IEC 60445:2021

IEC 60445 ®
Edition 7.0 2021-07
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
BASIC SAFETY PUBLICATION
Basic and safety principles for man-machine interface, marking and
identification – Identification of equipment terminals, conductor terminations
and conductors
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IEC 60445 ®
Edition 7.0 2021-07
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
BASIC SAFETY PUBLICATION
Basic and safety principles for man-machine interface, marking and
identification – Identification of equipment terminals, conductor terminations
and conductors
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 01.080.20; 13.110; 29.020 ISBN 978-2-8322-4189-9

– 2 – IEC 60445:2021 RLV © IEC 2021
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references. 6
3 Terms and definitions . 6
4 Methods of identification . 10
5 Application of identification means . 11
6 Identification by colours . 11
6.1 General . 11
6.2 Use of single colours . 12
6.2.1 Permitted colours The use of the single colours GREEN and YELLOW . 12
6.2.2 Neutral or mid-point conductor . 12
6.2.3 Line conductor in AC system . 12
6.2.4 Line conductor in DC system . 12
6.2.5 Functional earthing conductor . 12
6.3 Use of bi-colour combinations . 13
6.3.1 Permitted colours . 13
6.3.2 Protective conductor . 13
6.3.3 PEN conductor . 13
6.3.4 PEL conductor . 14
6.3.5 PEM conductor . 14
6.3.6 Protective bonding conductor . 14
7 Identification by alphanumeric notation . 14
7.1 General . 14
7.2 Equipment terminal identification – Marking principles . 15
7.3 Identification of certain designated conductors . 17
7.3.1 General . 17
7.3.2 Neutral conductor . 17
7.3.3 Protective conductor . 18
7.3.4 PEN conductor . 18
7.3.5 PEL conductor . 18
7.3.6 PEM conductor . 18
7.3.7 Protective bonding conductor . 18
7.3.8 Functional earthing conductor . 18
7.3.9 Functional bonding conductor . 18
7.3.10 Mid-point conductor . 18
7.3.11 Line conductor . 18
7.3.12 System-referencing-conductor . 19
Annex A (informative) Colours, alphanumeric notations and graphical symbols used
for identification of conductors and terminals . 20
Annex B (informative) List of notes concerning particular conditions in certain
countries . 22
Bibliography . 28

Figure 1 – Single element with two terminals . 15

Figure 2 – Single element with four terminals: Two endpoints and two intermediate
points . 15
Figure 3 – Three-phase equipment with six terminals . 16
Figure 4 – Three-element equipment with twelve terminals: Six endpoints and six
intermediate points . 16
Figure 5 – Equipment with groups of elements . 17
Figure 6 – Interconnection of equipment terminals and certain designated conductors . 17

Table A.1 – Colours, alphanumeric notations and graphical symbols used for
identification of conductors and terminals . 20

– 4 – IEC 60445:2021 RLV © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
BASIC AND SAFETY PRINCIPLES FOR MAN-MACHINE
INTERFACE, MARKING AND IDENTIFICATION –
IDENTIFICATION OF EQUIPMENT TERMINALS,
CONDUCTOR TERMINATIONS AND CONDUCTORS

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
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may participate in this preparatory work. International, governmental and non-governmental organizations liaising
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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
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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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
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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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes made to
the previous edition IEC 60445:2017. A vertical bar appears in the margin wherever a change has
been made. Additions are in green text, deletions are in strikethrough red text.

IEC 60445 has been prepared by IEC technical committee 3: Documentation, graphical symbols
and representations of technical information. It is an International Standard.
It has the status of a basic safety publication in accordance with IEC Guide 104.
This seventh edition cancels and replaces the sixth edition published in 2017. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the definitions have been aligned with IEC 60050-195:2021 and IEC 60050-826:— ;
b) the provisions for colour to be used for identification of certain designated conductors are
made requirements and not only recommendations;
c) introduction of a new subclause on marking of protective terminals for multiple power supply
inputs on equipment.
The text of this International Standard is based on the following documents:
FDIS Report on voting
3/1491/FDIS 3/1517/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
The reader's attention is drawn to the fact that Annex B 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 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.

