IEC 60364-4-44:2007

IEC 60364-4-44 ®
Edition 2.1 2015-09
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Low-voltage electrical installations –
Part 4-44: Protection for safety – Protection against voltage disturbances and
electromagnetic disturbances
Installations électriques à basse tension –
Partie 4-44: Protection pour assurer la sécurité – Protection contre les
perturbations de tension et les perturbations électromagnétiques

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.: +41 22 919 02 11
3, rue de Varembé Fax: +41 22 919 03 00
CH-1211 Geneva 20 info@iec.ch
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 more than 30 000 terms and
Technical Specifications, Technical Reports and other definitions in English and French, with equivalent terms in 15
documents. Available for PC, Mac OS, Android Tablets and additional languages. Also known as the International
iPad. Electrotechnical 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 More than 60 000 electrotechnical terminology entries in
variety of criteria (reference number, text, technical English and French extracted from the Terms and Definitions
committee,…). It also gives information on projects, replaced clause of IEC publications issued since 2002. Some entries
and withdrawn publications. have been 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: csc@iec.ch.
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.

Catalogue IEC - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
Application autonome pour consulter tous les renseignements
Le premier dictionnaire en ligne de termes électroniques et
bibliographiques sur les Normes internationales,
électriques. Il contient plus de 30 000 termes et définitions en
Spécifications techniques, Rapports techniques et autres
anglais et en français, ainsi que les termes équivalents dans
documents de l'IEC. Disponible pour PC, Mac OS, tablettes
15 langues additionnelles. Egalement appelé Vocabulaire
Android et iPad.
Electrotechnique International (IEV) en ligne.

Recherche de publications IEC - www.iec.ch/searchpub
Glossaire IEC - std.iec.ch/glossary
La recherche avancée permet de trouver des publications IEC Plus de 60 000 entrées terminologiques électrotechniques, en
en utilisant différents critères (numéro de référence, texte, anglais et en français, extraites des articles Termes et
comité d’études,…). Elle donne aussi des informations sur les Définitions des publications IEC parues depuis 2002. Plus
projets et les publications remplacées ou retirées. certaines entrées antérieures extraites des publications des

CE 37, 77, 86 et CISPR de l'IEC.
IEC Just Published - webstore.iec.ch/justpublished

Service Clients - webstore.iec.ch/csc
Restez informé sur les nouvelles publications IEC. Just
Published détaille les nouvelles publications parues. Si vous désirez nous donner des commentaires sur cette
Disponible en ligne et aussi une fois par mois par email. publication ou si vous avez des questions contactez-nous:
csc@iec.ch.
IEC 60364-4-44 ®
Edition 2.1 2015-09
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Low-voltage electrical installations –

Part 4-44: Protection for safety – Protection against voltage disturbances and

electromagnetic disturbances
Installations électriques à basse tension –

Partie 4-44: Protection pour assurer la sécurité – Protection contre les

perturbations de tension et les perturbations électromagnétiques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.100.10; 33.100.20; 91.140.50 ISBN 978-2-8322-2916-3

IEC 60364-4-44 ®
Edition 2.1 2015-09
CONSOLIDATED VERSION
REDLINE VERSION
VERSION REDLINE
colour
inside
Low-voltage electrical installations –
Part 4-44: Protection for safety – Protection against voltage disturbances and
electromagnetic disturbances
Installations électriques à basse tension –
Partie 4-44: Protection pour assurer la sécurité – Protection contre les
perturbations de tension et les perturbations électromagnétiques

– 2 – IEC 60364-4-44:2007+AMD1:2015 CSV
© IEC 2015
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
440.1 Scope . 8
440.2 Normative references . 8
441 (Vacant) . 9
442 Protection of low-voltage installations against temporary overvoltages due to earth
faults in the high-voltage system and due to faults in the low-voltage system . 9
442.1 Field of application . 9
442.1.1 General requirements . 10
442.1.2 Symbols . 10
442.2 Overvoltages in LV-systems during a high-voltage earth fault . 11
442.2.1 Magnitude and duration of power-frequency fault voltage . 12
442.2.2 Magnitude and duration of power-frequency stress voltages . 13
442.2.3 Requirements for calculation of limits . 14
442.3 Power-frequency stress voltage in case of loss of the neutral conductor in a
TN and TT system . 14
442.4 Power-frequency stress voltage in the event of an earth fault in an IT
system with distributed neutral . 14
442.5 Power-frequency stress voltage in the event of a short-circuit between a line
conductor and the neutral conductor . 15
443 Protection against transient overvoltages of atmospheric origin or due to switching . 15
443.1 General . 15
443.2 Classification of impulse withstand voltages (overvoltage categories) .
443.2.1 Purpose of classification of impulse withstand voltages
(overvoltage categories) .
443.2 Void . 16
443.3 Arrangements for overvoltage control .
443.3.1 Inherent overvoltage control .
443.3.2 Protective overvoltage control .
443.3 Terms and definitions . 16
443.4 Required impulse withstand voltage of equipment.
443.4 Overvoltage control . 17
443.5 Risk assessment method . 17
443.6 Classification of rated impulse voltages (overvoltage categories) . 19
443.6.1 Purpose of classification of rated impulse voltages (overvoltage
categories) . 19
443.26.2 Relationship between impulse withstand Rated impulse voltages of
equipment and overvoltage categories . 20
444 Measures against electromagnetic influences . 23
444.1 General . 23
444.2 (void) . 24
444.3 Definitions . 24
444.4 Mitigation of electromagnetic interference (EMI) . 25
444.4.1 Sources of EMI. 25
444.4.2 Measures to reduce EMI . 25
444.4.3 TN-system . 27
444.4.4 TT system . 31

© IEC 2015
444.4.5 IT system . 32
444.4.6 Multiple-source supply . 33
444.4.7 Transfer of supply . 36
444.4.8 Services entering a build ing . 38
444.4.9 Separate buildings . 39
444.4.10 Inside buildings . 39
444.4.11 Protective devices . 41
444.4.12 Signal cables . 41
444.5 Earthing and equipotential bonding . 41
444.5.1 Interconnection of earth electrodes . 41
444.5.2 Interconnection of incoming networks and earthing arrangements . 42
444.5.3 Different structures for the network of equipotential conductors and
earthing conductors . 42
444.5.4 Equipotential bonding networks in buildings with several floors . 44
444.5.5 Functional earthing conductor . 45
444.5.6 Commercial or industrial buildings containing significant amounts
of information technology equipm ent. 46
444.5.7 Earthing arrangements and equipotential bonding of information
technology installations for functional purposes . 46
444.6 Segregation of circuits . 47
444.6.1 General . 47
444.6.2 Design guidelines . 47
444.6.3 Installation guidelines . 48
444.7 Cable management systems . 49
444.7.1 General . 49
444.7.2 Design guidelines . 49
444.7.3 Installation guidelines . 50
445 Protection against undervoltage . 52
445.1 General requirements . 52

