SIST EN IEC 60709:2019

SLOVENSKI STANDARD
01-september-2019
Nadomešča:
SIST EN 60709:2010
Jedrske elektrarne - Merilna, nadzorna in elektroenergetska oprema za
zagotavljanje varnosti - Ločevanje (IEC 60709:2018)
Nuclear power plants - Instrumentation, control and electrical power systems important
to safety - Separation (IEC 60709:2018)
Kernkraftwerke - Leittechnik und elektrische Energieversorgungssysteme mit
sicherheitstechnischer Bedeutung - Physikalische und elektrische Trennung (IEC
60709:2018)
Centrales nucléaires de puissance - Systèmes d'instrumentation, de contrôle-commande
et d'alimentation électrique importants pour la sûreté - Séparation (IEC 60709:2018)
Ta slovenski standard je istoveten z: EN IEC 60709:2019
ICS:
27.120.20 Jedrske elektrarne. Varnost Nuclear power plants. Safety
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60709

NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2019
ICS 27.120.20 Supersedes EN 60709:2010
English Version
Nuclear power plants - Instrumentation, control and electrical
power systems important to safety - Separation
(IEC 60709:2018)
Centrales nucléaires de puissance - Systèmes Kernkraftwerke - Leittechnik und elektrische
d'instrumentation, de contrôle-commande et d'alimentation Energieversorgungssysteme mit sicherheitstechnischer
électrique importants pour la sûreté - Séparation Bedeutung - Physikalische und elektrische Trennung
(IEC 60709:2018) (IEC 60709:2018)
This European Standard was approved by CENELEC on 2019-06-17. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60709:2019 E
European foreword
This document (EN IEC 60709:2019) consists of the text of IEC 60709:2018 prepared by IEC/SC
45A: "Instrumentation, control and electrical power systems of nuclear facilities", of IEC/TC 45:
"Nuclear instrumentation".
The following dates are fixed:
• latest date by which this document has to be (dop) 2020-06-17
implemented at national level by publication of an
identical national standard or by endorsement
• latest date by which the national standards (dow) 2022-06-17
conflicting with this document have to be
withdrawn
This document supersedes EN 60709:2010.
As stated in the nuclear safety directive 2009/71/EURATOM, Chapter 1, Article 2, item 2, Member
States are not prevented from taking more stringent safety measures in the subject-matter covered by
the Directive, in compliance with Community law. In a similar manner, this European standard does
not prevent Member States from taking more stringent nuclear safety and/or security measures in the
subject-matter covered by this standard.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Endorsement notice
The text of the International Standard IEC 60709:2018 was approved by CENELEC as a European
Standard without any modification.

Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their

content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document
(including any amendments) applies.
NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod), the relevant

EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu.
Publication Year Title EN/HD Year

IEC 60071 series Insulation co-ordination EN 60071 series
IEC 60332 series Tests on electric and optical fibre cables EN 60332 series
under fire conditions
IEC 60364-4-41 -  Low-voltage electrical installations - Part 4-HD 60364-4-41 -
41: Protection for safety - Protection
against electric shock
IEC 60364-5-52 -  Low-voltage electrical installations - Part 5-HD 60364-5-52 -
52: Selection and erection of electrical
equipment - Wiring systems
IEC 60364-5-56 -  Low-voltage electrical installations - Part 5-- -
56: Selection and erection of electrical
equipment - Safety services
IEC 60909 series Short-circuit current calculation in three- - -
phase a.c. systems
IEC 60964 -  Nuclear power plants - Control rooms - - -
Design
IEC 61000 series Electromagnetic compatibility (EMC) - -
IEC 61226 -  Nuclear power plants - Instrumentation EN 61226 -
and control important to safety -
Classification of instrumentation and
control functions
IEC 61439-1 -  Low-voltage switchgear and controlgear EN 61439-1 -
assemblies - Part 1: General rules
IEC 61500 -  Nuclear power plants - Instrumentation - -
and control important to safety - Data
communication in systems performing
category A functions
IEC 61513 2011 Nuclear power plants - Instrumentation EN 61513 2013
and control important to safety - General
requirements for systems
IEC 61660 series Short-circuit currents in d.c. auxiliary EN 61660 series
installations in power plants and
substations
IEC 62003 -  Nuclear power plants - Instrumentation - -
and control important to safety -
Requirements for electromagnetic
compatibility testing
IEC 62808 -  Nuclear power plants - Instrumentation EN 62808 -
and control systems important to safety -
Design and qualification of isolation
devices
IEC/TR 62096 -  Nuclear power plants - Instrumentation - -
and control - Guidance for the decision on
modernization
IEC 63046 -  Nuclear power plants - Electrical systems - - -
General requirements
IAEA Safety 2016 Safety of Nuclear Power Plant: Design
Standard Series No.
SSR-2/1
IAEA Safety Guide - Safety classification of structures, systems
SSG-30 and components in Nuclear Power Plants
IAEA Safety Guide - Design of electrical power systems in
SSG-34 Nuclear Power Plants
IAEA Safety Guide 2016 Design of instrumentation and control
SSG-39 systems in Nuclear Power Plants