_____________
Third edition under preparation. Stage at time of publication: IEC FDIS 60050-826:2021.

– 6 – IEC 60445:2021 RLV © IEC 2021
BASIC AND SAFETY PRINCIPLES FOR MAN-MACHINE
INTERFACE, MARKING AND IDENTIFICATION –
IDENTIFICATION OF EQUIPMENT TERMINALS,
CONDUCTOR TERMINATIONS AND CONDUCTORS

1 Scope
This document applies to the identification and marking of terminals of electrical equipment
such as resistors, fuses, relays, contactors, transformers, rotating machines and, wherever
applicable, to combinations of such equipment (e.g. assemblies), and it also applies to the
identification of terminations of certain designated conductors. It also provides general rules for
the use of certain colours or alphanumeric notations to identify conductors with the aim of
avoiding ambiguity and ensuring safe operation. These conductor colours or and alphanumeric
notations are intended to be applied on cores, busbars, and electrical equipment, and in cables
or installations.
This basic safety publication focusing on safety essential requirements is primarily intended for
use by technical committees in the preparation of standards in accordance with the principles
laid down in IEC Guide 104 and ISO/IEC Guide 51.
It is not intended for use by manufacturers or certification bodies. One of the responsibilities of
a technical committee is, wherever applicable, to make use of basic safety publications in the
preparation of its publications. The requirements of this basic safety publication will not apply
unless specifically referred to or included in the relevant publications.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60417, Graphical symbols for use on equipment (available at http://www.graphical-
symbols.info/equipment)
IEC 60617, Graphical symbols for diagrams (available at http://std.iec.ch/iec60617)
IEC Guide 104, The preparation of safety publications and the use of basic safety publications
and group safety publications
ISO/IEC Guide 51, Safety aspects – Guidelines for their inclusion in standards
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

NOTE The terms are sorted in alphabetical order in the English language.
3.1
earthing
grounding, US
electric connections between conductive parts and local earth
[SOURCE: IEC 60050-195:2021, 195-01-24]
3.2
earthed protective bonding conductor earthed
protective bonding conductor which has a conductive path to local earth
3.3
electrical equipment
item used for such purposes as generation, conversion, transmission, distribution or utilization
of electric energy
Note 1 to entry: Examples of such items are electric machines, transformers, switchgear and controlgear,
measuring instruments, protective devices, wiring systems, current-using equipment.
[SOURCE: IEC 60050-826:2004—, 826-16-01]
3.4
electrical safety
freedom from risk that is not tolerable and which is caused by electricity
[SOURCE: IEC 60050-195:2021, 195-01-20]
3.5
equipotential bonding
provision of electric connections between conductive parts, intended to achieve equipotentiality
set of electric connections intended to achieve equipotentiality between conductive parts
[SOURCE: IEC 60050-195:19982021, 195-01-10]
3.6
equipotentiality
state when conductive parts are at a substantially equal electric potential
[SOURCE: IEC 60050-195: 19982021, 195-01-09]
3.7
functional bonding conductor
conductor provided for functional-equipotential-bonding
[SOURCE: IEC 60050-195:19982021, 195-02-16]
3.8
functional earthing
functional grounding, US
earthing a point or points in a system or in an installation or in equipment, for purposes other
than electrical safety
[SOURCE: IEC 60050-195/AMD1:2001:2021, 195-01-13]