Annex A (informative) Explanatory notes concerning 442.1 and 442.2 .
Annex A (informative) Examples of calculated risk level CRL for the use of SPDs . 55
Annex B (informative) Guidance for on overvoltage control by SPDs applied to
overhead lines . 57
Annex C (normative) Determination of the conventional length, d .
Annex C (informative) List of notes concerning certain countries . 61
Bibliography . 63

Figure 44.A1 – Representative schematic sketch for possible connections to earth in
substation and LV-installation and occurring overvoltages in case of faults . 11
Figure 44.A2 – Tolerable fault voltage due to an earth-fault in the HV system . 13
Figure 443.1 – Illustration of an installation showing the lengths to consider . 19
Figure 44.R1 – By-pass conductor for screen reinforcement to provide a common
equipotential bonding system . 26
Figure 44.R2 − Example of a substitute or by-pass equipotential bonding conductor in a
TT-system . 27
Figure 44.R3A − Avoidance of neutral conductor currents in a bonded structure by
using the TN-S system from the origin of the public supply up to and including the final
circuit within a building . 28

– 4 – IEC 60364-4-44:2007+AMD1:2015 CSV
© IEC 2015
Figure 44.R3B – Avoidance of neutral conductor currents in a bonded structure by using
a TN-S system downstream of a consumer’s private supply transformer . 29
Figure 44.R4 − TN-C-S system within an existing building installation . 30
Figure 44.R5 – TT system within a building installation . 31
Figure 44.R6 – IT system within a building installation . 32
Figure 44.R7A – TN multiple-source power supply with a non-suitable multiple
connection between PEN and earth . 33
Figure 44.R7B – TN multiple source power supplies to an installation with connection to
earth of the star points at one and the same point . 34
Figure 44.R8 – TT multiple-source power supplies to an installation with connection to
earth of the star points at one and the same point . 35
Figure 44.R9A − Three-phase alternative power supply with a 4-pole switch . 36
Figure 44.R9B – Neutral current flow in a three-phase alternative power supply with an
unsuitable 3-pole switch . 37
Figure 44.R9C − Single-phase alternative power supply with 2-pole switch . 38
Figure 44.R10 − Armoured cables and metal pipes entering the buildings (examples) . 39
Figure 44.R11 − Illustration of measures in an existing building . 40
Figure 44.R12 – Interconnected earth elec tr odes . 41
Figure 44.R13 – Examples of protective conductors in star network . 42
Figure 44.R14 – Example of multiple meshed bonding star network . 43
Figure 44.R15 – Example of a common meshed bonding star network . 44
Figure 44.R16 – Example of equipotential bonding networks in structures without
lightning protection systems . 45
Figure 44.R17A − Separation between power and information technology cables for
cable route lengths ≤ 35 m . 48
Figure 44.R17B − Separation between power and information technology cables for
cable route lengths > 35 m . 48
Figure 44.R18 – Separation of cables in wiring systems . 49
Figure 44.R19 – Cable arrangements in metal cable-trays . 50
Figure 44.R20 – Continuity of metallic system components . 51
Figure 44.R21 – Location of cables inside metallic construction elements . 51
Figure 44.R22 – Connection of metallic sections . 52
Figure 44.Q – Examples of how to apply d1, d2 and d3 for the determination of d .

Table 44.A1 – Power-frequency stress voltages and power-frequency fault voltage in
low-voltage s ys tem . 12
Table 44.A2 – Permissible power-frequency stress voltage . 14
Table 443.1 – Calculation of f . 18
env
Table 44.B 443.2 – Required rated impulse withstand voltage of equipment U . 23
W
Table B.1 – Different possibilities for IT systems.

© IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_______________
LOW-VOLTAGE ELECTRICAL INSTALLATIONS –
Part 4-44: Protection for safety –
Protection against voltage disturbances and
electromagnetic disturbances
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.
This consolidated version of the official IEC Standard and its amendment has been prepared
for user convenience.
IEC 60364-4-44 edition 2.1 contains the second edition (2007-08) [documents 64/1600/FDIS and
64/1609/RVD] and its amendment 1 (2015-09) [documents 64/2032/FDIS and 64/2073/RVD].
In this Redline version, a vertical line in the margin shows where the technical content is
modified by amendment 1. Additions are in green text, deletions are in strikethrough red text. A
separate Final version with all changes accepted is available in this publication.

– 6 – IEC 60364-4-44:2007+AMD1:2015 CSV
© IEC 2015
International Standard IEC 60364-4-44 has been prepared by IEC technical committee 64:
Electrical installations and protection against electric shock.
The document 64/1600/FDIS, circulated to the National Committees as Amendment 3, led to
the publication of the new edition.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 60364 series, under the general title Low-voltage electrical
installations, 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.
The reader's attention is drawn to the fact that Annex C lists all of the “in-some-country”
clauses on differing practices of a less permanent nature relating to the subject of this
standard.
The committee has decided that the contents of the base publication and its amendment will
remain unchanged until the stability date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
The contents of the corrigenda of May 2010 and October 2011 have been included in this
copy.
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.

© IEC 2015
INTRODUCTION
Part 4-44 of IEC 60364 covers the protection of electrical installations and measures against
voltage disturbances and electromagnetic disturbances.
The requirements are arranged into four clauses as follows:
Clause 442 Protection of low-voltage installations against temporary overvoltages due to
earth faults in the high-voltage system and due to faults in the low-voltage
system
Clause 443 Protection against overvoltages of atmospheric origin or due to switching
Clause 444 Measures against electromagnetic influences
Clause 445 Protection against undervoltage

