IEC 61558-2-15:2022

Safety of transformers, reactors, power supply units and combinations thereof - Part 2-15: Particular requirements and tests for isolating transformers for medical IT systems for the supply of medical locations

IEC 61558-2-15:2022 deals with safety of isolating transformers for medical IT systems for the supply of medical locations. This third edition cancels and replaces the second edition published in 2011. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- Adjustment of structure and references in accordance with IEC 61558-1:2017.
It has the status of a group safety publication in accordance with IEC Guide 104.

Sécurité des transformateurs, bobines d’inductance, blocs d'alimentation et des combinaisons de ces éléments - Partie 2-15: Exigences particulières et essais pour les transformateurs de séparation de circuits pour schémas IT médicaux pour l'alimentation des locaux à usages médicaux

L'IEC 61558-2-15:2022 traite de la sécurité des transformateurs de séparation de circuits pour schémas IT médicaux pour l’alimentation des locaux à usages médicaux. Cette troisième édition annule et remplace la deuxième édition parue en 2011. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- Ajustement de la structure et des références conformément à l'IEC 61558-1:2017.
Il a le statut de publication groupée de sécurité conformément au Guide IEC 104.

General Information

• Status: Published
• Publication Date: 01-May-2022
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 96 - Transformers and reactors
• Drafting Committee: MT 1 - TC 96/MT 1
• Current Stage: PPUB - Publication issued
• Start Date: 02-May-2022
• Completion Date: 27-May-2022

Relations

• Revises: IEC 61558-2-15:2011 - Safety of transformers, reactors, power supply units and combinations thereof - Part 2-15: Particular requirements and tests for isolating transformers for the supply of medical locations
• Effective Date: 05-Sep-2023

Overview

IEC 61558-2-15:2022 - third edition - is the international safety standard for isolating transformers for medical IT systems used to supply medical locations. This edition cancels and replaces the 2011 edition and constitutes a technical revision, aligning structure and normative references with IEC 61558-1:2017. It is published as a group safety publication (IEC Guide 104) and provides particular requirements and tests to ensure transformer safety in medical environments.

Key Topics

The standard covers functional and safety requirements, test methods and constructional rules specific to medical isolating transformers. Major technical topics include:

• Protection against electric shock and requirements for medical IT systems
• Insulation resistance, dielectric strength and leakage current measurement (including touch-current networks)
• Creepage distances, clearances and distances through insulation for safer designs in medical locations
• Heating, short‑circuit, overload and inrush current tests to verify thermal performance and protective devices
• Mechanical strength, ingress protection (IP) and resistance to dust/moisture relevant to hospital environments
• Marking, ratings, classification and user information required on equipment and documentation
• Construction, internal wiring, terminals, earthing provisions and components including thermal cut-outs and coated PCBs
• Special tests and methods such as glow-wire, tracking, vibration, routine (production) tests and examples for measurement points

These topics are supported by extensive annexes detailing measurement methods, test sequences and examples to aid conformity assessment.

Applications

IEC 61558-2-15:2022 is intended for designers, manufacturers and test laboratories involved with:

• Medical power supply design - isolating transformers that serve medical IT systems in hospitals, clinics and other medical locations
• Safety and compliance testing for medical transformer products prior to market entry
• Risk mitigation in biomedical engineering and facility power systems by ensuring safe insulation, leakage currents and protective measures
• Procurement and specification teams defining requirements for medical-grade transformers and power equipment

Using this standard helps demonstrate conformance with recognized electrical safety standards and reduce the risk of patient/operational hazards associated with transformer failures.

Who should use this standard

• Transformer and power supply manufacturers (medical grade)
• Safety and compliance engineers, test laboratories and certification bodies
• Biomedical engineers, hospital facilities and procurement specialists
• Regulatory and standards professionals responsible for medical electrical safety

Related standards

• IEC 61558-1:2017 (general requirements referenced and incorporated)
• Normative references cited within the document such as IEC 61032 and IEC 60664-1

Keywords: IEC 61558-2-15:2022, isolating transformers, medical IT systems, medical locations, transformer safety, dielectric strength, leakage current, creepage distances, clearances, electrical safety standard.

Standards Content (Sample)

IEC 61558-2-15 ®
Edition 3.0 2022-05
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-15: Particular requirements and tests for isolating transformers
for medical IT systems for the supply of medical locations

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IEC 61558-2-15 ®
Edition 3.0 2022-05
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-15: Particular requirements and tests for isolating transformers
for medical IT systems for the supply of medical locations
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-5041-9
– 2 – IEC 61558-2-15:2022 RLV © IEC 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 2
1 Scope . 8
2 Normative references . 9
3 Terms and definitions . 9
4 General requirements . 10
5 General notes on tests . 10
6 Ratings . 10
7 Classification . 11
8 Marking and other information . 11
9 Protection against electric shock . 12
10 Change of input voltage setting . 13
11 Output voltage and output current under load . 13
12 No-load output voltage . 13
13 Short-circuit voltage . 13
14 Heating . 14
15 Short-circuit and overload protection . 15
16 Mechanical strength . 15
17 Protection against harmful ingress of dust, solid objects and moisture . 15
18 Insulation resistance, dielectric strength and leakage current . 15
19 Construction . 18
20 Components . 20
21 Internal wiring . 20
22 Supply connection and other external flexible cable or cords . 20
23 Terminals for external conductors . 21
24 Provisions for protective earthing. 21
25 Screws and connections . 21
26 Creepage distances, clearances and distances through insulation . 21
27 Resistance to heat, fire and tracking . 21
28 Resistance to rusting . 21
Annexes . 22
Annex H (normative) Electronic circuits . 22
Annex L (normative) Routine tests (production tests) . 22
Bibliography . 23
Index of defined terms .

Figure 101 – Required circuit for measuring the leakage current from the output
winding to the earthing . 17
Figure 102 – Required circuit for measuring the leakage current at the protective
earthing conductor . 18

Table 101 – Symbols indicating the kind of transformer . 12
Table 102 – Additional dielectric strength test voltages . 16

– 4 – IEC 61558-2-15:2022 RLV © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-15: Particular requirements and tests for isolating transformers
for medical IT systems for the supply of medical locations

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
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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.
This redline version of the official IEC Standard allows the user to identify the changes made to
the previous edition IEC 61558-2-15:2011. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.

IEC 61558-2-15 has been prepared by IEC technical committee 96: Transformers, reactors,
power supply units and combinations thereof. It is an International Standard.
This third edition cancels and replaces the second edition published in 2011. 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;
The text of this International Standard is based on the following documents:
Draft Report on voting
96/535/FDIS 96/536/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 isolating
transformers for medical IT systems for the supply of medical locations.
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 61558-2-15:2022 RLV © IEC 2022
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.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates that it
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contents. Users should therefore print this document using a colour printer.

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 60364-4-41:2005, 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 61558-2-15:2022 RLV © IEC 2022
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-15: Particular requirements and tests for isolating transformers
for medical IT systems for the supply of medical locations

1 Scope
Replacement
This part of IEC 61558 deals with safety aspects of isolating transformers for medical IT
systems for the supply of medical locations.
NOTE 1 Safety includes electrical, thermal and mechanical aspects.
Unless otherwise specified, from here onward, the term transformer covers isolating
transformers for medical IT systems for the supply of medical locations.
This document is applicable to stationary, single-phase or three-phase, air-cooled (natural or
forced) independent dry-type isolating transformers for the supply of medical IT systems
system for group 2 medical locations, designed to be permanently connected to the fixed wiring
and intended to form the medical IT power system on the secondary side. The windings may
can be encapsulated or non-encapsulated.
NOTE 2 IT power systems are defined in IEC 60364-1.
NOTE 3 The installation rules for medical IT systems system for group 2 medical locations are
covered by IEC 60364-7-710.
NOTE 3 National installation rules of some countries have different or additional requirements listed in Annex C of
IEC 60364-7-710:2021.
NOTE 4 Transformers covered by this document are intended for medical IT systems for the
supply of medical locations. All other transformers or equipments connected downstream
from the transformer are not covered by this document.
The rated supply voltage does not exceed 1 000 V AC. The rated supply frequency and
internal operational frequency do not exceed 500 Hz.
The rated output is not less than 0,5 kVA and does not exceed 10 kVA for single-phase and
three-phase transformers for medical IT system for group 2 medical locations.
This document is can be applicable to isolating transformers intended to supply other medical
installations that are not group 2 medical locations without limitation of the rated output subject
to an agreement between the purchaser and the manufacturer.
NOTE 54 Transformers intended to supply power to distribution networks other than medical IT systems are not
included in the scope.
The no-load output voltage and the rated output voltage does not exceed 250 V AC for
single-phase or three-phase transformer (phase-to-phase voltage).
This document does not cover power supply units.
This document is not applicable to external circuits and their components intended to be
connected to the input terminals and output terminals of the transformers.