– 8 – IEC 60445:2021 RLV © IEC 2021
3.9
functional earthing conductor
functional grounding conductor, US
earthing conductor provided for functional earthing
[SOURCE: IEC 60050-195:19982021, 195-02-15]
3.10
functional-equipotential-bonding
equipotential bonding for operational reasons other than electrical safety
[SOURCE: IEC 60050-195:19982021, 195-01-16]
3.11
line conductor
DEPRECATED: phase conductor (in AC systems)
DEPRECATED: pole conductor (in DC systems)
conductor which is intended to be energized in normal operation and capable of contributing to
the transmission or distribution of electric energy but which is not a neutral conductor or mid-
point conductor
[SOURCE: IEC 60050-195:19982021, 195-02-08, modified – Note 1 to entry removed.]
3.12
local earth
local ground, US
part of the Earth that is in electric contact with an earth electrode and that has an electric
potential not necessarily equal to zero
[SOURCE: IEC 60050-195:2021, 195-01-03]
3.13
mid-point
common point between two symmetrical circuit elements of which the opposite ends are
electrically connected to different line conductors of the same circuit
[SOURCE: IEC 60050-195:2021, 195-02-04]
3.14
mid-point conductor
conductor electrically connected to the mid-point and capable of contributing to the distribution
of electric energy
[SOURCE: IEC 60050-195:19982021, 195-02-07]
3.15
neutral conductor
conductor electrically connected to the neutral point and capable of contributing to the
distribution of electric energy
[SOURCE: IEC 60050-195:19982021, 195-02-06]
3.16
neutral point
common point of a star-connected polyphase system
[SOURCE: IEC 60050-195:2021, 195-02-05]

3.17
PEL conductor
conductor combining the functions of both a protective earthing conductor and a line conductor
[SOURCE: IEC 60050-195:19982021, 195-02-14]
3.18
PEM conductor
conductor combining the functions of both a protective earthing conductor and a mid-point
conductor
[SOURCE: IEC 60050-195:19982021, 195-02-13]
3.19
PEN conductor
conductor combining the functions of both a protective earthing conductor and a neutral
conductor
[SOURCE: IEC 60050-195:19982021, 195-02-12]
3.20
protective bonding conductor
DEPRECATED: equipotential bonding conductor
protective conductor provided for protective-equipotential-bonding
[SOURCE: IEC 60050-195:19982021, 195-02-10]
3.21
protective conductor
(identification: PE)
equipment grounding conductor, US
grounding electrode conductor, US
conductor provided for purposes of safety, for example protection against electric shock
electrical safety
Note 1 to entry: The terms "equipment grounding conductor" and "grounding electrode conductor" are used in the
US depending on their application.
[SOURCE: IEC 60050-195:19982021, 195-02-09, modified – Two synonyms and Note 1 to entry
have been added.]
3.22
protective earthing
protective grounding, US
earthing a point or points in a system or in an installation or in equipment, for purposes of
electrical safety
[SOURCE: IEC 60050-195:20012021, 195-01-11]
3.23
protective earthing conductor
PE conductor
protective grounding conductor, US
protective conductor provided for protective earthing
[SOURCE: IEC 60050-195:19982021, 195-02-11]

– 10 – IEC 60445:2021 RLV © IEC 2021
3.24
protective-equipotential-bonding
equipotential bonding for the purposes of electrical safety
[SOURCE: IEC 60050-195:19982021, 195-01-15]
3.19
earth, verb
ground, verb,US
make an electric connection between a given point in a system of in an installation or in
equipment and a local earth
Note 1 to entry: The connection to local earth may be
– intentional, or
– unintentional or accidental
and may be permanent or temporary.
[SOURCE: IEC 60050-195:1998, 195-01-08]
3.25
protective terminal
terminal provided on equipment and intended for the electric connection with a protective
conductor
[SOURCE: IEC 60050-195:2021, 195-02-43]
3.26
system-referencing-conductor
conductor between a live conductor and the earthing arrangement to enable the live conductor
to be substantially at the same potential as the Earth
[SOURCE: IEC 60050-826: —, 826-13-38]
3.27
terminal
conductive part of electrical equipment provided for connecting that electrical equipment to one
or more external conductors
[SOURCE: IEC 60050-151:2001, 151-12-12, modified – "device, electric circuit or electric
network" is replaced by "electrical equipment", and Note 1 to entry is removed.]
3.28
unearthed protective bonding conductor unearthed
protective bonding conductor without a conductive path to local earth which is isolated from the
Earth
4 Methods of identification
Where the identification of equipment terminals and of terminations of certain designated
conductors is considered necessary, it shall be effected by the use of one or more of the
following methods:
– the physical or relative location of the equipment terminals or of terminations of certain
designated conductors;
– a colour code for equipment terminals and terminations of certain designated conductors in
accordance with Clause 6;
– graphical symbols in accordance with IEC 60417. If additional symbols are required, these
shall be consistent with IEC 60617;