– 8 – IEC 60364-4-44:2007+AMD1:2015 CSV
© IEC 2015
LOW-VOLTAGE ELECTRICAL INSTALLATIONS –

Part 4-44: Protection for safety –
Protection against voltage disturbances and
electromagnetic disturbances
440.1 Scope
The rules of this Part of IEC 60364 are intended to provide requirements for the safety of
electrical installations in the event of voltage disturbances and electromagnetic disturbances
generated for different specified reasons.
The rules of this part are not intended to apply to systems for distribution of energy to the
public, or power generation and transmission for such systems (see the scope of IEC 60364-1)
although such disturbances may be conducted into or between electrical installations via these
supply systems.
440.2 Normative references
The following referenced documents are indispensable for the application 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 60038:1983 2009, IEC standard voltages
IEC 60050-604:1987, International Electrotechnical Vocabulary – Chapter 604: Generation,
transmission and distribution of electricity – Operation
IEC 60364-1, Low-voltage electrical installations – Part 1: Fundamental principles, assessment
of general characteristics, definitions
IEC 60364-4-41:2005, Electrical installations of buildings – Part 4-41: Protection for safety –
Protection against electric shock
IEC 60364-5-53:2001, Electrical installations of buildings - Part 5-53: Selection and erection of
electrical equipment - Isolation, switching and control
IEC 60364-5-53:2001/AMD1:2002
IEC 60364-5-53:2001/AMD2:2015
IEC 60364-5-54:2002, Electrical installations of buildings − Part 5-54: Selection and erection of
electrical equipment – Earthing arrangements and protective bonding conductors
IEC 60479-1:2005, Effects of current on human beings and livestock – Part 1: General aspects
IEC 60664-1:2007, Insulation co-ordination for equipment within low-voltage systems – Part 1:
Principles, requirements and tests
IEC 60950-1, Information technology equipment – Safety – Part 1: General requirements
IEC 61000-2-5:1995, Electromagnetic compatibility (EMC) − Part 2: Environment − Section 5:
Classification of electromagnetic environments – Basic EMC publication
IEC 61000-6-1, Electromagnetic compatibility (EMC) – Part 6-1: Generic standards – Immunity
for residential, commercial and light-industrial environments
___________
A third edition is currently in preparation.

© IEC 2015
IEC 61000-6-2, Electromagnetic compatibility (EMC) – Part 6-2: Generic standards – Immunity
for industrial environments
IEC 61000-6-3, Electromagnetic compatibility (EMC) – Part 6-3: Generic standards – Emission
standard for residential, commercial and light-industrial environments
IEC 61000-6-4, Electromagnetic compatibility (EMC) – Part 6-4: Generic standards – Emission
standard for industrial environments

IEC 61558-2-1, Safety of power transformers, power supplies, reactors and similar products –
Part 2-1: Particular requirements for tests for separating transformers and power supplies
incorporating separating transformers for general applications
IEC 61558-2-4, Safety of power transformers, power supply units and similar – Part 2-4:
Particular requirements for isolating transformers for general use
IEC 61558-2-6, Safety of power transformers, power supply units and similar – Part 2-6:
Particular requirements for safety isolating transformers for general use
IEC 61558-2-15, Safety of power transformers, power supply units and similar – Part 2-15:
Particular requirements for isolating transformers for the supply of medical locations
IEC 61643 (all parts), Low-voltage surge protective devices
IEC 61643-11:2011, Low-voltage surge protective devices – Part 11: Surge protective devices
connected to low-voltage power systems – Requirements and test methods
IEC 61643-22, Low-voltage surge protective devices – Part 22: Surge protective devices
connected to telecommunications and signalling networks – Selection and application
principles
IEC 61936-1, Power installations exceeding 1 kV a.c. – Part 1: Common rules
IEC 62305 (all parts), Protection against lightning
IEC 62305-1, Protection against lightning – Part 1: General principles
IEC 62305-3, Protection against lightning – Part 3: Physical damage to structures and life
hazard
IEC 62305-4, Protection against lightning – Part 4: Electrical and electronic systems within
structures
441 (Vacant)
442 Protection of low-voltage installations against temporary overvoltages due
to earth faults in the high-voltage system and due to faults in the low-
voltage system
442.1 Field of application
The rules of this clause provide requirements for the safety of low-voltage installation in the
event of
– a fault between the high-voltage system and earth in the transformer substation that
supplies the low-voltage installation,
– a loss of the supply neutral in the low-voltage system,

– 10 – IEC 60364-4-44:2007+AMD1:2015 CSV
© IEC 2015
– a short-circuit between a line conductor and neutral,
– an accidental earthing of a line conductor of a low-voltage IT-system.
The requirements for the earthing arrangement at the transformer substation are given in
IEC 61936-1.
442.1.1 General requirements
As Clause 442 covers faults between a high-voltage line and the earth in the HV/LV substation,
it gives rules for the designer and installer of the substation. It is necessary to have the
following information concerning the high-voltage system:
– quality of the system earthing;
– maximum level of earth fault current;
– resistance of the earthing arrangement.
The following subclauses consider four situations as proposed in 442.1, which generally cause
the most severe temporary overvoltages such as defined in IEC 60050-604:
– fault between the high-voltage system(s) and earth (see 442.2);
– loss of the neutral in a low-voltage system (see 442.3);
– accidental earthing of a low-voltage IT system (see 442.4);
– short-circuit in the low-voltage installation (see 442.5).
442.1.2 Symbols
In Clause 442 the following symbols are used (see Figure 44.A1):
I part of the earth fault current in the high-voltage system that flows through the earthing
E
arrangement of the transformer substation.
R resistance of the earthing arrangement of the transformer substation.
E
resistance of the earthing arrangement of the exposed-conductive-parts of the
R
A
equipment of the low-voltage installation.
R resistance of the earthing arrangement of the low-voltage system neutral, for low-
B
voltage systems in which the earthing arrangements of the transformer substation and
of the low-voltage system neutral are electrically independent.
U in TN- and TT-systems: nominal a.c. r.m.s. line voltage to earth
o
in IT-systems: nominal a.c. voltage between line conductor and neutral conductor or
mid point conductor, as appropriate
U power-frequency fault voltage that appears in the low-voltage system between exposed-
f
conductive-parts and earth for the duration of the fault.
U power-frequency stress voltage between the line conductor and the exposed-
conductive-parts of the low-voltage equipment of the transformer substation during the
fault.
U power-frequency stress voltage between the line conductor and the exposed-
conductive-parts of the low-voltage equipment of the low-voltage installation during the
fault.
NOTE 1 The power-frequency stress voltage (U and U ) is the voltage that appears across the insulation of low-
1 2
voltage equipment and across surge protective devices connected to the low-voltage system.

