IEC 60205:2016

Calculation of the effective parameters of magnetic piece parts

IEC 60205:2016 specifies uniform rules for the calculation of the effective parameters of closed circuits of ferromagnetic material. This edition includes the following significant technical changes with respect to the previous edition:
a) addition, in 5.1, of the drawing of a core of rectangular cross-section with chamfer;
b) addition, in 5.1.3, of the equation of a core of rectangular cross-section with chamfer;
c) equations in 5.1.4, 5.6, 5.7, 5.8, 5.9, 5.11, 5.12, 5.14 are amended or replaced;
d) drawings RM6-S and RM6-R in 5.7 are amended;
e) addition of EC-cores, see 5.15.
The contents of the corrigendum of July 2018 have been included in this copy.

Calcul des paramètres effectifs des pièces magnétiques

L'IEC 60205:2016 définit des règles uniformes pour le calcul des paramètres effectifs des circuits fermés de matériaux ferromagnétiques.
La présente édition inclut les modifications techniques majeures suivantes par rapport à l’édition précédente:
a) ajout, en 5.1, du dessin d’un noyau de section transversale rectangulaire avec chanfrein;
b) ajout, en 5.1.3, de l’équation d’un noyau de section transversale rectangulaire avec chanfrein;
c) les équations en 5.1.4, 5.6, 5.7, 5.8, 5.9, 5.11, 5.12, 5.14 sont amendées ou remplacées;
d) les dessins RM6-S et RM6-R en 5.7 sont amendés;
e) ajout de noyaux EC, voir 5.15.
Le contenu du corrigendum de juillet 2018 a été pris en considération dans cet exemplaire.

General Information

• Status: Published
• Publication Date: 17-Nov-2016
• ICS: 29.100.10 - Magnetic components
• Technical Committee: TC 51 - Magnetic components, ferrite and magnetic powder materials
• Drafting Committee: MT 1 - TC 51/MT 1
• Current Stage: PPUB - Publication issued
• Start Date: 18-Nov-2016
• Completion Date: 15-Jan-2017

Relations

• Corrected By: IEC 60205:2016/COR1:2018 - Corrigendum 1 - Calculation of the effective parameters of magnetic piece parts
• Effective Date: 05-Sep-2023
• Revises: IEC 60205:2006 - Calculation of the effective parameters of magnetic piece parts
• Effective Date: 05-Sep-2023
• Revises: IEC 60205:2006/AMD1:2009 - Amendment 1 - Calculation of the effective parameters of magnetic piece parts
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 60205 ®
Edition 4.0 2016-11
INTERNATIONAL
STANDARD
Calculation of the effective parameters of magnetic piece parts
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.

IEC Central Office Tel.: [phone]
3, rue de Varembé Fax: [phone]
CH-1211 Geneva 20 [e-mail]
Switzerland 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.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 20 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 15 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 65 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

CISPR.
IEC Just Published - webstore.iec.ch/justpublished

Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: [e-mail].
IEC 60205 ®
Edition 4.0 2016-11
INTERNATIONAL
STANDARD
Calculation of the effective parameters of magnetic piece parts

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.100.10 ISBN 978-2-8322-3775-5

– 2 – IEC 60205:2016 © IEC 2016
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions. 7
4 Basic rules applicable to this standard . 7
5 Formulae for the various types of cores . 8
5.1 Ring cores . 8
5.1.1 Ring cores in general . 8
5.1.2 For ring cores of rectangular cross-section with sharp corners . 9
5.1.3 For ring cores of rectangular cross-section with an appreciable average
rounding radius r . 9
5.1.4 For ring cores of rectangular cross-section with appreciable chamfer c . 9
5.1.5 For ring cores of trapezoidal cross-section with sharp corners . 9
5.1.6 For ring cores of trapezoidal cross-section with an appreciable average
rounding radius r . 9
5.1.7 For ring cores of cross-section with circular arc frontal sides . 9
5.2 Pair of U-cores of rectangular section . 10
5.3 Pair of U-cores of rounded section . 10
5.4 Pair of E-cores of rectangular section . 11
5.5 Pair of ETD/EER-cores . 12
5.6 Pair of pot-cores . 14
5.7 Pair of RM-cores . 16
5.8 Pair of EP-cores . 20
5.9 Pair of PM-cores . 21
5.10 Pair of EL-cores . 23
5.11 Pair of ER-cores (low profile) . 25
5.12 Pair of PQ-cores . 28
5.13 Pair of EFD-cores. 31
5.14 Pair of E planar-cores . 33
5.15 Pair of EC-cores . 34
Bibliography . 37

Figure 1 – Ring cores . 8
Figure 2 – Pair of U-cores of the rectangular section . 10
Figure 3 – Pair of U-cores of rounded section . 11
Figure 4 – Pair of E-cores of rectangular section . 12
Figure 5 – Pair of ETD/EER-cores . 13
Figure 6 – Pair of pot-cores . 14
Figure 7 – Pair of RM-cores . 18
Figure 8 – Pair of EP-cores . 20
Figure 9 – Pair of PM-cores . 22
Figure 10 – Pair of EL-cores . 23

Figure 11 – PLT(plate)-cores . 24
Figure 12 – Pair of ER-cores (low profile) . 26
Figure 13 – PLT(plate)-cores . 26
Figure 14 – Pair of PQ-cores . 28
Figure 15 – PQ-cores . 29
Figure 16 – PLT(plate)-cores . 29
Figure 17 – Pair of EFD-cores . 31
Figure 18 – Pair of E planar-cores . 33
Figure 19 – PLT(plate)-cores . 33
Figure 20 – Pair of EC-cores . 35

– 4 – IEC 60205:2016 © IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CALCULATION OF THE EFFECTIVE PARAMETERS
OF MAGNETIC PIECE PARTS
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.
International Standard IEC 60205 has been prepared by IEC technical committee 51: Magnetic
components, ferrite and and magnetic powder materials.
This fourth edition cancels and replaces the third edition published in 2006 and
Amendment 1:2009. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) addition, in 5.1, of the drawing of a core of rectangular cross-section with chamfer;
b) addition, in 5.1.3, of the equation of a core of rectangular cross-section with chamfer;
c) equations in 5.1.4, 5.6, 5.7, 5.8, 5.9, 5.11, 5.12, 5.14 are amended or replaced;
d) drawings RM6-S and RM6-R in 5.7 are amended;
e) addition of EC-cores, see 5.15.

