IEC 60255-27:2023

Measuring relays and protection equipment - Part 27: Product safety requirements

IEC 60255-27:2023 specifies the product safety requirements for measuring relays and protection equipment having a rated AC voltage up to 1 000 V, or a rated DC voltage up to 1 500 V. This document specifies essential safety requirements to minimize the risk of fire and hazards caused by electric shock or injury to the user and property. This document specifies only product safety requirements; functional performance of the equipment is not covered. This document covers all the ways in which the equipment can be mounted and used in cabinets, racks and panels. This document also applies to auxiliary devices such as shunts, series resistors, transformers, auxiliary control panels, display devices, etc., that are used in conjunction with measuring relays and protection equipment and are tested together.

Relais de mesure et dispositifs de protection - Partie 27: Exigences de sécurité des produits

L'IEC 60255-27:2023 spécifie les exigences de sécurité des produits pour les relais de mesure et les dispositifs de protection avec une tension assignée en courant alternatif inférieure ou égale à 1 000 V ou avec une tension assignée en courant continu inférieure ou égale à 1 500 V. Le présent document spécifie les exigences de sécurité fondamentales pour réduire le plus possible les risques d'incendie et de dangers causés par un choc électrique ou les risques de blessure de l'utilisateur et de dégradation matérielle. Le présent document spécifie uniquement les exigences de sécurité des produits; les performances fonctionnelles du matériel ne sont pas couvertes. En revanche, le présent document couvre tous les modes qui peuvent être utilisés pour le montage et l'utilisation du dispositif dans des baies, des racks ou des panneaux. Le présent document s'applique aussi aux dispositifs auxiliaires comme les shunts, résistances série, transformateurs, panneaux de commande auxiliaires, dispositifs d'affichage, etc., qui sont utilisés conjointement avec les relais de mesure et les dispositifs de protection et sont soumis à l'essai ensemble.

General Information

• Status: Published
• Publication Date: 06-Feb-2023
• ICS: 29.120.70 - Relays
• Technical Committee: TC 95 - Measuring relays and protection equipment
• Drafting Committee: MT 3 - TC 95/MT 3
• Current Stage: PPUB - Publication issued
• Start Date: 27-Jan-2023
• Completion Date: 07-Feb-2023

Relations

• Revises: IEC 60255-27:2013 - Measuring relays and protection equipment - Part 27: Product safety requirements
• Effective Date: 05-Sep-2023

Overview

IEC 60255-27:2023 - Measuring relays and protection equipment - Part 27: Product safety requirements specifies product safety requirements for measuring relays and protection equipment with a rated AC voltage up to 1 000 V or a rated DC voltage up to 1 500 V. The standard focuses on minimizing risks of electric shock, fire, and injury to users and property. It addresses only product safety (not functional performance) and covers equipment mounting in cabinets, racks and panels as well as auxiliary devices (shunts, series resistors, transformers, auxiliary control panels, displays) that are tested together with the equipment.

Key topics and technical requirements

• Protection against electric shock: insulation, protective impedance, bonding, accessible parts and requirements for single-fault conditions.
• Earthing and protective bonding: general earthing rules, functional earthing, and protective conductor connections.
• Clearances and creepage distances: guidance for determining required distances and rated insulation/impulse voltages (see normative guidance).
• Mechanical safety: stability, moving parts, edges and corners, and mechanical security of terminations.
• Flammability and fire resistance: fire enclosures, flame barriers, material flammability requirements, minimizing ignition sources and assessing fire risk under normal and single-fault conditions.
• Design for safety: component integrity, climatic and environmental considerations, electrical connections, and special hazards (explosion, lasers, high-intensity light).
• Marking, documentation and packaging: identification, terminal and fuse marking, installation and maintenance instructions, warning labels and documentation durability.
• Testing and conformity: type and routine safety tests, climatic/mechanical tests, electrical safety tests, and verification procedures.
• Normative annexes: isolation class examples, rated impulse voltages, and guidance for clearances/creepage.

Practical applications

• Use IEC 60255-27 for product design and risk reduction when developing measuring relays and protection devices intended for use up to the specified voltage limits.
• Support type testing and product certification by manufacturers and third‑party labs to demonstrate compliance with product safety requirements.
• Guide installation and maintenance practices for utilities and panel builders to ensure safe mounting and wiring in racks and cabinets.
• Inform procurement and compliance teams when specifying safety-related requirements for protection equipment and associated auxiliary devices.

Who should use this standard

• Relay and protection equipment manufacturers and design engineers
• Test laboratories and conformity assessment bodies
• Utility and industrial specifiers, panel builders and system integrators
• Safety, compliance and regulatory professionals responsible for electrical equipment.

Related standards

• Other parts of the IEC 60255 series (measuring relays and protection equipment) and applicable IEC product-safety guidance for electrical equipment and components.