© IEC 2015
The following additional symbols are used in respect of IT-systems in which the exposed-
conductive-parts of the equipment of the low-voltage installation are connected to an earthing
arrangement that is electrically independent of the earthing arrangement of the transformer
substation.
I fault current that flows through the earthing arrangement of the exposed-conductive-
h
parts of the equipment of the low-voltage installation during a period when there is a
high-voltage fault and a first fault in the low-voltage installation (see Table 44.A1).
I fault current, in accordance with 411.6.2, that flows through the earthing arrangement
d
of the exposed-conductive-parts of the low-voltage installation during the first fault in a
low-voltage system (see Table 44.A1).
Z impedance (e.g. IMD internal impedance, artificial neutral impedance) between the low-
voltage system and an earthing arrangement.
NOTE 2 An earthing arrangement may be considered electrically independent of another earthing arrangement if a
rise of potential with respect to earth in one earthing arrangement does not cause an unacceptable rise of potential
with respect to earth in the other earthing arrangement. See IEC 61936-1.
442.2 Overvoltages in LV-systems during a high-voltage earth fault
In case of a fault to earth on the HV-side of the substation, the following types of overvoltage
may affect the LV-installation:
• power frequency fault-voltage (U );
f
• power frequency stress-voltages (U and U ).
1 2
Table 44.A1 provides the relevant methods of calculation for the different types of
overvoltages.
NOTE 1 Table 44.A1 deals with IT systems with a neutral point only. For IT systems with no neutral point, the
formulae should be adjusted accordingly.

Substation U
LV Installation
U
HV LV
L1
L2
L3
or N or PEN
Z
I R R R U
E E B A f
IEC  1379/07
Figure 44.A1 – Representative schematic sketch for possible connections to earth
in substation and LV-installation and occurring overvoltages in case of faults

– 12 – IEC 60364-4-44:2007+AMD1:2015 CSV
© IEC 2015
Where high- and low-voltage earthing systems exist in proximity to each other, two practices
are presently used:
– interconnection of all high-voltage (R ) and low-voltage (R ) earthing systems;
E B
– separation of high-voltage (R ) from low-voltage (R ) earthing systems.
E B
The general method used is interconnection. The high- and low-voltage earthing systems shall
be interconnected if the low-voltage system is totally confined within the area covered by the
high-voltage earthing system (see IEC 61936-1).
NOTE 2 Details of the different types of system earthing (TN, TT, IT) are shown in IEC 60364-1.
Table 44.A1 – Power-frequency stress voltages and power-frequency fault
voltage in low-voltage system
Types of
Types of earth
system U U U
1 2 f
connections
earthing
R and R connected U *) 0 *)
R × I + U
E B o
E E o
TT
R and R separated R × I + U U *) 0 *)
E B
E E o o
R and R connected U *) U *) R × I **)
E B
o o E E
TN
R and R separated U *) 0 *)
E B R × I + U
o
E E o
U *) 0 *)
R × I + U
o
E E o
R and Z connected
E
R and R separated
E A
R × I
U × 3 R × I + U × 3
A h
o E E o
U *) U *) R × I
o o E E
R and Z connected
E
IT R and R interconnected
E A
R × I
U × 3 U × 3
E E
o o
R × I + U U *) 0 *)
E E o o
R and Z separated
E
R and R separated
E A
R × I
R × I + U × 3 U × 3
A d
E E o o
*) No consideration needs to be given.
**) See 442.2.1 second paragraph.
With existing earth fault in the installation.

NOTE 3 The requirements for U and U are derived from design criteria for insulation of low-voltage equipment
1 2
with regard to temporary power-frequency overvoltage (see also Table 44.A2).
NOTE 4 In a system whose neutral is connected to the earthing arrangement of the transformer substation, such
temporary power-frequency overvoltage is also to be expected across insulation which is not in an earthed
enclosure when the equipment is outside a building.
NOTE 5 In TT- and TN-systems the statement “connected” and “separated” refers to the electrical connection
between R and R . For IT-systems it refers to the electrical connection between R and Z and the connection
E B E
between RE and RA.
442.2.1 Magnitude and duration of power-frequency fault voltage
The magnitude and the duration of the fault voltage U (as calculated in Table 44.A1) which
f
appears in the LV installation between exposed-conductive-parts and earth, shall not exceed
the values given for U by the curve of Figure 44.A2 for the duration of the fault.
f
© IEC 2015
Normally, the PEN conductor of the low-voltage system is connected to earth at more than one
point. In this case, the total resistance is reduced. For these multiple grounded PEN
conductors, U can be calculated as:
f
U = 0,5 R ×I
f E E
Fault voltage duration
1 200
1 100
1 000
10 100 1 000 10 000
Time of duration t  (ms)
IEC  1380/07
Figure 44.A2 – Tolerable fault voltage due to an earth-fault in the HV system
NOTE The curve shown in Figure 44.A2 is taken from IEC 61936-1. On the basis of probabilistic and statistical
evidence this curve represents a low level of risk for the simple worst case where the low voltage system neutral
conductor is earthed only at the transformer substation earthing arrangements. Guidance is provided in
IEC 61936-1 concerning other situations.
442.2.2 Magnitude and duration of power-frequency stress voltages
The magnitude and the duration of the power-frequency stress voltage (U and U ) as
1 2
calculated in Table 44.A1 of the low-voltage equipment in the low-voltage installation due to an
earth fault in the high-voltage system shall not exceed the requirements given in Table 44.A2.

Fault voltage U (V)
f
– 14 – IEC 60364-4-44:2007+AMD1:2015 CSV
© IEC 2015
Table 44.A2 – Permissible power-frequency stress voltage
Duration of the earth fault in the Permissible power-frequency stress voltage on equipment
high-voltage system in low-voltage installations
t U
>5 s U + 250 V
o
≤5 s U + 1 200 V
o
In systems without a neutral conductor, U shall be the line-to-line voltage.
o
NOTE 1 The first line of the table relates to high-voltage systems having long disconnection times, for example,
isolated neutral and resonant earthed high-voltage systems. The second line relates to high-voltage systems
having short disconnection times, for example low-impedance earthed high-voltage systems. Both lines together
are relevant design criteria for insulation of low-voltage equipment with regard to temporary power frequency
overvoltage, see IEC 60664-1.
NOTE 2 In a system whose neutral is connected to the earthing arrangement of the transformer substation,
such temporary power-frequency overvoltage is also to be expected across insulation which is not in an earthed
enclosure when the equipment is outside a building.
442.2.3 Requirements for calculation of limits
Where required by Table 44.A1, the permissible power-frequency stress voltage shall not
exceed the value given in Table 44.A2.
Where required by Table 44.A1, the permissible power-frequency fault voltage shall not exceed
the value given in Figure 44.A2.
The requirements of 442.2.1 and 442.2.2 are deemed to be fulfilled for installations receiving a
supply at low-voltage from a public electricity distribution system.
To fulfil the above requirements, coordination between the HV-system operator and the LV-
system installer is necessary. Compliance with the above requirements mainly falls into the
res
...