– an alphanumeric notation in accordance with the system laid down in Clause 7.
To keep consistency with the documentation, conductor and equipment terminal designation,
the alphanumeric notation is recommended.
Identification of conductors by colours shall be in accordance with the requirements provided
in Clause 6. Identification of conductors by alphanumeric notation shall be in accordance with
the requirements provided in Clause 7.
NOTE 1 It is recognised that for complex systems and installations additional marking and labelling are used for
reasons other than safety, see for example IEC 62491.
NOTE 2 Annex A contains Table A.1 which provides an overview of identifications of certain designated conductors
and equipment terminals to which these conductors are likely to be connected.
5 Application of identification means
The identifying colour, graphical symbol or alphanumeric notation shall be located on, or
adjacent to, the corresponding terminal.
When more than one identification method is used and confusion is possible, the correlation
between the methods shall be clarified in the associated documentation.
When no confusion is possible, the juxtaposition of numerical and alphanumeric notation may
be applied.
Terminals and conductors used for earthing or equipotential bonding are divided concerning
according to their purpose of earthing/bonding into the two basic concepts of protective earthing
purposes and functional earthing purposes:
– If a terminal or conductor fulfils the requirements for both protective earthing purposes and
functional earthing purposes, it shall be designated as a protective earthing terminal or
protective earthing conductor, respectively.
– If the requirements for protective earthing purposes are not met by a functional earthing
terminal or functional earthing conductor intended for functional purposes, it the terminal or
conductor shall not be marked with an identification of a protective earthing terminal or
protective earthing conductor, respectively.
– The requirements for functional earthing are to or functional-equipotential-bonding shall be
defined by the manufacturer or the relevant product committee and should be specified
within the documentation of the equipment.
NOTE 1 For example, requirements for handling electromagnetic compatibility (EMC) issues.
NOTE 2 Annex A contains Table A.1 which provides an overview of identifications of certain designated conductors
and equipment terminals to which these conductors are likely to be connected.
6 Identification by colours
6.1 General
For identification of conductors, only the following colours are permitted shall be used:
BLACK, BROWN, RED, ORANGE, GREEN, YELLOW, BLUE, VIOLET, GREY, WHITE,
PINK, TURQUOISE.
NOTE This list of colours is derived from IEC 60757.
The identification by colour shall be used at terminations and preferably throughout the length
of the conductor either by the colour of the insulation or by colour markers, except for bare
conductors where the colour identification shall be at termination and connection points.

– 12 – IEC 60445:2021 RLV © IEC 2021
Identification by colour or marking is not required for:
– concentric conductors of cables,
– metal sheath or armour of cables when used as a protective conductor,
– bare conductors where permanent identification is not practicable,
– extraneous-conductive-parts used as a protective conductor,
– exposed-conductive-parts used as a protective conductor.
Additional markings, for example alphanumerical, are allowed, provided that the colour
identification remains unambiguous.
Where conductors shall be identified by colours, the requirements of 6.2 and 6.3 apply.
6.2 Use of single colours
6.2.1 Permitted colours The use of the single colours GREEN and YELLOW
The single colours GREEN and YELLOW are shall only permitted be used where confusion with
the colouring of the conductors in accordance with 6.3.2 to 6.3.6 is not likely to occur.
6.2.2 Neutral or mid-point conductor
Where a circuit includes A neutral or mid-point conductor shall be identified by the colour BLUE,
the colour used for this purpose shall be BLUE. In order to avoid confusion with other colours
it is recommended to use an unsaturated colour BLUE, often called "light blue".
Where a neutral or mid-point conductor is present, the colour BLUE shall not be used for
identifying any other conductor where confusion is possible. In the absence of a neutral or mid-
point conductor within the whole wiring system, a conductor identified by the colour BLUE may
be used for identifying a conductor with any other purpose, except as a protective conductor.
If identification by colour is used, Bare conductors used as neutral or mid-point conductors shall
be either coloured by a BLUE stripe, 15 mm to 100 mm wide in each unit or enclosure and at
each accessible position, or coloured BLUE throughout their length.
NOTE In IEC 60079-11, the colour BLUE is used for the marking by colour of terminals, terminal boxes, plugs and
sockets of intrinsically-safe circuits.
6.2.3 Line conductor in AC system
For Line conductors in AC systems shall be identified by the preferred colours are BLACK,
BROWN and or GREY.
NOTE The sequence of colour codes in 6.2.3 is in alphabetical order in the English language, and does not indicate
any preferred phasing or direction of rotation.
6.2.4 Line conductor in DC system
For Line conductors in DC systems shall be identified by the preferred colours are colour:
– RED for the positive line conductor,
– WHITE for the negative line conductor.
6.2.5 Functional earthing conductor
For colour marking of A functional earthing conductor shall be identified by the preferred colour
is PINK. The colour need only be applied at the terminations and at points of connection. It is
only necessary to apply the identification at the terminations and at points of connection.