Transformers covered by this document are used in applications where double or reinforced
insulation between circuits is required by the installation rules or by the appliance specification.
NOTE 6 Attention is drawn to the following, if necessary:
– additional requirements for transformers intended to be used in vehicles, on board ships,
and aircraft , additional requirements (from other applicable standards, national rules, etc.
may be necessary);
– measures to protect the enclosure and the components inside the enclosure against
external influences such as fungus, vermin, termites, solar-radiation, and icing should also
be considered;
– the different conditions for transportation, storage, and operation of the transformers
should also be considered;
– additional requirements in accordance with other appropriate standards and national rules
may be applicable to transformers intended for use in special environments.
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.
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 61558-1:20052017, Safety of power transformers, power supplies, reactors and similar
products Safety of transformers, reactors, power supply units and combinations thereof –
Part 1: General requirements and tests
3 Terms and definitions
This clause of Part 1 is applicable, except as follows:
For the purposes of this document, the terms and definitions given in Part 1 apply, except as
follows:
ISO and IEC maintain terminology 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
Addition
3.1.101
isolating transformer for medical IT systems for the supply of medical locations
isolating transformer used for the supply of medical IT systems system for group 2 medical
locations, designed to be permanently connected and with double or reinforced insulation
between each part of the transformer (body, screen, circuits, thermal sensitive device) except
between the core and the body
– 10 – IEC 61558-2-15:2022 RLV © IEC 2022
3.2.101
medical IT system
electric IT system fulfilling all specific additional requirements of group 2 medical locations
[SOURCE: IEC 60364-7-710:2021, 710.3.10, modified – Note 1 to entry has been deleted.]
3.5.101
rated input current
unput input current assigned to the transformer by the manufacturer, when the transformer is
loaded with rated output
3.6.101
no-load input current
input current when the transformer is connected to the rated supply voltage, at the rated
supply frequency, with no-load on the output
3.6.1012
inrush current
maximum instantaneous value of the no-load input current of the transformer (peak value)
when the transformer is switched on at rated supply voltage
3.47.101
functional screening
separation between two windings or between a winding and the core or shielding of a part or of
the whole transformer, by means of an interposed conductive screen for functional reasons
4 General requirements
This clause of Part 1 is applicable.
5 General notes on tests
This clause of Part 1 is applicable.
6 Ratings
This clause of Part 1 is applicable except as follows:
Replacement Addition
6.101 The rated output voltage (phase-to-phase voltage) shall not exceed 250 V AC for
single-phase or three-phase transformers (phase-to-phase voltage).
6.102 The rated output shall not be less than 0,5 kVA and shall not exceed 10 kVA for single-
phase or three-phase transformers.
Transformers intended to supply other medical installations that are not group 2 medical
locations without limitation of the rated output shall be subject to an agreement between the
purchaser and the manufacturer.
6.103 The rated frequency and internal operational frequency shall not exceed 500 Hz.
6.104 The rated supply voltage shall not exceed 1 000 V AC.

Compliance with the requirements of 6.101 to 6.104 shall be verified checked by inspection of
the marking.
7 Classification
This clause of Part 1 is applicable, except as follows:
Replacement
7.2 Replacement:
According to short-circuit protection or protection against abnormal conditions:
– non-short-circuit proof transformer.
Transformers shall be non-short-circuit proof transformers in accordance with the short-
circuit characteristic or protection against abnormal use.
7.4
Transformers shall be stationary transformers.
7.5
Transformers shall be classified for continuous duty.
7.8
Transformers shall be classified for overvoltage category III.
8 Marking and other information
This clause of Part 1 is applicable except as follows:
8.1 h)
Replacement
Replace the first sentence by the following: Relevant graphical symbols shown in 8.11 indicating
the type of transformer;
Replace the content up to the first semi-colon by the following:
relevant graphical symbols shown in Table 101 that indicate the kind of transformer
t) Addition:
Transformers shall be marked with the measured short-circuit voltage expressed as a
percentage of the rated supply voltage.
8.1 s)
Replacement
– 12 – IEC 61558-2-15:2022 RLV © IEC 2022
Transformers shall be marked with the measured short-circuit voltage expressed as a
percentage of the rated supply voltage.
Addition
8.1.101 When the inrush current exceeds 8 times the peak value of the rated input current,
the resulting value shall be marked on the transformer.
8.6
Addition
All terminals shall be clearly marked.
8.11
Addition
Table 101 – Symbols indicating the kind of transformer
Symbol or graphical symbol Explanation or title Identification
non-short-circuit proof isolating transformer for the IEC 60417-5972
supply of medical locations (DB 2010-08)

Non-short-circuit proof isolating transformers
IEC 60417-5972:2003-08
for medical IT systems for the supply of
group 2 medical locations
NOTE This symbol is not applicable for
transformers > 10 kVA
8.14
Addition
The instruction sheet shall state: "Screens whose connection to the earthing is necessary for
compliance with the leakage current requirements of Clause 18 shall be connected to the
earthing."
The instruction sheet shall qualify the type of temperature sensor built in the transformer, if any.
The instruction sheet shall give the required value of the circuit of the transformer, when it is
allowed by national installation rules.
The instruction sheet shall include type and characteristic of sensor to over-temperature
monitoring, if any.
The rated input current shall be provided as information given either on the transformer
marking or made available in the manufacturer's catalogue or similar.

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.
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 shall be measured when the transformer is connected to the
rated supply voltage at the rated supply frequency and at the rated ambient temperature.
12.101 The no-load output voltage (phase-to-phase voltage) shall not exceed 250 V AC for
single-phase or three-phase transformers.
12.102 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:
V −V
no-load load
× 100 (%)
V
load
where V is the no-load output voltage and V is the output voltage under load.
no-load load
Compliance with the requirements of 12.101 and 12.102 shall be verified by measuring the no-
load output voltage and output voltage under load, at the rated ambient temperature when
the transformer is connected to the rated supply voltage at the rated supply frequency.
The difference between the no-load output voltage and the output voltage under load shall
not exceed 5 %.
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 5 %.
The ratio is determined by Formula (1):
UU−
no-load load
×100 %
( )
(1)
U
load
– 14 – IEC 61558-2-15:2022 RLV © IEC 2022
where
U is the no-load output voltage, expressed in V;
no-load
U is the no-load output voltage, expressed in V.
load
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 transformer is connected to the rated
supply voltage at the rated supply frequency.
13 Short-circuit voltage
This clause of Part 1 is not applicable.
Replacement
13 Short-circuit voltage and inrush currents
13.1 The short-circuit voltage shall be measured and marked on the transformer.
Compliance shall be verified checked by measurement.
13.2 The no-load input current shall not exceed 3 % of the rated input current at the rated
supply voltage.
This requirement shall be fulfilled by construction of the transformer without the use of any
capacitors in the transformer circuits (input/output) or in the installation.
Compliance shall be verified checked by measurements.
13.3 The inrush current shall not exceed 8 times the peak value of the rated input current.
However, it is allowed to increase this value to 12 times the peak value of rated input current
provided, if the latter value shall be reflected is marked on the transformer marking.
This requirement shall be fulfilled by construction of the transformer without the use of any
electronic devices and additional measures in the transformer or in the installation.
Compliance shall be verified checked by the following test:
The transformer with no-load operation is connected to the rated supply voltage. The test
supply voltage is then switched on and off 20 times at random intervals of approximately 20 s.
NOTE The on-off switching-on and -off may be carried out only twice, if a device is used to
switch on at the most unfavourable electrical angle of the supply voltage.
The voltage drop of the supply source shall be such that the voltage drop does not exceed 2 %
as a result of the inrush current.
The inrush current shall not exceed 8 times or 12 times the peak value of the rated input
current, respectively, during any of the switching events operations.
14 Heating
This clause of Part 1 is applicable, except as follows:

Addition
14.101 Immediately after the test of in accordance with 14.1 an additional heating test is
required with 150 % of the load for 30 min. After the test the temperature shall not exceed the
values of Table 1 2 increased by 25 %.
15 Short-circuit and overload protection
This clause of Part 1 is applicable, except as follows:
Addition:
Isolating transformers for the supply of medical locations are non-short-circuit proof
transformers. The overload must be monitored by a temperature monitoring system. The test
of 15.3 of Part 1 will be carried out. When the circuit breaker is allowed by national installation
rules the value for a circuit-breaker shall be mentioned in the instruction sheet.
15.1 Short circuit and overload test method
Replacement
Transformers shall be non-short-circuit proof transformers.
15.4 Non-short-circuit proof transformers
Addition
The overload shall be monitored by an overload current and over-temperature monitoring
warning system.
NOTE 1 For information about monitoring of overload and over-temperature of isolating transformers for medical
IT system see Annex B of IEC 61557-8:2014.
NOTE 2 In some countries a circuit breaker is allowed by national installation rules.
NOTE 3 In Spain, monitoring of overload and over-temperature is not required.
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:
18.2 Insulation resistance
th th
Table 7: Replacement of the 6 and 7 lines by the following:

– 16 – IEC 61558-2-15:2022 RLV © IEC 2022
Replacement:
th th
Replace the 6 and 7 lines of Table 13 by the following three new lines:
Insulation to be tested Insulation
resistance
MΩ
Between each input circuit and all other input circuits connected together 7
Between each output circuit and all other output circuits connected together 7
Between input and output circuits (double reinforced insulation) 7

Addition
NOTE In Australia, higher insulation resistance values are required.
18.3 Dielectric strength test
Table 8a: Addition:
Addition
In addition, the dielectric strength tests according to Table 102 shall be performed.
Table 102 – Additional dielectric strength test voltages
Application of dielectric strength test voltage Working voltage
V
< 50 100 150 300 600 1 000
Between live parts of adjacent input circuits not
500 1 400 2 800 4 200 5 000 5 500
intended to be connected together
Between live parts of adjacent output circuits not 500 1 400 2 800 4 200 5 000 5 500
intended to be connected together

Addition
18.101 The leakage current of the output winding to the earthing shall not exceed 0,5 mA,
when measured under the no-load condition, and at the room temperature with the transformer
supplied at the rated voltage and the rated frequency, as shown in Figure 101.
For this test the core and the functional screen, if any, shall be connected to the earthing.

The test shall be carried out with all combinations of S1 and S2.
For three-phase transformers the switch S1 is used only in closed position. The measurements with switch S2 are
repeated connecting it, in turn, to all phases.
The current is measured with an ammeter of negligible impedance.
NOTE 1 In Japan, the leakage current of the output winding is limited to 0,1 mA maximum.
NOTE 2 In Australia, additional leakage current limits apply.
Figure 101 – Required circuit for measuring the leakage current
from the output winding to the earthing
Compliance shall be verified checked by measurements.
18.102 The leakage current through the protective earthing conductor from the enclosure to
the earthing, shall not exceed 0,5 mA when measured at room temperature under no-load
condition with the transformer supplied at the rated voltage and the rated frequency as shown
in Figure 102.
– 18 – IEC 61558-2-15:2022 RLV © IEC 2022

The test shall be carried out with all combinations of S1.
For three-phase transformers the switch S1 is used only in closed position.
The current is measured with an ammeter of negligible impedance.
The core, if not connected to the enclosure, and the functional screen, if any, shall be connected to earth.
Figure 102 – Required circuit for measuring the leakage current
at the protective earthing conductor
Compliance shall be verified checked by measurements.
19 Construction
This clause of Part 1 is applicable, except as follows:
Replacement of 19.1 (19.1.1 to 19.1.4.10) by the following
19.1 The input and output circuits shall be electrically separated from each other and the
construction shall be such that there is no possibility of any connection between these circuits,
either directly or indirectly, via other conductive parts, except by deliberate action.
Compliance is checked by inspection and measurements, taking Clauses 18 and 26 into
consideration.
19.1.101 The insulation between the input and output winding(s) shall consist of double or
reinforced insulation (rated for the working voltage). The insulation between the input
winding(s) and the body, and between the output winding(s) and the body, shall consist of
double or reinforced insulation (rated for the working voltage).
19.1.101.1 When the input winding(s) are not intended to be connected in series or parallel,
they shall be separated from one another each other and from other circuits by double or
reinforced insulation (rated for the working voltage).

The input winding(s), intended to be connected in series or parallel, may be separated from
each other by basic insulation (rated for the working voltage).
19.1.101.2 The output winding(s) shall be separated from each other and from other circuits
by double or reinforced insulation (rated for the working voltage).
19.1.101.3 The functional screening, if any, shall be separated from the core, the windings
and from the body by double or reinforced insulation (rated for the working voltage).
19.1.101.4 If the transformers are provided with a functional screening placed between the
input and the output windings, the functional screening shall be constructed of a metal foil
so that the adjacent turns overlap without short-circuiting. The lead out of the functional
screening shall be provided with separate terminals.
For concentric windings, the width of the functional screening shall be approximately equal to
the axial winding length of the input winding. For non-concentric windings, the width of the
functional screening shall be approximately equal to the radial winding length of the input
winding. If the functional screening is constructed of only one turn it shall be provided with
an insulated overlap of not less than 3 mm.
19.1.102 For transformers with intermediate conductive parts (e.g. the iron core) not
connected to the body and located between the input and output windings, the insulation
between the intermediate conductive parts and the input windings, and between the
intermediate conductive parts and the output windings shall consist of at least basic
insulation (rated for the working voltage).
NOTE An intermediate conductive part not separated from the input or output windings or
the body by at least basic insulation is considered to be connected to the relevant part(s).
The insulation between the input and output windings via the intermediate conductive part
shall consist of double or reinforced insulation; the insulation between the input windings
and the body, and between the output windings and the body, via the intermediate
conductive part shall consist of double or reinforced insulation (rated for the working
voltage).
19.1.103 Transformers shall not be provided with capacitors electrically connecting the input
and the output circuits and/or resistors.
Compliance shall be verified checked by inspection.
19.1.104 The input and output terminals for the connection of external wiring shall be so
located that the distance measured between the points of introduction of the conductors into
these terminals is not less than 25 mm. If a barrier is used to obtain this distance, the
measurement shall be made over and around the barrier which shall be of insulating material
and permanently fixed to the transformer.
Compliance shall be verified checked by inspection and by measurement, disregarding the
intermediate conductive parts.
19.1.105 If the monitoring of the over-temperature in accordance with 15.4 is required, the
thermal sensitive device (bimetal, PTC or similar) shall be built-in and shall be connected to
separate terminals for external connections.
NOTE The terminals are intended to connect the temperature thermal sensitive device to an acoustical and optical
temperature monitoring device visual indicators and/or audible signal located in the medical location and intended to
warn the medical staff.
– 20 – IEC 61558-2-15:2022 RLV © IEC 2022
The temperature thermal sensitive device shall be rated to the class of the insulation system
minus 10 °C.
19.1.106 If a single-phase transformer is provided with a midpoint in the output winding, it
shall be connected to a separate terminal.
19.1.107 Three-phase transformers shall be provided with the vector group star-star or star-
delta design.
19.1.108 The star point of the output winding in three-phase transformers with vector group
star-star design shall be connected to a separate terminal.
NOTE The terminal is intended for connection to an external medical insulation monitoring device (MED-IMD) in
accordance with IEC 61557-8, if applicable.
19.1.109 The star point of the input winding in three-phase transformers with vector group
star-star or star-delta design shall be connected to a separate terminal.
NOTE The terminal is intended for connection to the neutral point of the supply in order to allow asymmetrical
loading.
19.1.110 Isolating transformers for the supply of medical locations shall be stationary
transformers.
20 Components
This clause of Part 1 is applicable, except as follows:
20.3 Replacement:
Socket-outlets are not allowed to connect the output circuit of the transformer to the electrical
installation of the medical room.
20.6
Replacement
Socket-outlets shall not be directly connected to the output circuit of the transformer without
appropriate protection in accordance with the corresponding installation rules.
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, except as follows:
22.3
Addition
22.3.101 Transformers shall be designed for permanent connection.
22.4 to 22.7 This subclause of Part 1 is not applicable.

Isolating transformers for the supply of medical locations shall be designed for permanent
connection.
Subclauses 22.4 to 22.7 are not 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.

– 22 – IEC 61558-2-15:2022 RLV © IEC 2022
Annexes
The Annexes of Part 1 are applicable, except as follows:

Annex H
(normative)
Electronic circuits
This Annex of Part 1 is not applicable.

