IEC 61558-2-6:2009

Safety of transformers, reactors, power supply units and similar products for supply voltages up to 1 100 V - Part 2-6: Particular requirements and tests for safety isolating transformers and power supply units incorporating safety isolating transformers

IEC 61558-2-6:2009 deals with the safety of safety isolating transformers for general applications and power supply units incorporating safety isolating transformers for general applications. Transformers incorporating electronic circuits are also covered by this standard. This second edition cancels and replaces the first edition published in 1997. It constitutes a technical revision. The main changes consist of updating this part in accordance with Part 1 (2005), and increasing the supply voltages up to 1 100 V to be in line with the standards of TC 14. This part has the status of a group safety publication in accordance with IEC Guide 104. This part is intended to be used in conjunction with the latest edition of IEC 61558-1 and its amendments. It is based on the second edition (2005) of that standard. It is the recommendation of the committee that the content of this publication be adopted for implementation nationally not earlier than 12 months from the date of publication.

Sécurité des transformateurs, bobines d'inductance, blocs d'alimentation et produits analogues pour des tensions d'alimentation jusqu'à 1 100 V - Partie 2-6: Règles particulières et essais pour les transformateurs de sécurité et les blocs d'alimentation incorporant des transformateurs de sécurité

La CEI 61558-2-6:2009 traite de la sécurité des transformateurs de sécurité pour applications d'ordre général et des blocs d'alimentation incorporant des transformateurs de sécurité pour applications d'ordre général. Les transformateurs incorporant des circuits électroniques sont également couverts par la présente norme. Cette deuxième édition annule et remplace la première édition publiée en 1997. Elle constitue une révision technique. Les principales modifications consistent en la mise à jour de la présente partie 2-6 conformément à la Partie 1 (2005), et l'augmentation de la tension d'alimentation jusqu'à 1 100 V pour être en conformité avec les normes du TC 14. La présente partie a le statut de publication groupée de sécurité conformément au Guide CEI 104. La présente partie est destinée à être utilisée avec la dernière édition de la CEI 61558-1 et ses amendements. Elle est basée sur la seconde édition (2005) de cette norme. Le comité recommande que le contenu de cette publication soit entériné au niveau national au plus tôt 12 mois après la date de publication.

General Information

• Status: Published
• Publication Date: 10-Feb-2009
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 96 - Transformers, reactors, power supply units, and combinations thereof
• Drafting Committee: MT 1 - TC 96/MT 1
• Current Stage: DELPUB - Deleted Publication
• Start Date: 05-Jul-2019
• Completion Date: 18-May-2021

Relations

• Revised: IEC 61558-2-6:2021 - Safety of transformers, reactors, power supply units and combinations thereof - Part 2-6: Particular requirements and tests for safety isolating transformers and power supply units incorporating safety isolating transformers for general applications
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 61558-2-6
®
Edition 2.0 2009-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of transformers, reactors, power supply units and similar products for
supply voltages up to 1 100 V –
Part 2-6: Particular requirements and tests for safety isolating transformers and
power supply units incorporating safety isolating transformers

Sécurité des transformateurs, bobines d’inductance, blocs d'alimentation et
produits analogues pour des tensions d’alimentation jusqu'à 1 100 V –
Partie 2-6: Règles particulières et essais pour les transformateurs de sécurité et
les blocs d'alimentation incorporant des transformateurs de sécurité

IEC 61558-2-6:2009

---------------------- Page: 1 ----------------------
THIS PUBLICATION IS COPYRIGHT PROTECTED
Copyright © 2009 IEC, Geneva, Switzerland

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by
any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or
IEC's member National Committee in the country of the requester.
If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,
please contact the address below or your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur.
Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette
publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.

IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: [e-mail]
Web: www.iec.ch

About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
ƒ Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
ƒ IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
ƒ Electropedia: www.electropedia.org
The world's leading online dictionary of electronic and electrical terms containing more than 20 000 terms and definitions
in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
ƒ Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: [e-mail]
Tel.: [phone]
Fax: [phone]


