IEC 61643-12:2008

IEC 61643-12
Edition 2.0 2008-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Low-voltage surge protective devices –
Part 12: Surge protective devices connected to low-voltage power distribution
systems – Selection and application principles

Parafoudres basse tension –
Partie 12: Parafoudres connectés aux réseaux de distribution basse tension –
Principes de choix et d'application

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IEC 61643-12
Edition 2.0 2008-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Low-voltage surge protective devices –
Part 12: Surge protective devices connected to low-voltage power distribution
systems – Selection and application principles

Parafoudres basse tension –
Partie 12: Parafoudres connectés aux réseaux de distribution basse tension –
Principes de choix et d'application

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XG
CODE PRIX
ICS 29.240; 29.240.10 ISBN 978-2-88910-550-2
– 2 – 61643-12 © IEC:2008
CONTENTS
FOREWORD.8

0 Introduction .11

0.1 General .11

0.2 Keys to understanding the structure of this standard .11

1 Scope.13

2 Normative references .13

3 Terms, definitions and abbreviated terms .14

3.1 Terms and definitions .14
3.2 List of abbreviations and acronyms used in this standard .25
4 Systems and equipment to be protected .26
4.1 Low-voltage power distribution systems.26
4.1.1 Lightning overvoltages and currents .27
4.1.2 Switching overvoltages .28
4.1.3 Temporary overvoltages U .28
TOV
4.2 Characteristics of the equipment to be protected .30
5 Surge protective devices .31
5.1 Basic functions of SPDs .31
5.2 Additional requirements.31
5.3 Classification of SPDs .31
5.3.1 SPD: classification.31
5.3.2 Typical design and topologies.32
5.4 Characteristics of SPDs.33
5.4.1 Service conditions described in IEC 61643-1 .33
5.4.2 List of parameters for SPD selection.34
5.5 Additional information on characteristics of SPDs.35
5.5.1 Information related to power-frequency voltages.35
5.5.2 Information related to surge currents .36
5.5.3 Information related to voltage protection level provided by SPDs.37
5.5.4 Information related to SPD failure modes .39
5.5.5 Information related to short-circuit withstand .40
5.5.6 Information related to load current I and to voltage drop (for two-
L
port SPDs or one-port SPDs with separate input and output
terminals) .40

5.5.7 Information related to change of characteristics of SPDs .40
6 Application of SPDs in low-voltage power distribution systems .40
6.1 Installation and its effect on the protection given by SPDs.40
6.1.1 Possible modes of protection and installation .41
6.1.2 Influence of the oscillation phenomena on the protective distance
(called separation distance in some countries) .43
6.1.3 Influence of the connecting lead length.44
6.1.4 Need for additional protection.45
6.1.5 Consideration regarding location of the SPD depending on the
classes of test .46
6.1.6 Protection zone concept .46
6.2 Selection of SPD .48
6.2.1 Selection of U , U , I , I , I and U of the SPD.49
c T n imp max oc
6.2.2 Protective distance .52

61643-12 © IEC:2008 – 3 –
6.2.3 Prospective life and failure mode.53

6.2.4 Interaction between SPDs and other devices.53

6.2.5 Choice of the voltage protection level U .54

p
6.2.6 Coordination between the chosen SPD and other SPDs .55

6.3 Characteristics of auxiliary devices.57

6.3.1 Disconnecting devices .57

6.3.2 Event counters .57

6.3.3 Status indicator .57

7 Risk analysis .57

Annex A (informative) Typical information given with inquiries and tenders and
explanation of testing procedures .59
A.1 Information given with inquiries .59
A.1.1 System data .59
A.1.2 SPD application considerations .59
A.1.3 Characteristics of SPD .59
A.1.4 Additional equipment and fittings.60
A.1.5 Any special abnormal conditions .60
A.2 Information given with tender.60
A.3 Explanation of testing procedures used in IEC 61643-1 .60
A.3.1 Determination of U for SPDs tested according to class I and class II tests.60
res
A.3.2 Impulse waveshape for assessment of U .61
res
A.3.3 Influence of a back filter on determination of U .61
res
A.3.4 Operating duty test for SPDs .61
A.3.5 TOV failure test .62
A.3.6 Differences in the testing conditions of Type 1 (test class I), 2 (test class II)
and 3 (test class III) SPDs.62
A.3.7 Short-circuit withstand capability test in conjunction with overcurrent
protection (if any) .63
Annex B (informative) Examples of relationship between U and the nominal voltage
c
used in some systems and example of relationship between U and U for ZnO
p c
varistor .64
B.1 Relationship between U and the nominal voltage of the system .64
c
B.2 Relationship between U and U for a ZnO varistor.64
p c
Annex C (informative) Environment – Surge voltages in LV systems .66
C.1 General .66