Annex L
(normative)
Routine tests (production tests)
This Annex of Part 1 is applicable, except as follows:
Addition
L.101 Checking of the short-circuit voltage
The short-circuit voltage shall not exceed the marked value.
L.102 Checking of the no-load input current
The no-load input current shall not exceed 3 % of the rated input current.
L.103 Checking of the inrush current
The inrush current shall not exceed 8 times the peak value of the rated input current or the
marked value on the label, if any.
Compliance is checked by Subclause 13.103.

Bibliography
The Bibliography of Part 1 is applicable, except as follows:
Addition
IEC 61558 (all parts), Safety of transformers, reactors, power supply units and combinations
thereof
IEC 60364-1:2005, Low-voltage electrical installations – Part 1: Fundamental principles,
assessment of general chara
...

IEC 61558-2-15 EXV ®
Edition 3.0 2022-09
EXTENDED VERSION
INTERNATIONAL
STANDARD
colour
This extended version of IEC 61558-2-15:2022 includes the content of
inside
the references made to IEC 61558-1:2017
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-15: Particular requirements and tests for isolating transformers
for medical IT systems for the supply of medical locations
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IEC 61558-2-15 EXV ®
Edition 3.0 2022-09
EXTENDED VERSION
INTERNATIONAL
STANDARD
colour
This extended version of IEC 61558-2-15:2022 includes the content of inside
the references made to IEC 61558-1:2017
GROUP SAFETY PUBLICATION
Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-15: Particular requirements and tests for isolating transformers
for medical IT systems for the supply of medical locations
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-5675-6
– 2 – IEC 61558-2-15:2022 EXV © IEC 2022
CONTENTS
FOREWORD .6
INTRODUCTION .9
1 Scope . 10
2 Normative references . 11
3 Terms and definitions . 14
4 General requirements . 28
5 General notes on tests . 29
6 Ratings . 31
7 Classification . 31
8 Marking and other information . 32
9 Protection against electric shock . 38
10 Change of input voltage setting . 42
11 Output voltage and output current under load . 43
12 No-load output voltage . 44
13 Short-circuit voltage and inrush currents . 44
14 Heating . 45
15 Short-circuit and overload protection. 53
16 Mechanical strength . 58
17 Protection against harmful ingress of dust, solid objects and moisture . 63
18 Insulation resistance, dielectric strength and leakage current . 67
19 Construction . 74
20 Components . 86
21 Internal wiring . 91
22 Supply connection and other external flexible cable or cords . 91
23 Terminals for external conductors . 97
24 Provisions for protective earthing . 99
25 Screws and connections . 100
26 Creepage distances, clearances and distances through insulation . 103
27 Resistance to heat, fire and tracking . 116
28 Resistance to rusting. 120

Annex A (normative) Measurement of creepage distances and clearances . 121
Annex B (normative) Testing a series of transformers . 125
Annex C (void) . 127
Annex D (void) . 128
Annex E (normative) Glow-wire test . 129
Annex F (normative) Requirements for manually operated switches which are parts of
transformers assembly . 130
Annex G (normative) Tracking test . 133
Annex H (normative) Electronic circuits . 134
Annex I (informative) Dimensions for rectangular cross-section connectors of
transformers, basic dimensions and coordination . 135

Annex J (normative) Measuring network for touch-currents . 138
Annex K (normative) Insulated winding wires . 139
Annex L (normative) Routine tests (production tests) . 142
Annex M (informative) Examples to be used as a guide for 19.1 . 144
Annex N (informative) Examples for checking points of dielectric strength test voltages. 147
Annex O (void) . 149
Annex P (informative) Examples for measurement points of creepage distances and
clearances . 150
Annex Q (informative) Explanation of IP numbers for degrees of protection . 153
Annex R (normative) Explanations of the application of 6.1.2.2.1 of IEC 60664-1:2007 . 156
Annex S (void) . 158
Annex T (void) . 159
Annex U (void) . 160
Annex V (informative) Symbols to be used for thermal cut-outs . 161
Annex W (normative) Coated printed circuit boards . 162
Bibliography . 163
Index of defined terms . 165

Figure 2 – Mounting box for flush-type transformer . 30
Figure 3 – Test pin (see IEC 61032, test probe 13). 40
Figure 4 – Standard test finger (see IEC 61032, test probe B) . 41
Figure 5 – Example of back-to-back method – Single phase . 49
Figure 6 – Example of back-to-back method – Three phase . 49
Figure 7 – Amplitude spectrum density for random testing . 62
Figure 8 – Normalised spectrum of shock . 63
Figure 9 – Test voltage sequence . 70
Figure 10 – Test configuration: single-phase equipment on star TN or TT system . 72
Figure 101 – Required circuit for measuring the leakage current from the output winding
to the earthing. 73
Figure 102 – Required circuit for measuring the leakage current at the protective earthing
conductor. 74
Figure 11 – Abrasion resistance test for insulating coated layers . 79
Figure 12 – Flexing test apparatus . 95
Figure 13 – Test arrangement for checking mechanical withstanding of insulating
materials in thin sheet layers . 108
Figure 14 – Ball-pressure apparatus . 116
Figure A.1 – Example 1 . 121
Figure A.2 – Example 2 . 122
Figure A.3 – Example 3 . 122
Figure A.4 – Example 4 . 122
Figure A.5 – Example 5 . 123
Figure A.6 – Example 6 . 123

– 4 – IEC 61558-2-15:2022 EXV © IEC 2022
Figure A.7 – Example 7 . 124
Figure A.8 – Example 8 . 124
Figure J.1 – Measuring network for touch-current . 138
Figure M.1 – Examples for concentric type constructions . 144
Figure M.2 – Examples for side-by-side type constructions . 145
Figure M.3 – Examples for winding constructions without screen . 145
Figure M.4 – Examples for wrapped winding constructions . 146
Figure M.5 – Examples for winding constructions with screen . 146
Figure N.1 – Transformer of class I construction with metal enclosure . 147
Figure N.2 – Transformer of class II construction with metal enclosure . 148
Figure N.3 – Transformer of class II construction with enclosure of insulating material . 148
Figure P.1 – Transformer of class I construction . 150
Figure P.2 – Transformer of class I construction with earthed metal screen . 151
Figure P.3 – Transformer of class II construction with metal enclosure . 151
Figure P.4 – Transformer of class II construction with enclosure of insulating material . 152
Figure V.1 – Restored by manual operation. 161
Figure V.2 – Restored by disconnection of the supply . 161
Figure V.3 – Thermal link (see 3.3.5) . 161
Figure V.4 – Self-resetting thermal cut-out . 161

Table 1 – Symbols used on equipment or in instructions . 35
Table 101 – Symbols indicating the kind of transformer . 36
Table 2 – Values of maximum temperatures in normal use . 50
Table 3 – Explanation of the maximum winding temperatures required in Table 2 . 51
Table 4 – Test temperature and testing time (in days) per cycle . 52
Table 5 – Maximum values of temperatures under short-circuit or overload conditions . 55
Table 6 – Values of T and k for fuses . 56
Table 7 – Pull force on pins . 60
Table 8 – Conditions for vibration testing (random) . 61
Table 9 – Amplitude spectrum density ASD values for accelerated life testing . 61
Table 10 – Frequency values depending on the weight of the specimen . 62
Table 11 – Excitation values for vibration testing . 62
Table 12 – Solid-object-proof transformer test . 65
Table 13 – Values of insulation resistance . 68
Table 14 – Table of dielectric strength test voltages . 69
Table 102 – Additional dielectric strength test voltages. 70
Table 15 – Limits for currents . 72
Table 17 – Pull and torque to be applied to external flexible cables or cords fixed to
stationary and portable transformers . 96
Table 18 – Torque to be applied to screws and connections . 101
Table 19 – Torque test on glands. 103
Table 20 – Clearances in mm . 109

Table 21 – Creepage distances in mm . 110
Table 22 – Distance through insulation in mm . 111
Table 23 – Creepage distances and clearance between terminals for external connection . 112
Table 24 – Values of FIW wires with minimum overall diameter and minimum test
voltages according to the total enamel increase . 114
Table A.1 – Width of groove values depending on the pollution degree . 121
Table F.1 – Peak surge current of additional loads . 131
Table I.1 – Dimensions of rectangular copper connectors . 136
Table K.1 – Mandrel diameter . 140
Table K.2 – Oven temperature . 140
Table Q.1 – Degrees of protection against access to hazardous parts indicated by the
first characteristic numera . 154
Table Q.2 – Degrees of protection against solid foreign objects indicated by the first
characteristic numeral . 154
Table Q.3 – Degrees of protection indicated by the second characteristic numeral . 155
Table R.1 – Impulse test voltage according to 6.1.2.2.1 of IEC 60664-1:2007 . 156

– 6 – IEC 61558-2-15:2022 EXV © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-15: Particular requirements and tests for isolating transformers
for medical IT systems for the supply of medical locations

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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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
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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.
This extended version (EXV) of the official IEC Standard provides the user with a
comprehensive content of the Standard.
Particular subclauses of IEC 61558-1:2017 are displayed in the content on a blue
background.
IEC 61558-2-15 has been prepared by IEC technical committee 96: Transformers, reactors,
power supply units and combinations thereof. It is an International Standard.
This third edition cancels and replaces the second edition published in 2011. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
1) Adjustment of structure and references in accordance with IEC 61558-1:2017;
The text of this International Standard is based on the following documents:
Draft Report on voting
96/535/FDIS 96/536/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 isolating
transformers for medical IT systems for the supply of medical locations.
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.