To be published.
IEC 60709 ®
Edition 3.0 2018-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear power plants – Instrumentation, control and electrical power systems

important to safety – Separation

Centrales nucléaires de puissance – Systèmes d’instrumentation, de contrôle-

commande et d'alimentation électrique importants pour la sûreté – Séparation

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.120.20 ISBN 978-2-8322-5582-7

– 2 – IEC 60709:2018  IEC 2018
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 10
1.1 General . 10
1.2 Application: new and pre-existing plants . 10
2 Normative references . 11
3 Terms and definitions . 12
4 Abbreviated terms . 15
5 Principles and requirements for separation . 16
5.1 Principles . 16
5.1.1 General . 16
5.1.2 Separation reasoning and boundaries . 16
5.1.3 Plant safety principles and requirements . 17
5.2 Safety class separation requirements . 17
5.3 Associated circuits . 18
5.3.1 General . 18
5.3.2 Criteria . 19
5.4 Separation issues at existing plants . 20
5.4.1 General . 20
5.4.2 Criteria . 20
6 Separation design basis . 20
6.1 Design inputs . 20
6.2 Environmental conditions and hazards . 21
6.2.1 General . 21
6.2.2 Environmental conditions . 21
6.2.3 External hazards. 21
6.2.4 Internal hazards . 21
6.2.5 Fire protection . 22
6.3 EMI/EMC . 22
6.4 Electrical fault . 22
6.5 Requirements from non-nuclear technical standards . 22
6.6 Requirements from special operating conditions . 22
7 Electrical isolation . 23
7.1 Principles . 23
7.1.1 General . 23
7.1.2 Overvoltage barrier . 23
7.1.3 Short circuit / Overcurrent protection . 23
7.1.4 Electrical nonreactive (retroaction free) . 24
7.1.5 Galvanic isolation (electrical insulation) . 24
7.2 Isolation devices . 24
7.2.1 General . 24
7.2.2 Isolation characteristics . 25
7.2.3 Actuation priority . 25
8 Physical separation . 26
8.1 Principles . 26