C.2 Lightning overvoltages.66
C.2.1 Surges transferred from MV to the LV system.67
C.2.2 Overvoltages caused by direct flashes to LV distribution systems.67
C.2.3 Induced overvoltages in LV distribution systems.68
C.2.4 Overvoltages caused by flashes to a lightning protection systems or an area
of close vicinity.68
C.3 Switching overvoltages.69
C.3.1 General description .70
C.3.2 Circuit-breaker and switch operations.70
C.3.3 Fuse operations (current-limiting fuses).71
Annex D (informative) Partial lightning current calculations.72
Annex E (informative) TOV in the low-voltage system due to faults between high-
voltage systems and earth .75

– 4 – 61643-12 © IEC:2008
E.1 General .75

E.2 Example of a TT system – Calculation of the possible temporary overvoltages .76

E.2.1 Possible stresses on equipment in low-voltage installations due to earth

faults in a high-voltage system .76

E.2.2 Characteristics of the high-voltage system .77

E.2.3 TOV in low-voltage system due to faults in the high-voltage system .77

E.2.4 Conclusions .78

E.3 Values of the temporary overvoltages according to IEC 60364-4-44 .78

E.4 Values of the temporary overvoltages for the US TN C-S system.88

Annex F (informative) Coordination rules and principles.90
F.1 General .90
F.2 Analytical studies: simple case of the coordination of two ZnO varistor based SPDs .90
F.2.1 General .90
F.2.2 Conclusion .92
F.3 Analytical study: case of coordination between a gap-based SPD and a ZnO
varistor based SPD.93
F.3.1 General .93
F.3.2 Example of the calculation of the estimated values required for a decoupling
inductance between a gap and a varistor.94
F.3.3 Conclusion .95
F.4 Analytical study: general coordination of two SPDs .95
F.5 Let-through energy (LTE) method .96
F.5.1 General .96
F.5.2 Method.97
Annex G (informative) Examples of application .99
G.1 Domestic application .99
G.2 Industrial application .101
G.3 Presence of a lightning protection system.105
Annex H (informative) Examples of application of the risk analysis .107
Annex I (informative) System stresses .111
I.1 Lightning overvoltages and currents [4.1.1] . 111
I.1.1 Aspects of the power distribution system that affect the need for an SPD .111
I.1.2 Sharing of surge current within a structure .111

I.2 Switching overvoltages [4.1.2] .112
I.3 Temporary overvoltages U [4.1.3] .113
TOV
Annex J (informative) Criteria for selection of SPDs. 114
J.1 U temporary overvoltage characteristic [5.5.1.2].114
T
J.2 SPD failure modes [5.5.4].114
Annex K (informative) Application of SPDs .117
K.1 Location and protection given by SPDs [6.1].117
K.1.1 Possible modes of protection and installation [6.1.1] . 117
K.1.2 Influence of the oscillation phenomena on the protective distance [6.1.2] . 126
K.1.3 Protection zone concept [6.1.6] .127
K.2 Selection of SPDs .129
K.2.1 Selection of U [6.2.1] .129
c
K.2.2 Coordination problems [6.2.6.2].130

61643-12 © IEC:2008 – 5 –
K.2.3 Practical cases [6.2.6.3] .132

Annex L (informative) Risk analysis .133

L.1 Group A – Environmental.133

L.2 Group B – Equipment and facilities.133

L.3 Group C – Economics and service interruption . 134

L.4 Group D – Safety.135

L.5 Group E – Cost of protection .135

Annex M (informative) Immunity vs. insulation withstand. 136

Annex N (informative) Examples of SPD installation in power distribution boards in

some countries .138
Annex O (informative) Coordination when equipment has both signalling and power
terminals.143
Annex P (informative) Short circuit backup protection and surge withstand . 150
P.1 Introduction .150
P.2 Information single shot 8/20 and 10/350 fuses withstand . 150
P.3 Fuse Influencing factors (reduction) for preconditioning and operating duty test .151
P.4 Specific examples with estimated range of factors for reduction of single shot fuse
withstand.151
Bibliography.153

Figure 1 – Examples of one-port SPDs .19
Figure 2 – Examples of two-port SPDs.20
Figure 3 – Output voltage response of one-port and two-port SPDs to a combination
wave impulse.22
Figure 4 – Maximum values of U according to IEC 60634-4-44.30
TOV
Figure 5 – Examples of components and combinations of components .33
Figure 6 – Relationship between U , U , U and U .35
p c cs
Figure 7 – Typical curve of U versus I for ZnO varistors.38
res
Figure 8 – Typical curve for a spark gap .39
Figure 9 – Flowchart for SPD application .41
Figure 10 – Connection Type 1 (CT1) .42
Figure 11 – Connection Type 2 (CT2) .42