A propos de la CEI
La Commission Electrotechnique Internationale (CEI) est la première organisation mondiale qui élabore et publie des
normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications CEI
Le contenu technique des publications de la CEI est constamment revu. Veuillez vous assurer que vous possédez
l’édition la plus récente, un corrigendum ou amendement peut avoir été publié.
ƒ Catalogue des publications de la CEI: www.iec.ch/searchpub/cur_fut-f.htm
Le Catalogue en-ligne de la CEI vous permet d’effectuer des recherches en utilisant différents critères (numéro de référence,
texte, comité d’études,…). Il donne aussi des informations sur les projets et les publications retirées ou remplacées.
ƒ Just Published CEI: www.iec.ch/online_news/justpub
Restez informé sur les nouvelles publications de la CEI. Just Published détaille deux fois par mois les nouvelles
publications parues. Disponible en-ligne et aussi par email.
ƒ Electropedia: www.electropedia.org
Le premier dictionnaire en ligne au monde de termes électroniques et électriques. Il contient plus de 20 000 termes et
définitions en anglais et en français, ainsi que les termes équivalents dans les langues additionnelles. Egalement appelé
Vocabulaire Electrotechnique International en ligne.
ƒ Service Clients: www.iec.ch/webstore/custserv/custserv_entry-f.htm
Si vous désirez nous donner des commentaires sur cette publication ou si vous avez des questions, visitez le FAQ du
Service clients ou contactez-nous:
Email: [e-mail]
Tél.: [phone]
Fax: [phone]

---------------------- Page: 2 ----------------------
IEC 61558-2-6
®
Edition 2.0 2009-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GROUP SAFETY PUBLICATION
PUBLICATION GROUPÉE DE SÉCURITÉ
Safety of transformers, reactors, power supply units and similar products for
supply voltages up to 1 100 V –
Part 2-6: Particular requirements and tests for safety isolating transformers and
power supply units incorporating safety isolating transformers

Sécurité des transformateurs, bobines d’inductance, blocs d'alimentation et
produits analogues pour des tensions d’alimentation jusqu'à 1 100 V –
Partie 2-6: Règles particulières et essais pour les transformateurs de sécurité et
les blocs d'alimentation incorporant des transformateurs de sécurité

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
N
CODE PRIX
ICS 29.180 ISBN 978-2-88910-541-0
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

---------------------- Page: 3 ----------------------
– 2 – 61558-2-6 © IEC:2009
CONTENTS
FOREWORD.3
1 Scope.5
2 Normative references .6
3 Terms and definitions .6
4 General requirements .6
5 General notes on tests .6
6 Ratings.6
7 Classification.7
8 Marking and other information .7
9 Protection against electric shock .7
10 Change of input voltage setting .7
11 Output voltage and output current under load .7
12 No-load output voltage .7
13 Short-circuit voltage .8
14 Heating .8
15 Short-circuit and overload protection .8
16 Mechanical strength .9
17 Protection against harmful ingress of dust, solid objects and moisture.9
18 Insulation resistance, dielectric strength and leakage current .9
19 Construction .9
20 Components .11
21 Internal wiring.11
22 Supply connection and other external flexible cable or cords .11
23 Terminals for external conductors.11
24 Provisions for protective earthing .11
25 Screws and connections .11
26 Creepage distances, clearances and distances through insulation.12
27 Resistance to heat, fire and tracking.12
28 Resistance to rusting.12
Annexes .13
Annex C Creepage distances (cr), clearances (cl) and distances through insulation
(dti) Material group II (400 ≤CTI <600) .13
Annex D Creepage distances (cr), clearances (cl) and distances through insulation
(dti) Material group I (CTI ≥600) .13
Annex R Explanations of the application of 4.2 of IEC 60664-1:2007 (see IEC 61558-1
Subclause 26.2).13
Bibliography.14

8
Table 101 – Output voltage difference .

---------------------- Page: 4 ----------------------
61558-2-6 © IEC:2009 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________

SAFETY OF TRANSFORMERS, REACTORS, POWER SUPPLY UNITS
AND SIMILAR PRODUCTS FOR SUPPLY VOLTAGES UP TO 1 100 V –

Part 2-6: Particular requirements and tests
for safety isolating transformers and power supply units
incorporating safety isolating transformers


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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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.
International standard IEC 61558-2-6 has been prepared by IEC technical committee 96:
Transformers, reactors, power supply units and similar products for low voltages up to
1 100 V.
This second edition cancels and replaces the first edition published in 1997. It constitutes a
technical revision. The main changes consist of updating this part in accordance with Part 1
(2005), and increasing the supply voltages up to 1 100 V to be in line with the standards of TC
14.
This part has the status of a group safety publication in accordance with IEC Guide 104:
(1997): The preparation of safety publications and the use of basic safety publications and
group safety publications.

