IEC 60664-1:2020/AMD1:2025

IEC 60664-1 ®
Edition 3.0 2025-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ
HORIZONTAL PUBLICATION
PUBLICATION HORIZONTALE
AMENDEMENT 1
AMENDEMENT 1
Insulation coordination for equipment within low-voltage supply systems –
Part 1: Principles, requirements and tests

Coordination de l'isolement des matériels dans les réseaux d'énergie électrique
à basse tension –
Partie 1: Principes, exigences et essais
ICS 29.080.30  ISBN 978-2-8327-0344-1

IEC 60664-1:2020-05/AMD1:2025-05(en-fr)

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– 2 – IEC 60664-1:2020/AMD1:2025
© IEC 2025
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATION COORDINATION FOR EQUIPMENT
WITHIN LOW-VOLTAGE SUPPLY SYSTEMS –

Part 1: Principles, requirements and tests

AMENDMENT 1
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,
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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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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
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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Amendment 1 to IEC 60664:2020 has been prepared by IEC technical committee 109:
Insulation co-ordination for low-voltage equipment.
The text of this Amendment is based on the following documents:
Draft Report on voting
109/235/FDIS 109/240/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
© IEC 2025
The language used for the development of this Amendment 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/.
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, or
• revised.
___________
Throughout the document (except in the Bibliography), delete:
IEC 60364-4-44:2007
and replace with:
IEC 60364-4-44:2024.
1 Scope
Replace the first paragraph with the following:
This part of IEC 60664 deals with insulation coordination for electrical equipment having a
rated voltage up to AC 1 000 V or DC 1 500 V connected to low-voltage supply systems.
NOTE 1 Throughout this document, the term equipment is used with the meaning of electrical equipment.
Renumber NOTE 1 and NOTE 2 respectively as NOTE 2 and NOTE 3.
Add, at the end of the existing last paragraph, the following NOTE:
NOTE 4 Further explanations and examples with regard to the use of this document are provided in
IEC TR 60664-2-1.
– 4 – IEC 60664-1:2020/AMD1:2025
© IEC 2025
3.1 Terms and definitions
Add the following new terms:
3.1.48
electric power network
particular installations, substations, lines or cables for the transmission and distribution of
electricity
Note 1 to entry: The boundaries of the different parts of this network are defined by appropriate criteria, such as
geographical situation, ownership, voltage, etc.
[SOURCE: IEC 60050-601:1985, 601-01-02]
3.1.49
electrical installation
assembly of electrical equipment which is used for the generation, transmission, conversion,
distribution and/or use of electric energy
Note 1 to entry: The electrical installation includes energy sources e.g. local power supplies such as batteries,
capacitors and all other sources of stored electric energy.
[SOURCE: IEC 60050-651:2014, 651-26-01, modified – "e.g. local power supplies" has been
added to the Note to entry.]
3.1.50
electrical equipment
item used for 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, and current-using equipment.
[SOURCE: IEC 60050-826:2022, 826-16-01]
3.1.51
electrochemical migration
transport of ions in an electrolyte due to an electric field
[SOURCE: IEC 60050-114:2014, 114-04-06]

4.2.2.5 Attenuation of transient overvoltage levels
Add, after third paragraph, the following:
Technical committees shall consider the end of life of the means to limit transient overvoltages.

4.3.2 Equipment energized directly from the mains supply
Replace the existing text of 4.3.2 with the following:
Equipment is considered to be energized directly from the mains supply when the equipment
is galvanically connected to an electric power network (either public or private).

© IEC 2025
When defining the rated impulse withstand voltage of equipment, technical committees shall
take into account the following overvoltage categories:
– Overvoltage category IV applies at, or in the proximity of, the point where an electrical
installation is connected to an electric power network.
NOTE 1 Equipment of overvoltage category IV has a very high impulse withstand capability providing the
required high degree of reliability at these locations, for example upstream of the main distribution board.
– Overvoltage category III applies in an electrical installation downstream of and including
the main distribution board.
NOTE 2 Examples of such equipment include distribution boards, local generation, circuit-breakers, wiring
systems (see IEC 60050-826:2022, 826-15-01), including cables, busbars, junction boxes, switches, socket-
outlets) and equipment for industrial use and some other equipment, e.g. stationary motors.
– Overvoltage category II applies for equipment connected to an electrical installation.
NOTE 3 Examples of such equipment are appliances, portable tools and similar loads with pluggable or
permanent connection to the electrical installation.
– Overvoltage category I applies to equipment that may only be connected to an electrical
installation when specific measures are provided.
NOTE 4 Such specific measures are related to transient overvoltages as well as to temporary overvoltages
and are addressed in 4.3.4.
Where a higher degree of reliability and availability is necessary, equipment having higher rated
impulse withstand voltage should be considered (see 5.2.2.2).