– 8 – IEC 61558-2-15:2022 EXV © IEC 2022
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.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it
contains colours which are considered to be useful for the correct understanding of its
contents. Users should therefore print this document using a colour printer.

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 60364-4-41:2005, 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.

– 10 – IEC 61558-2-15:2022 EXV © IEC 2022
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-15: Particular requirements and tests for isolating transformers
for medical IT systems for the supply of medical locations

1 Scope
This part of IEC 61558 deals with safety of isolating transformers for medical IT systems
for the supply of medical locations.
NOTE 1 Safety includes electrical, thermal and mechanical aspects.
Unless otherwise specified, from here onward, the term transformer covers isolating
transformers for medical IT systems for the supply of medical locations.
This document is applicable to stationary, single-phase or three-phase, air-cooled (natural or
forced) dry-type isolating transformers for the supply of medical IT system for group 2
medical locations, designed to be permanently connected to the fixed wiring and intended to
form the medical IT system on the secondary side. The windings can be encapsulated or non-
encapsulated.
NOTE 2 IT systems are defined in IEC 60364-1.
The installation rules for medical IT system for group 2 medical locations are covered by
IEC 60364-7-710.
NOTE 3 National installation rules of some countries have different or additional requirements listed in Annex C of
IEC 60364-7-710:2021.
Transformers covered by this document are intended for medical IT systems for the supply
of medical locations. All other transformers or equipment are not covered by this document.
The rated supply voltage does not exceed 1 000 V AC. The rated supply frequency and
internal operational frequency do not exceed 500 Hz.
The rated output is not less than 0,5 kVA and does not exceed 10 kVA for single-phase and
three-phase transformers for medical IT system for group 2 medical locations.
This document can be applicable to isolating transformers intended to supply other medical
installations that are not group 2 medical locations without limitation of the rated output subject
to an agreement between the purchaser and the manufacturer.
NOTE 4 Transformers intended to supply distribution networks other than medical IT systems are not included in
the scope.
The no-load output voltage and the rated output voltage does not exceed 250 V AC for
single-phase or three-phase transformer (phase-to-phase voltage).
This document does not cover power supply units.
This document is not applicable to external circuits and their components intended to be
connected to the input terminals and output terminals of the transformers.
Transformers covered by this document are used in applications where double or reinforced
insulation between circuits is required by the installation rules or by the appliance specification.

Attention is drawn to the following, if necessary:
– additional requirements for transformers 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 transformers;
– additional requirements in accordance with other appropriate standards and national rules
may be applicable to transformers intended for use in special environments.
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.
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
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 60065:2014, Audio, video and similar electronic apparatus – Safety requirements
IEC 60068-2-6, Environmental testing – Part 2-6: Tests – Test FC: Vibration (sinusoidal)
IEC 60068-2-14, Environmental testing – Part 2-14: Tests – Test N: Change of temperature
IEC 60068-2-31, Environmental testing – Part 2-31: Tests – Test Ec: Rough handling shocks,
primarily for equipment-type specimens
IEC 60068-2-75, Environmental testing – Part 2-75: Tests – Test Eh: Hammer tests
IEC 60076-1, Power transformers – Part 1: General
IEC 60076-11:2004, Power transformers – Part 11: Dry-type transformers
IEC TR 60083, Plugs and socket-outlets for domestic and similar general use standardized in
member countries of IEC
IEC 60085:2007, Electrical insulation – Thermal evaluation and designation
IEC 60112:2003, Method for the determination of the proof and the comparative tracking indices
of solid insulating materials
IEC 60127 (all parts), Miniature fuses
IEC 60127-3, Miniature fuses – Part 3: Sub-miniature fuse-links
IEC 60216 (all parts), Electrical insulating materials – Thermal endurance properties

– 12 – IEC 61558-2-15:2022 EXV © IEC 2022
IEC 60227 (all parts), Polyvinyl chloride insulated cables of rated voltages up to and including
450/750 V
IEC 60227-5:2011, Polyvinyl chloride insulated cables of rated voltages up to and including
450/750 V – Part 5: Flexible cables (cords)
IEC 60245 (all parts), Rubber insulated cables – Rated voltages up to and including 450/750 V
IEC 60245-4:2011, Rubber insulated cables – Rated voltages up to and including 450/750 V –
Part 4: Cords and flexible cables
IEC 60269 (all parts), Low voltage fuses
IEC 60269-2:2013, Low voltage fuses – Part 2: Supplementary requirements for fuses for use
by authorized persons (fuses mainly for industrial application) – Examples of standardized
systems of fuses A to K
IEC 60269-3:2010, Low voltage fuses – Part 3: Supplementary requirements for fuses for use
by unskilled persons (fuses mainly for household or similar applications) – Examples of
standardized systems of fuses A to F
IEC 60309 (all parts), Plugs, socket-outlets and couplers for industrial purposes
IEC 60317 (all parts), Specifications for particular types of windings wires
IEC 60317-0-7:2012, Specifications for particular types of winding wires – Part 0-7: General
requirements – Fully insulated (FIW) zero-defect enamelled round copper wire with nominal
conductor diameter of 0,040 mm to 1,600 mm
IEC 60317-56, Specifications for particular types of winding wires – Part 56: Solderable fully
insulated (FIW) zero-defect polyurethane enamelled round copper wire with nominal conductor
diameter 0,040 mm to 1,600 mm, class 180
IEC 60320 (all parts), Appliance couplers for household and similar general purposes
IEC 60320-2-3, Appliance couplers for household and similar general purposes – Part 2-3:
Appliance couplers with a degree of protection higher than IPX0
IEC 60384-14:2013, Fixed capacitors for use in electronic equipment – Part 14: Sectional
specification: Fixed capacitors for electromagnetic interference suppression and connection to
the supply mains
IEC 60417, Grapahical symbols for use on equipment
(available at http://www.graphical-symbols.info/equipment)
IEC 60454 (all parts), Pressure-sensitive adhesive tapes for electrical purposes
IEC 60529:1989, Degrees of protection provided by enclosures (IP Code)
IEC 60529:1989/AMD1:1999
IEC 60529:1989/AMD2:2013
IEC 60664-1:2007, Insulation coordination for equipment within low voltage systems – Part 1:
Principles, requirements and tests
IEC 60664-3:2016, Insulation coordination for equipment within low-voltage systems – Part 3:
Use of coating, potting or moulding for protection against pollution