The text of this standard is based on the following documents:
FDIS Report on voting
51/1149/FDIS 51/1156/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until
the stability date indicated on the IEC website under "http://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.
A bilingual version of this publication may be issued at a later date.
The contents of the corrigendum of July 2018 have been included in this copy.

– 6 – IEC 60205:2016 © IEC 2016
INTRODUCTION
The purpose of this revision is to provide formulae by which everybody can reach the same
effective parameter values. Firstly, it is necessary to have a sufficient number of significant
figures when figures are rounded off in the process of calculation. Additionally, some of the
calculation formulae have been changed to get closer to the actual shape.
In this revision, the basic idea of calculation has not been changed. Recently, analysis of the
magnetic field in the core has been considerably improved, so that, based on these ideas,
development of new approaches and formulae can be expected.
Furthermore, the new “EC-cores” have been added.
The parameters in the existing IEC standards will be revised with the outcome from the
formulae of this document.
CALCULATION OF THE EFFECTIVE PARAMETERS
OF MAGNETIC PIECE PARTS
1 Scope
This document specifies uniform rules for the calculation of the effective parameters of closed
circuits of ferromagnetic material.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
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
4 Basic rules applicable to this standard
4.1 All results shall be expressed in units based on millimetres, shall be accurate to three
significant figures, but to derive l , A , and V the values of C and C shall be calculated to
e e e 1 2
five significant figures. All angles are in radians.
NOTE The purpose of specifying this degree of accuracy is only to ensure that parameters calculated at different
establishments are identical and it is not intended to imply that the parameters are capable of being determined to
this accuracy.
4.2 A is the nominal value of the smallest cross-section. A is the geometrical cross-
min g
section of a ring core with rectangular shape. All the dimensions used to calculate A shall be
min
the mean values between the tolerance limits quoted on the appropriate piece part drawing. All
results shall be expressed in units based on millimetres, and shall be accurate to three
significant figures.
The minimum physical cross-section area A is given as: A = min (A )
min min i
NOTE A to be used for the measurement of the saturation flux density B on ring cores with rectangular cross-
g max
section.
4.3 Calculations are only applicable to the component parts of a closed magnetic circuit.
4.4 All dimensions used for the purpose of calculations shall be the mean value within the
tolerance limits quoted on the appropriate piece part drawing.
4.5 All irregularities in the outline of the core, such as small cut-outs, notches, chamfers, etc.
shall be ignored unless otherwise described.

– 8 – IEC 60205:2016 © IEC 2016
4.6 When the calculation involves the sharp corner of a piece part, then the mean length of
flux path for that corner shall be taken as the mean circular path joining the centres of area of
the two adjacent uniform sections, and the cross-sectional area associated with that length
shall be taken as the average area of the two adjacent uniform sections.
Calculation of effective parameters l , A and V .
e e e
The effective parameters can be defined as
2 3 2
l = C /C A = C / C V = l A = C / C
e 1 2 e 1 2 e e e 1 2
where
is the effective magnetic length of the core (mm);
l
e
A is the effective cross-sectional area (mm );
e
V is the effective volume (mm );
e
−1
C is the core constant (mm );
−3
C is the core constant (mm ).
5 Formulae for the various types of cores
5.1 Ring cores
5.1.1 Ring cores in general
Drawings of ring cores are shown in Figure 1.
X
α
β
c
r
r
4×
4×
r
ϕ
h
X h h h
X-X X-X X-X X-X
IEC
Figure 1 – Ring cores
2π
C =
h ln(d / d )
e 1 2
4π(1/ d − 1/ d )
2 1
C =
h ln (d / d )
e 1 2
d /2
d /2
c
d /2
d /2
5.1.2 For ring cores of rectangular cross-section with sharp corners
h = h
e
The geometrical cross-section of a ring core with rectangular shape A is given as:
g
d − d
2 1
A = h
g
5.1.3 For ring cores of rectangular cross-section with an appreciable average
rounding radius r
1,7168r
h = h(1− k ) k =
e 1 1
( )
h d − d
1 2
5.1.4 For ring cores of rectangular cross-section with appreciable chamfer c
4c
h = h(1− k ) k =
e 3 3
( )
h d − d
1 2
The geometrical cross-section of a ring core with appre
...

IEC 60205 ®
Edition 4.0 2016-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Calculation of the effective parameters of magnetic piece parts

Calcul des paramètres effectifs des pièces magnétiques

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 l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des
questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez
les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.

IEC Central Office Tel.: [phone]
3, rue de Varembé [e-mail]
CH-1211 Geneva 20 www.iec.ch
Switzerland
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 corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform IEC online collection - oc.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews. With a subscription you will always
committee, …). It also gives information on projects, replaced have access to up to date content tailored to your needs.
and withdrawn publications.
Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
The world's leading online dictionary on electrotechnology,
Stay up to date on all new IEC publications. Just Published
containing more than 22 000 terminological entries in English
details all new publications released. Available online and
and French, with equivalent terms in 18 additional languages.
once a month by email.
Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Customer Service Centre - webstore.iec.ch/csc
If you wish to give us your feedback on this publication or
need further assistance, please contact the Customer Service
Centre: [e-mail].
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) 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 IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.