---------------------- Page: 5 ----------------------
– 4 – 61558-2-6 © IEC:2009
The text of this standard is based on the following documents:
FDIS Report on voting
96/317/FDIS 96/322/RVD

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
This part is intended to be used in conjunction with the latest edition of IEC 61558-1 and its
amendments. It is based on the second edition (2005) of that standard.
This part supplements or modifies the corresponding clauses in IEC 61558-1, so as to convert
that publication into the IEC standard: Particular requirements and tests for safety isolating
transformers and power supply units incorporating safety isolating transformers.
A list of all parts of the IEC 61558 series can be found on the IEC website under the title:
Safety of transformers, reactors, power supply units and similar products for supply voltages
up to 1 100 V.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
Where a particular subclause of Part 1 is not mentioned in this part, that subclause applies as
far as is reasonable. Where this part states "addition", "modification" or "replacement", the
relevant text of Part 1 is to be adapted accordingly.
In this part, the following print types are used:
– requirements proper: in roman type;
– test specifications: in italic type;
– explanatory matter: in smaller roman type:
In the text of this part, the words in bold are defined in Clause 3.
Subclauses, notes, figures and tables additional to those in Part 1 are numbered starting from
101; supplementary annexes are entitled AA, BB, etc.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
NOTE The attention of National Committees is drawn to the fact that equipment manufacturers and testing
organizations may need a transitional period following publication of a new, amended or revised IEC publication in
which to make products in accordance with the new requirements and to equip themselves for conducting new or
revised tests.
It is the recommendation of the committee that the content of this publication be adopted for implementation
nationally not earlier than 12 months from the date of publication.

---------------------- Page: 6 ----------------------
61558-2-6 © IEC:2009 – 5 –
SAFETY OF TRANSFORMERS, REACTORS, POWER SUPPLY UNITS
AND SIMILAR PRODUCTS FOR SUPPLY VOLTAGES UP TO 1 100 V –

Part 2-6: Particular requirements and tests
for safety isolating transformers and power supply units
incorporating safety isolating transformers



1 Scope
Replacement:
This part of IEC 61558 deals with the safety of safety isolating transformers for general
applications and power supply units incorporating safety isolating transformers for
general applications. Transformers incorporating electronic circuits are also covered by this
standard.
NOTE 1 Safety includes electrical, thermal and mechanical aspects.
Unless otherwise specified, from here onward, the term transformer covers safety isolating
transformers for general applications and power supply units incorporating safety
isolating transformers for general applications.
NOTE 2 For power supply units (linear) this part is applicable. For switch mode power supply units, IEC 61558-2-16 is
applicable together with this part.
This part is applicable to stationary or portable, single-phase or polyphase, air-cooled
(natural or forced) independent or associated dry- type transformers. The windings may be
encapsulated or non-encapsulated.
The rated supply voltage does not exceed 1 100 V a.c., and the rated supply frequency
and the internal operating frequencies do not exceed 500 Hz.
The rated output does not exceed:
– 10 kVA for single-phase transformers;
– 16 kVA for polyphase transformers.
This part is applicable to transformers without limitation of the rated output subject to an
agreement between the purchaser and the manufacturer.
NOTE 3 Transformers intended to supply distribution networks are not included in the scope.
The no-load output voltage or the rated output voltage does not exceed 50 V a.c. or 120 V
ripple-free d.c.
This part 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 part are used in applications where double or reinforced
insulation between circuits is required by the installation rules or by the end product
standard.
NOTE 4 Attention is drawn to the following:
– 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;

---------------------- Page: 7 ----------------------
– 6 – 61558-2-6 © IEC:2009
– 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.
NOTE 5 Future technological development of transformers may necessitate a need to increase the upper limit of
the frequencies, until then this part may be used as a guidance document.
2 Normative references
This clause of Part 1 is applicable except as follows.
Addition:
IEC 61558-1 :2005, Safety of power transformers, power supplies, reactors and similar
products – Part 1: General requirements and tests
3 Terms and definitions
This clause of Part 1 is applicable.
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 50 V a.c. or 120 V ripple-free d.c.
6.102 The rated output shall not exceed:
– 10 kVA for single-phase transformers;
– 16 kVA for polyphase transformers.
Transformers without limitation of the rated output shall be subject to agreement between
the purchaser and the manufacturer.
6.103 The rated supply frequency and the internal operating frequencies shall not
exceed 500 Hz.
6.104 The rated supply voltage shall not exceed 1 100 V a.c.
Compliance with the requirements of 6.101 to 6.104 is checked by inspection of the marking.