IEC 60709:2018  IEC 2018 – 3 –
8.1.1 General . 26
8.1.2 Separation by distance . 26
8.1.3 Structural separation . 26
8.2 Separation of cables and cable support structures . 26
8.2.1 General . 26
8.2.2 Divisional separation of redundant cables and cable support structures . 27
8.2.3 Separation of system cables and cable supporting structures of different
safety classes . 27
8.2.4 Separation of signal cables from power cables . 28
8.2.5 Reduced separation distances . 28
8.2.6 Associated circuits . 28
8.2.7 Separation of cables from tubes or pipes . 28
8.2.8 General routing considerations . 28
8.2.9 Identification . 28
8.3 Separation of components inside the I&C and electrical system important to
safety . 28
8.3.1 Divisional separation of redundant components inside the I&C and
electrical system important to safety . 28
8.3.2 Separation of components of different safety classes . 29
8.3.3 Installation of equipment of different voltage levels . 29
8.3.4 Reduced separation distances . 29
8.3.5 Associated circuits . 30
8.3.6 Separation of components from sources of hazards . 30
8.4 Control room cabinets, desks, panels and related cables . 30
9 Verification . 31
Annex A (normative) Relation to IAEA guidelines and IEC 61226 . 32
A.1 Object of this Annex . 32
A.2 Applicability of this document . 32
A.3 IAEA Guidelines, applicable for this document . 32
A.4 IEC standards, applicable for the safety categorization and classification . 32
A.5 Defence in Depth levels, simplified definitions . 33
Annex B (informative) Examples of separation realizations . 34
B.1 Object of this Annex . 34
B.2 Example of physical separation . 34
B.2.1 General . 34
B.2.2 Examples of physical separation by distance . 34
B.2.3 Examples of physical separation by structure . 36
B.3 Example of electrical isolation . 37
B.3.1 General . 37
B.3.2 Examples of overvoltage barriers . 37
B.3.3 Examples of short circuit / overcurrent protection . 38
B.3.4 Examples of galvanic isolation . 39
B.4 Example of EMC protection . 40
B.5 Associated circuits . 41
Annex C (informative) Examples of design errors and I&C and electrical failure events . 43
C.1 Object of this Annex . 43
C.2 Design errors . 43
C.3 I&C and electrical system failure events . 43
C.3.1 General . 43

– 4 – IEC 60709:2018  IEC 2018
C.3.2 Single random failure . 43
C.3.3 Multiple failures from a single common cause . 43
Annex D (informative) Functional independence and independence of communication . 44
D.1 Object of this Annex . 44
D.2 Functional independence . 44
D.2.1 General . 44
D.2.2 Independence from control system . 44
D.3 Independence of communication . 45
Bibliography . 46

Figure 1 – Physical separation by structure or distance . 17
Figure 2 – Separation by electrical isolation . 17
Figure 3 – Electrical Isolation measures and selection of components . 23
Figure B.1 – Separation of cable supporting structures by distance . 35
Figure B.2 – Separation of cable trays by distance. 35
Figure B.3 – Separation by structures . 36
Figure B.4 – Overvoltage barriers in I&C systems . 37
Figure B.5 – Overvoltage protection in electrical systems . 38
Figure B.6 – Short circuit protection in case of a cross-connection . 39
Figure B.7 – Galvanic isolation in I&C systems . 39
Figure B.8 – Galvanic isolation in electrical systems . 40
Figure B.9 – EMC protection of I&C cables . 41
Figure B.10 – Examples of associated circuits . 42

IEC 60709:2018  IEC 2018 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS –
INSTRUMENTATION, CONTROL AND ELECTRICAL
POWER SYSTEMS IMPORTANT TO SAFETY – SEPARATION