Recherche de publications IEC - IEC online collection - oc.iec.ch
webstore.iec.ch/advsearchform Découvrez notre puissant moteur de recherche et consultez
La recherche avancée permet de trouver des publications IEC gratuitement tous les aperçus des publications. Avec un
en utilisant différents critères (numéro de référence, texte, abonnement, vous aurez toujours accès à un contenu à jour
comité d’études, …). Elle donne aussi des informations sur adapté à vos besoins.
les projets et les publications remplacées ou retirées.

Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
Le premier dictionnaire d'électrotechnologie en ligne au
Restez informé sur les nouvelles publications IEC. Just
monde, avec plus de 22 000 articles terminologiques en
Published détaille les nouvelles publications parues.
anglais et en français, ainsi que les termes équivalents dans
Disponible en ligne et une fois par mois par email.
16 langues additionnelles. Egalement appelé Vocabulaire

Electrotechnique International (IEV) en ligne.
Service Clients - webstore.iec.ch/csc

Si vous désirez nous donner des commentaires sur cette
publication ou si vous avez des questions contactez-nous:
[e-mail].
IEC 60205 ®
Edition 4.0 2016-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Calculation of the effective parameters of magnetic piece parts

Calcul des paramètres effectifs des pièces magnétiques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.100.10 ISBN 978-2-8322-9263-1

– 2 – IEC 60205:2016 © IEC 2016
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Basic rules applicable to this standard . 7
5 Formulae for the various types of cores . 8
5.1 Ring cores . 8
5.1.1 Ring cores in general . 8
5.1.2 For ring cores of rectangular cross-section with sharp corners . 9
5.1.3 For ring cores of rectangular cross-section with an appreciable average
rounding radius r . 9
5.1.4 For ring cores of rectangular cross-section with appreciable chamfer c . 9
5.1.5 For ring cores of trapezoidal cross-section with sharp corners . 9
5.1.6 For ring cores of trapezoidal cross-section with an appreciable average
rounding radius r . 9
5.1.7 For ring cores of cross-section with circular arc frontal sides . 9
5.2 Pair of U-cores of rectangular section . 10
5.3 Pair of U-cores of rounded section . 10
5.4 Pair of E-cores of rectangular section . 11
5.5 Pair of ETD/EER-cores . 12
5.6 Pair of pot-cores . 14
5.7 Pair of RM-cores . 16
5.8 Pair of EP-cores. 20
5.9 Pair of PM-cores . 21
5.10 Pair of EL-cores . 23
5.11 Pair of ER-cores (low profile) . 25
5.12 Pair of PQ-cores . 28
5.13 Pair of EFD-cores . 31
5.14 Pair of E planar-cores . 33
5.15 Pair of EC-cores . 34
Bibliography . 37

Figure 1 – Ring cores . 8
Figure 2 – Pair of U-cores of the rectangular section . 10
Figure 3 – Pair of U-cores of rounded section . 11
Figure 4 – Pair of E-cores of rectangular section . 12
Figure 5 – Pair of ETD/EER-cores . 13
Figure 6 – Pair of pot-cores . 14
Figure 7 – Pair of RM-cores . 18
Figure 8 – Pair of EP-cores . 20
Figure 9 – Pair of PM-cores . 22
Figure 10 – Pair of EL-cores . 23

Figure 11 – PLT(plate)-cores . 24
Figure 12 – Pair of ER-cores (low profile) . 26
Figure 13 – PLT(plate)-cores . 26
Figure 14 – Pair of PQ-cores . 28
Figure 15 – PQ-cores . 29
Figure 16 – PLT(plate)-cores . 29
Figure 17 – Pair of EFD-cores . 31
Figure 18 – Pair of E planar-cores . 33
Figure 19 – PLT(plate)-cores . 33
Figure 20 – Pair of EC-cores . 35

– 4 – IEC 60205:2016 © IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CALCULATION OF THE EFFECTIVE PARAMETERS
OF MAGNETIC PIECE PARTS
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.
International Standard IEC 60205 has been prepared by IEC technical committee 51:
Magnetic components, ferrite and and magnetic powder materials.
This fourth edition cancels and replaces the third edition published in 2006 and
Amendment 1:2009. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) addition, in 5.1, of the drawing of a core of rectangular cross-section with chamfer;
b) addition, in 5.1.3, of the equation of a core of rectangular cross-section with chamfer;
c) equations in 5.1.4, 5.6, 5.7, 5.8, 5.9, 5.11, 5.12, 5.14 are amended or replaced;
d) drawings RM6-S and RM6-R in 5.7 are amended;
e) addition of EC-cores, see 5.15.

The text of this standard is based on the following documents:
FDIS Report on voting
51/1149/FDIS 51/1156/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://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.
The contents of the corrigendum of July 2018 have been included in this copy.