---------------------- Page: 8 ----------------------
61558-2-6 © IEC:2009 – 7 –
7 Classification
This clause of Part 1 is applicable.
8 Marking and other information
This clause of Part 1 is applicable except as follows:
8.1 h) Replacement:
Replace the first sentence by the following: Relevant graphical symbols shown in 8.11
indicating the kind of transformer;
8.11 Addition:
Symbol or Explanation or title Identification
graphical symbol
Fail-safe safety isolating transformer 60417-5222

F

Non-short-circuit-proof safety isolating 60417-5946
transformer


Short-circuit-proof safety isolating transformer 60417-5947
(inherently or non-inherently)

9 Protection against electric shock
This clause of Part 1 is applicable.
10 Change of input voltage setting
This clause of Part 1 is applicable.
11 Output voltage and output current under load
This clause of Part 1 is applicable.
12 No-load output voltage
This clause of Part 1 is applicable except as follows:
Addition:
The no-load output voltage is measured when the transformer is connected to the rated
supply voltage at the rated supply frequency at ambient temperature.
12.101 The no-load output voltage shall not exceed 50 V a.c. or 120 V ripple-free d.c.

---------------------- Page: 9 ----------------------
– 8 – 61558-2-6 © IEC:2009
For independent transformers, this output voltage limitation applies even when output
windings, not intended for interconnection, are connected in series.
NOTE The requirement for series connection does not apply to associated or IP 00 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:
U −U
no-load load
×100 (%)
U
load
where U is the no-load output voltage and U is the output voltage under load.
no-load load
Compliance with the requirements 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.
The difference shall not exceed the values shown in Table 101.
Table 101 – Output voltage difference
Type of transformer Difference between no-load output voltage and
Rated output output voltage under load
VA %
Inherently short-circuit-proof transformers:
– up to and including 63 100
– over 63 up to and including 630 50
– over 630 20
Other transformers:
– up to and including 10 100
– over 10 up to and including 25 50
– over 25 up to and including 63 20
– over 63 up to and including 250 15
– over 250 up to and including 630 10
– over 630 5

13 Short-circuit voltage
This clause of Part 1 is applicable.
14 Heating
This clause of Part 1 is applicable.
15 Short-circuit and overload protection
This clause of Part 1 is applicable.

---------------------- Page: 10 ----------------------
61558-2-6 © IEC:2009 – 9 –
16 Mechanical strength
This clause of Part 1 is applicable.
17 Protection against harmful ingress of dust, solid objects and moisture
This clause of Part 1 is applicable.
18 Insulation resistance, dielectric strength and leakage current
This clause of Part 1 is applicable.
19 Construction
This clause of Part 1 is applicable except as follows:
Replace 19.1 of Part 1 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.
19.1.1 The insulation between input and output winding(s) shall consist of double or
reinforced insulation (rated for the working voltage) unless the requirements in 19.1.3 are
complied with.
In addition, the following applies:
– for class I transformers not intended for connection to the mains supply by means of
a plug, the insulation between the input windings and the body connected to earth
shall consist of at least basic insulation rated for the input voltage. The insulation
between the output windings and the body connected to earth, shall consist of at
least basic insulation (rated for the output voltage);
– for class I transformers intended for connection to the mains supply by means of a
plug, the insulation between the input windings and the body shall consist of at least
basic insulation, and the insulation between the output windings and the body shall
consist of at least supplementary insulation (both basic and supplementary
insulations rated for the working voltage);
– for class II transformers, the insulation between the input windings and the body
shall consist of double or reinforced insulation (rated for the input voltage). The
insulation between the output windings and the body, shall consist of double or
reinforced insulation (rated for the output voltage), for SELV circuits basic
insulation only is required.
19.1.2 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 following
requirements are applicable:
19.1.2.1 for class I and class II transformers, the insulation between the input and
output windings via the intermediate conductive parts shall consist of double or
reinforced insulation (rated for the working voltage);

---------------------- Page: 11 ----------------------
– 10 – 61558-2-6 © IEC:2009
– for class II transformers, the insulation between the input windings and the
body, and between the output windings and the body via the intermediate
conductive parts shall consist of double or reinforced insulation (rated for the
input and output voltage), for SELV circuits basic insulation only is required;
– for transformer different from independent (IP00), the insulation between the
input and output windings via the intermediate conductive parts shall consist
of double or reinforced insulation (rated for the working voltage).
19.1.2.2 as alternative to 19.1.2.1 for class I transformer not intended to be
connected by means of a plug and for transformer different from independent (IP00),
if the construction assure that all laminated plates of the iron core are connected to
earth (e.g by soldering / welding) and if in the data sheet or instruction sheet clearly
state that the safety of the transformer depends on the earth connection and that is
not possible to use in class II equipment, than the following apply: the insulation
between the input windings and the intermediate conductive part connected to
earth, and between the output windings and the intermediate conductive part
connected to earth, shall consist of at least basic insulation (rated for the input and
output voltage);
19.1.2.3 in addition to 19.1.2.1 and 19.1.2.2 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
input and output 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).
19.1.3 For class I transformers not intended for connection to the mains supply by means
...