Add the following new subclause:
4.3.4 Equipment requiring specific measures
When equipment is designed for overvoltage category I and is intended to be connected to an
electrical installation, all the following measures and verifications shall be considered by
technical committees:
– the mains supply to which the equipment is intended to be connected, excludes by design
the occurrence of temporary overvoltages with peak values above the rated impulse
withstand voltage of the equipment;
NOTE 1 In TN-system, for example, there are no significant temporary overvoltages exceeding the rated
impulse withstand voltage of equipment designed for overvoltage category I.
– transient overvoltages are limited to not exceed the rated impulse withstand voltage of
the equipment by appropriate means, e.g. SPDs.
NOTE 2 SPDs are primarily designed to limit transient overvoltages. However they are also tested with certain
temporary overvoltages; for more explanations see the IEC 61643 series.
– the required impulse withstand voltage at the relevant location is tested and confirmed for
the equipment in conjunction with the intended protection means, to ensure not only the
withstand voltage, but also the necessary coordination and withstand as related to impulse
energy.
NOTE 3 More information about system level immunity is given in IEC TR 61643-03.

– 6 – IEC 60664-1:2020/AMD1:2025
© IEC 2025
5.2.5 Dimensioning of clearances of basic insulation, supplementary insulation and
reinforced insulation
Replace the existing second paragraph with the following:
With respect to impulse withstand voltages, clearances of reinforced insulation shall be
dimensioned as specified in Table F.2 corresponding to the rated impulse withstand voltage
but one step higher in the preferred series of values in 4.2.2.1 than that specified for basic
insulation.
If the impulse withstand voltage required for basic insulation is:
– other than a value taken from the preferred series, or
– 12 kV (highest value of the preferred series),
reinforced insulation shall be dimensioned to withstand 160 % of the impulse withstand
voltage required for basic insulation. In those cases, linear interpolation of Table F.2 is
allowed.
Add, at the end of the third paragraph (excluding the note), the following:
Linear interpolation of Table F.8 is allowed.

5.3.2.1 General
Add, at the end of the existing paragraph, the following:
See also the informative Annex I for additional considerations of electrochemical migration
phenomenon of creepage distances for DC applications.

5.4.3.2 Temporary withstand overvoltages
Replace the sentence following the list in the first paragraph with the following:
where U is the nominal line-to-neutral voltage of supply systems, except:
– in IT system without a neutral conductor, where U is the line-to-line voltage;
– in TN or TT system (earthed system) without a distributed neutral conductor, where U is
the line-to-earth voltage.
Add the following NOTE 3:
NOTE 3 The different types of system earthing are described in IEC 60364-1.

6.2.1 General
Replace the second and third paragraphs with the following:

© IEC 2025
In general, the stresses for clearances caused by transient overvoltages are assessed by the
impulse voltage test, which may be substituted by an AC or a DC voltage test (see 6.2.2.1.3).
When verifying clearances within equipment by an impulse voltage test according to 6.2.2.1, it
is necessary to ensure that the specified impulse voltage appears at the clearances under test.
An AC test according to 6.2.2.1.3.2 is required at the respective peak voltage as determined in
5.2.2.4, if:
– the withstand against steady-state working voltages, recurring peak voltages or peak
value of temporary overvoltages according to 5.2.2.4 is decisive for the dimensioning of
clearances (i.e. when – per 5.2.2.1 – any of the above voltages are larger than the impulse
withstand voltage determined on the basis of 5.2.2.2 and 5.2.2.3), and,
– those clearances are smaller than the Case A values of Table F.8.
In such instance, the AC test voltage shall be corrected for the actual test altitude, according
to Table F.6 or according to 6.2.2.1.4, to cover any test voltage.

6.2.2.1.4 Altitude correction for testing at altitudes different than 2 000 m
In the seventh paragraph replace:
k is the altitude correction for clearance correction (see Table F.10);
d
with
k is the altitude correction for clearance correction (see Table F.10 for altitude below 2 000 m,
d
and Table A.2 for altitude above 2 000 m);

6.4.5.1 Test method
Replace the last sentence with the following:
For appropriate requirements for test equipment see IEC 61180.

6.4.7 DC voltage test
Replace all text after the NOTE 1 until the end of the subclause with the following:
For appropriate requirements for test equipment, see IEC 61180.

Figure 14 – Creepage distance and clearance with conductive floating part
Delete the note to Figure 14 and replace with:
NOTE The minimum clearance d and minimum clearance D shall be applied to the lowest value of Table F.2
considering their respective pollution degree.

– 8 – IEC 60664-1:2020/AMD1:2025
© IEC 2025
Table F.5 – Creepage distances to avoid failure due to tracking
Replace Footnote a with the following new Footnote:
a
This voltage is for:
– functional insulation, the steady-state working voltage (see 5.3.4),
– basic insulation and supplementary insulation of the circuit energized directly from the mains supply (see
5.3.5), the voltage rationalized through Table F.3 or or Table F.4, based on the rated voltage of the
equipment, or the rated insulation voltage,
– basic insulation and supplementary insulation of a system, equipment and internal circuits not energized
directly from the mains supply (see 5.3.5), the highest RMS voltage which can occur in the system, equipment
or internal circuit when supplied at rated voltage and under the most onerous combination of conditions of
operation within equipment rating.