– 6 – IEC 60205:2016 © IEC 2016
INTRODUCTION
The purpose of this revision is to provide formulae by which everybody can reach the same
effective parameter values. Firstly, it is necessary to have a sufficient number of significant
figures when figures are rounded off in the process of calculation. Additionally, some of the
calculation formulae have been changed to get closer to the actual shape.
In this revision, the basic idea of calculation has not been changed. Recently, analysis of the
magnetic field in the core has been considerably improved, so that, based on these ideas,
development of new approaches and formulae can be expected.
Furthermore, the new “EC-cores” have been added.
The parameters in the existing IEC standards will be revised with the outcome from the
formulae of this document.
CALCULATION OF THE EFFECTIVE PARAMETERS
OF MAGNETIC PIECE PARTS
1 Scope
This document specifies uniform rules for the calculation of the effective parameters of closed
circuits of ferromagnetic material.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
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
4 Basic rules applicable to this standard
4.1 All results shall be expressed in units based on millimetres, shall be accurate to three
significant figures, but to derive l , A and V the values of C and C shall be calculated to
e e e 1 2
five significant figures. All angles are in radians.
NOTE The purpose of specifying this degree of accuracy is only to ensure that parameters calculated at different
establishments are identical and it is not intended to imply that the parameters are capable of being determined to
this accuracy.
4.2 A is the nominal value of the smallest cross-section. A is the geometrical cross-
min g
section of a ring core with rectangular shape. All the dimensions used to calculate A shall
min
be the mean values between the tolerance limits quoted on the appropriate piece part drawing.
All results shall be expressed in units based on millimetres, and shall be accurate to three
significant figures.
The minimum physical cross-section area A is given as: A = min (A )
min min i
NOTE A to be used for the measurement of the saturation flux density B on ring cores with rectangular cross-
g max
section.
4.3 Calculations are only applicable to the component parts of a closed magnetic circuit.
4.4 All dimensions used for the purpose of calculations shall be the mean value within the
tolerance limits quoted on the appropriate piece part drawing.
4.5 All irregularities in the outline of the core, such as small cut-outs, notches, chamfers,
etc. shall be ignored unless otherwise described.

– 8 – IEC 60205:2016 © IEC 2016
4.6 When the calculation involves the sharp corner of a piece part, then the mean length of
flux path for that corner shall be taken as the mean circular path joining the centres of area of
the two adjacent uniform sections, and the cross-sectional area associated with that length
shall be taken as the average area of the two adjacent uniform sections.
Calculation of effective parameters l , A and V .
e e e
The effective parameters can be defined as
2 3 2
l = C /C A = C / C V = l A = C / C
e 1 2 e 1 2 e e e 1 2
where
is the effective magnetic length of the core (mm);
l
e
A is the effective cross-sectional area (mm );
e
V is the effective volume (mm );
e
−1
C is the core constant (mm );
−3
C is the core constant (mm ).
5 Formulae for the various types of cores
5.1 Ring cores
5.1.1 Ring cores in general
Drawings of ring cores are shown in Figure 1.
X
α
β
c0
r
r
4×
4×
r
ϕ
h
X h h h
X-X X-X X-X X-X
IEC
Figure 1 – Ring cores
2π
C =
h ln(d / d )
e 1 2
4π(1/ d − 1/ d )
2 1
C =
2 3
h ln (d / d )
e 1 2
d /2
d /2
c
d2/2
d /2
5.1.2 For ring cores of rectangular cross-section with sharp corners
h = h
e
The geometrical cross-section of a ring core with rectangular shape A is given as:
g
d − d
2 1
A = h
g
5.1.3 For ring cores of rectangular cross-section with an appreciable average
rounding radius r
1,7168r
h = h(1− k ) k =
e 1 1
h(d − d )
1 2
5.1.4 For ring cores of rectangular cross-section with appreciable chamfer c
4c
h = h(1− k ) k =
e 3 3
h(d − d )
1 2
The geometrical cross-section of a ring core with appreciable chamfer shape A is given as:
g
d − d
2 1
A = h − 2c
g 0
5.1.5 For ring cores of trapezoidal cross-section with sharp corners
h(tanα + tan β )
h = h(1− k ) k =
e 2 2
d − d
1 2
5.1.6 For ring cores of trapezoidal cross-section with an appreciable average
rounding radius r
h = h(1− k − k )
e 1 2
5.1.7 For ring cores of cross-section with circular arc frontal sides
d − d
 ϕ sinϕ ϕ 
1 2
h = h − 2sin − − 
e
2 2 2
 
4 sin (ϕ / 2)
d − d
1 2
ϕ = 2arcsin
4r
.
When the winding is uniformly distributed over a ring core, it may be expected that, at all
points inside the ring core, the flux lines will be parallel to its surface.
No leakage flux will therefore leave or enter the ring core. This justifies the use of a
theoretically more correct derivation of the effective parameters, which does not make use of
the assumption that the flux is uniformly distributed over the cross-section.

– 10 – IEC 60205:2016 © IEC 2016
5.2 Pair of U-cores of rectangular section
Drawings of a pair of U-cores of the rectangular section are shown in Figure 2.
q
l1
l″ l′
4 4
X
A1
Area
h
Y Y
A2
Area
A3
Area
l″ l′
5 5
X
Y-Y
l3
X-X
IEC
Figure 2 – Pair of U-cores of the rectangular section
Length of flux path associated with area A :
l = l′ + l′′
2 2 2
Mean length of flux paths at corners:
π
′ ′′
l = l + l = (p + h)
4 4 4
π
′ ′′
l = l + l = (s + h)
5 5 5
Mean areas associated with l and l :
4 5
A + A
1 2
A =
A + A
2 3
A =
5 5
l l
i i
C = C =
1 ∑ 2 ∑
A
i A
i=1 i=1 i
5.3 Pair of U-cores of rounded section
Drawings of a pair of U-cores of the rounded section are shown in Figure 3.

q
l″
l′
s p
l1
p
l″4 X l′
A
Area
h
Y Y
A2
Area
A
Area
Y-Y l′5
l″
5 X
s
l3
X-X
IEC
Figure 3 – Pair of U-cores of rounded section
In calculating A ignore any ridges introduced for the purpose of facilitating manufacture.
Length of flux path associated with area A :
l = l′ + l′′
2 2 2
Mean length of flux path at corners:
π
′ ′′
l = l + l = (p + h)
4 4 4
π
′ ′′
l = l + l = (s + h)
5 5 5
Mean areas associated with l and l :
4 5
A + A
1 2
A =
A + A
2 3
A =
5 5
l l
i i
C = C =
1 ∑ 2 ∑
A
i A
i
i=1 i=1
5.4 Pair of E-cores of rectangular section
Drawings of a pair of E-cores of the rectangular section are shown in Figure 4.