Standards Content (Sample)

IEC 60255-27 ®
Edition 3.0 2023-02
COMMENTED VERSION
INTERNATIONAL
STANDARD
colour
inside
Measuring relays and protection equipment –
Part 27: Product safety requirements
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Secretariat Tel.: [phone]
3, rue de Varembé [e-mail]
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

IEC publications search - webstore.iec.ch/advsearchform IEC Products & Services Portal - products.iec.ch
The advanced search enables to find IEC publications by a
Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews. With a subscription you will always
committee, …). It also gives information on projects, replaced have access to up to date content tailored to your needs.
and withdrawn publications.
Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
The world's leading online dictionary on electrotechnology,
Stay up to date on all new IEC publications. Just Published
containing more than 22 300 terminological entries in English
details all new publications released. Available online and
and French, with equivalent terms in 19 additional languages.
once a month by email.
Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Customer Service Centre - webstore.iec.ch/csc

If you wish to give us your feedback on this publication or
need further assistance, please contact the Customer Service
Centre: [e-mail].
IEC 60255-27 ®
Edition 3.0 2023-02
COMMENTED VERSION
INTERNATIONAL
STANDARD
colour
inside
Measuring relays and protection equipment –
Part 27: Product safety requirements
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.120.70 ISBN 978-2-8322-6472-0

– 2 – IEC 60255-27:2023 CMV © IEC 2023
CONTENTS
FOREWORD .8
INTRODUCTION . 11

1 Scope . 12
2 Normative references . 13
3 Terms and definitions . 14
4 General safety requirements.
4.1 General .
4.2 Earthing requirements.
4 Protection against electric shock . 26
5.1 General .
Introductory remark .
4.1 Protection from contact with hazardous-live-parts . 27
4.1.1 General . 27
4.1.2 Insulation . 27
4.1.3 Equipment case enclosure and barriers . 27
4.1.4 Hazardous live terminations using stranded wire . 28
Discharge of capacitors .
4.2 Protective impedance . 29
4.3 Accessible parts . 30
4.3.1 General . 30
4.3.2 Determination of accessible parts . 30
4.3.3 Permissible limits for accessible parts . 31
4.4 Bonding to the protective conductor Earthing and protective bonding
requirements . 32
4.4.1 General . 32
4.4.2 Insulation between live parts and accessible conductive parts. 33
4.4.3 Protective bonding . 33
4.5 Functional earthing earthed circuits . 34
4.6 Protective conductor connection. 34
4.7 High leakage current . 34
4.8 Solid insulation . 35
4.8.1 General . 35
4.8.2 Requirements . 35
4.9 Clearances and creepage distances . 35
4.9.1 General . 35
4.9.2 Clearances . 36
4.9.3 Creepage distances . 37
4.10 Single fault conditions . 38
4.10.1 Testing in single fault condition . 38
4.10.2 Application of single fault condition . 38
4.10.3 Duration of tests . 40
4.10.4 Compliance . 40
5 Mechanical aspects . 41
5.1 Protection against mechanical hazards . 41
5.1.1 Stability . 41

5.1.2 Moving parts . 41
5.1.3 Edges and corners . 42
5.2 Mechanical requirements . 42
5.3 Mechanical security of terminations . 42
6 Flammability and resistance to fire. 42
6.1 General . 42
6.2 Requirements for protection against the spread of fire . 42
6.3 General hazards from overheating and fire . 45
6.3.1 Equipment Surface temperature limits for protection against burns . 45
6.3.2 Hazardous gases and chemicals . 46
6.4 Minimization of fire risk . 46
6.4.1 General . 46
6.4.2 Eliminating or reducing the sources of ignition within the equipment . 47
6.5 Cabling and fusing . 47
6.6 Flammability of materials and components . 48
6.6.1 General . 48
6.6.2 Materials for components and other parts inside fire enclosures . 48
6.6.3 Materials for fire enclosures . 49
6.6.4 Materials for components and other parts outside fire enclosures . 49
6.7 Fire ignition sources . 50
6.8 Conditions for a fire enclosure. 50
6.8.1 Parts requiring a fire enclosure . 50
6.8.2 Parts not requiring a fire enclosure. 50
6.9 Requirements for primary circuits and circuits exceeding ELV limits
Fire enclosures and flame barriers . 51
6.9.1 General . 51
6.9.2 Fire enclosures and flame barrier requirements . 51
6.10 Assessment of the fire risk due to a single fault condition . 54
6.10.1 Guidelines for maximum acceptable temperatures when subjecting a
circuit or component to a single fault condition . 54
6.10.2 Temperature of windings under normal condition use or a single fault
condition . 54
6.10.3 Compliance Conformity of equipment with requirements for protection
against the spread of fire . 55
6.11 Limited-energy circuit . 55
7 General and fundamental design requirements for safety . 56
7.1 Climatic conditions for safety . 56
7.2 Electrical connections . 56
7.3 Components . 57
7.3.1 General . 57
7.3.2 High-integrity part or component . 57
8.4 Connection to telecommunication networks .
7.4 Connection to other equipment. 58
7.5 Laser High-intensity light sources . 58
7.6 Explosion . 58
7.6.1 General . 58
7.6.2 Components at risk of explosion . 58
8 Marking, documentation and packaging . 59
8.1 Marking . 59

– 4 – IEC 60255-27:2023 CMV © IEC 2023
8.1.1 General . 59
8.1.2 Identification . 59
8.1.3 Auxiliary supplies, VT, CT, I/O (Input/Output) measurands, inputs and
outputs . 60
8.1.4 Fuses . 61
8.1.5 Measuring circuit terminals . 62
8.1.6 Terminals and operating devices . 62
8.1.7 Equipment protected by double or reinforced insulation . 63
8.1.8 Batteries . 63
8.1.9 Test voltage marking . 66
8.1.10 Warning markings . 67
8.1.11 Marking durability . 67
8.2 Documentation . 68
8.2.1 General . 68
8.2.2 Equipment ratings . 68
8.2.3 Equipment installation . 69
8.2.4 Equipment commissioning and maintenance . 69
8.2.5 Equipment operation . 70
8.3 Packaging . 70
9 Type tests and routine tests . 70
9.1 General . 70
9.2 Safety type tests . 72
9.3 Routine testing or sample testing . 73
9.4 Conditions for testing . 73
9.5 Verification procedure . 73
9.6 Tests . 74
9.6.1 Climatic environmental tests . 74
9.6.2 Mechanical tests. 74
9.6.3 Clearances and creepage distances . 75
9.6.4 Safety-related electrical tests . 76
9.6.5 Electrical environment and flammability . 82
9.6.6 Reverse polarity and slow ramp test . 84
9.6.7 Resistance to mechanical stress . 85