IEC 60691:2015, Thermal-links – Requirements and application guide
IEC 60695-2-10:2013, Fire hazard testing – Part 2-10: Glowing/hot-wire based test methods –
Glow-wire apparatus and common test procedure
IEC 60695-2-11:2014, Fire hazard testing – Part 2-11: Glowing/hot-wire based test methods –
Glow-wire flammability test method for end-products
IEC 60721-3-2, Classification of environmental conditions – Part 3: Classification of groups of
environmental parameters and their severities – Section 2: Transportation
IEC 60730 (all parts), Automatic electrical controls
IEC 60730-1:2013, Automatic electrical controls – Part 1: General requirements
IEC 60851-3:2009, Winding wires – Test methods: Part 3: Mechanical properties
IEC 60851-5:2008, Winding wires – Test methods: Part 5: Electrical properties
IEC 60851-6:2012, Winding wires – Test methods: Part 6: Thermal properties
IEC 60884-1:2002, Plugs and socket-outlets for household and similar purposes – Part 1:
General requirements
IEC 60884-1:2002/AMD1:2006
IEC 60884-1:2002/AMD2:2013
IEC 60884-2-4, Plugs and socket-outlets for household and similar purposes – Part 2-4:
Particular requirements for plugs and socket-outlets for SELV
IEC 60898 (all parts), Electrical accessories – Circuit-breakers for overcurrent protection for
household and similar installations
IEC 60906-1, IEC system of plugs and socket-outlets for household and similar purposes – Part
1: Plugs and socket-outlets 16 A 250 V a.c.
IEC 60906-3, IEC system of plugs and socket-outlets for household and similar purposes –
Part 3: SELV plugs and socket-outlets, 16 A 6 V, 12 V, 24 V, 48 V, a.c. and d.c.
IEC 60947-7-1, Low-voltage switchgear and controlgear – Part 7-1: Ancillary equipment –
Terminal blocks for copper conductors
IEC 60990:2016, Methods of measurement of touch current and protective conductor current
IEC 60998-2-1, Connecting devices for low-voltage circuits for household and similar purposes
– Part 2-1: Particular requirements for connecting devices as separate entities with screw-type
clamping units
IEC 60998-2-2, Connecting devices for low-voltage circuits for household and similar purposes
– Part 2-2: Particular requirements for connecting devices as separate entities with screwless-
type clamping units
IEC 60999-1, Connecting devices – Electrical copper conductors – Safety requirements for
screw-type and screwless-type clamping units – Part 1: General requirements and particular
2 2
requirements for clamping units for conductors from 0,2 mm up to 35 mm (included)
IEC 61032, Protection of persons and equipment by enclosures – Probes for verification

– 14 – IEC 61558-2-15:2022 EXV © IEC 2022
IEC 61058-1:2016, Switches for appliances – Part 1: General requirements
IEC 61058-1-1:2016, Switches for appliances – Part 1-1: Requirements for mechanical switches
IEC 61140:2016, Protection against electric shock – Common aspects for installation and
equipment
IEC 61373, Railway applications – Rolling stock equipment – Shock and vibration tests
IEC 61558-1:2017, Safety of transformers, reactors, power supply units and combinations
thereof – Part 1: General requirements and tests
ISO 8820 (all parts), Road vehicles – Fuse-links
EN 50075:1990, Specification for flat non-wirable two-pole plugs 2.5 A 250 V, with cord, for the
connection of class II-equipment for household and similar purposes
DIN 43671:1975, Copper bus bars; design for continuous current
DIN 43670:1975, Aluminium bus bars; design for continuous current
DIN 43670-2:1985, Aluminium bus bars copper cladding; design for continuous current
3 Terms and definitions
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
NOTE Further definitions of transformers intended for particular use are indicated in the relevant parts of
IEC 61558-2.
When the term transformer is used it covers transformer, reactor and power supply unit where applicable.
Unless otherwise specified, the terms “voltage” and “current” imply the RMS values of alternating voltage and current,
and for direct voltage and current, they imply the corresponding arithmetic mean values.
"Ripple-free" is conventionally an RMS ripple voltage not more than 10 % of the DC component.
An index of often used terms and definitions is provided at the end of this document.
3.1 Transformers
3.1.1
transformer
static piece of apparatus with two or more windings which, by electromagnetic induction,
transforms a system of alternating voltage and current into another system of voltage and
current usually of different values and at the same frequency for the purpose of transmitting
electrical power
Note 1 to entry: The term frequency also implies that the waveform remains the same.
[SOURCE: IEC 60050-421:1990, 421-01-01, modified – “power” deleted and “NOTE” added]
3.1.2
isolating transformer
transformer with protective separation between the input winding(s) and output winding(s)

3.1.3
safety isolating transformer
isolating transformer designed to deliver SELV (safety extra-low voltage) or PELV (protective
extra-low voltage)
3.1.4
separating transformer
transformer with input winding(s) separated from the output winding(s) by at least basic
insulation
3.1.5
auto-transformer
transformer in which input and output windings have a common part
Note 1 to entry: Auto-transformers may have supplementary windings or tappings for adjustment purposes.
Note 2 to entry: Transformers with windings separated at least by functional insulation and electrically connected,
will be treated as auto-transformers.
3.1.6
associated transformer
transformer designed to supply a specific appliance or equipment, or a part of them, and being
either an incorporated transformer or a transformer for specific use
3.1.6.1
incorporated transformer
associated transformer designed to be built into a specific appliance or equipment, or into a
part of them, and the enclosure of which provides protection against electric shock
3.1.6.2
transformer for specific use
associated transformer fixed to or delivered with the appliance or equipment, without being
incorporated in this appliance or equipment and having its own enclosure which provides
protection against electric shock
3.1.7
independent transformer
transformer designed to supply unspecified appliances and intended to be used without any
additional enclosure which provides protection against electric shock
Note 1 to entry: Such a transformer can be either a portable transformer or a stationary transformer.
3.1.8
void
3.1.9
short-circuit proof transformer
transformer not exceeding the specified temperature limits when overloaded or short-circuited,
and which continues to meet all the requirements of this document after removal of the overload
or short-circuit and is not required to operate continuously under short-circuit or overload
condition
Note 1 to entry: “Continues to meet all the requirements of this document” does not imply that all types of short-
circuit proof transformers continue to operate.
3.1.9.1
non-inherently short-circuit proof transformer
short-circuit proof transformer equipped with a protective device or with an intentional weak
part which opens the input circuit or the output circuit, or reduces the current in the input
circuit or the output circuit when the transformer is overloaded or short-circuited, and

-----------------
...

IEC 61558-2-15 ®
Edition 3.0 2022-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ

Safety of transformers, reactors, power supply units and combinations thereof –
Part 2-15: Particular requirements and tests for isolating transformers
for medical IT systems for the supply of medical locations

Sécurité des transformateurs, bobines d’inductance, blocs d'alimentation et
des combinaisons de ces éléments –
Partie 2-15: Exigences particulières et essais pour les transformateurs de
séparation de circuits pour schémas IT médicaux pour l’alimentation des
locaux à usages médicaux
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IEC 61558-2-15 ®
Edition 3.0 2022-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ

Safety of transformers, reactors, power supply units and combinations thereof –

Part 2-15: Particular requirements and tests for isolating transformers

for medical IT systems for the supply of medical locations

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

des combinaisons de ces éléments –

Partie 2-15: Exigences particulières et essais pour les transformateurs de

séparation de circuits pour schémas IT médicaux pour l’alimentation des

locaux à usages médicaux
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180 ISBN 978-2-8322-1101-9

– 2 – IEC 61558-2-15:2022 © IEC 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 8
3 Terms and definitions . 8
4 General requirements . 9
5 General notes on tests . 9
6 Ratings . 9
7 Classification . 10
8 Marking and other information . 10
9 Protection against electric shock . 11
10 Change of input voltage setting . 11
11 Output voltage and output current under load . 11
12 No-load output voltage . 11
13 Short-circuit voltage . 12
14 Heating . 13
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 . 16
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. 19
25 Screws and connections . 19
26 Creepage distances, clearances and distances through insulation . 19
27 Resistance to heat, fire and tracking . 19
28 Resistance to rusting . 19
Annexes . 20
Annex H (normative) Electronic circuits . 20
Annex L (normative) Routine tests (production tests) . 20
Bibliography . 21

Figure 101 – Required circuit for measuring the leakage current from the output
winding to the earthing . 15
Figure 102 – Required circuit for measuring the leakage current at the protective
earthing conductor . 16

Table 101 – Symbols indicating the kind of transformer . 11
Table 102 – Additional dielectric strength test voltages . 14

– 4 – IEC 61558-2-15:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-15: Particular requirements and tests for isolating transformers
for medical IT systems for the supply of medical locations

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
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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.
IEC 61558-2-15 has been prepared by IEC technical committee 96: Transformers, reactors,
power supply units and combinations thereof. It is an International Standard.
This third edition cancels and replaces the second edition published in 2011. 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;

The text of this International Standard is based on the following documents:
Draft Report on voting
96/535/FDIS 96/536/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 isolating
transformers for medical IT systems for the supply of medical locations.
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.
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.
– 6 – IEC 61558-2-15:2022 © IEC 2022
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 60364-4-41:2005, 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.