s
l″
l′
– 12 – IEC 60205:2016 © IEC 2016
w
l1
X
l
A
Area
Y Y
A
Area
l3
h
A
l
Area
A
Area
A
Area
Y-Y
X
X-X
IEC
Figure 4 – Pair of E-cores of rectangular section
Area of half the centre limb: A
Mean length of flux paths at corners:
π
l = (p + h)
d
π  
l =  + h
8 2
 
Mean areas associated with l and l :
4 5
A + A
1 2
A =
A + A
2 3
A =
5 5
l l
i i
C = C =
1 ∑ 2 ∑
A
i 2A
i=1 i=1 i
5.5 Pair of ETD/EER-cores
Drawings of a pair of ETD/EER-cores are shown in Figure 5.

w
l
p
d /2
b
l
X 1
l
Ac
Area
Y Y
A′3
Area
A″
l3
Area
h
l
A3
Area
A2
Area
A1
Area
Y-Y
X
X-X
IEC
Figure 5 – Pair of ETD/EER-cores
 1 
A is equal to the rectangle b a − c less the cap or segment A
1 c
 
 
1 b 1
2 2
 
A = d arcsin − b d − b
c 2 2
 
4 d 4
 
 
1 1 1 b
2 2
 
A = ab − b d − b − d arcsin
1 2 2
 
2 4 4 d
 
Mean length of flux path at back walls:
1 d
 
2 2
l = d + d − b −
 
2 2 2
4   2
NOTE l is taken from the mean value of (d − d ) and ( ) .
c − d / 2
2 2 3 3
Area of half the centre limb:
′ ′′
A = A + A
3 3 3
The condition to obtain A' = A" is
3 3
S = 0,2980d
1 3
Mean length of flux path at corners:
π
l = (p + h)
b
l
a
d
c
d /2
S
1 p
– 14 – IEC 60205:2016 © IEC 2016
a d
where p = − l −
2 2
π
l = (2S + h)
5 1
Mean areas associated with l and l :
4 5
A + A
1 2
A =
A + A
2 3
A =
5 5
l l
i i
C = C =
1 ∑ 2 ∑
A
2A
i
i=1 i=1 i
5.6 Pair of pot-cores
Drawings of a pair of pot-cores are shown in Figure 6.
l1 h
a
l′4
A″1
X l″
Area
A′1
Area
A
d1/2
Area
l
d /2
A6
Area
l″ l′
5 5
d /2
d /2
A″
Area
A′
Area
X
X-X
IEC
Figure 6 – Pair of pot-cores
Area of outer ring:
A = A′ + A′′
1 1 1
= A" is
The condition to obtain A'
1 1
d 1
2 2
S = − + (d + d )
1 1 2
2 8
Area of centre limb:
b
θ
l″ l″
2 6
S
S
l′ l′
2 6
′ ′′
A = A + A
3 3 3
The condition to obtain A' = A" is
3 3
d
2 2
S = − (d + d )
2 3 4
2 8
Area of ring:
2 2
A = (π − nθ )(d − d )
1 1 2
2b
θ = arcsin
d + d
1 2
where
b is the slot width;
n is the number of slots.
Core factors associated with l :
l
1 a
= ln
A πh d
2 3
l a − d
2 3
=
2 2 2
A π ad h
2 3
Area of centre limb:
π
2 2
A = (d − d )
3 3 4
Mean length of flux paths at corners:
π
′ ′′
l = l + l = (2S + h)
4 4 4 1
π
′ ′′
l = l + l = (2S + h)
5 5 2
Areas associated with l and l :
4 5
A for cores with back-wall slot:
1 h
2 2
A = (π − nθ )(d − d ) + (πd − nb)
4 1 2 2
8 2
A for cores without back-wall slot:
– 16 – IEC 60205:2016 © IEC 2016
1 π
2 2
A = (π − nθ )(d − d ) + d h
4 1 2 2
8 2
π
2 2
A = (d − d + 4d h)
5 3 4 3
Core factors associated with l :
l 1 d
6 2
= ln
A (π − nθ )h a
l d − a
6 2
=
2 2
A ad (π − nθ ) h
6 6
l l
i i
C = C =
1 ∑ 2 ∑
A
A
i
i=1 i=1 i
5.7 Pair of RM-cores
Drawings of a pair of RM-cores Type 1 through Type 4 are shown in Figure 7.
This calculation is also applicable to the core type without a hole.

Type 1 – RM6–S
l′4
A8
l″
X
p
ϕ
l
min
l
A7
A3
β
d /2
l″5
l′5
d3/2
lmax
d /2
e
X
h
l1
c
A1/2
X-X
IEC
Type 2 – RM7
A8
X
p
ϕ
lmin
A7
A
d /2
β
d3/2
lmax
d2/2
b
e
X
c
A1/2
IEC
Type 3 – RM4, RM5, RM8, RM10, RM12, RM14
A8
p ϕ
l
min A3
l′
max
d /2
β
l″max d3/2
d /2
e
c
A /2
l l′ l″
max = max + max
IEC
α
α
α
a
a
l″
a
l′
– 18 – IEC 60205:2016 © IEC 2016
Type 4 – RM6–R
A8
X
p
ϕ
l
min
A7
A3
β
d /2
d3/2
l
max
d /2
e
X
c
A1/2
IEC
Figure 7 – Pair of RM-cores
Total area of the outer leg:
1  π  β 1
 
2 2 2
A = a 1+ tan β −  − d − p
 
1 2
2 4 2 2
 
 
e
where β = α − arcsin
d
Core factors associated with l :
d
ln f
l d
2 3
=
A Dπh
l + l A
min max 7
where f = , D =
2l A
min 8
l = l′ + l′′
2 2 2
l (1 d − 1 d )f
2 3 2
=
2 2
A (Dπh)
Type 1, Type 4:
1 1
2 2
l = (d + d )− d d cos(α − β )
max 2 3 2 3
4 2
α
a
Type 2:
1   1 b
l = d + d  − d d cos(α − β ) −
max 2 2 3
ϕ
4 2
 