Annex A (normative) Isolation class requirements and example diagrams . 87
A.1 General . 87
A.2 Hazardous live voltage (HLV) . 87
A.3 Symbols . 89
A.4 Typical insulation examples complying with the requirements of Table A.2 . 91
Annex B (normative) Rated impulse voltages . 96
Annex C (normative) Guidance for the determination of clearance, creepage distance
and withstand voltages . 97
C.1 General . 97
C.1.1 Introductory remark . 97
C.1.2 Rated insulation voltages . 97
C.1.3 Determination of rated insulation voltage . 98
C.1.4 Determination of rated impulse voltage. 98
C.1.5 Switching overvoltages generated by equipment . 99
C.1.6 lnsulation material . 99

C.1.7 Overvoltage categories . 99
C.2 Determination of clearances, creepage distances and withstand voltages . 100
C.2.1 Guidance for determination of clearances, creepage distances and
withstand voltages . 100
C.2.2 Determination of clearances, creepage distances and withstand
voltages . 103
Annex D (informative) Components . 110
D.1 General . 110
D.2 Introductory remark . 110
D.3 Transformers . 110
D.4 Equipment primary circuit capacitors . 111
D.5 Coil devices – transformers, instrument transformers and transducers,
reactors, and operating coils of relays and contactors with multiple windings
and/or screen . 111
D.5.1 Coil windings . 111
D.5.2 Insulating foil . 112
D.5.3 Interposing protective screen . 112
D.5.4 Safety isolation transformers. 112
D.6 Electromechanical components . 112
D.7 Semiconductor components and semiconductor configurations . 112
D.8 Connectors and terminal blocks . 113
D.9 Voltage dependent resistors (VDRs) . 113
D.10 Intentional radio transmitters . 114
Annex E (normative) External wiring terminations . 115
E.1 General . 115
E.2 Permanently connected equipment . 115
E.3 Conductors . 115
E.4 Terminals . 116
Annex F (informative) Examples of battery protection . 117
Annex G (informative) Risk assessment . 118
G.1 General . 118
G.2 Risk assessment procedure . 118
G.3 Achieving tolerable risk . 119
G.4 An application of risk assessment procedures. 120
Bibliography . 121
List of comments . 123

Figure 1 – Flow chart showing requirements for protection against the spread of fire . 45
Figure 2 – Baffle . 52
Figure 3 – Location and extent of a flame barrier . 53
Figure 4 – Voltage ramp test . 84
Figure 5 – Impact test with sphere . 86
Figure A.1 – Equipment with SELV input and/or output (I/O) . 92
Figure A.2 – Equipment with PELV input and/or output (I/O) . 93
Figure A.3 – Equipment with PEB input and/or output (I/O) . 94
Figure A.4 – Equipment with ELV input and/or output (I/O) . 95
Figure C.1 – Guidance for determination of clearances, creepage distances and
withstand voltages . 102

– 6 – IEC 60255-27:2023 CMV © IEC 2023
Figure F.1 – Non-rechargeable battery protection . 117
Figure F.2 – Rechargeable battery protection . 117
Figure G.1 – Iterative process of risk assessment and risk reduction . 118
Figure G.2 – Risk reduction . 119

Table 1 – Equipment enclosure requirements for protection against electric shock . 28
Table 2 – Current levels under normal conditions use . 32
Table 3 – Charge or energy of capacitance levels under normal conditions use . 32
Table 4 – Altitude multiplication factor . 36
Table 5 – Current levels in single fault condition . 41
Table 6 – Maximum temperature under normal conditions use and at an ambient
temperature of 40 °C . 46
Table 7 – Acceptable perforation in the bottom of an equipment case . 54
Table 8 – Insulation material of windings. 55
Table 9 – Limits of maximum available current . 56
Table 10 – Overcurrent protective device . 56
Table 11 – Fuse types . 62
Table 12 – Symbols. 65
Table 13 – Symbols for marking of test voltage(s) . 66
Table 14 – Overview of tests . 70
Table 14 – AC test voltages .
Table 15 – Impulse generator characteristics . 76
Table 16 – Guidance for routine and sample dielectric voltage testing for safety –
Informative . 81
Table 17 – Limiting dynamic values . 83
Table 18 – Impact energy levels, test height and corresponding IK codes . 86
Table A.1 – Circuit isolation class for product circuits and/or groups . 87
Table A.2 – Insulation requirement between any two circuits . 89
Table B.1 – Rated impulse voltages (waveform: 1,2/50 µs) . 96
Table C.1 – Comparative tracking index (CTI) . 99
Table C.2 – Functional insulation, pollution degree 1, overvoltage category I . 103
Table C.3 – Functional insulation, pollution degree 2, overvoltage category I . 104
Table C.4 – Functional, basic or supplementary insulation, pollution degree 1,
overvoltage category II . 104
Table C.5 – Functional, basic or supplementary insulation, pollution degree 2,
overvoltage category II . 105
Table C.6 – Functional, basic or supplementary insulation, pollution degree 1,
overvoltage category III . 105
Table C.7 – Functional, basic or supplementary insulation, pollution degree 2,
overvoltage category III . 106
Table C.8 – Double or reinforced insulation, pollution degree 1, overvoltage category II . 106
Table C.9 – Double or reinforced insulation, pollution degree 2, overvoltage category II . 107
Table C.10 – Double or reinforced insulation, pollution degree 1, overvoltage category III . 107
Table C.11 – Double or reinforced insulation, pollution degree 2, overvoltage category III . 108