6.3 Use of bi-colour combinations
6.3.1 Permitted colours
Combinations of Any two of the colours listed in 6.1 are permitted may be combined, provided
there is no risk of confusion.
To avoid any such confusion, the colour GREEN and the colour YELLOW shall not be used in
colour combinations other than the combination GREEN-AND-YELLOW.
The colour combination GREEN-AND-YELLOW is restricted to shall only be used for the
purposes specified in 6.3.2 to 6.3.6.
6.3.2 Protective conductor
The protective conductor shall be identified by the bi-colour combination
GREEN-AND-YELLOW.
GREEN-AND-YELLOW is the only colour combination recognized for identifying the protective
conductor.
For a PEN, PEM, and PEL conductor, additional requirements are given in 6.3.3 to 6.3.5.
The colour combination GREEN-AND-YELLOW shall be such that, on any 15 mm length of the
conductor where colour coding is applied, one of these colours covers at least 30 % and not
more than 70 % of the surface of the conductor, the other colour covering the remainder of that
surface.
If bare conductors used as protective conductors are provided with colouring they shall be
coloured GREEN-AND-YELLOW, either throughout the whole length of each conductor or in
each compartment or unit or at each accessible position. If adhesive tape is used, only
bi-coloured GREEN-AND-YELLOW tape shall be applied.
Where the protective conductor can be easily identified by its shape, construction or position,
for example a concentric conductor, colour coding throughout its length is not necessary but
the ends or accessible positions should be clearly identified by the graphical symbol IEC 60417-

5019 (2006-08) "Protective earth; protective ground", , or the bi-colour combination
GREEN-AND-YELLOW or the alphanumeric notation PE.
If extraneous conductive parts are used as a PE protective conductor, identification by colours
is not necessary.
6.3.3 PEN conductor
A PEN conductor, when insulated, shall be marked identified by one of the following methods:
– GREEN-AND-YELLOW coloured insulation throughout its length and with, in addition, BLUE
colour markings at the terminations and points of connection; or
– BLUE coloured insulation throughout its length and with, in addition, GREEN-AND-YELLOW
coloured markings at the terminations and points of connection.
The method to be applied within a country should be decided by the National Committee and
not on an individual basis.
The additional BLUE coloured markings at the termination and points of connection may be
omitted once either provided one of the following two conditions is met:

– 14 – IEC 60445:2021 RLV © IEC 2021
– in electrical equipment, if relevant requirements are included in specific product standards
or within a country;
– in the case of wiring systems, for example those used in industry, if decided by the relevant
committee.
6.3.4 PEL conductor
A PEL conductor, when insulated, shall be marked identified by GREEN-AND-YELLOW
coloured insulation throughout its length and with, in addition, BLUE coloured markings at its
terminations and points of connection of the PEL conductor.
The additional BLUE coloured markings at the termination and points of connection may be
omitted once either provided one of the following two conditions is met:
– in electrical equipment, if relevant requirements are included in specific product standards
or within a country;
– in the case of wiring systems, for example those used in industry, if decided by the relevant
committee.
If confusion with a PEN or PEM conductor is likely, the alphanumeric designation as given in
7.3.5 shall be indicated at the terminations and points of connection.
6.3.5 PEM conductor
A PEM conductor, when insulated, shall be marked identified by GREEN-AND-YELLOW
coloured insulation throughout its length and with, in addition, BLUE coloured markings at its
terminations and points of connection of the PEM conductor.
The additional BLUE coloured markings at the termination and points of connection may be
omitted once either provided one of the following two conditions is met:
– in electrical equipment, if relevant requirements are included in specific product standards
or within a country;
– in the case of wiring systems, for example those used in industry, if decided by the relevant
committee.
If confusion with a PEN or PEL conductor is likely, the alphanumeric designation given in 7.3.6
shall be indicated at the terminations and points of connection.
6.3.6 Protective bonding conductor
A protective bonding conductor shall be identified by the bi-colour combination
GREEN-AND-YELLOW as specified in 6.3.1 6.3.2.
7 Identification by alphanumeric notation
7.1 General
If letters and/or numerals are used for identification, letters shall be uppercase Latin characters
only and numerals shall be Arabic numerals.
It is recommended that the reference letters for DC elements be chosen from the first part of
the alphabet and reference letters for AC elements from the second part.
Letters "I" and "O" shall not be used for identification to prevent confusion with the numerals
"1" and "0"; the alphanumeric signs "+" and "−" may be used.
In order to avoid any confusion, unattached numerals 6 and 9 shall be underlined.

All alphanumeric notations shall be in strong contrast to the colour of the background
(e.g. insulation).
The alphanumeric identification shall be clearly legible and durable.
NOTE For evaluation of the durability, see IEC 60227-2.
The alphanumeric system applies to identification of conductors and of conductors in a group
of conductors. Conductors with GREEN-AND-YELLOW coloured insulation shall only be
identified as a certain designated conductor in accordance with 7.3.3 to 7.3.9.
The alphanumeric identifications specified in 7.3 shall not be used for any purpose other than
that specified.
Where no confusion is possible, parts of the complete alphanumeric notation laid down in the
marking principles set out in 7.2 may be omitted.
7.2 Equipment terminal identification – Marking principles
7.2.1 Marking of equipment terminals is (or should be) based on the principles provided in
7.2.2 to 7.2.5.
7.2.2 The two endpoints of an element are should be distinguished by consecutive reference
numbers, the odd number being lower than the even number, for example 1 and 2
(see Figure 1).
Figure 1 – Single element with two terminals
7.2.3 The intermediate points of a single element are should be distinguished by reference
numbers, preferably in a numerical order, for example 3, 4, 5, etc. The reference numbers
chosen for intermediate points shall be higher than those chosen for the endpoints; their
numbering commences at the point which lies closest to the endpoint with the lower reference
number. Thus, for example, the intermediate points of an element with the endpoints 1 and 2
will be denoted by the reference numbers 3 and 4 (see Figure 2).

Figure 2 – Single element with four terminals: Two endpoints
and two intermediate points
– 16 – IEC 60445:2021 RLV © IEC 2021
7.2.4 If several similar elements are combined in a group of elements, then one of the
following methods for marking the elements shall be used:
– the two endpoints and intermediate points, if any, are distinguished by letters preceding the
reference numbers referred to in 7.2.2 and 7.2.3, for example U, V, W corresponding to the
phases of a three-phase AC system (see Figure 3);

Figure 3 – Three-phase equipment with six terminals
– the two endpoints and intermediate points, if any, are should be distinguished by numbers
preceding the reference numbers referred to in 7.2.2 and 7.2.3 where a phase identification
is not necessary or possible. To avoid confusion, these numbers shall be separated by a
full stop. For example, the endpoints of one element may be marked 1.1 and 1.2, those of
another element, 2.1 and 2.2 (see Figure 4);
NOTE For examples of an unambiguous terminal designation with respect to the object to which the terminal
belongs, see IEC 61666:2010, Annex A.