SAFETY OF TRANSFORMERS, REACTORS,
POWER SUPPLY UNITS AND COMBINATIONS THEREOF –

Part 2-15: Particular requirements and tests for isolating transformers
for medical IT systems for the supply of medical locations

1 Scope
Replacement
This part of IEC 61558 deals with safety of isolating transformers for medical IT systems
for the supply of medical locations.
NOTE 1 Safety includes electrical, thermal and mechanical aspects.
Unless otherwise specified, from here onward, the term transformer covers isolating
transformers for medical IT systems for the supply of medical locations.
This document is applicable to stationary, single-phase or three-phase, air-cooled (natural or
forced) dry-type isolating transformers for the supply of medical IT system for group 2
medical locations, designed to be permanently connected to the fixed wiring and intended to
form the medical IT system on the secondary side. The windings can be encapsulated or non-
encapsulated.
NOTE 2 IT systems are defined in IEC 60364-1.
The installation rules for medical IT system for group 2 medical locations are covered by
IEC 60364-7-710.
NOTE 3 National installation rules of some countries have different or additional requirements listed in Annex C of
IEC 60364-7-710:2021.
Transformers covered by this document are intended for medical IT systems for the supply
of medical locations. All other transformers or equipment are not covered by this document.
The rated supply voltage does not exceed 1 000 V AC. The rated supply frequency and
internal operational frequency do not exceed 500 Hz.
The rated output is not less than 0,5 kVA and does not exceed 10 kVA for single-phase and
three-phase transformers for medical IT system for group 2 medical locations.
This document can be applicable to isolating transformers intended to supply other medical
installations that are not group 2 medical locations without limitation of the rated output subject
to an agreement between the purchaser and the manufacturer.
NOTE 4 Transformers intended to supply distribution networks other than medical IT systems are not included in
the scope.
The no-load output voltage and the rated output voltage does not exceed 250 V AC for
single-phase or three-phase transformer (phase-to-phase voltage).
This document does not cover power supply units.
This document is not applicable to external circuits and their components intended to be
connected to the input terminals and output terminals of the transformers.

– 8 – IEC 61558-2-15:2022 © IEC 2022
Transformers covered by this document are used in applications where double or reinforced
insulation between circuits is required by the installation rules or by the appliance specification.
Attention is drawn to the following, if necessary:
– additional requirements for transformers 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 transformers;
– additional requirements in accordance with other appropriate standards and national rules
may be applicable to transformers intended for use in special environments.
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.
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 61558-1:2017, Safety of transformers, reactors, power supply units and combinations
thereof – Part 1: General requirements and tests
3 Terms and definitions
For the purposes of this document, the terms and definitions given in Part 1 apply, except as
follows:
ISO and IEC maintain terminology 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
Addition
3.1.101
isolating transformer for medical IT systems for the supply of medical locations
isolating transformer used for the supply of medical IT system for group 2 medical locations,
designed to be permanently connected and with double or reinforced insulation between each
part of the transformer (body, screen, circuits, thermal sensitive device) except between the
core and the body
3.2.101
medical IT system
electric IT system fulfilling all specific additional requirements of group 2 medical locations
[SOURCE: IEC 60364-7-710:2021, 710.3.10, modified – Note 1 to entry has been deleted.]

3.5.101
rated input current
input current assigned to the transformer by the manufacturer, when the transformer is loaded
with rated output
3.6.101
no-load input current
input current when the transformer is connected to the rated supply voltage, at the rated
supply frequency, with no-load on the output
3.6.102
inrush current
maximum instantaneous value of the no-load input current of the transformer (peak value)
when the transformer is switched on at rated supply voltage
3.7.101
functional screening
separation between two windings or between a winding and the core or shielding of a part or of
the whole transformer, by means of an interposed conductive screen for functional reasons
4 General requirements
This clause of Part 1 is applicable.
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 250 V AC for single-phase or three-phase
transformers (phase-to-phase voltage).
6.102 The rated output shall not be less than 0,5 kVA and shall not exceed 10 kVA for single-
phase or three-phase transformers.
Transformers intended to supply other medical installations that are not group 2 medical
locations without limitation of the rated output shall be subject to an agreement between the
purchaser and the manufacturer.
6.103 The rated frequency and internal operational frequency shall not exceed 500 Hz.
6.104 The rated supply voltage shall not exceed 1 000 V AC.
Compliance with the requirements of 6.101 to 6.104 shall be checked by inspection of the
marking.
– 10 – IEC 61558-2-15:2022 © IEC 2022
7 Classification
This clause of Part 1 is applicable, except as follows:
Replacement
7.2
Transformers shall be non-short-circuit proof transformers in accordance with the short-
circuit characteristic or protection against abnormal use.
7.4
Transformers shall be stationary transformers.
7.5
Transformers shall be classified for continuous duty.
7.8
Transformers shall be classified for overvoltage category III.
8 Marking and other information
This clause of Part 1 is applicable except as follows:
8.1 h)
Replacement
Replace the content up to the first semi-colon by the following:
relevant graphical symbols shown in Table 101 that indicate the kind of transformer
8.1 s)
Replacement
Transformers shall be marked with the measured short-circuit voltage expressed as a
percentage of the rated supply voltage.
Addition
8.1.101 When the inrush current exceeds 8 times the peak value of the rated input current,
the resulting value shall be marked on the transformer.
8.6
Addition
All terminals shall be clearly marked.

8.11
Addition
Table 101 – Symbols indicating the kind of transformer
Symbol or graphical symbol Explanation or title Identification
Non-short-circuit proof isolating transformers IEC 60417-5972:2003-08
for medical IT systems for the supply of
group 2 medical locations
NOTE This symbol is not applicable for
transformers > 10 kVA
8.14
Addition
The instruction sheet shall state: "Screens whose connection to the earthing is necessary for
compliance with the leakage current requirements of Clause 18 shall be connected to the
earthing."
The instruction sheet shall include type and characteristic of sensor to over-temperature
monitoring, if any.
The rated input current shall be provided as information given either on the transformer
marking or made available in the manufacturer's catalogue or similar.
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.
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
12.101 The no-load output voltage (phase-to-phase voltage) shall not exceed 250 V AC for
single-phase or three-phase transformers.
12.102 The difference between the no-load output voltage and the output voltage under
load shall not be excessive.
– 12 – IEC 61558-2-15:2022 © IEC 2022
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 5 %.
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
U is the no-load output voltage, expressed in V.
load
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 transformer is connected to the rated
supply voltage at the rated supply frequency.
13 Short-circuit voltage
This clause of Part 1 is not applicable.
Replacement
13 Short-circuit voltage and inrush currents
13.1 The short-circuit voltage shall be measured and marked on the transformer.
Compliance shall be checked by measurement.
13.2 The no-load input current shall not exceed 3 % of the rated input current at the rated
supply voltage.
This requirement shall be fulfilled by construction of the transformer without the use of any
capacitors in the transformer circuits (input/output) or in the installation.
Compliance shall be checked by measurements.
13.3 The inrush current shall not exceed 8 times the peak value of the rated input current.
However, it is allowed to increase this value to 12 times the peak value of rated input current,
if the latter value is marked on the transformer.
This requirement shall be fulfilled by construction of the transformer without the use of any
electronic devices and additional measures in the transformer or in the installation.
Compliance shall be checked by the following test:
The transformer with no-load operation is connected to the rated supply voltage. The test
supply voltage is then switched on and off 20 times at random intervals of approximately 20 s.
The on-off switching may be carried out only twice, if a device is used to switch on at the most
unfavourable electrical angle of the supply voltage.