Table C.12 – Test voltage multiplication site correction factor for proving the clearance
in air . 108
Table C.13 – Reduction of the pollution degree of internal environment through the use
of additional protection within the equipment . 109
Table E.1 – Range of conductor sizes to be accepted by terminals . 116
Table E.2 – Sizes of terminal studs or screws directly securing supply conductors . 116
Table G.1 – Severity of harm . 120
Table G.2 – Probability of harm . 120
Table G.3 – Risk category . 120

– 8 – IEC 60255-27:2023 CMV © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASURING RELAYS AND PROTECTION EQUIPMENT –

Part 27: Product safety requirements

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 commented version (CMV) of the official standard IEC 60255-27:2023 edition 3.0
allows the user to identify the changes made to the previous IEC 60255-27:2013
edition 2.0. Furthermore, comments from IEC TC 95 experts are provided to explain the
reasons of the most relevant changes, or to clarify any part of the content.
A vertical bar appears in the margin wherever a change has been made. Additions are in
green text, deletions are in strikethrough red text. Experts' comments are identified by a
blue-background number. Mouse over a number to display a pop-up note with the
comment.
This publication contains the CMV and the official standard. The full list of comments is
available at the end of the CMV.

IEC 60255-27 has been prepared by IEC technical committee 95: Measuring relays and
protection equipment. It is an International Standard.
This third edition cancels and replaces the second edition published in 2013. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) conflicting statements removed;
b) scope clarified and statement added that all clauses of the standard are required not just
type tests;
c) terminology, definitions and documentation requirements aligned with IEC 60255-1;
d) alignment with IEC 61010-1, e.g. HLV definitions;
e) ingress protection clarified;
f) dielectric and impulse tests added to mechanical and environmental test requirements;
g) insulation resistance requirements updated for alignment with other product safety
standards;
h) sample testing removed;
i) short time limiting thermal overload added;
j) resistance to mechanical stress added;
k) low-power voltage and current transformer ports added;
l) Annex C tables updated to align with base standards;
m) Annex D voltage dependent resistors and radio transmitters added;
n) Annex G for risk assessment added.
The text of this International Standard is based on the following documents:
Draft Report on voting
95/516/FDIS 95/526/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/publications.
A list of all parts in the IEC 60255 series, published under the general title Measuring relays
and protection equipment, can be found on the IEC website.

– 10 – IEC 60255-27:2023 CMV © IEC 2023
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under 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 document 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.

INTRODUCTION
In order to demonstrate that the equipment is safe, it was previously necessary to refer to
general safety standards such as IEC 61010-1 in addition to IEC 60664-1.
These general safety standards specify requirements for general product types or product
families in order to reduce the risk of fire, electric shock or injury to the user. The product types
do not include measuring relays and protection equipment. These standards also take into
account single-fault conditions.
Reference to all these various standards created confusion due to conflicting requirements, for
example, different clearances, creepage distances and test voltages etc., for the same rated
voltages.
The aim of this standard is:
• to remove confusion due to conflicting requirements between existing standards;
• to achieve a uniform approach throughout the international industry for measuring relays
and protection equipment.
This product safety standard for measuring relays and protection equipment takes the general
product safety standards and IEC 60664-1 as the base, defining those issues specific to
measuring relays and protection equipment.
This document specifies the safety requirements that are generally applicable to all equipment
within its scope. These requirements may be supplemented by general product safety standards
and IEC 60664-1.
– 12 – IEC 60255-27:2023 CMV © IEC 2023
MEASURING RELAYS AND PROTECTION EQUIPMENT –

Part 27: Product safety requirements

1 Scope
This part of IEC 60255 describes specifies the product safety requirements for measuring
relays and protection equipment having a rated AC voltage up to 1 000 V with a rated frequency
up to 65 Hz, or a rated DC voltage up to 1 500 V. Above these limits, IEC 60664-1 is applicable
for the determination of clearance, creepage distance and withstand test voltage.
This document details specifies essential safety requirements to minimize the risk of fire and
hazards caused by electric shock or injury to the user and property. This document specifies
only product safety requirements; functional performance of the equipment is not covered. 1
This standard does not cover the safety requirements of installations. This document covers all
the ways in which the equipment may can be mounted and used in cubicles cabinets, racks and
panels, and also retesting. This document also applies to auxiliary devices such as shunts,
series resistors, transformers, auxiliary control panels, display devices, etc., that are used in
conjunction with measuring relays and protection equipment and are tested together.
pment such as network switches used in conjunction with
It is possible that ancillary equi
measuring relays and protection equipment may need needs to comply with additional safety
requirements.
This standard is intended to describe only product safety requirements; therefore, functional
performance of the equipment is not covered.
Functional safety requirements, including EMC functional safety, are not covered by this
standard. Functional safety risk analysis is not within the scope of this product safety standard.
This document does not specify the implementation of individual equipment, circuits and
components.
The object of this standard is to have a comprehensive standard that covers all aspects of
product safety and the related type and routine tests, for measuring relays and protection
equipment.
This document applies to equipment designed to be safe at least under the following
environmental conditions:
– indoor use;
– altitude up to 2 000 m, in accordance with IEC 60255-1;
– external operating temperature range, in accordance with IEC 60255-1;
– rated ambient temperature range, in accordance with IEC 60255-1;
– maximum external relative humidity 95 %, non-condensing, in accordance with
IEC 60255-1;
– supply fluctuations in accordance with IEC 60255-1;
– operating range of auxiliary energizing voltage in accordance with IEC 60255-1;
– applicable supply overvoltage category;
– external pollution degree 1 and external pollution degree 2.