IEC 60364-4-44 ®
Edition 2.2 2018-01
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Low-voltage electrical installations –
Part 4-44: Protection for safety – Protection against voltage disturbances and
electromagnetic disturbances
Installations électriques à basse tension –
Partie 4-44: Protection pour assurer la sécurité – Protection contre les
perturbations de tension et les perturbations électromagnétiques

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.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
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 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 21 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.

IEC publications search - webstore.iec.ch/advsearchform IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 67 000 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: sales@iec.ch.
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.

Catalogue IEC - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
Application autonome pour consulter tous les renseignements
Le premier dictionnaire en ligne de termes électroniques et
bibliographiques sur les Normes internationales,
électriques. Il contient 21 000 termes et définitions en anglais
Spécifications techniques, Rapports techniques et autres
et en français, ainsi que les termes équivalents dans 16
documents de l'IEC. Disponible pour PC, Mac OS, tablettes
langues additionnelles. Egalement appelé Vocabulaire
Android et iPad.
Electrotechnique International (IEV) en ligne.

Recherche de publications IEC -
Glossaire IEC - std.iec.ch/glossary
webstore.iec.ch/advsearchform
67 000 entrées terminologiques électrotechniques, en anglais
La recherche avancée permet de trouver des publications IEC et en français, extraites des articles Termes et Définitions des
en utilisant différents critères (numéro de référence, texte, publications IEC parues depuis 2002. Plus certaines entrées
comité d’études,…). Elle donne aussi des informations sur les antérieures extraites des publications des CE 37, 77, 86 et
projets et les publications remplacées ou retirées. CISPR de l'IEC.

IEC Just Published - webstore.iec.ch/justpublished Service Clients - webstore.iec.ch/csc
Restez informé sur les nouvelles publications IEC. Just Si vous désirez nous donner des commentaires sur cette
Published détaille les nouvelles publications parues. publication ou si vous avez des questions contactez-nous:
Disponible en ligne et aussi une fois par mois par email. sales@iec.ch.

IEC 60364-4-44 ®
Edition 2.2 2018-01
CONSOLIDATED VERSION
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Low-voltage electrical installations –

Part 4-44: Protection for safety – Protection against voltage disturbances and

electromagnetic disturbances
Installations électriques à basse tension –

Partie 4-44: Protection pour assurer la sécurité – Protection contre les

perturbations de tension et les perturbations électromagnétiques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.100.10; 33.100.20; 91.140.50 ISBN 978-2-8322-5286-4

IEC 60364-4-44 ®
Edition 2.2 2018-01
CONSOLIDATED VERSION
REDLINE VERSION
VERSION REDLINE
colour
inside
Low-voltage electrical installations –
Part 4-44: Protection for safety – Protection against voltage disturbances and
electromagnetic disturbances
Installations électriques à basse tension –
Partie 4-44: Protection pour assurer la sécurité – Protection contre les
perturbations de tension et les perturbations électromagnétiques

– 2 – IEC 60364-4-44:2007+AMD1:2015
+AMD2:2018 CSV © IEC 2018
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
440.1 Scope . 8
440.2 Normative references . 8
441 (Vacant) . 10
442 Protection of low-voltage installations against temporary overvoltages due to earth
faults in the high-voltage system and due to faults in the low-voltage system . 10
442.1 Field of application . 10
442.1.1 General requirements . 10
442.1.2 Symbols . 10
442.2 Overvoltages in LV-systems during a high-voltage earth fault . 11
442.2.1 Magnitude and duration of power-frequency fault voltage . 13
442.2.2 Magnitude and duration of power-frequency stress voltages . 14
442.2.3 Requirements for calculation of limits . 15
442.3 Power-frequency stress voltage in case of loss of the neutral conductor
in a TN and TT system . 15
442.4 Power-frequency stress voltage in the event of an earth fault in an IT
system with distributed neutral . 15
442.5 Power-frequency stress voltage in the event of a short-circuit between
a line conductor and the neutral conductor . 16
443 Protection against transient overvoltages of atmospheric origin or due to switching . 16
443.1 General . 16
443.2 Void . 17
443.3 Terms and definitions . 17
443.4 Overvoltage control . 18
443.5 Risk assessment method . 18
443.26 Classification of rated impulse voltages (overvoltage categories) . 20
443.26.1 Purpose of classification of rated impulse voltages (overvoltage
categories) . 20
443.26.2 Relationship between impulse withstand Rated impulse voltages of
equipment and overvoltage categories . 21
443.3 Arrangements for overvoltage control .
443.3.1 Inherent overvoltage control .
443.3.2 Protective overvoltage control .
443.4 Required impulse withstand voltage of equipment.
444 Measures against electromagnetic influences . 24
444.1 General . 24
444.2 (void) . 25
444.3 Definitions . 25
444.4 Mitigation of electromagnetic interference (EMI) . 26
444.4.1 Sources of EMI . 26
444.4.2 Measures to reduce EMI . 26
444.4.3 TN-system . 28
444.4.4 TT system . 32
444.4.5 IT system . 33
444.4.6 Multiple-source supply . 34
444.4.7 Transfer of supply . 37

+AMD2:2018 CSV © IEC 2018
444.4.8 Services entering a building . 39
444.4.9 Separate buildings . 40
444.4.10 Inside buildings . 40
444.4.11 Protective devices . 42
444.4.12 Signal cables . 42
444.5 Earthing and equipotential bonding . 42
444.5.1 Interconnection of earth electrodes . 42
444.5.2 Interconnection of incoming networks and earthing arrangements . 43
444.5.3 Different structures for the network of equipotential conductors and
earthing conductors . 43
444.5.4 Equipotential bonding networks in buildings with several floors . 45
444.5.5 Functional earthing conductor . 46
444.5.6 Commercial or industrial buildings containing significant amounts
of information technology equipment . 47
444.5.7 Earthing arrangements and equipotential bonding of information
technology installations for functional purposes . 47
444.6 Segregation of circuits . 48
444.6.1 General . 48
444.6.2 Design guidelines requirements . 48
444.6.3 Installation guidelines Conditions for zero segregation . 51
444.7 Cable management systems . 52
444.7.1 General . 52
444.7.2 Design guidelines . 52
444.7.3 Installation guidelines . 53
445 Protection against undervoltage . 54
445.1 General requirements . 54
Annex A (informative) Explanatory notes concerning 442.1 and 442.2 .
Annex A (informative) Examples of calculated risk level CRL for the use of SPDs . 58
Annex B (informative) Guidance for on overvoltage control by SPDs applied to
overhead lines . 60
Annex C (normative) Determination of the conventional length, d .
Annex C (informative) List of notes concerning certain countries . 64

