage is set
from minimum to maximum operation rated supply voltage range assigned by the
manufacturer for each output level
4 General requirements
This clause of Part 1 is applicable.
5 General notes on test
This clause of Part 1 is applicable.

61558-2-26 © IEC:2013 – 9 –
6 Ratings
This clause of Part 1 is applicable except as follows:
Addition:
6.101 The rated supply voltages and rated output voltages shall not exceed 1 000 V a.c. The
rated supply frequency shall not exceed 500 Hz.
For specific application corresponding to the other parts 2 of IEC 61558 series, the necessary
requirements of the relevant parts 2 are applicable in addition to the requirements listed in
this part. Where two requirements are in conflict, the most severe take precedence.
This standard in combination with part 2-16 is also applicable to switch mode power supply
and for transformer, power supply unit and switch mode power supply unit all for saving
energy with internal operational frequency higher than 500 Hz and with rated output
exceeding to 1 kVA.
6.102 The rated output shall not exceed:
– 150 kVA for single-phase transformer, power supply unit and switch mode power
supply unit all for saving energy, except for transformer and power supply unit all for
saving energy subject to an agreement between the purchasers and the manufacturer;
– 400 kVA for three-phase transformer and power supply unit all for saving energy,
except for transformer and power supply unit all for saving energy subject to an
agreement between the purchaser and the manufacturer.
7 Classification
This clause of Part 1 is applicable except as follows:
Replacement:
7.3 According to the location:
– Indoor, or
– outdoor
and according to the degree of protection ensured by the enclosure and defined in
accordance with IEC 60529 (IP code).
Addition:
7.101 According to the type of regulation of the output voltages for three phase
transformer, power supply unit and switch mode power supply unit all for saving
energy:
– designed to supply single phase load;
– designed to supply three phase load.
8 Marking and other information
This clause of Part 1 is applicable except as follows:
8.6
– 10 – 61558-2-26 © IEC:2013
Addition:
If auxiliary input terminals are used, it (control signal, communication channel, etc.) shall be
clearly indicated in the transformer, power supply unit and switch mode power supply
unit all for saving energy.
8.11
Addition:
Symbol or graphical symbol Explanation or title Identification
Transformer and power supply
IEC 60417-6177
unit all for saving energy.
(DB:2012-11)
8.13
Addition:
Three-phase transformer, power supply unit and switch mode power supply unit all for
saving energy that is formed by three or more independent single-phase transformer,
power supply unit and switch mode power supply unit all for saving energy; marking
shall be on each one of the single-phase transformers, power supply unit and switch
mode power supply unit all for saving energy.
Addition:
8.101 Additional information
The details for a correct usage and maintenance of the installation shall be either registered
somewhere on the device itself or on the instructions that the manufacturer supplies. They are
as follows:
• installation instructions set up service and maintenance, for safe functions;
• external functioning conditions if required by the end applications (e.g. vibrations);
• declared values from manufacturer to comply 11.1.101 to 11.1.103;
• classification according to type of regulation, 7.101;
• classification according to the location, 7.3. and the IP degree;
• incorporated transformer, power supply unit and switch mode power supply unit all
for saving energy shall include documentation by the manufacturer, including the
methods to obtain the IP degree of protection defined, according to 19.101;
• information on internal failure procedures when internal by-pass shall be put into
practice, according to 19.102;
• the technology and the type of incorporated transformers used. A guide for this
information is in Annex BB.
9 Protection against electric shock
This clause of Part 1 is applicable except as follows:

61558-2-26 © IEC:2013 – 11 –
9.1.2 Accessibility to hazardous live parts
Addition:
Hazardous live parts shall not be accessible by the standard test finger after opening of doors
which give access the user to switch or regulating device like push button, handles, operating
levers, knobs, even if this operation is made by tools.
10 Change of input voltage setting
This clause of part 1 is applicable.
11 Output voltage and output current under load
This clause of Part 1 is applicable except as follows:
11.1
Addition:
In case of three phase transformer, power supply unit and switch mode power supply
unit all for saving energy designed to supply single phase load, the test shall be carried out
by changing the input voltage, as required, on each phase at any time and verifying the output
voltage on all the phases. For all other three phase transformers and power supply units
all for saving energy the input voltage shall be changed simultaneously on the three phases.
In case of specific application it is recommended to use the specific load (e.g. luminaries), for
checking.
Addition:
11.1.101 The output voltage for each output level shall not differ from the assigned value
and the tolerance declared by the manufacturer.
The minimum output level shall not differ from the assigned value by more than - 0,5 %.
Compliance is checked with the transformer, power supply unit and switch mode power
supply unit all for saving energy successively connected to the minimum and maximum
supply voltage of the operation rated supply range, while the transformer and power
supply unit all for saving energy is loaded with an impedance or specific load resulting in
the rated output.
1.1.102 The stabilization time shall not exceed the values declared by the manufacturer for
each output level.
Compliance is checked with the transformer, power supply unit and switch mode power
supply unit all for saving energy successively connected to the minimum and maximum
supply voltage of the operation rated supply range, while the transformer and power
supply unit all for saving energy is loaded with an impedance or specific load resulting to
the rated output. The maximum time to return to the output voltage for each output level is
measured.
11.1.103 The output level change speed shall be checked as follows:
Compliance is checked with the transformer, power supply unit and switch mode power
supply unit all for saving energy connected to the maximum supply voltage of the

– 12 – 61558-2-26 © IEC:2013
operation rated supply range, while the transformer and power supply unit all for saving
energy is loaded with an impedance or specific load resulting to the rated output, and then
changes the output level to another. The output levels change speed shall be in
compliance with the value declared by the manufacture with tolerance of ± 10 %.
12 No-load output voltage
This clause of part 1 is applicable except as follows:
Addition:
The difference between the no-load output voltage and the output voltage under load shall
not be excessive.
The difference is expressed as a percentage of the latter voltage calculated according to the
following formula:
U – U
no-load load
____________________________
× 100 (%)
U
load
where U is the no-load output voltage and U is the output voltage under load.
no-load load
Compliance with the requirements shall be verified by measuring the no-load output voltage
and output voltage under load, at the rated ambient temperature when the transformer,
power supply unit and switch mode power supply unit is connected to the rated supply
voltage at the rated supply frequency.
The difference shall not exceed the values shown in Table 101.
Table 101 – Output voltage difference
Type of transformer Difference between the no-load output
Rated output voltage and the output voltage under load
VA %
Up to including 63 20
Over 63 up to including 250 15
Over 250 up to including 630 10
Over 630 5
13 Short-circuit voltage
This clause of part 1 is applicable.
14 Heating
This clause of Part 1 is applicable with the following modification.
Addition:
14.101 Transformer, power supply unit and switch mode power supply unit all for
saving energy are supplied at the rated supply voltage and loaded with an impedance
producing the rated output, at the rated output voltage and, for a.c. current, at the rated

61558-2-26 © IEC:2013 – 13 –
power factor. In accordance with manufacturer declaration, in case of transformers which are
not influenced by the power factor, the impedance can be a specific load (e.g. inductive or
capacitive). The value of the output current is measured when steady state is established.
NOTE Other test methods giving the same results in the heating test can be used (e.g. test method described in
IEC 60076 series).
Then the supply voltage is increased or reduced (the most unfavourable situation) by 10 %
and the output current is adjusted to the same value measured before. The output current is
not adjusted for independent transformer and power supply unit all for saving energy.
After this, no change is made in the circuit. The test is repeated under no-load condition if this
is a more unfavourable situation.
15 Short circuit and overload protection
This clause of Part 1 is applicable.
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.
19 Construction
This clause of Part 1 is applicable except as follows:
Addition:
19.101 Independent transformer
Transformer, power supply unit and switch mode power supply unit all for saving
energy designed for outdoor use, shall be at least IP44. Independent transformer, power
supply unit and switch mode power supply unit all for saving energy designed for indoor
use shall be at least IP20.
Compliance is checked in the installation according to the manufacturer’s instructions.
19.102 Internal by-pass
The transformer, power supply unit and switch mode power supply unit all for saving
energy shall be designed with an electronic or electromechanical system that connects the
input supply with the output line if the transformer and power supply unit all for saving
energy has some internal problems. The internal by-pass disconnects the stabilization and
adjusting function to ensure the energy supply to the devices connected.
The failure conditions, under which the internal by-pass should function, have to be defined
by the manufacturer and indicated in the instruction manual or on additional information.