– applicable pollution degree of the intended environment (pollution degree 2 in most cases).
The equipment will normally be installed in a restricted access area within a power station,
substation or industrial/retail environment. The environmental conditions specified for the
equipment in IEC 60255-1 apply. This standard considers the normal environmental conditions
of corrosion caused by humidity but does not cover corrosion by atmospheric pollution.
It is assumed that access to the equipment during installation, maintenance, normal service and
decommissioning is restricted to users aware of working procedures necessary to ensure
safety.
This product safety standard takes precedence over general standards for matters of safety.
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 60050 (all parts), International Electrotechnical Vocabulary (available at

IEC 60085, Electrical insulation – Thermal evaluation and designation
IEC 60127-1, Miniature fuses – Part 1: Definitions for miniature fuses and general requirements
for miniature fuse-links
IEC 60255-1, Measuring relays and protection equipment – Part 1: Common requirements
IEC 60255-21-1, Electrical relays – Part 21: Vibration, shock, bump and seismic tests on
measuring relays and protection equipment – Section One: Vibration tests (sinusoidal)
IEC 60255-21-2, Electrical relays – Part 21: Vibration, shock, bump and seismic tests on
measuring relays and protection equipment – Section Two: Shock and bump tests
IEC 60255-21-3, Electrical relays – Part 21: Vibration, shock, bump and seismic tests on
measuring relays and protection equipment – Section 3: Seismic tests
IEC 60255-26:2013, Measuring relays and protection equipment – Part 26: Electromagnetic
compatibility requirements
IEC 60352-1, Solderless connections – Part 1: Wrapped connections – General requirements,
test methods and practical guidance
IEC 60352-2, Solderless connections – Part 2: Crimped connections – General requirements,
test methods and practical guidance
IEC 60417, Graphical symbols for use on equipment. Available at: http://www.graphical-
symbols.info/equipment
IEC 60529:1989, Degrees of protection provided by enclosures (IP
...

IEC 60255-27 ®
Edition 3.0 2023-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Measuring relays and protection equipment –
Part 27: Product safety requirements
Relais de mesure et dispositifs de protection –
Partie 27: Exigences de sécurité des produits
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 Secretariat Tel.: [phone]
3, rue de Varembé [e-mail]
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.
About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.
IEC publications search - webstore.iec.ch/advsearchform IEC Products & Services Portal - products.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews. With a subscription you will always have
committee, …). It also gives information on projects, replaced access to up to date content tailored to your needs.
and withdrawn publications.
Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
The world's leading online dictionary on electrotechnology,
Stay up to date on all new IEC publications. Just Published
containing more than 22 300 terminological entries in English
details all new publications released. Available online and once
and French, with equivalent terms in 19 additional languages.
a month by email.
Also known as the International Electrotechnical Vocabulary
(IEV) online.
IEC Customer Service Centre - webstore.iec.ch/csc
If you wish to give us your feedback on this publication or need
further assistance, please contact the Customer Service
Centre: [e-mail].
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) est la première organisation mondiale qui élabore et publie des
Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.
A propos des publications IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.
Recherche de publications IEC - Découvrez notre puissant moteur de recherche et consultez
webstore.iec.ch/advsearchform gratuitement tous les aperçus des publications. Avec un
La recherche avancée permet de trouver des publications IEC abonnement, vous aurez toujours accès à un contenu à jour
en utilisant différents critères (numéro de référence, texte, adapté à vos besoins.
comité d’études, …). Elle donne aussi des informations sur les
projets et les publications remplacées ou retirées. Electropedia - www.electropedia.org
Le premier dictionnaire d'électrotechnologie en ligne au monde,
IEC Just Published - webstore.iec.ch/justpublished
avec plus de 22 300 articles terminologiques en anglais et en
Restez informé sur les nouvelles publications IEC. Just
français, ainsi que les termes équivalents dans 19 langues
Published détaille les nouvelles publications parues.
additionnelles. Egalement appelé Vocabulaire
Disponible en ligne et une fois par mois par email.
Electrotechnique International (IEV) en ligne.
Service Clients - webstore.iec.ch/csc
Si vous désirez nous donner des commentaires sur cette
publication ou si vous avez des questions contactez-nous:
[e-mail].
IEC Products & Services Portal - products.iec.ch