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 60709 has been prepared by subcommittee 45A: Instrumentation,
control and electrical power systems of nuclear facilities, of IEC technical committee 45:
Nuclear instrumentation.
This third edition cancels and replaces the second edition published in 2004. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) include requirements referring to the separation principle in electrical systems important to
safety;
b) define separation criteria for I&C and electrical systems in a generic way;
c) restructure the standard following the criteria;
d) consider interferences between I&C and electrical equipment from different safety
classes;
– 6 – IEC 60709:2018  IEC 2018
e) align with the new revisions of IAEA documents and broaden the scope to include other
aspects of separation;
f) cover new technologies that either present unique separation issues or provide new
means of achieving separation;
g) enhance requirements and guidance for areas of cable congestion, e.g. control room,
cable spreading galleries, etc;
h) introduce the concept of “associated circuits” (from US practice) to deal with equipment
not important to safety and cables that are not separated from safety equipment and
cables;
i) address the implications of low energy circuits, such as the possible use of analysis to
reduce the minimum separation distance;
j) review existing requirements, update terminology and definitions;
k) provide guidance for the application of the standard to existing plants.
The text of this International Standard is based on the following documents:
FDIS Report on voting
45A/1185/FDIS 45A/1195/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.
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 60709:2018  IEC 2018 – 7 –
INTRODUCTION
a) Background, main issues and organization of the standard
I&C and electrical systems important to safety in nuclear power plants need to tolerate the
effects of plant / equipment faults as well as internal and external hazards. Various
techniques are available to increase the level of tolerability of I&C and electrical systems to
such effects, including the provision of independent systems, subsystems and equipment. For
claims to be made of independence between such systems and equipment, adequate
separation should be provided and maintained. This standard provides generic technical
requirements and recommendations for the implementation of separation in the design of I&C
and electrical systems.
The object of this standard is as follows:
– in Clause 5 to present the principles for separation of I&C and/or electrical systems.
Subclause 5.4 focuses on modernization of existing nuclear power plants;
– in Clause 6, to define the separation design basis, including inputs, and to identify a
certain number of possible causes of internal and external hazards;
– in Clause 7, to establish the electrical isolation measures for I&C and electrical systems
important to safety and also requirements referring isolation devices;
– in Clause 8, to give requirements to be fulfilled for cabling and component separation
within an I&C and electrical system important to safety.
b) Situation of the current standard in the structure of the SC 45A standard series
IEC 60709 is a document of the second level, directly referenced by IEC 61513 and
IEC 63046 in regard to physical separation and electrical isolation being required between
subsystems of different safety trains of I&C and electrical systems important to safety, and
between I&C and electrical systems important to safety and those that are not important to
safety and between different defence in depth levels.
IEC 61226, that is consistent with IAEA SSG-30, establishes the principles of categorization
of I&C and electrical functions and the classification of structures, systems and components
(SSC) according to their level of importance to safety. IEC 61226 refers to IEC 60709 as the
normative standard regarding requirements for separation.
For more details on the relation of this standard to IAEA guidelines and IEC 61226, see
Annex A to this standard.
c) Recommendations and limitations regarding the application of the Standard
IEC 60709 applies to I&C and electrical systems and equipment important to safety. It
establishes requirements for physical and electrical separation as one means to provide
independence between the functions performed in those systems and equipment. Other
aspects of independence that may be required to address concerns of common cause failure
are not included in this standard. Furthermore, separation criteria due to security
requirements are also not considered.
The requirements given in this standard for the separation of safety classes can be applied to
separation for other design constraints, such as the defence in depth concept. These rules
shall be defined at the beginning of a project by a separation concept.
The separation of safety class 1 from other classes, as used in this standard, is only an
example of the application of the requirements of the standard.