Figure 4 – Three-element equipment with twelve terminals:
Six endpoints and six intermediate points
– in the case of terminal blocks, the numerical identification should be in numerical order.
Further detailed requirements on terminal markings and identification may be given by relevant
product committees.
7.2.5 Similar groups of elements having the same reference letters are should be
distinguished by a numerical prefix to the reference letters (see Figure 5 a) and Figure 5 b)).

a) Three-phase equipment b) Two-phase equipment with two groups of
with two groups of elements elements with four terminals each not intended to
be connected to certain designated conductors

Figure 5 – Equipment with groups of elements
Figure 6 illustrates the interconnection of equipment terminals and certain designated
conductors, marked in accordance with the alphanumeric notation.

Figure 6 – Interconnection of equipment terminals and certain designated conductors
7.2.6 Where a piece of equipment has more than one incoming supply point, the terminal at
the supply points for connection to an external protective conductor shall be marked with the
designation "PE".
7.3 Identification of certain designated conductors
7.3.1 General
Equipment terminals which are intended to be connected directly or indirectly to certain
designated conductors, and terminations of certain designated conductors shall be marked with
reference letters or graphical symbols or both reference letters and graphical symbols according
to Table A.1.
7.3.2 Neutral conductor
The alphanumeric identification of a neutral conductor shall be "N".

– 18 – IEC 60445:2021 RLV © IEC 2021
7.3.3 Protective conductor
The alphanumeric identification of a protective conductor shall be "PE". This identification also
applies for a protective earthing conductor.
7.3.4 PEN conductor
The alphanumeric identification of a PEN conductor shall be "PEN".
7.3.5 PEL conductor
The alphanumeric identification of a PEL conductor shall be "PEL".
7.3.6 PEM conductor
The alphanumeric identification of a PEM conductor shall be "PEM".
7.3.7 Protective bonding conductor
7.3.7.1 General
The alphanumeric identification of a protective bonding conductor shall be "PB".
A protective bonding conductor will in most cases be an earthed protective bonding conductor.
In those cases where a distinction between an earthed protective bonding conductor and an
unearthed protective bonding conductor is necessary (for example, within electro-medical
installations), the earthed protective bonding conductor shall be identified in accordance with
7.3.7.2 and the unearthed protective bonding conductor shall be identified in accordance with
7.3.7.3.
7.3.7.2 Earthed protective bonding conductor earthed
If it is necessary to distinguish between an earthed protective bonding conductor earthed and
an unearthed protective bonding conductor unearthed, the alphanumeric identification of a the
earthed protective bonding conductor earthed shall be "PBE".
7.3.7.3 Unearthed protective bonding conductor unearthed
If it is necessary to distinguish between an earthed protective bonding conductor earthed and
an unearthed protective bonding conductor unearthed, the alphanumeric identification of a the
unearthed protective bonding conductor unearthed shall be "PBU".
7.3.8 Functional earthing conductor
The alphanumeric identification of a functional earthing conductor shall be "FE".
7.3.9 Functional bonding conductor
The alphanumeric identification of a functional bonding conductor shall be "FB".
7.3.10 Mid-point conductor
The alphanumeric identification of a mid-point conductor shall be "M".
7.3.11 Line conductor
The alphanumeric identification of a line conductor shall start with the letter "L" suffixed by:
– for an AC circuit in AC systems, a sequential number of line conductors, starting with the
digit one "1";
– for a DC circuit in DC systems, with the sign "+" (PLUS SIGN) for the positive line conductor
and with the sign "−" (MINUS SIGN) for the negative line conductor.
If no more than one line conductor is used, the suffix may be omitted.
7.3.12 System-referencing-conductor
The alphanumeric identification of a system-referencing-conductor shall be "SRC".

– 20 – IEC 60445:2021 RLV © IEC 2021
Table A.1 – Colours, alphanumeric notations an
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