IEC 60255-27 ®
Edition 3.0 2023-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Measuring relays and protection equipment –
Part 27: Product safety requirements
Relais de mesure et dispositifs de protection –
Partie 27: Exigences de sécurité des produits
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.120.70 ISBN 978-2-8322-6322-8
– 2 – IEC 60255-27:2023 © IEC 2023
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 12
4 Protection against electric shock . 20
4.1 Protection from contact with hazardous-live-parts . 20
4.1.1 General . 20
4.1.2 Insulation . 21
4.1.3 Equipment enclosure and barriers . 21
4.1.4 Hazardous live terminations using stranded wire . 22
4.2 Protective impedance. 22
4.3 Accessible parts. 23
4.3.1 General . 23
4.3.2 Determination of accessible parts . 23
4.3.3 Permissible limits for accessible parts . 24
4.4 Earthing and protective bonding requirements . 25
4.4.1 General . 25
4.4.2 Insulation between live parts and accessible conductive parts . 25
4.4.3 Protective bonding . 26
4.5 Functional earthed circuits . 26
4.6 Protective conductor connection . 27
4.7 High leakage current . 27
4.8 Solid insulation . 27
4.8.1 General . 27
4.8.2 Requirements . 28
4.9 Clearances and creepage distances . 28
4.9.1 General . 28
4.9.2 Clearances . 28
4.9.3 Creepage distances . 29
4.10 Single fault conditions . 30
4.10.1 Testing in single fault condition . 30
4.10.2 Application of single fault condition . 30
4.10.3 Duration of tests . 32
4.10.4 Compliance . 32
5 Mechanical aspects . 33
5.1 Protection against mechanical hazards . 33
5.1.1 Stability . 33
5.1.2 Moving parts . 33
5.1.3 Edges and corners . 34
5.2 Mechanical requirements . 34
5.3 Mechanical security of terminations . 34
6 Flammability and resistance to fire . 34
6.1 General . 34
6.2 Requirements for protection against the spread of fire . 34
6.3 General hazards from overheating and fire . 36

6.3.1 Surface temperature limits for protection against burns . 36
6.3.2 Hazardous gases and chemicals . 36
6.4 Minimization of fire risk . 36
6.4.1 General . 36
6.4.2 Eliminating or reducing the sources of ignition within the equipment . 37
6.5 Cabling and fusing . 37
6.6 Flammability of materials and components . 37
6.6.1 General . 37
6.6.2 Materials for components and other parts inside fire enclosures . 38
6.6.3 Materials for fire enclosures . 38
6.6.4 Materials for components and other parts outside fire enclosures . 39
6.7 Fire ignition sources. 39
6.8 Conditions for a fire enclosure . 40
6.8.1 Parts requiring a fire enclosure . 40
6.8.2 Parts not requiring a fire enclosure . 40
6.9 Fire enclosures and flame barriers . 41
6.9.1 General . 41
6.9.2 Fire enclosures and flame barrier requirements . 41
6.10 Assessment of the fire risk due to a single fault condition . 43
6.10.1 Guidelines for maximum acceptable temperatures when subjecting a
circuit or component to a single fault condition . 43
6.10.2 Temperature of windings under normal use or a single fault condition . 43
6.10.3 Conformity of equipment with requirements for protection against the

spread of fire . 43
6.11 Limited-energy circuit . 44
7 General and fundamental design requirements for safety . 45
7.1 Climatic conditions for safety . 45
7.2 Electrical connections . 45
7.3 Components . 45
7.3.1 General . 45
7.3.2 High-integrity part or component . 45
7.4 Connection to other equipment . 46
7.5 High-intensity light sources . 46
7.6 Explosion . 46
7.6.1 General . 46
7.6.2 Components at risk of explosion . 46
8 Marking, documentation and packaging . 47
8.1 Marking . 47
8.1.1 General . 47
8.1.2 Identification . 47
8.1.3 Auxiliary supplies, measurands, inputs and outputs . 48
8.1.4 Fuses . 49
8.1.5 Measuring circuit terminals . 50
8.1.6 Terminals and operating devices . 50
8.1.7 Equipment protected by double or reinforced insulation . 51
8.1.8 Batteries . 51
8.1.9 Test voltage marking . 53
8.1.10 Warning markings . 53
8.1.11 Marking durability . 54

– 4 – IEC 60255-27:2023 © IEC 2023
8.2 Documentation . 54
8.2.1 General . 54
8.2.2 Equipment ratings . 54
8.2.3 Equipment installation . 55
8.2.4 Equipment commissioning and maintenance . 55
8.2.5 Equipment operation . 56
8.3 Packaging . 56
9 Type tests and routine tests . 56
9.1 General . 56
9.2 Safety type tests . 58
9.3 Routine testing . 58
9.4 Conditions for testing . 58
9.5 Verification procedure . 58
9.6 Tests . 59
9.6.1 Climatic environmental tests . 59
9.6.2 Mechanical tests . 60
9.6.3 Clearances and creepage distances . 60
9.6.4 Safety-related electrical tests. 60
9.6.5 Electrical environment and flammability . 65
9.6.6 Reverse polarity and slow ramp test . 67
9.6.7 Resistance to mechanical stress . 68
Annex A (normative)  Isolation class requirements and example diagrams . 70
A.1 General . 70
A.2 Hazardous live voltage (HLV) . 70
A.3 Symbols . 71
A.4 Typical insulation examples complying with the requirements of Table A.2 . 73
Annex B (normative) Rated impulse voltages . 76
Annex C (normative) Guidance for the determination of clearance, creepage distance
and withstand voltages . 77
C.1 General . 77
C.1.1 Introductory remark . 77
C.1.2 Rated insulation voltages . 77
C.1.3 Determination of rated insulation voltage . 78
C.1.4 Determination of rated impulse voltage . 78
C.1.5 Switching overvoltages generated by equipment . 79
C.1.6 lnsulation material . 79
C.1.7 Overvoltage categories . 79
C.2 Determination of clearances, creepage distances and withstand voltages . 80
C.2.1 Guidance for determination of clearances, creepage distances and

withstand voltages . 80
C.2.2 Determination of clearances, creepage distances and withstand
voltages . 82
Annex D (informative) Components . 88
D.1 General . 88
D.2 Introductory remark . 88
D.3 Transformers . 88
D.4 Equipment primary circuit capacitors . 88