Figure 44.A1 – Representative schematic sketch for possible connections to earth in
substation and LV-installation and occurring overvoltages in case of faults . 12
Figure 44.A2 – Tolerable fault voltage due to an earth-fault in the HV system . 14
Figure 443.1 – Illustration of an installation showing the lengths to consider . 20
Figure 44.R1 – By-pass conductor for screen reinforcement to provide a common
equipotential bonding system . 27
Figure 44.R2 − Example of a substitute or by-pass equipotential bonding conductor in a
TT-system . 28
Figure 44.R3A − Avoidance of neutral conductor currents in a bonded structure by
using the TN-S system from the origin of the public supply up to and including the final
circuit within a building . 29
Figure 44.R3B – Avoidance of neutral conductor currents in a bonded structure by using
a TN-S system downstream of a consumer’s private supply transformer . 30
Figure 44.R4 − TN-C-S system within an existing building installation . 31
Figure 44.R5 – TT system within a building installation . 32
Figure 44.R6 – IT system within a building installation . 33

– 4 – IEC 60364-4-44:2007+AMD1:2015
+AMD2:2018 CSV © IEC 2018
Figure 44.R7A – TN multiple-source power supply with a non-suitable multiple
connection between PEN and earth . 34
Figure 44.R7B – TN multiple source power supplies to an installation with connection to
earth of the star points at one and the same point . 35
Figure 44.R8 – TT multiple-source power supplies to an installation with connection to
earth of the star points at one and the same point . 36
Figure 44.R9A − Three-phase alternative power supply with a 4-pole switch . 37
Figure 44.R9B – Neutral current flow in a three-phase alternative power supply with an
unsuitable 3-pole switch . 38
Figure 44.R9C − Single-phase alternative power supply with 2-pole switch . 39
Figure 44.R10 − Armoured cables and metal pipes entering the buildings (examples) . 40
Figure 44.R11 − Illustration of measures in an existing building . 41
Figure 44.R12 – Interconnected earth electrodes . 42
Figure 44.R13 – Examples of protective conductors in star network . 43
Figure 44.R14 – Example of multiple meshed bonding star network . 44
Figure 44.R15 – Example of a common meshed bonding star network . 45
Figure 44.R16 – Example of equipotential bonding networks in structures without
lightning protection systems . 46
Figure 44.R17 – Example of cable separation distance . 51
Figure 44.R17A − Separation between power and information technology cables for
cable route lengths ≤ 35 m .
Figure 44.R17B − Separation between power and information technology cables for
cable route lengths > 35 m .
Figure 44.R18 – Separation of cables in wiring systems .
Figure 44.R19 – Cable arrangements in metal cable-trays . 53
Figure 44.R20 – Continuity of metallic system components . 53
Figure 44.R21 – Location of cables inside metallic construction elements . 54
Figure 44.R22 – Connection of metallic sections . 54
Figure 44.Q – Examples of how to apply d , d and d for the determination of d .
1 2 3
Bibliography . 66

Table 44.A1 – Power-frequency stress voltages and power-frequency fault voltage in
low-voltage system . 13
Table 44.A2 – Permissible power-frequency stress voltage . 15
Table 443.1 – Calculation of f . 19
env
Table 44.B 443.2 – Required rated impulse withstand voltage of equipment U . 24
W
Table 444.1 – Summary of minimum separation distances where the specification
and/or intended application of the information and communication technology cable is
not available . 50
Table B.1 – Different possibilities for IT systems.

+AMD2:2018 CSV © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_______________
LOW-VOLTAGE ELECTRICAL INSTALLATIONS –
Part 4-44: Protection for safety –
Protection against voltage disturbances and
electromagnetic disturbances
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.
This consolidated version of the official IEC Standard and its amendments has been prepared
for user convenience.
IEC 60364-4-44 edition 2.2 contains the second edition (2007-08) [documents 64/1600/FDIS and
64/1609/RVD] and its corrigenda 1 (2010-05) and 2 (2011-10), its amendment 1
(2015-09) [documents 64/2032/FDIS and 64/2073/RVD] and its corrigendum (2016-08), and its
amendment 2 (2018-01) [documents 65C/684/FDIS and 65C/691/RVD].
In this Redline version, a vertical line in the margin shows where the technical content is
modified by amendments 1 and 2. Additions are in green text, deletions are in strikethrough red
text. A separate Final version with all changes accepted is available in this publication.

– 6 – IEC 60364-4-44:2007+AMD1:2015
+AMD2:2018 CSV © IEC 2018
International Standard IEC 60364-4-44 has been prepared by IEC technical committee 64:
Electrical installations and protection against electric shock.
The document 64/1600/FDIS, circulated to the National Committees as Amendment 3, led to
the publication of the new edition.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 60364 series, under the general title Low-voltage electrical
installations, 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.
The reader's attention is drawn to the fact that Annex C lists all of the “in-some-country”
clauses on differing practices of a less permanent nature relating to the subject of this
standard.
The committee has decided that the contents of the base publication and its amendments will
remain unchanged until the stability date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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.

+AMD2:2018 CSV © IEC 2018
INTRODUCTION
Part 4-44 of IEC 60364 covers the protection of electrical installations and measures against
voltage disturbances and electromagnetic disturbances.
The requirements are arranged into four clauses as follows:
Clause 442 Protection of low-voltage installations against temporary overvoltages due to
earth faults in the high-voltage system and due to faults in the low-voltage
system
Clause 443 Protection against overvoltages of atmospheric origin or due to switching
Clause 444 Measures against electromagnetic influences
Clause 445 Protection against undervoltage