The voltage drop of the supply source shall not exceed 2 % as a result of the inrush current.
The inrush current shall not exceed 8 times or 12 times the peak value of the rated input
current during any of the switching operations.
14 Heating
This clause of Part 1 is applicable, except as follows:
Addition
14.101 Immediately after the test in accordance with 14.1 an additional heating test is required
with 150 % of the load for 30 min. After the test the temperature shall not exceed the values of
Table 2 increased by 25 %.
15 Short-circuit and overload protection
This clause of Part 1 is applicable, except as follows:
15.1 Short circuit and overload test method
Replacement
Transformers shall be non-short-circuit proof transformers.
15.4 Non-short-circuit proof transformers
Addition
The overload shall be monitored by an overload current and over-temperature monitoring
warning system.
NOTE 1 For information about monitoring of overload and over-temperature of isolating transformers for medical
IT system see Annex B of IEC 61557-8:2014.
NOTE 2 In some countries a circuit breaker is allowed by national installation rules.
NOTE 3 In Spain, monitoring of overload and over-temperature is not required.
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:

– 14 – IEC 61558-2-15:2022 © IEC 2022
18.2 Insulation resistance
Replacement:
th th
Replace the 6 and 7 lines of Table 13 by the following three new lines:
Insulation
Insulation to be tested
resistance
MΩ
Between each input circuit and all other input circuits connected together 7
Between each output circuit and all other output circuits connected together 7
Between input and output circuits (double reinforced insulation) 7

Addition
NOTE In Australia, higher insulation resistance values are required.
18.3 Dielectric strength test
Addition
In addition, the dielectric strength tests according to Table 102 shall be performed.
Table 102 – Additional dielectric strength test voltages
Working voltage
Application of dielectric strength test voltage
V
< 50 100 150 300 600 1 000
Between live parts of adjacent input circuits not 500 1 400 2 800 4 200 5 000 5 500
intended to be connected together
Between live parts of adjacent output circuits not 500 1 400 2 800 4 200 5 000 5 500
intended to be connected together

Addition
18.101 The leakage current of the output winding to the earthing shall not exceed 0,5 mA,
when measured under the no-load condition, and at the room temperature with the transformer
supplied at the rated voltage and the rated frequency, as shown in Figure 101.
For this test the core and the functional screen, if any, shall be connected to the earthing.

The test shall be carried out with all combinations of S1 and S2.
For three-phase transformers the switch S1 is used only in closed position. The measurements with switch S2 are
repeated connecting it, in turn, to all phases.
The current is measured with an ammeter of negligible impedance.
NOTE 1 In Japan, the leakage current of the output winding is limited to 0,1 mA maximum.
NOTE 2 In Australia, additional leakage current limits apply.
Figure 101 – Required circuit for measuring the leakage current
from the output winding to the earthing
Compliance shall be checked by measurements.
18.102 The leakage current through the protective earthing conductor from the enclosure to
the earthing, shall not exceed 0,5 mA when measured at room temperature under no-load
condition with the transformer supplied at the rated voltage and the rated frequency as shown
in Figure 102.
– 16 – IEC 61558-2-15:2022 © IEC 2022

The test shall be carried out with all combinations of S1.
For three-phase transformers the switch S1 is used only in closed position.
The current is measured with an ammeter of negligible impedance.
The core, if not connected to the enclosure, and the functional screen, if any, shall be connected to earth.
Figure 102 – Required circuit for measuring the leakage current
at the protective earthing conductor
Compliance shall be checked by measurements.
19 Construction
This clause of Part 1 is applicable, except as follows:
Replacement of 19.1 (19.1.1 to 19.1.4.10) by the following
19.1 The input and output circuits shall be electrically separated from each other and the
construction shall be such that there is no possibility of any connection between these circuits,
either directly or indirectly, via other conductive parts, except by deliberate action.
Compliance is checked by inspection and measurements, taking Clauses 18 and 26 into
consideration.
19.1.101 The insulation between the input and output winding(s) shall consist of double or
reinforced insulation (rated for the working voltage). The insulation between the input
winding(s) and the body, and between the output winding(s) and the body, shall consist of
double or reinforced insulation (rated for the working voltage).

19.1.101.1 When the input winding(s) are not intended to be connected in series or parallel,
they shall be separated from each other and from other circuits by double or reinforced
insulation (rated for the working voltage).
The input winding(s), intended to be connected in series or parallel, may be separated from
each other by basic insulation (rated for the working voltage).
19.1.101.2 The output winding(s) shall be separated from each other and from other circuits
by double or reinforced insulation (rated for the working voltage).
19.1.101.3 The functional screening, if any, shall be separated from the core, the windings
and from the body by double or reinforced insulation (rated for the working voltage).
19.1.101.4 If the transformers are provided with a functional screening placed between the
input and the output windings, the functional screening shall be constructed of a metal foil
so that the adjacent turns overlap without short-circuiting. The lead out of the functional
screening shall be provided with separate terminals.
For concentric windings, the width of the functional screening shall be approximately equal to
the axial winding length of the input winding. For non-concentric windings, the width of the
functional screening shall be approximately equal to the radial winding length of the input
winding. If the functional screening is constructed of only one turn it shall be provided with
an insulated overlap of not less than 3 mm.
19.1.102 For transformers with intermediate conductive parts (e.g. the iron core) not
connected to the body and located between the input and output windings, the insulation
between the intermediate conductive parts and the input windings, and between the
intermediate conductive parts and the output windings shall consist of at least basic
insulation (rated for the working voltage).
An intermediate conductive part not separated from the input or output windings or the
body by at least basic insulation is considered to be connected to the relevant part(s).
The insulation between the input and output windings via the intermediate conductive part
shall consist of double or reinforced insulation; the insulation between the input windings
and the body, and between the output windings and the body, via the intermediate
conductive part shall consist of double or reinforced insulation (rated for the working
voltage).
19.1.103 Transformers shall not be provided with capacitors and/or resistors.
Compliance shall be checked by inspection.
19.1.104 The input and output terminals for the connection of external wiring shall be so
located that the distance measured between the points of introduction of the conductors into
these terminals is not less than 25 mm. If a barrier is used to obtain this distance, the
measurement shall be made over and around the barrier which shall be of insulating material
and permanently fixed to the transformer.
Compliance shall be checked by inspection and by measurement, disregarding the
intermediate conductive parts.
19.1.105 If the monitoring of the over-temperature in accordance with 15.4 is required, the
thermal sensitive device (bimetal, PTC or similar) shall be built-in and shall be connected to
separate terminals for external connections.
NOTE The terminals are intended to connect the thermal sensitive device to visual indicators and/or audible signal
located in the medical location and intended to warn the medical staff.

– 18 – IEC 61558-2-15:2022 © IEC 2022
The thermal sensitive device shall be rated to the class of the insulation system minus 10 °C.
19.1.106 If a single-phase transformer is provided with a midpoint in the output winding, it
shall be connected to a separate terminal.
19.1.107 Three-phase transformers shall be provided with the vector group star-star or star-
delta design.
19.1.108 The star point of the output winding in three-phase transformers with vector group
star-star design shall be connected to a separate terminal.
NOTE The terminal is intended for connection to an external medical insulation monitoring device (MED-IMD) in
accordance with IEC 61557-8, if applicable.
19.1.109 The star point of the input winding in three-phase transformers with vector group
star-star or star-delta design shall be connected to a separate terminal.
NOTE The terminal is intended for connection to the neutral point of the supply in order to allow asymmetrical
loading.
20 Components
This clause of Part 1 is applicable, except as follows:
20.6
Replacement
Socket-outlets shall not be directly connected to the output circuit of the transformer without
appropriate protection in accordance with the corresponding installation rules.
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, except as follows:
22.3
Addition
22.3.101 Transformers shall be designed for permanent connection.
22.4 to 22.7
Subclauses 22.4 to 22.7 are not 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.

– 20 – IEC 61558-2-15:2022 © IEC 2022
Annexes
The Annexes of Part 1 are applicable, except as follows:

Annex H
(normative)
Electronic circuits
This Annex of Part 1 is not applicable.

Annex L
(normative)
Routine tests (production tests)
This Annex of Part 1 is applicable, except as follows:
Addition
L.101 Checking of the short-circuit voltage
The short-circuit voltage shall not exceed the marked value.
L.102 Checking of the no-load input current
The no-load input current shall not exceed 3 % of the rated input current.
L.103 Checking of the inrush current
The inrush current shall not exceed 8 times the peak value of the rated input current or the
marked value on the label, if any.
Compliance is checked by Subclause 13.103.

Bibliography
The Bibliography of Part 1 is applicable, except as follows:
Addition
IEC 61558 (all parts), Safety of transformers, reactors, power supply units and combinations
thereof
IEC 60364-1:2005, Low-voltage electrical installations – Part 1: Fundamental principles,
assessment of general characteristics, definitions
IEC 60364-4-41:2005, Low-voltage electrical installations – Part 4-41: Protection for safety –
Protection against electric shock
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 60364-7-710:2021, Low-voltage electrical installations – Part 7-710: Requirements for
special installations or locations – Medical locations
IEC 61557-8:2014, Electrical safety in low voltage distribution systems up to 1 000 V a.c. and
1 500 V d.c. – Equipment for testing, measuring or monitoring of protective measures – Part 8:
Insulation monitoring devices for IT systems
ISO/IEC Guide 51:2014, Safety aspects – Guidelines for their inclusion in standards
IEC Guide 104:2019, The prepara
...