D.5 Coil devices – transformers, instrument transformers and transducers,
reactors, and operating coils of relays and contactors with multiple windings
and/or screen . 89
D.5.1 Coil windings . 89
D.5.2 Insulating foil . 90
D.5.3 Interposing protective screen . 90
D.5.4 Safety isolation transformers . 90
D.6 Electromechanical components . 90
D.7 Semiconductor components and semiconductor configurations . 90
D.8 Connectors and terminal blocks . 91
D.9 Voltage dependent resistors (VDRs) . 91
D.10 Intentional radio transmitters . 92
Annex E (normative) External wiring terminations . 93
E.1 General . 93
E.2 Permanently connected equipment . 93
E.3 Conductors . 93
E.4 Terminals . 94
Annex F (informative) Examples of battery protection . 95
Annex G (informative) Risk assessment . 96
G.1 General . 96
G.2 Risk assessment procedure . 96
G.3 Achieving tolerable risk . 97
G.4 An application of risk assessment procedures . 98
Bibliography . 99

Figure 1 – Flow chart showing requirements for protection against the spread of fire . 35
Figure 2 – Baffle . 41
Figure 3 – Location and extent of a flame barrier . 42
Figure 4 – Voltage ramp test . 67
Figure 5 – Impact test with sphere . 69
Figure A.1 – Equipment with SELV input and/or output (I/O) . 74
Figure A.2 – Equipment with PELV input and/or output (I/O) . 74
Figure A.3 – Equipment with PEB input and/or output (I/O) . 75
Figure A.4 – Equipment with ELV input and/or output (I/O) . 75
Figure C.1 – Guidance for determination of clearances, creepage distances and
withstand voltages . 81
Figure F.1 – Non-rechargeable battery protection . 95
Figure F.2 – Rechargeable battery protection . 95
Figure G.1 – Iterative process of risk assessment and risk reduction . 96
Figure G.2 – Risk reduction . 97

Table 1 – Equipment enclosure requirements for protection against electric shock . 21
Table 2 – Current levels under normal use . 25
Table 3 – Charge or energy of capacitance levels under normal use . 25
Table 4 – Altitude multiplication factor . 29
Table 5 – Current levels in single fault condition . 33

– 6 – IEC 60255-27:2023 © IEC 2023
Table 6 – Maximum temperature under normal use and at an ambient temperature of
40 °C . 36
Table 7 – Acceptable perforation in the bottom of an equipment case . 42
Table 8 – Insulation material of windings . 43
Table 9 – Limits of maximum available current . 44
Table 10 – Overcurrent protective device . 44
Table 11 – Fuse types . 49
Table 12 – Symbols . 52
Table 13 – Symbols for marking of test voltage(s) . 53
Table 14 – Overview of tests . 57
Table 15 – Impulse generator characteristics . 61
Table 16 – Guidance for routine dielectric voltage testing for safety . 64
Table 17 – Limiting dynamic values . 66
Table 18 – Impact energy levels, test height and corresponding IK codes . 69
Table A.1 – Circuit isolation class for product circuits and/or groups . 70
Table A.2 – Insulation requirement between any two circuits . 72
Table B.1 – Rated impulse voltages (waveform: 1,2/50 µs) . 76
Table C.1 – Comparative tracking index (CTI) . 79
Table C.2 – Functional insulation, pollution degree 1, overvoltage category I . 82
Table C.3 – Functional insulation, pollution degree 2, overvoltage category I . 83
Table C.4 – Functional, basic or supplementary insulation, pollution degree 1,

overvoltage category II . 83
Table C.5 – Functional, basic or supplementary insulation, pollution degree 2,
overvoltage category II . 84
Table C.6 – Functional, basic or supplementary insulation, pollution degree 1,
overvoltage category III . 84
Table C.7 – Functional, basic or supplementary insulation, pollution degree 2,

overvoltage category III . 85
Table C.8 – Double or reinforced insulation, pollution degree 1,
overvoltage category II . 85
Table C.9 – Double or reinforced insulation, pollution degree 2,
overvoltage category II . 86
Table C.10 – Double or reinforced insulation, pollution degree 1,

overvoltage category III . 86
Table C.11 – Double or reinforced insulation, pollution degree 2,
overvoltage category III . 87
Table C.12 – Test site correction factor for proving the clearance in air . 87
Table C.13 – Reduction of the pollution degree of internal environment through the
use of additional protection within the equipment . 87
Table E.1 – Range of conductor sizes to be accepted by terminals . 94
Table E.2 – Sizes of terminal studs or screws directly securing supply conductors . 94
Table G.1 – Severity of harm . 98
Table G.2 – Probability of harm . 98
Table G.3 – Risk category . 98

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASURING RELAYS AND PROTECTION EQUIPMENT –

Part 27: Product safety requirements

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.
IEC 60255-27 has been prepared by IEC technical committee 95: Measuring relays and
protection equipment. It is an International Standard.
This third edition cancels and replaces the second edition published in 2013. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) conflicting statements removed;
b) scope clarified and statement added that all clauses of the standard are required not just
type tests;
c) terminology, definitions and documentation requirements aligned with IEC 60255-1;
d) alignment with IEC 61010-1, e.g. HLV definitions;
e) ingress protection clarified;
f) dielectric and impulse tests added to mechanical and environmental test requirements;