– 8 – IEC 60364-4-44:2007+AMD1:2015
+AMD2:2018 CSV © IEC 2018
LOW-VOLTAGE ELECTRICAL INSTALLATIONS –

Part 4-44: Protection for safety –
Protection against voltage disturbances and
electromagnetic disturbances
440.1 Scope
The rules of this Part of IEC 60364 are intended to provide requirements for the safety of
electrical installations in the event of voltage disturbances and electromagnetic disturbances
generated for different specified reasons.
The rules of this part are not intended to apply to systems for distribution of energy to the
public, or power generation and transmission for such systems (see the scope of IEC 60364-1)
although such disturbances may be conducted into or between electrical installations via these
supply systems.
440.2 Normative references
The following referenced documents are indispensable for the application 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 60038:1983 2009, IEC standard voltages
IEC 60050-604:1987, International Electrotechnical Vocabulary – Chapter 604: Generation,
transmission and distribution of electricity – Operation
IEC 60364-1, Low-voltage electrical installations – Part 1: Fundamental principles, assessment
of general characteristics, definitions
IEC 60364-4-41:2005, Electrical installations of buildings – Part 4-41: Protection for safety –
Protection against electric shock
IEC 60364-5-52, Low-voltage electrical installations – Part 5-52: Selection and erection of
electrical equipment – Wiring systems
IEC 60364-5-53:2001, Electrical installations of buildings - Part 5-53: Selection and erection of
electrical equipment - Isolation, switching and control
IEC 60364-5-53:2001/AMD1:2002
IEC 60364-5-53:2001/AMD2:2015
IEC 60364-5-54:2002, Electrical installations of buildings − Part 5-54: Selection and erection of
electrical equipment – Earthing arrangements and protective bonding conductors
IEC 60479-1:2005, Effects of current on human beings and livestock – Part 1: General aspects
IEC 60664-1:2007, Insulation co-ordination for equipment within low-voltage systems – Part 1:
Principles, requirements and tests
IEC 60950-1, Information technology equipment – Safety – Part 1: General requirements
IEC 61000-2-5:1995, Electromagnetic compatibility (EMC) − Part 2: Environment − Section 5:
Classification of electromagnetic environments – Basic EMC publication
___________
A third edition is currently in preparation.

+AMD2:2018 CSV © IEC 2018
IEC 61000-6-1, Electromagnetic compatibility (EMC) – Part 6-1: Generic standards – Immunity
for residential, commercial and light-industrial environments
IEC 61000-6-2, Electromagnetic compatibility (EMC) – Part 6-2: Generic standards – Immunity
for industrial environments
IEC 61000-6-3, Electromagnetic compatibility (EMC) – Part 6-3: Generic standards – Emission
standard for residential, commercial and light-industrial environments
IEC 61000-6-4, Electromagnetic compatibility (EMC) – Part 6-4: Generic standards – Emission
standard for industrial environments

IEC 61156 (all parts), Multicore and symmetrical pair/quad cables for digital communication
IEC 61196-7, Coaxial communication cables – Part 7: Sectional specification for cables for
BCT cabling in accordance with ISO/IEC 15018 – Indoor drop cables for systems operating at 5
MHz – 3 000 MHz
IEC 61558-2-1, Safety of power transformers, power supplies, reactors and similar products –
Part 2-1: Particular requirements for tests for separating transformers and power supplies
incorporating separating transformers for general applications
IEC 61558-2-4, Safety of power transformers, power supply units and similar – Part 2-4:
Particular requirements for isolating transformers for general use
IEC 61558-2-6, Safety of power transformers, power supply units and similar – Part 2-6:
Particular requirements for safety isolating transformers for general use
IEC 61558-2-15, Safety of power transformers, power supply units and similar – Part 2-15:
Particular requirements for isolating transformers for the supply of medical locations
IEC 61643 (all parts), Low-voltage surge protective devices
IEC 61643-11:2011, Low-voltage surge protective devices – Part 11: Surge protective devices
connected to low-voltage power systems – Requirements and test methods
IEC 61643-22, Low-voltage surge protective devices – Part 22: Surge protective devices
connected to telecommunications and signalling networks – Selection and application
principles
IEC 61936-1, Power installations exceeding 1 kV a.c. – Part 1: Common rules
IEC 62305 (all parts), Protection against lightning
IEC 62305-1, Protection against lightning – Part 1: General principles
IEC 62305-3, Protection against lightning – Part 3: Physical damage to structures and life
hazard
IEC 62305-4, Protection against lightning – Part 4: Electrical and electronic systems within
structures
ISO/IEC 11801-1, Information technology – Generic cabling for customer premises – Part 1:
General requirements
ISO/IEC 14763-2:2012, Information technology – Implementation and operation of customer
premises cabling – Part 2: Planning and installation
ISO/IEC 14763-2:2012/AMD1:2015
ISO/IEC TR 29106, Information technology – Generic cabling – Introduction to the MICE
environmental classification
– 10 – IEC 60364-4-44:2007+AMD1:2015
+AMD2:2018 CSV © IEC 2018
441 (Vacant)
442 Protection of low-voltage installations against temporary overvoltages due
to earth faults in the high-voltage system and due to faults in the low-
voltage system
442.1 Field of application
The rules of this clause provide requirements for the safety of low-voltage installation in the
event of
– a fault between the high-voltage system and earth in the transformer substation that
supplies the low-voltage installation,
– a loss of the supply neutral in the low-voltage system,
– a short-circuit between a line conductor and neutral,
– an accidental earthing of a line conductor of a low-voltage IT-system.
The requirements for the earthing arrangement at the transformer substation are given in
IEC 61936-1.
442.1.1 General requirements
As Clause 442 covers faults between a high-voltage line and the earth in the HV/LV substation,
it gives rules for the designer and installer of the substation. It is necessary to have the
following information concerning the high-voltage system:
– quality of the system earthing;
– maximum level of earth fault current;
– resistance of the earthing arrangement.
The following subclauses consider four situations as proposed in 442.1, which generally cause
the most severe temporary overvoltages such as defined in IEC 60050-604:
– fault between the high-voltage system(s) and earth (see 442.2);
– loss of the neutral in a low-voltage system (see 442.3);
– accidental earthing of a low-voltage IT system (see 442.4);
– short-circuit in the low-voltage installation (see 442.5).
442.1.2 Symbols
In Clause 442 the following symbols are used (see Figure 44.A1):
I part of the earth fault current in the high-voltage system that flows through the earthing
E
arrangement of the transformer substation.
R resistance of the earthing arrangement of the transformer substation.
E
R resistance of the earthing arrangement of the exposed-conductive-parts of the
A
equipment of the low-voltage installation.
R resistance of the earthing arrangement of the low-voltage system neutral, for low-
B
voltage systems in which the earthing arrangements of the transformer substation and
of the low-voltage system neutral are electrically independent.
U in TN- and TT-systems: nominal a.c. r.m.s. line voltage to earth
o
+AMD2:2018 CSV © IEC 2018
in IT-systems: nominal a.c. voltage between line conductor and neutral conductor or
mid point conductor, as appropriate
U power-frequency fault voltage that appears in the low-voltage system between exposed-
f
conductive-parts and earth for the duration of the fault.
U power-frequency stress voltage between the line conductor and the exposed-
conductive-parts of the low-voltage equipment of the transformer substation during the
fault.
U power-frequency stress voltage between the line conductor and the exposed-
conductive-parts of the low-voltage equipment of the low-voltage installation during the
fault.
NOTE 1 The power-frequency stress voltage (U and U ) is the voltage that appears across the insulation of low-
1 2
voltage equipment and across surge protective devices connected to the low-voltage system.
The following additional symbols are used in respect of IT-systems in which the exposed-
conductive-parts of the equipment of the low-voltage installation are connected to an earthing
arrangement that is electrically independent of the earthing arrangement of the transformer
substation.
I fault current that flows through the earthing arrangement of the exposed-conductive-
h
parts of the equipment of the low-voltage installation during a period when there is a
high-voltage fault and a first fault in the low-voltage installation (see Table 44.A1).
I fault current, in accordance with 411.6.2, that flows through the earthing arrangement
d
of the exposed-conductive-parts of the low-voltage installation during the first fault in a
low-voltage system (see Table 44.A1).
Z impedance (e.g. IMD internal impedance, artificial neutral impedance) between the low-
voltage system and an earthing arrangement.
NOTE 2 An earthing arrangement may be considered electrically independent of another earthing arrangement if a
rise of potential with respect to earth in one earthing arrangement does not cause an unacceptable rise of potential
with respect to earth in the other earthing arrangement. See IEC 61936-1.
442.2 Overvoltages in LV-systems during a high-voltage earth fault
In case of a fault to earth on the HV-side of the substation, the following types of overvoltage
may affect the LV-installation:
• power frequency fault-voltage (U );
f
• power frequency stress-voltages (U and U ).
1 2
Table 44.A1 provides the relevant methods of calculation for the different types of
overvoltages.
NOTE 1 Table 44.A1 deals with IT systems with a neutral point only. For IT systems with no neutral point, the
formulae should be adjusted accordingly.