– 14 – 61558-2-26 © IEC:2013
NOTE Switch-off devices for maintenance task or protective devices are not considered as internal by-pass
systems.
Compliance is checked with the following test:
– the transformer and power supply unit all for saving energy is connected, at rated
ambient temperature, to the rated supply voltage and with an impedance or specific
load resulting to the rated output. The transformer and power supply unit all for
saving energy select in the minimum output level;
– then the transformer and power supply unit all for saving energy is checked with all
the failure conditions described in the manufacturer additional information that should
activate the internal by-pass system;
– for each failure condition the output voltage shall be the same to the supply voltage.
In order to run this test it may be necessary to put forward a specific device prepared with all
the connections to cause all failure condition.
19.103 Incorporating transformer
The transformer, power supply unit and switch mode power supply unit all for saving
energy shall be tested according to this part 2-26 and to the parts 2 corresponding to the
incorporating transformers. A guide for this construction information is in Annex BB.
19.104 Output overvoltage protection
A transformer, power supply unit and switch mode power supply unit all for saving
energy which can generate an output voltage higher that the supply voltage, in case of
internal fault, shall be provided with a device that disconnects the output circuit when the
output voltage exceeds the maximum value of the rated supply voltage range.
In some case the output overvoltage protection device may operate also under internal by
pass operating condition.
This device is not required if the transformer and power supply unit all for saving energy
cannot generate output voltage higher that the supply voltage in case of internal fault.
Compliance is checked with the following test:
The transformer and power supply unit all for saving energy is operating in fault
conditions.
Examination of the apparatus and its circuits diagram will generally show the fault conditions
which should be applied.
One of the following fault conditions shall be applied:
• a fault condition on the electronic circuit as specified in Annex H of Part 1;
• one relay fail its operation and the contacts remain in short circuit or in open circuit
condition;
• a motor driver is locked in the most unfavorable condition;
• a possible fault condition identified by the transformer manufacturer.
The supply voltage is adjusted at minimum and maximum of the rated supply voltage range.
In these conditions the output voltage shall not exceed 10 % more than the rated output
voltage.
61558-2-26 © IEC:2013 – 15 –
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 cables 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.
27 Resistance to heat, fire and tracking
This clause of Part 1 is applicable.
28 Resistance to rusting
This clause of Part 1 is applicable.

– 16 – 61558-2-26 © IEC:2013
Annexes
The annexes of Part 1 are applicable, except as follows:
Addition:
Annex B
(normative)
Testing a series of transformers
B.1
Addition to item b):
6) The incorporated transformers are covered by the same Part 2, see Annex BB .

Annex L
(normative)
Routine tests (production test)
L.2 Checking of no-load output voltage
Addition:
The no-load output voltage has to be measured at nominal output level and minimum
output level
L.4 Checking of protective devices mounting
Addition:
The operation of the internal by-pass has to be checked.

61558-2-26 © IEC:2013 – 17 –
Additional annexes:
Annex AA
(informative)
Saving energy
AA.1 Saving energy
The saving energy of transformer, power supply unit and switch mode power supply unit
all for saving energy depends on the saving power at the different output levels and
operating time at each output levels.
The maximum saving power ratio (SP ) is the percentage between the saved input power (at
lin
minimum output level) and the input power of the rated output with the transformer and
power supply unit all for saving energy connected at rated power factor and at nominal
output level.
The maximum saving power ratio shall include the efficiency of the transformer and power
supply unit all for saving energy.
Compliance is checked with transformer, power supply unit and switch mode power
supply unit all for saving energy connected to the rated supply voltage and rated supply
frequency, while the transformer and power supply unit all for saving energy is loaded
with impedance producing the rated output, at the rated output voltage and for a.c. current,
at the rated power factor. The impedance used for this evaluation shall be with linear
behavior over the output voltage range.
With the nominal output level, the input power of the transformer and power supply unit all
for saving energy shall be measured, P
.
inl
NOTE 1 The value of P may be found by calculation as the sum of the rated output and the losses of the
inl.
transformer and power supply unit all for saving energy at full load.
With the minimum output level, the input power of the transformer and power supply unit
all for saving energy shall be measured, P
ill
NOTE 2 The value of P may be found by calculation as the sum of the output delivered and the losses of the
ill
transformer and power supply unit all for saving energy. The calculation has to be done with the values found
at minimum output level.
The maximum saving power ratio is expressed as a percentage calculated according to the
following formula:
(P P )
–
inl ill
_________________________
(%) = × 100
SP
lin
P
inl
In addition to the maximum saving power ratio other saving power ratios with different output
levels may be calculated with the same method.
In case of non-linear load the result o
...