– 8 – IEC 60709:2018  IEC 2018
d) Description of the structure of the IEC SC 45A standard series and relationships
with other IEC documents and other bodies documents (IAEA, ISO)
The top-level documents of the IEC SC 45A standard series are IEC 61513 and IEC 63046.
IEC 61513 provides general requirements for I&C systems and equipment that are used to
perform functions important to safety in NPPs. IEC 63046 provides general requirements for
electrical power systems of NPPs; it covers power supply systems including the supply
systems of the I&C systems. IEC 61513 and IEC 63046 are to be considered in conjunction
and at the same level. IEC 61513 and IEC 63046 structure the IEC SC 45A standard series
and shape a complete framework establishing general requirements for instrumentation,
control and electrical systems for nuclear power plants.
IEC 61513 and IEC 63046 refer directly to other IEC SC 45A standards for general topics
related to categorization of functions and classification of systems, qualification, separation,
defence against common cause failure, control room design, electromagnetic compatibility,
cybersecurity, software and hardware aspects for programmable digital systems, coordination
of safety and security requirements and management of ageing. The standards referenced
directly at this second level should be considered together with IEC 61513 and IEC 63046 as
a consistent document set.
At a third level, IEC SC 45A standards not directly referenced by IEC 61513 or by IEC 63046
are standards related to specific equipment, technical methods, or specific activities. Usually
these documents, which make reference to second-level documents for general topics, can be
used on their own.
A fourth level extending the IEC SC45A standard series, corresponds to the Technical
Reports which are not normative.
The IEC SC 45A standards series consistently implements and details the safety and security
principles and basic aspects provided in the relevant IAEA safety standards and in the
relevant documents of the IAEA nuclear security series (NSS). In particular this includes the
IAEA requirements SSR-2/1, establishing safety requirements related to the design of nuclear
power plants (NPPs), the IAEA safety guide SSG-30 dealing with the safety classification of
structures, systems and components in NPPs, the IAEA safety guide SSG-39 dealing with the
design of instrumentation and control systems for NPPs, the IAEA safety guide SSG-34
dealing with the design of electrical power systems for NPPs and the implementing guide
NSS17 for computer security at nuclear facilities. The safety and security terminology and
definitions used by SC 45A standards are consistent with those used by the IAEA.
IEC 61513 and IEC 63046 have adopted a presentation format similar to the basic safety
publication IEC 61508 with an overall life-cycle framework and a system life-cycle framework.
Regarding nuclear safety, IEC 61513 and IEC 63046 provide the interpretation of the general
requirements of IEC 61508-1, IEC 61508-2 and IEC 61508-4, for the nuclear application
sector. In this framework IEC 60880, IEC 62138 and IEC 62566 correspond to IEC 61508-3
for the nuclear application sector. IEC 61513 and IEC 63046 refer to ISO as well as to IAEA
GS-R part 2 and IAEA GS-G-3.1 and IAEA GS-G-3.5 for topics related to quality assurance
(QA). At level 2, regarding nuclear security, IEC 62645 is the entry document for the
IEC SC 45A security standards. It builds upon the valid high level principles and main
concepts of the generic security standards, in particular ISO/IEC 27001 and ISO/IEC 27002; it
adapts them and completes them to fit the nuclear context and coordinates with the
IEC 62443 series. At level 2, IEC 60964 is the entry document for the IEC SC 45A control
rooms standards and IEC 62342 is the entry document for the ageing management standards.
NOTE 1 It is assumed that for the design of I&C systems in NPPs that implement conventional safety functions
(e.g. to address worker safety, asset protection, chemical hazards, process energy hazards) international or
national standards would be applied.

IEC 60709:2018  IEC 2018 – 9 –
NOTE 2 IEC SC 45A domain was extended in 2013 to cover electrical systems. In 2014 and 2015 discussions
were held in IEC SC 45A to decide how and where general requirements for the design of electrical systems were
to be considered. IEC SC 45A experts recommended that an independent standard be developed at the same level
as IEC 61513 to establish general requirements for electrical systems. Project IEC 63046 is now launched to cover
this objective. When IEC 63046 will be published this NOTE 2 of the introduction of IEC SC 45A standards will be
suppressed.
– 10 – IEC 60709:2018  IEC 2018
NUCLEAR POWER PLANTS –
INSTRUMENTATION, CONTROL AND ELECTRICAL
POWER SYSTEMS IMPORTANT TO SAFETY – SEPARATION

1 Scope
1.1 General
This document is applicable to nuclear power plant instrumentation and control (I&C) and
electrical systems and equipment, whose functions are required to be independent due to
their contribution to:
• a redundant or diverse safety group;
• different defence in depth levels;
• different safety classes and also with non-classified (NC) systems.
It is also applicable to temporary installations which are part of those I&C and electrical
systems important to safety (for example, auxiliary equipment for commissioning tests and
experiments or mobile power supply systems). Clause 7 is intended particularly for electrical
isolation, Clause 8 is intended particularly for the cabling and the arrangement of equipment
of I&C and electrical systems important to safety.
This document applies to I&C and electrical systems of new nuclear power plants and to I&C
and electrical upgrading or back-fitting of existing plants. For existing plants see 1.2 and 5.4.
Where independence is required by general safety standards such as IAEA safety guides,