Replace Table F.6, including the title, with the following new table and title:
Table F.6 – Test voltages for verifying clearances at different altitudes
Impulse test Impulse test Impulse test Impulse test voltage
Rated impulse
voltage voltage voltage at 1 000 m altitude
withstand voltage
a at sea level at 200 m altitude at 500 m altitude

Û Û Û Û
Û
kV kV kV kV
kV
0,33 0,357 0,355 0,350 0,344
0,5 0,541 0,537 0,531 0,521
0,8 0,934 0,920 0,899 0,865
1,5 1,751 1,725 1,685 1,622
2,5 3,077 3,015 2,922 2,778
4,0 4,923 4,824 4,675 4,444
6,0 7,385 7,236 7,013 6,666
8,0 9,847 9,648 9,350 8,888
10,0 12,522 12,247 11,839 11,207
12,0 15,026 14,697 14,207 13,449
15,0 18,783 18,372 17,759 16,811
NOTE 1 Explanations concerning the influencing factors (air pressure, altitude, temperature, humidity) with
respect to electric strength of clearances are given in 4.7 and altitude correction in 6.2.2.1.4
NOTE 2 When testing clearances, associated solid insulation will be subjected to the test voltage. As the
impulse test voltage of Table F.6 is increased with respect to the rated impulse withstand voltage, solid
insulation will be designed accordingly. This results in an increased impulse withstand capability of the solid
insulation.
a
Rated impulse withstand voltage referred at 2 000 m altitude Û kV

© IEC 2025
Add the following new Annex I:
Annex I
(informative)
Electrochemical migration of creepage distances in DC applications
I.1 The phenomenon of electrochemical migration
The process of electrochemical migration is the formation of an electrically conductive
dendrite which can bridge across conductors and is greatly facilitated by many factors, the most
critical being the presence of water in the form of either humidity or condensation, or both.
Other factors that influence this process are voltage bias, conductivity of substrate materials
and environmental contaminants.
Technical committees should consider if additional measures are necessary to prevent
degradation due to electrochemical migration and subsequent possible breakdown of the
insulating surface.
To minimize the risk of electrochemical migration, additional measures can be considered
such as:
– selecting metal materials on which electrochemical migration is known to be less likely to
occur, (e.g. avoiding the use of Ag);
– application of coatings to the conductors, for example on printed wiring boards (see
IEC 60664-3);
– avoiding the use of printed wiring board material containing contaminants that accelerate
the occurrence of migration;
– using material where the insulation resistance between conductors is ≥ 10 Ω.
NOTE It can be possible to use a material with less than 10 Ω, however the risk of electrochemical
migration is increased depending on the temperature with or without humidity.
– installation of equipment inside of enclosures which prevent condensation. Care should be
taken in the selection of the environment and orientation of equipment and components;
– heating by anti-condensation heaters or self-heating, for example of power conductors;
– using creepage distances greater than those specified in Table F.5.
For printed wiring board, additional explanations and information on this phenomenon of
electrochemical reactions like migration or corrosion and ionic contamination on the surface of
a printed circuit board are further developed in IEC TR 61191-9 and IEC TR 62866.

– 10 – IEC 60664-1:2020/AMD1:2025
© IEC 2025
I.2 Effect of electrochemical migration on creepage distances in DC
applications
In DC applications, electrochemical migration can affect creepage distances. Under a
permanent electric field, ions can migrate, potentially forming a conductive pathway or dendrites,
in the case of metal ions, with a needle or tree-branch-like metal structure that can reduce
creepage distances or connect neighboring conductors.
Available results indicate that this phenomenon can affect the insulation coordination and
potentially create a short-circuit of conductors, which can lead to significant damage to the
equipment and risk of harm at any voltage, and in particular when the voltage is higher than
1 000 V DC.
NOTE For further information, see the following publications:
Kamosawa, Yoshiruma, and Noto, (1994). Investigation of tracking degradation by DC voltage application - IEEE
Xplore Document;
Chandrasekar, S., Sarathi, R. and Danikas, M. (2006). Analysis of Surface Degradation of Silicone Rubber Insulation
Due to Tracking Under Different Voltage Profiles.

© IEC 2025
Bibliography
Replace:
IEC 61643:2011, Low-voltage surge protective devices
With:
IEC 61643 (all parts), Low-voltage surge protective devices

Replace:
IEC 60050-826, International Electrotechnical Vocabulary (IEV) – Part 826: Electrical
installations (available at http://www.electropedia.org)
With:
IEC 60050-826:2022, International Electrotechnical Vocabulary (IEV) – Part 826: Electrical
installations (available at http://www.electropedia.org)

Replace
IEC 60364-4-44:2007, Low-voltage electrical installations – Part 4-44: Protection for safety –
Protection against voltage disturbances and electromagnetic disturbances
IEC 60364-4-44:2007/AMD1:2015
IEC 60364-4-44:2007/AMD2:2018
With
IEC 60364-4-44:2024, Low-voltage electrical installations – Part 4-44: Protection for safety –
Protection against voltage disturb
...