2sin
Type 3:
1 ϕ
l = [e tanβ − c(1− sin )]
max
ϕ
2tanβ ⋅ sin
Type 1:
 
1 β 1 1  ϕ  π
2 2
2 2
A = d + e tan β − e tan α − − d
 
 
7 2 3
4 2 2 2 2 4
 
 
Type 4:
1 β 1 1 ϕ π
 
2 2 2
A = d + d d sin(α − β ) + (c − d ) tan − d
 
7 2 2 3 3 3
4 2 2 2 2 4
 
Type 2:
 
1 β π 1  ϕ  1
2 2
2 2 2
A = d − d + (b − e )tan α − + e tan β
 
 
7 2 3
4 2 4 2 2 2
 
 
Type 3:
1 β π 1
 
2 2 2
A = d − d + c tan(α − β )
 
7 2 3
4 2 4 2
 
α
2 2
A = (d − d )
8 2 3
Area of centre pole:
π
2 2
A = (d − d )
3 3 4
Mean length of flux paths at corners and mean areas associated with these:
π 1 1
 
′ ′′
l = l + l = h + a − d 
4 4 4 2
4 2 2
 
A = (A + 2βd h)
4 1 2
– 20 – IEC 60205:2016 © IEC 2016
 
π 1
 
2 2
′ ′′
l = l + l = d + h − (d + d )
 
5 5 5 3 3 4
4 2
 
 
1 π
 
2 2
A = (d − d )+ 2αd h
 
5 3 4 3
2 4
 
5 5
l l
i i
C = C =
1 2
∑ ∑
A
i A
i=1 i=1 i
This calculation ignores the effect of spring recesses and stud recesses. These can have
some influence on the outcome of the calculation, especially for smaller cores.
5.8 Pair of EP-cores
Drawings of a pair of EP-cores are shown in Figure 8.
l1 l″
b 4
l′4
X
A3
l
d /2
α
d /2
l″
l′ 5
A
h2
c
h
X
X-X
IEC
Figure 8 – Pair of EP-cores
As a pair:
l h
1 2
=
A
ab − πd / 8 − d c
1 1
l h
1 2
=
2 2 2
A (ab − πd / 8 − d c)
1 1 1
l 2 d
2 1
= ln
A (π − α )(h − h ) d
2 1 2 2
a
l′
l″
l 4(d − d )
2 1 2
=
2 2 2
A (π − α ) (h − h ) d d
2 1 2 1 2
l h 4h
3 2 2
= =
2 2
A
3 πd
 d 
π 
 
l h 16h
3 2 2
= =
2 4 2 4
A π d
 d 
3 2
2 2
π
 
 
Areas associated with l and l :
4 5
π  d h − h 
1 1 2
l = l′ + l′′ = γ − +
 
4 4 4
2 2 4
 
2 2
(π − α )d + 2(ab − πd / 8 − d d / 2)
1 1 1 2
γ =
4(π − α )
where y is a hypothetical radius bisecting the cross-sectional area of the ring.
 d d h h 
1 π  
1 2 1 2
A = ab − d − + (π − α )d  − 
 
4 1 1
2 8 2 2 2
 
 
π d h − h
 
2 1 2
′ ′′
l = l + l = 0,292 89 + 
5 5 5
2 2 4
 
 
π d d
 
2 2
A = + (h − h )
 
5 1 2
2 4 2
 
 
5 5
l l
i i
C = C =
1 2
∑ ∑
A
A
i=1 i i=1 i
5.9 Pair of PM-cores
Drawings of a pair of PM-cores are shown in Figure 9.

– 22 – IEC 60205:2016 © IEC 2016
c
l″4
l
l′4 1
b
X
e
l3
d
ϕ
lmax
l″5
l′
β
d1
A7
A
α
h2
X
h1
X-X IEC
Figure 9 – Pair of PM-cores
Total area of the leg:
β
2 2
( )
A = d − d − 2bt
1 1 2
f
where β = α − arcsin
d
Core factors associated with l :
l = l′ + l′′
2 2 2
d
ln g
l d
2 3
=
A Dπ(h − h )/ 2
2 1 2
l + l A
min max 7
where g = , D =
2l A
min 8
1 1
2 2
l = (d + d )− d d cos(α − β )
max 2 3 2 3
4 2
l (1 d −1 d )g
2 3 2
=
2 2
A {Dπ(h − h ) 2}
2 1 2
β 1 1  ϕ  π
2 2
2 2
A = d + f tan β − f tan α − − d
 
7 2 3
8 8 8 2 16
 
l
min
t
ƒ
l′
l″ 2
d
d
d
α
2 2
A = (d − d )
8 2 3
Area of centre limb:
π
2 2
A = (d − d )
3 3 4
Mean length of flux paths at corners and mean areas associated with these:
π
′ ′′
l = l + l = (h − h + d − d )
4 4 4 1 2 1 2
A = {A + βd (h − h )}
4 1 2 1 2
h − h
π 1
2 2
1 2
′ ′′
l = l + l = {d + − (d + d ) }
5 5 5 3 3 4
4 2 2
π (h − h )
2 2
1 2
A = (d − d ) + αd
5 3 4 3
8 2
5 5
l l
i i
C = C =
1 ∑ 2 ∑
A
i A
i=1 i=1 i
5.10 Pair of EL-cores
Drawings of a pair of EL-cores and PLT(plate)-cores are shown in Figure 10 and Figure 11.
EL + PLT (plate)-cores use EL core formulae.
C B
l
D
F2
l
l
l5
R
IEC
Figure 10 – Pair of EL-cores
F
H
E
A
l
– 24 – IEC 60205:2016 © IEC 2016
C
B2
IEC
Figure 11 – PLT(plate)-cores
Area of outer leg:
1 1
 