– 8 – IEC 60255-27:2023 © IEC 2023
g) insulation resistance requirements updated for alignment with other product safety
standards;
h) sample testing removed;
i) short time limiting thermal overload added;
j) resistance to mechanical stress added;
k) low-power voltage and current transformer ports added;
l) Annex C tables updated to align with base standards;
m) Annex D voltage dependent resistors and radio transmitters added;
n) Annex G for risk assessment added.
The text of this International Standard is based on the following documents:
Draft Report on voting
95/516/FDIS 95/526/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/publications.
A list of all parts in the IEC 60255 series, published under the general title Measuring relays
and protection equipment, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under 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.
INTRODUCTION
This document specifies the safety requirements that are generally applicable to all equipment
within its scope. These requirements may be supplemented by general product safety standards
and IEC 60664-1.
– 10 – IEC 60255-27:2023 © IEC 2023
MEASURING RELAYS AND PROTECTION EQUIPMENT –

Part 27: Product safety requirements

1 Scope
This part of IEC 60255 specifies the product safety requirements for measuring relays and
protection equipment having a rated AC voltage up to 1 000 V, or a rated DC voltage up to
1 500 V. Above these limits, IEC 60664-1 is applicable for the determination of clearance,
creepage distance and withstand test voltage.
This document specifies essential safety requirements to minimize the risk of fire and hazards
caused by electric shock or injury to the user and property. This document specifies only product
safety requirements; functional performance of the equipment is not covered.
This document covers all the ways in which the equipment can be mounted and used in
cabinets, racks and panels. This document also applies to auxiliary devices such as shunts,
series resistors, transformers, auxiliary control panels, display devices, etc., that are used in
conjunction with measuring relays and protection equipment and are tested together.
It is possible that ancillary equipment such as network switches used in conjunction with
measuring relays and protection equipment needs to comply with additional safety
requirements.
This document does not specify the implementation of individual equipment, circuits and
components.
This document applies to equipment designed to be safe at least under the following
environmental conditions:
– indoor use;
– altitude up to 2 000 m, in accordance with IEC 60255-1;
– rated ambient temperature range, in accordance with IEC 60255-1;
– maximum external relative humidity, in accordance with IEC 60255-1;
– operating range of auxiliary energizing voltage in accordance with IEC 60255-1;
– applicable overvoltage category;
– applicable pollution degree of the intended environment (pollution degree 2 in most cases).
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 60085, Electrical insulation – Thermal evaluation and designation
IEC 60127-1, Miniature fuses – Part 1: Definitions for miniature fuses and general requirements
for miniature fuse-links
IEC 60255-1, Measuring relays and protection equipment – Part 1: Common requirements

IEC 60255-26, Measuring relays and protection equipment – Part 26: Electromagnetic
compatibility requirements
IEC 60352-1, Solderless connections – Part 1: Wrapped connections – General requirements,
test methods and practical guidance
IEC 60352-2, Solderless connections – Part 2: Crimped connections – General requirements,
test methods and practical guidance
IEC 60417, Graphical symbols for use on equipment. Available at: http://www.graphical-
symbols.info/equipment
IEC 60529:1989, Degrees of protection provided by enclosures (IP Code)
IEC 60529:1989/AMD1:1999
IEC 60529:1989/AMD2:2013
IEC 60664-1:2020, Insulation coordination for equipment within low-voltage supply systems –
Part 1: Principles, requirements and tests
IEC 60664-3, Insulation coordination for equipment within low-voltage systems – Part 3: Use of
coating, potting or moulding for protection against pollution
IEC TS 60695-2-20, Fire hazard testing – Part 2-20: Glowing/hot-wire based test methods –
Hot-wire coil test method – Apparatus, test method and guidance
IEC 60695-11-10, Fire hazard testing – Part 11-10: Test flames – 50 W horizontal and vertical
flame test methods
IEC 60825-1, Safety of laser products – Part 1: Equipment classification and requirements
IEC 60990:2016, Methods of measurement of touch current and protective conductor current
IEC 61010-1:2010, Safety requirements for electrical equipment for measurement, control, and
laboratory use – Part 1: General requirements
IEC 61010-1:2010/AMD1:2016
IEC 61032, Protection of persons and equipment by enclosures – Probes for verification
IEC 61051-2:2021, Varistors for use in electronic equipment – Part 2: Sectional specification
for surge suppression varistors
IEC 61180, High-voltage test techniques for low-voltage equipment – Definitions, test and
procedure requirements, test equipment
IEC 61869-6, Instrument transformers – Part 6: Additional general requirements for low-power
instrument transformers
IEC 61869-10, Instrument transformers – Part 10: Additional requirements for low-power
passive current transformers
IEC 61869-11, Instrument transformers – Part 11: Additional requirements for low-power
passive voltage transformers
IEC 62151, Safety of equipment electrically connected to a telecommunication network

– 12 – IEC 60255-27:2023 © IEC 2023
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
accessible conductive part
conductive part of electrical equipment touchable under normal use
3.2
accessible part
part which can be touched under normal use with a standard rigid or jointed test finger as
specified in 6.2 of IEC 61010-1:2010 and IEC 61010-1:2010/AMD1:2016
Note 1 to entry: Circuits intended to be connected to an external accessible circuit are considered as accessible
conductive parts, for example wired network ports.
3.3
adjacent circuit
independent c
...