Figure 12 – Influence of SPD connecting lead lengths .45
Figure 13 – Need for additional protection .46
Figure 14 – Flowchart for the selection of an SPD .48
Figure 15 – U and U .51
T TOV
Figure 16 – Typical use of two SPDs – Electrical drawing .55
Figure D.1 – Simple calculation of the sum of partial lightning currents into the power
distribution system.72
Figure E.1 – Temporary power-frequency overvoltage caused by an earth fault in the
high-voltage system.76
Figure E.2 – TN systems.79
Figure E.3 – TT systems.80
Figure E.4 – IT system, example a.81
Figure E.5 – IT system, example b.82

– 6 – 61643-12 © IEC:2008
Figure E.6 – IT system, example c1 .83

Figure E.7 – IT system, example c2 .84

Figure E.8 – IT system, example d.85

Figure E.9 – IT system, example e1.86

Figure E.10 – IT system, example e2 .87

Figure E.11 – US TN-C-S System .88

Figure F.1 – Two ZnO varistors with the same nominal discharge current .91

Figure F.2 – Two ZnO varistors with different nominal discharge currents.92

Figure F.3 – Example of coordination of a gap-based SPD and a ZnO varistor based
SPD.95
Figure F.4 – LTE – Coordination method with standard pulse parameters .96
Figure G.1 – Domestic installation .100
Figure G.2 – Industrial installation .103
Figure G.3 – Circuitry of industrial installation.104
Figure G.4 – example for a lightning protection system . 106
Figure I.1 – Example of diversion of lightning current into the external services (TT
system).112
Figure J.1 – Typical curve for U of an SPD .114
T
Figure J.2 – Internal disconnector in the case of a two-port SPD .115
Figure J.3 – Use of parallel SPDs .116
Figure K.1 – Installation of surge protective devices in TN-systems . 118
Figure K.2a –Connection Type 1.119
Figure K.2b – Connection Type 2.120
Figure K.2 – Installation of surge protective devices in TT-systems (SPD downstream
of the RCD) .120
Figure K.3 – Installation of surge protective devices in TT-systems (SPD upstream of
the RCD) .121
Figure K.4 – Installation of surge protective devices in IT-systems without distributed
neutral .122
Figure K.5 – Typical installation of SPD at the entrance of the installation in case of a
TN C-S system .123
Figure K.6 – General way of installing one-port SPDs . 124
Figure K.7 – Examples of acceptable and unacceptable SPD installations regarding

EMC aspects .125
Figure K.8 – Physical and electrical representations of a system where equipment
being protected is separated from the SPD giving protection .126
Figure K.9 – Possible oscillation between a ZnO SPD and the equipment to be
protected .126
Figure K.10 – Example of voltage doubling .127
Figure K.11 – Subdivision of a building into protection zones. 128
Figure K.12a –Residual voltage on varistors .130
Figure K.12b – Sharing of current between two varistors . 131
Figure K.12 – Coordination of two ZnO varistors:.131
Figure N.1 – A wiring diagram of an SPD connected on the load side of the main
incoming isolator via a separate isolator (which could be included in the SPD
enclosure).138

61643-12 © IEC:2008 – 7 –
Figure N.2 – SPD connected to the nearest available outgoing MCB to the incoming

supply (TNS installation typically seen in the UK) .139

Figure N.3 – A single line-wiring diagram of an SPD connected in shunt on the first

outgoing way of the distribution panel via a fuse (or MCB) . 140

Figure N.4 – SPD connected to the nearest available circuit breaker on the incoming
supply (US three phase 4W + G, TN-C-S installation).141

Figure N.5 – SPD connected to the nearest available circuit breaker on the incoming

supply (US single (split) phase 3W + G, 120/240 V system - typical for residential and

small office applications).142

Figure O.1 – Example of a PC with modem in a US power and communication system . 144

Figure O.2 – Schematic of circuit of Figure O.1 used for experimental test . 145
Figure O.3 – voltage recorded across reference points for the PC/modem during a
surge in the example .146
Figure O.4 – typical TT system used for simulations .147
Figure O.5 – Voltage and current waveshapes when a multiservice SPD is applied to
circuit of Figure O.1 .149

Table 1 – Maximum TOV values as given in IEC 60634-4-44 .29
Table 2 – Preferred values of I .37
imp
Table 3 – Possible modes of protection for various LV systems .43
Table 4 – Minimum recommended Uc of the SPD for various power systems .49
Table 5 – Typical TOV test values .50
Table B.1 – Relationship between U and nominal system voltage .64
c
Table B.2 – Relationship between U /U for ZnO varistors .65
p c
Table F.1 – .98
Table F.2 – .98
Table F.3 – .98
Table O.1 – Simulation results .148
Table P.1 – Examples of ratio between single shot withstand and full
preconditioning/operating duty test .152