2 2
A = (A − E)C − 4 R − πR
 
2 4
 
Mean length of flux path at outer leg:
l = D
Area of back wall:
A = (C + (F − F )+ πF /2)(B − D)
2 2 1 1
Mean length of flux at back wall:
 E F 
l =  − 
2 2
 
Area of centre limb:
1  1 
A = πF + (F − F )F
3  1 2 1 1
2 4
 
Mean length of flux path at centre limb:
l = D
Area of outside corner:
A + A
1 21
A =
where A = (B − D)C
A
Mean length of flux path at outside corner:
 
π  A E 
l =  − + (B − D)
 
 
8 2 2
 
 
Area of inside corner:
A + A
23 3
A =
where A = ((F −F ) + πF /2)(B − D)
23 2 1 1
Mean length of flux path at inside corner:
 
π A
l =  + (B − D)
 
8 F
 2 
5 5
l l
i i
C = C =
1 ∑ 2 ∑
A
2A
i
i=1 i=1 i
2 3 2
l = C /C A = C /C V = C /C
e 1 2 e 1 2 e 1 2
5.11 Pair of ER-cores (low profile)
Drawings of a pair of ER-cores (low profile) and PLT(plate)-cores are shown in Figure 12 and
Figure 13.
ER + PLT (plate)-cores use ER core formulae.

– 26 – IEC 60205:2016 © IEC 2016
B
l
C
D
l4
l3
l
A
A
A′ A′3
β
A″3
A″3
α
A
A 3
IEC
Figure 12 – Pair of ER-cores (low profile)
C
B2
IEC
Figure 13 – PLT(plate)-cores
Area of outer leg:
 
1 αE EG
 
A = C(A − G)− − sinα
 
2 4 4
 
where
α = arccos (G/E)
Mean length of flux path at outer leg:

G
F
E
A
A
S
S
l
l = D
Area of back wall:
A = C(B − D)
Mean length of flux path at back wall:
 2 2 
l = E + G + C − 2F
 
4  
Area of centre limb:
1  1 
A = πF
 
2 4
 
Mean length of flux path at centre limb:
l = D
Area of outside corner:
A + A
1 2
A =
Mean length of flux path at outside corner:
π
l = (p + h)
where
A E
h = B − D p = −
2 2
Area of inside corner:
A + A
2 3
A =
Mean length of flux path at inside corner:
π
l = (2S + h)
5 1
The condition to obtain A′ = A″ is
3 3
SF= 1−=cos β 0,29801F
( )
– 28 – IEC 60205:2016 © IEC 2016
5 5
l l
i i
C = C =
1 2
∑ ∑
A
2A
i=1 i i=1 i
2 3 2
l = C /C A = C /C V = C /C
e 1 2 e 1 2 e 1 2
5.12 Pair of PQ-cores
Drawings of a pair of PQ-cores and PLT(plate)-cores are shown in Figure 14, Figure 15 and
Figure 16.
PQ + PLT (plate)-cores use PQ core formulae.
NOTE 1 This calculation ignores the effect of spring recesses.
NOTE 2 The equations below are consistent with those given in IEC 62317-13.
′
″
l 4
A8 l
X 4
A
α
β
l3
l
max
′
″ l
l 5
A
L
A1/2
X
h
l1
D
C
B
X-X
IEC
d
x
x
IEC
Figure 14 – Pair of PQ-cores
Area of outer leg:
βE 1
A = C(A − G) − + GI
2 2
A
l
min
J
G
F
F/2
E
E/2
″
l
′
l
where
 G 
β = arccos
 
E
 
I = E sin β
Mean length of flux path at outer leg:
l = 2D
Core factors associated with l :
For l , A the elemental radius dr shown in Figure 15 is the elemental length of the flux path in
2 2
the integral below. The radius vector extends from F/2 to E/2 for the entire circle. The
effective length l for the section is multiplied by f. The area is the physical area multiplied by
2i
K.
r
dr
IEC
Figure 15 – PQ-cores
C B
IEC
Figure 16 – PLT(plate)-cores
E
l f f  E 
2i
= dr = ln
 
∫F
A K2πr(B − D) 2πK(B − D) F
 
E
A
F
– 30 – IEC 60205:2016 © IEC 2016
E E
l 2 fdx 2 f dx 1/ F −1/ E
2 2
= = = f
∫F ∫F
2 2 2 2 2 2
2πx
A [2Kπ(B − D)] x K π (B − D)
{2K [ (B − D)]}
2 2
where
A A
7 7
K = =
π
A
2 2
(E − F )
2 2
A = (βE − αF + GL − JI )
 L 
α = arctan
 
J
 
l + l
min max
f =
2l
min
2 2
E + F − 2EF cos(α − β )
l =
max
Define the other two physical areas in the flux path at back wall.
A = 2αF(B − D)
A = 2βE(B − D)
The mathematical area A is given as A > A > A .
2 10 2 9
Area of centre limb:
A = πF
Mean length of flux path at centre limb:
l = 2D
Area of outside corner:
1 1
A = (A + A ) = [A + 2E(B − D)β ]
4 1 10 1
2 2
Mean length of flux path at outside corner:
π 1 1
 
' "
l = l + l = (B − D) + A − E
 
4 4 4
4 2 2
 
Area of inside corner:
1 π  F 
A = (A + A ) = + F(B − D)α
 
5 3 9
2 2 2
 
Mean length of flux path at inside corner:
 
 
π 1
' "
 
 
l = l + l = (B − D) + 1− F
5 5 5
 
 
  