IEC 61513 (for I&C), IEC 63046 (for electrical systems) and other project constraints, one
aspect of achieving this independence is physical separation and electrical isolation between
the systems and their equipment that perform safety functions. This document defines the
assessments needed and the technical requirements to be met for I&C and electrical systems,
equipment or cables for which separation is required. Those means are to achieve adequate
physical separation and electrical isolation between redundant sections of a system and
between a higher and lower class systems. This separation is needed to prevent or minimise
the impact on safety that could result from faults and failures which could be propagated or
affect several sections of a system or several systems.
The requirements for functions, and their associated systems and equipment, to be
independent are normally defined in detail in the project documentation; the method of
determining and defining these requirements is not the subject of this document.
Following IAEA SSR-2/1 Requirement 21, separation means by physical separation, electrical
isolation, functional independence and independence of communication are considered. In
this document physical separation and electrical isolation are treated. Functional
independence and independence of communication are not considered in this document.
More details referring to functional independence, independence from control systems and
independence of communication are given in Annex D.
1.2 Application: new and pre-existing plants
This document applies to the I&C and electrical of new nuclear power plants as well as to up-
grading or back-fitting of existing plants.
For existing plants, only a subset of requirements is applicable and this subset is normally
specified and argued at the beginning of any project.

IEC 60709:2018  IEC 2018 – 11 –
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 60071 (all parts), Insulation co-ordination
IEC 60332 (all parts), Tests on electric cables under fire conditions
IEC 60364-4-41, Low-voltage electrical installations – 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 60364-5-56, Low-voltage electrical installations – Part 5-56: Selection and erection of
electrical equipment – Safety services
IEC 60909 (all parts), Short-circuit currents in three-phase a.c. systems
IEC 60964, Nuclear power plants – Control rooms – Design
IEC 61000 (all parts), Electromagnetic compatibility (EMC)
IEC 61226, Nuclear power plants – Instrumentation and control important to safety –
Classification of instrumentation and control functions
IEC 61439-1, Low voltage switchgear and controlgear assemblies – Part 1: General rules
IEC 61500, Nuclear power plants – Instrumentation and control important to safety – Data
communication in systems performing category A functions
IEC 61513:2011, Nuclear power plants – Instrumentation and control important to safety –
General requirements for systems
IEC 61660 (all parts), Short-circuit currents in d.c. auxiliary installations in power plants and
substations
IEC 62003, Nuclear power plants – Instrumentation and control important to safety –
Requirements for electromagnetic compatibility testing
IEC TR 62096, Nuclear power plants – Instrumentation and control – Guidance for the
decision on modernisation
IEC 62808, Nuclear power plants – Instrumentation and control systems important to safety –
Design and qualification of isolation devices
IEC 63046, Nuclear power plants – Electrical systems – General requirements
IAEA Safety Standard Series No. SSR-2/1:2016, Safety of Nuclear Power Plant: Design
____________
To be published.
– 12 – IEC 60709:2018  IEC 2018
IAEA Safety Guide SSG-30, Safety classification of structures, systems and components in
Nuclear Power Plants
IAEA Safety Guide SSG-34, Design of electrical power systems in Nuclear Power Plants
IAEA Safety Guide SSG-39:2016, Design of instrumentation and control systems in Nuclear
Power Plants
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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
3.1
associated circuit
circuit of a lower safety class that is not physically separated or is not electrically isolated
from the circuit(s) of the higher class by acceptable separation distances, safety class
structures, barriers, or electrical isolation devices, but meets suitable criteria for safety.
Circuits include the interconnecting cabling and the connected loads
3.2
barrier
device or structure interposed between redundant equipment or circuits important to safety, or
between equipment or circuits important to safety and a potential source of damage to limit
damage to the I&C system or electrical system important to safety to an acceptable level
Note 1 to entry: The following definition is to be found in the IAEA Safety Glossary edition 2016: “A physical
obstruction that prevents or inhibits the movement of people, radionuclides
...