FprEN IEC 61643-361:2026

SLOVENSKI STANDARD
oSIST prEN IEC 61643-361:2025
01-julij-2025
Nizkonapetostni sestavni deli za zaščito pred prenapetostnimi udari - 361. del:
Prenapetostni izolacijski transformatorji (SIT) za nizkonapetostne napajalne
sisteme - Zahteve in preskusne metode
Low-voltage surge protective components - Part 361: Surge isolation transformers (SITs)
connected to low-voltage distribution system - Requirements and test methods
Composants de protection contre les surtensions dans les réseaux basse tension -
Partie 361: Transformateurs d’isolement contre les surtensions (SIT) connectés aux
réseaux de distribution basse tension - Exigences et méthodes d’essai
Ta slovenski standard je istoveten z: prEN IEC 61643-361:2025
ICS:
29.120.50 Varovalke in druga Fuses and other overcurrent
nadtokovna zaščita protection devices
oSIST prEN IEC 61643-361:2025 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN IEC 61643-361:2025
oSIST prEN IEC 61643-361:2025
37B/252/CDV
COMMITTEE DRAFT FOR VOTE (CDV)

PROJECT NUMBER:
IEC 61643-361 ED1
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2025-06-06 2025-08-29
SUPERSEDES DOCUMENTS:
37B/247/CD, 37B/250/CC
IEC SC 37B : COMPONENTS FOR LOW-VOLTAGE SURGE PROTECTION
SECRETARIAT: SECRETARY:
United States of America Mr David Richmond
OF INTEREST TO THE FOLLOWING COMMITTEES: HORIZONTAL FUNCTION(S):

ASPECTS CONCERNED:
Electromagnetic Compatibility
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
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The CENELEC members are invited to vote through the
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This document is still under study and subject to change. It should not be used for reference purposes.
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Countries” clauses to be included should this proposal proceed. Recipients are reminded that the CDV stage is
the final stage for submitting ISC clauses. (SEE AC/22/2007 OR NEW GUIDANCE DOC).

TITLE:
Low-voltage surge protective components - Part 361: Surge isolation transformers (SITs)
connected to low-voltage distribution system – Requirements and test methods