5 5
l l
i i
C = C =
1 2
∑ ∑
A
i A
i =1 i =1 i
The minimum physical cross-section area A is given as:
min
A = min (A , A , A , A , A )
min 1 3 4 5 9
2 3
C C C
1 1 1
l = A = V =
e e e
C C
2 2 C
5.13 Pair of EFD-cores
Drawings of a pair of EFD-cores are shown in Figure 17.
C
K B
l
F2
D
l
l3
l
IEC
Figure 17 – Pair of EFD-cores
Area of outer leg:
C(A − E)
A =
Mean length of flux path at outer leg:
l = D
F
E
A
q
l
– 32 – IEC 60205:2016 © IEC 2016
Area of back wall:
A = C(B − D)
Mean length of flux at back wall:
E − F
l =
Area of centre limb:
F F − 2q
1 2
A =
where q: chamfer
Mean length of flux path at centre limb:
l = D
Area of outside corner:
(A + A )
1 2
A =
Mean length of flux path at outside corner:
π A − E
 
l =  + (B − D)
8 2
 
Area of inside corner:
A + A
2 3
A =
Mean length of flux path at inside corner:
 
2 2
π  F C − F − 2K B − D 
   
1 2
l = +   +  
 
4 4 2 2
   
 
 
5 5
l l
i i
C = C =
1 2
∑ ∑
A
2A
i
i=1 i=1 i
2 3
C C
C
1 1
l = A = V =
e e e
C C
2 2 C
5.14 Pair of E planar-cores
Drawings of a pair of E planar-cores and PLT(plate)-cores are shown in Figure 18 and
Figure 19.
E planar + PLT (plate)-cores use E planar core formulae.
B
C
l
D
l
R1
l3
R2
l
IEC
Figure 18 – Pair of E planar-cores
B2
C
IEC
Figure 19 – PLT(plate)-cores
Area of outer leg:
C(A − E)  π 
2 2
A = − 4 R − R 
1 1 1
2 4
 
Mean length of flux path at outer leg:
l = D
Area of back wall:
( )
A = C B − D
F
E
A
A
l
– 34 – IEC 60205:2016 © IEC 2016
Mean length of flux at back wall:
E − F
l =
Area of centre limb:
FC π
2 2
A = − 2(R − R )
3 2 2
2 4
Mean length of flux path at centre limb:
l = D
Area of outside corner:
A + A
1 2
A =
Mean length of flux path at outside corner:
π A − E
 
l =  + (B − D)
8 2
 
Area of inside corner:
( )
A + A
2 3
A =
Mean length of flux path at inside corner:
π F
 
l =  + (B − D)
8 2
 
5 5
l l
i i
C = C =
1 2
∑ ∑
A
2A
i
i=1 i=1 i
2 3
C C C
1 1 1
l = A = V =
e e e
C C
C
2 2
5.15 Pair of EC-cores
Drawings of a pair of EC-cores are shown in Figure 20.

C
X
l1 S
l
AS
Area
A
c
Area
Y
Y
A′
Area
l3
A″3
Area
h l5
A3
Area
A2
Area
A1
Area
Y-Y
X-X
X
IEC
Figure 20 – Pair of EC-cores
 1 
A is equal to the rectangle C A − c less the segment A and the segment A .
1 c s
 
1  C  1
2 2 2
A = E arcsin  − C E − C
c
4 E 4
 
S(A − T − S) πS
A = +
S
2 8
1 1 1 C S(A − T − S) πS
 
2 2 2
A = AC − C E − C − E arcsin  − −
2 4 4 E 2 8
 
Mean length of flux path at back walls:
1 F
 
2 2
l = E + E − C −
 
4 2
 
NOTE l is taken from the mean value of and .
(c − F / 2)
( )
2 E − F
Area of half the centre limb:
′ ′′
A = A + A
3 3 3
The condition to obtain A' = A" is
3 3
S = 0,2980 F
C
l
A
T
E
c (small letter)
F/2
p
S
– 36 – IEC 60205:2016 © IEC 2016
Mean length of flux path at corners:
π
l = (p + h)
F
A
where p = − l −
2 2
π
l = (2S + h)
5 1
Mean areas associated with l and l :
4 5
A + A
1 2
A =
A + A
2 3
A =
5 5
l l
i i
C = C =
1 2
∑ ∑
A
i 2A
i=1 i=1 i
Bibliography
IEC 62317-13, Ferrite cores – Dimensions – Part 13: PQ-cores for use in power supply
applications
____________
– 38 – IEC 60205:2016 © IEC 2016
SOMMAIRE
AVANT-PROPOS . 40
INTRODUCTION . 42
1 Domaine d’application . 43
2 Références normatives . 43
3 Termes et définitions . 43
4 Règles fondamentales applicables à cette norme . 43
5 Formules pour les différents types de noyaux . 44
5.1 Noyaux toriques . 44
5.1.1 Noyaux toriques en général . 44
5.1.2 Pour les noyaux toriques de section transversale rectangulaire à angles
vifs . 45
5.1.3 Pour les noyaux toriques de section transversale rectangulaire avec un
rayon de l'arrondi moyen appréciable r . 45
5.1.4 Pour les noyaux toriques de section transversale rectangulaire avec
chanfrein appréciable c . 45
5.1.5 Pour les noyaux toriques de section transversale trapézoïdale à angles
vifs . 45
5.1.6 Pour les noyaux toriques de section transversale trapézoïdale avec un
rayon de l'arrondi moyen appréciable r . 45
5.1.7 Pour les noyaux toriques de section transversale à côtés frontaux à arc
circulaire. 45
5.2 Paire de noyaux U de section rectangulaire . 46
5.3 Paire de noyaux U de section circulaire . 46
5.4 Paire de noyaux E de section rectangulaire . 47
5.5 Paire de noyaux ETD/EER . 48
5.6 Paire de noyaux P.
...