– 8 – 61643-12 © IEC:2008
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
LOW-VOLTAGE SURGE PROTECTIVE DEVICES –

Part 12: Surge protective devices connected

to low-voltage power distribution systems –

Selection and application principles

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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International Standard IEC 61643-12 has been prepared by subcommittee 37A: Low-voltage
surge protective devices, of IEC technical committee 37: Surge arresters.
This second edition of IEC 61643-12 cancels and replaces the first edition published in 2002.
It constitutes a technical revision. Specific change with respect to the previous edition is the
incorporation of Amendment 1, which was not published separately due to the number of
changes and pages.
This standard shall be used in conjunction with IEC 61643-1:2005, Low-voltage surge
protective devices – Part 1: Surge protective devices connected to low-voltage power
distribution systems – Requirements and tests.

61643-12 © IEC:2008 – 9 –
The text of this standard is based on the following documents:

FDIS Report on voting
37A/209/FDIS 37A/212/RVD
This publication has been drafted in accordance with the ISO/IEC Directives, Part 3.

IEC TC 37, SC 37A and SC 37B have adopted a new numbering scheme for all IEC

publications developed within these committees.

In this standard, the IEC 61643 series of publications covers all the publications from SC 37A

and SC 37B according to the table below with the common general title Low-voltage surge
protective devices.
Present
Publication Title
document
IEC 61643 Low-voltage surge protective devices –
IEC 61643-11 Low-voltage surge protective devices – Part 11: Surge protective devices IEC 61643-1
connected to low-voltage power distribution systems – Performance
requirements and testing methods
IEC 61643-12 Low-voltage surge protective devices – Part 12: Surge protective devices IEC 61643-12
connected to low-voltage power distribution systems – Selection and
application principles
IEC 61643-21 Low-voltage surge protective devices – Part 21: Surge protective devices IEC 61643-21
connected to telecommunications and signalling networks – Performance
requirements and testing methods
IEC 61643-22 Low-voltage surge protective devices – Part 22: Surge protective devices IEC 61643-22
connected to telecommunications and signalling networks – Selection and
application principles
IEC 61643-301
Low-voltage surge protective devices – Part 301: Components for surge
protective devices – General test specifications
IEC 61643-302 Low-voltage surge protective devices – Part 302: Components for surge
protective devices – General performance specifications
IEC 61643-303 Low-voltage surge protective devices – Part 303: Components for surge
protective devices – General selection and application principles
IEC 61643-311 Low-voltage surge protective devices – Part 311: Components for surge IEC 61643-311
protective devices – Test specification for gas discharge tubes (GDTs)
IEC 61643-312 Low-voltage surge protective devices – Part 312: Components for surge
protective devices –Performance specification for gas discharge tubes (GDTs)
IEC 61643-313 Low-voltage surge protective devices – Part 313: Components for surge
protective devices – Selection and applications principles for gas discharge
tubes (GDTs)
IEC 61643-321 Low-voltage surge protective devices – Part 321: Components for surge IEC 61643-321

protective devices – Test specification for avalanche breakdown diodes
(ABDs)
IEC 61643-322 Low-voltage surge protective devices – Part 322: Components for surge
protective devices – Performance specification for avalanche breakdown
diodes (ABDs)
IEC 61643-323
Low-voltage surge protective devices – Part 323: Components for surge
protective devices – Selection and applications principles for avalanche
breakdown diodes (ABDs)
IEC 61643-331 Low-voltage surge protective devices – Part 331: Components for surge IEC 61643-331
protective devices – Test specification for metal oxide varistors (MOVs)
IEC 61643-332
Low-voltage surge protective devices – Part 332: Components for surge
protective devices – Performance specification for metal oxide varistors
(MOVs)
IEC 61643-333
Low-voltage surge protective devices – Part 333: Components for surge
protective devices – Selection and application principles for metal oxide
varistors (MOVs)
IEC 61643-341 Low-voltage surge protective devices – Part 341: Components for surge IEC 61643-341
protective devices – Test specification for thyristor surge suppressors (TSSs)

– 10 – 61643-12 © IEC:2008
IEC 61643-342 Low-voltage surge protective devices – Part 342: Components for surge

protective devices – Performance specification for thyristor surge

suppressors (TSSs)
IEC 61643-343 Low-voltage surge protective devices – Part 343: Components for surge
protective devices – Selection and application principles for thyristor surge

suppressors (TSSs)
The committee has decided that the contents of this publication will remain unchanged until

the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in

the data related to the specific publication. At this date, the publication will be

• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
61643-12 © IEC:2008 – 11 –
0 Introduction
0.1 General
Surge protective devices (SPDs) are used to protect, under specified conditions, electrical

systems and equipment against various overvoltages and impulse currents, such as lightning

and switching surges.
SPDs shall be selected according to their environmental conditions and the acceptable failure

rate of the equipment and t
...