– 12 – IEC 60364-4-44:2007+AMD1:2015
+AMD2:2018 CSV © IEC 2018
Substation U LV Installation
U
HV LV
L1
L2
L3
or N or PEN
Z
I R R R U
E E B A f
IEC  1379/07
Figure 44.A1 – Representative schematic sketch for possible connections to earth
in substation and LV-installation and occurring overvoltages in case of faults
Where high- and low-voltage earthing systems exist in proximity to each other, two practices
are presently used:
– interconnection of all high-voltage (R ) and low-voltage (R ) earthing systems;
E B
– separation of high-voltage (R ) from low-voltage (R ) earthing systems.
E B
The general method used is interconnection. The high- and low-voltage earthing systems shall
be interconnected if the low-voltage system is totally confined within the area covered by the
high-voltage earthing system (see IEC 61936-1).
NOTE 2 Details of the different types of system earthing (TN, TT, IT) are shown in IEC 60364-1.

+AMD2:2018 CSV © IEC 2018
Table 44.A1 – Power-frequency stress voltages and power-frequency fault
voltage in low-voltage system
Types of
Types of earth
system U U U
1 2 f
connections
earthing
R and R connected U *) R × I + U 0 *)
E B
o E E o
TT
R and R separated U *) 0 *)
R × I + U
E B
o
E E o
R and R connected U *) U *)
E B R × I **)
o o
E E
TN
R and R separated R × I + U U *) 0 *)
E B
E E o o
U *) R × I + U 0 *)
o E E o
R and Z connected
E
R and R separated
E A
R × I
U × 3 R × I + U × 3
A h
o E E o
U *) U *) R × I
o o E E
R and Z connected
E
R and R interconnected
IT E A
R × I
U × 3 U × 3
E E
o o
R × I + U U *) 0 *)
E E o o
R and Z separated
E
R and R separated
E A
R × I
R × I + U × 3 U × 3
A d
E E o o
*) No consideration needs to be given.
**) See 442.2.1 second paragraph.
With existing earth fault in the installation.

NOTE 3 The requirements for U and U are derived from design criteria for insulation of low-voltage equipment
1 2
with regard to temporary power-frequency overvoltage (see also Table 44.A2).
NOTE 4 In a system whose neutral is connected to the earthing arrangement of the transformer substation, such
temporary power-frequency overvoltage is also to be expected across insulation which is not in an earthed
enclosure when the equipment is outside a building.
NOTE 5 In TT- and TN-systems the statement “connected” and “separated” refers to the electrical connection
between R and R . For IT-systems it refers to the electrical connection between R and Z and the connection
E B E
between R and R .
E A
442.2.1 Magnitude and duration of power-frequency fault voltage
The magnitude and the duration of the fault voltage U (as calculated in Table 44.A1) which
f
appears in the LV installation between exposed-conductive-parts and earth, shall not exceed
the values given for U by the curve of Figure 44.A2 for the duration of the fault.
f
Normally, the PEN conductor of the low-voltage system is connected to earth at more than one
point. In this case, the total resistance is reduced. For these multiple grounded PEN
conductors, U can be calculated as:
f
U = 0,5 R ×I
f E E
– 14 – IEC 60364-4-44:2007+AMD1:2015
+AMD2:2018 CSV © IEC 2018
Fault voltage duration
1 200
1 100
1 000
10 100 1 000 10 000
Time of duration t  (ms)
IEC  1380/07
Figure 44.A2 – Tolerable fault voltage due to an earth-fault in the HV system
NOTE The curve shown in Figure 44.A2 is taken from IEC 61936-1. On the basis of probabilistic and statistical
evidence this curve represents a low level of risk for the simple worst case where the low voltage system neutral
conductor is earthed only at the transformer substation earthing arrangements. Guidance is provided in
IEC 61936-1 concerning other situations.
442.2.2 Magnitude and duration of power-frequency stress voltages
The magnitude and the duration of the power-frequency stress voltage (U and U ) as
1 2
calculated in Table 44.A1 of the low-voltage equipment in the low-voltage installation due to an
earth fault in the high-voltage system shall not exceed the requirements given in Table 44.A2.

Fault voltage U (V)
f
+AMD2:2018 CSV © IEC 2018
Table 44.A2 – Permissible power-frequency stress voltage
Duration of the earth fault in the Permissible power-frequency stress voltage on equipment
high-voltage system in low-voltage installations
t U
>5 s U + 250 V
o
≤5 s U + 1 200 V
o
In systems without a neutral conductor, U shall be the line-to-line voltage.
o
NOTE 1 The fir
...