PROPOSED STABILITY DATE: 2030
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oSIST prEN IEC 61643-361:2025
2 IEC CDV 61643-361 ED1 © IEC 2025
1 CONTENTS
3 FOREWORD . 3
4 INTRODUCTION . 5
5 1 Scope . 6
6 2 Normative references . 6
7 3 Terms, definitions and symbols . 6
8 3.1 Terms and definition . 6
9 3.2 Symbols . 8
10 3.3 Abbreviations and acronyms . 8
11 4 Service condition . 9
12 4.1 Temperature range . 9
13 4.2 Humidity range. 9
14 4.3 Altitude and air pressure . 9
15 5 SIT surge condition . 9
16 5.2 SITs surge mitigation . 10
17 6 Electrical requirements . 11
18 6.1 General . 11
19 6.2 Insulation resistance . 11
20 6.3 Power frequency withstand voltage . 11
21 6.4 Impulse withstand voltage . 12
22 7 Type tests . 12
23 7.1 General . 12
24 7.2 Test condition . 12
25 7.3 Sample preparation . 12
26 7.4 Insulation resistance . 12
27 7.5 Power frequency withstand voltage . 13
28 7.6 Impulse withstand voltage . 14
29 Annex A (informative) 1,2/50 impulse . 17
30 Bibliography . 18
32 Figure 1– Symbol of SIT for single phase low-voltage power system . 8
33 Figure 2–Symbol of SIT for single phase low-voltage power system . 8
34 Figure 3 – SITs under common mode surge condition . 11
35 Figure 4 – Sample preparation . 12
36 Figure 5 – Test circuit of insulation resistance . 13
37 Figure 6 – Power frequency withstand voltage test circuit . 14
38 Figure 7 – Construction of pass/fail template from the 1,2/50 open-circuit waveform . 15
39 Figure 8 – Pass/fail template and test waveforms . 15
40 Figure 9 – Impulse withstand voltage test circuit . 16
41 Figure A.1 – 1,2/50 time periods and voltage amplitudes . 17
43 Table 1 – List of abbreviations and acronyms used in this standard . 8
44 Table 2 – Conditions used for test . 12
45 Table A.1 – 1,2/50 voltage impulse generator parameters . 17
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47 INTERNATIONAL ELECTROTECHNICAL COMMISSION
48 IEC SC37B JWG5
50 LOW-VOLTAGE SURGE PROTECTIVE COMPONENTS –
52 Part 361: Surge isolation transformers (SITs) connected to low-voltage
53 distribution system – Requirements and test methods
56 FOREWORD
57 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
58 all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
59 co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
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64 with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
65 Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
66 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
67 consensus of opinion on the relevant subjects since each technical committee has representation from all
68 interested IEC National Committees.
69 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
70 Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
71 Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
72 misinterpretation by any end user.
73 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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75 any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
76 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
77 assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
78 services carried out by independent certification bodies.
79 6) All users should ensure that they have the latest edition of this publication.
80 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
81 members of its technical committees and IEC National Committees for any personal injury, property damage or
82 other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
83 expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
84 Publications.
85 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
86 indispensable for the correct application of this publication.
87 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
88 rights. IEC shall not be held responsible for identifying any or all such patent rights.
89 International Standard IEC 61643-361 has been prepared by subcommittee SC37B JWG5, of
90 IEC technical committee TC37
91 This edition includes the following significant technical changes with respect to the previous
92 edition:
93 a) .;
94 b)
95 The text of this International Standard is based on the following documents:
Draft Report on voting
XX/XX/FDIS XX/XX/RVD
97 Full information on the voting for its approval can be found in the report on voting indicated in
98 the above table.
99 The language used for the development of this International Standard is English [change
100 language if necessary].
oSIST prEN IEC 61643-361:2025
4 IEC CDV 61643-361 ED1 © IEC 2025
101 This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
102 accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
103 at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
104 described in greater detail at http://www.iec.ch/standardsdev/publications.
105 The committee has decided that the contents of this document will remain unchanged until the
106 stability date indicated on the IEC website under webstore.iec.ch in the data related to the
107 specific document. At this date, the document will be
108 • reconfirmed,
109 • withdrawn,
110 • replaced by a revised edition, or
111 • amended.
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113 INTRODUCTION
114 This standard cover SITs (surge isolation transformers) whose rated impulse withstand
115 voltage coordinates with the expected surge environment of the installation location.
116 This type of surge protective component, SPC, isolates and attenuates transient voltage
117 in conjunction with current diverting components (or SPDs).
118 SITs are a product with specific enhanced insulation layers between the primary and
119 secondary windings and an shield (electric screen) inserted between primary and
120 secondary. With these shields and specific enhanced insulation layers, the surge that
121 appears between the primary winding and earth (common-mode) is greatly attenuated
122 and appears between the secondary winding and earth. SITs are product with a
123 particularly improved impulse withstand voltage compared to ordinary isolating
124 transformers.
125 SITs should be protected by SPDs at their primary side to avoid any damage to the SIT
126 itself. SITs are intended to be used in surge protection to establish lightning protection
127 zones.
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6 IEC CDV 61643-361 ED1 © IEC 2025
129 LOW-VOLTAGE SURGE PROTECTIVE COMPONENTS –
131 Part 361: Surge isolation transformers (SITs) connected to low-voltage
132 distribution system – Requirements and test methods
136 1 Scope
137 This part of IEC 61643 applies to surge isolation transformers (SITs) dedicated to surge
138 mitigation and for connection to 50/60 Hz power circuits and equipment rated up to 1 000V rms.
139 This document covers the surge and mitigation performance of SITs with an impulse withstand
140 voltage performance at least 30 kV, and provides standard methods for testing and rating.
141 This document covers surge-related parameters but does not address typical transformer tests and
142 parameters covered by the IEC 61558 series. This document also does not cover SIT operation under
143 differential mode lightning surge conditions.
144 2 Normative references
145 The following documents are referred to in the text in such a way that some or all of their content
146 constitutes requirements of this document. For dated references, only the edition cited applies.
147 For undated references, the latest edition of the referenced document (including any
148 amendments) applies.
149 IEC/TR 60664-2-1 Ed. 2.0, Insulation coordination for equipment within low-voltage systems -
150 Part 2-1: Application guide - Explanation of the application of the IEC 60664 series,
151 dimensioning examples and dielectric testing
152 IEC 60060-1 Ed. 3.0:2010, High-voltage test techniques - Part 1: General definitions and test
153 requirements
154 IEC 60068-1 Ed. 7.0:2013, Environmental testing - Part 1: General and guidance
156 3 Terms, definitions and symbols
157 3.1 Terms and definition
158 For the purposes of this document, the following terms and definitions apply.
159 ISO and IEC maintain terminological databases for use in standardization at the following
160 addresses:
161 • IEC Electropedia: available at http://www.electropedia.org/
162 • ISO Online browsing platform: available at http://www.iso.org/obp
163 3.1.1
164 surge isolation transformer, SIT
165 isolation transformer which has high impulse withstand voltage with shielding between primary
166 and secondary windings
167 3.1.2
168 electric screen, electric shield (US)
169 screen of conductive material intended to reduce the penetration of an electric field into a given
170 region
171 [SOURCE: IEC 60050-151-13-10]

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172 3.1.3
173 clearance
174 shortest distance in air between two conductive parts or between conductive parts and earthed
175 parts
176 [SOURCE: IEC 60664-1:2020, 3.1.4, modified]
177 3.1.4
178 creepage distance
179 shortest distance along the surface of a solid insulating material between two conductive parts
180 [SOURCE: IEC 60050-151:2001, 151-15-50]
181 3.1.5
182 impulse withstand voltage
183 highest peak value of impulse voltage of prescribed form and polarity which does not cause
184 breakdown of insulation under specified condition
185 [SOURCE: IEC 60664-1:2020, 3.1.15]
186 3.1.6
187 electric insulation
188 Part of an electrotechnical product which separates the conducting parts at different electrical
189 potentials during operation or insulates such parts from the surroundings
190 [SOURCE: IEC 60664-1:2020, 3.1.28]
191 3.1.7
192 insulation resistance
193 resistance under specified condition between two conductive elements separated by insulation
194 materials
195 [SOURCE: IEC 60050-151-15-43]
196 3.1.8
197 power frequency withstand voltage
198 rms value of sinusoidal power frequency voltage that the insulation of the given equipment can
199 withstand during tests made under specified conditions and for a specified duration
200 [SOURCE: IEC 60050-614-03-22]
201 3.1.9
202 electric breakdown
203 failure of insulation under electric stress when the discharge completely bridges the insulation,
204 thus reducing the voltage between the electrodes almost to zero
205 [SOURCE: IEC 60664-1:2020, 3.1.44]
206 3.1.10
207 virtual f
...