CLC/TS 61643-12:2009

SLOVENSKI STANDARD
01-april-2010
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SIST-TS CLC/TS 61643-12:2007
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Low-voltage surge protective devices -- Part 12: Surge protective devices connected to
low-voltage power distribution systems - Selection and application principles
Überspannungsschutzgeräte für Niederspannung - Teil 12: Überspannungsschutzgeräte
für den Einsatz in Niederspannungsanlagen - Auswahl und Anwendungsgrundsätze
Parafoudres basse tension -- Partie 12: Parafoudres connectés aux réseaux de
distribution basse tension - Principes de choix et d'application
Ta slovenski standard je istoveten z: CLC/TS 61643-12:2009
ICS:
29.120.50 9DURYDONHLQGUXJD Fuses and other overcurrent
PHGWRNRYQD]DãþLWD protection devices
29.240.10 Transformatorske postaje. Substations. Surge arresters
Prenapetostni odvodniki
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL SPECIFICATION
CLC/TS 61643-12
SPÉCIFICATION TECHNIQUE
December 2009
TECHNISCHE SPEZIFIKATION
ICS 29.240; 29.240.10 Supersedes CLC/TS 61643-12:2006

English version
Low-voltage surge protective devices -
Part 12: Surge protective devices connected to low-voltage power
distribution systems -
Selection and application principles
(IEC 61643-12:2008, modified)
Parafoudres basse tension -  Überspannungsschutzgeräte
Partie 12: Parafoudres connectés für Niederspannung -
aux réseaux de distribution basse tension - Teil 12: Überspannungsschutzgeräte
Principes de choix et d'application für den Einsatz
(CEI 61643-12:2008, modifiée) in Niederspannungsanlagen -
Auswahl und Anwendungsgrundsätze
(IEC 61643-12:2008, modifiziert)

This Technical Specification was approved by CENELEC on 2009-10-30.

CENELEC members are required to announce the existence of this TS in the same way as for an EN and to
make the TS available promptly at national level in an appropriate form. It is permissible to keep conflicting
national standards in force.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: Avenue Marnix 17, B - 1000 Brussels

© 2009 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. CLC/TS 61643-12:2009 E

Foreword
This Technical Specification consists of the text of the International Standard IEC 61643-12:2008
prepared by SC 37A, Low-voltage surge protective devices, of IEC TC 37, Surge arresters, together
with the common modifications prepared by the Technical Committee CENELEC TC 37A, Low voltage
surge protective devices.
The text of the draft was circulated for voting in accordance with the Internal Regulations, Part 2,
Subclause 11.3.3.3 and was accepted by CENELEC as CLC/TS 61643-12 on 2009-10-30.
This Technical Specification supersedes CLC/TS 61643-12:2006.
The following date was fixed:
– latest date by which the existence of the CLC/TS
has to be announced at national level (doa) 2010-04-30
This Technical Specification is to be used in conjunction with EN 61643-11:2002.
__________
– 3 – CLC/TS 61643-12:2009
Contents
0 Introduction .6
0.1 General .6
0.2 Keys to understanding the structure of this Technical Specification .6
1 Scope .8
2 Normative references .8
3 Terms, definitions and abbreviated terms .9
3.1 Terms and definitions .9
3.2 List of variables and abbreviations used in this Technical Specification . 14
4 Systems and equipment to be protected . 15
4.1 Low-voltage power distribution systems . 15
4.2 Characteristics of the equipment to be protected . 18
5 Surge protective devices . 19
5.1 Basic functions of SPDs . 19
5.2 Additional requirements . 19
5.3 Classification of SPDs . 19
5.4 Characteristics of SPDs . 21
5.5 Additional information on characteristics of SPDs . 22
6 Application of SPDs in low-voltage power distribution systems . 27
6.1 Installation and its effect on the protection given by SPDs . 27
6.2 Selection of SPD . 35
6.3 Characteristics of auxiliary devices . 43
7 Risk analysis. 43
8 Co-ordination where equipment has both signalling and power terminals . 44
Annex A (informative) Examples of various SPD technologies . 45
A.1 Examples of internal circuits for one port and two port SPDs . 45
A.2 Response of SPDs to a combination wave impulse . 47
Annex B (informative) Explanation of testing procedures used in EN 61643-11 . 48
B.1 Determination of U for SPDs tested in accordance with class I and class II tests . 48
res
B.2 Impulse waveshape for assessment of U . 48
res
B.3 Influence of a back filter on determination of U . 48
res
B.4 Operating duty test for SPDs . 49
B.5 TOV failure test . 50
B.6 Differences in the testing conditions of Type 1 (test class I), 2 (test class II) and
3 (tests class III) SPDs . 50
B.7 Short-circuit withstand capability test in conjunction with overcurrent protection
(if any) . 51
Annex C (informative) Partial lightning current calculations . 52
Annex D (informative) Examples of application of CLC/TS 61643-12 . 54
D.1 Domestic application . 54
D.2 Industrial application . 55
D.3 Presence of a lightning protection system . 60
Annex E (informative) Examples of application of the risk analysis . 61
Annex F (informative) Consideration for SPDs when Type 1 SPDs are to be applied . 65
Annex G (informative) Immunity versus insulation withstand . 67

Annex H (informative) Examples of SPD installation in power distribution boards in some
countries . 69
Annex I (informative) Short circuit backup protection and surge withstand . 72
I.1 Introduction . 72
I.2 Information single shot 8/20 and 10/350 fuses withstand. . 72
I.3 Fuse influencing factors (reduction) for preconditioning and operating duty test . 73
I.4 Specific examples with estimated range of factors for reduction of single shot fuse
withstand. . 73
Annex J (informative) SPD coordination test principles . 75
J.1 Introduction . 75
J.2 Coordination criteria . 75
J.3 Coordination techniques . 75
J.4 Coordination test . 76
Annex K (informative) Simple calculation of I for a Type 1 SPD in case of a building
imp
protected by a LPS . 79
Bibliography . 81

Figures
Figure 1 – Examples of components and combinations of components . 20
Figure 2 – Relationship between U , U , U and U . 22
p 0 c cs
Figure 3 – Typical curve of U versus I for ZnO varistors . 25
res
Figure 4 – Typical curve for a spark gap . 25
Figure 5 – Flowchart for SPD application . 27
Figure 6 – Connection Type 1 . 29
Figure 7 – Connection Type 2 . 30
Figure 8 – Influence of SPD connecting lead lengths . 33
Figure 9 – Need for additional protection . 34
Figure 10 – Flowchart for the selection of an SPD . 35
Figure 11 – Typical use of two SPDs – Electrical drawing . 41
Figure A.1 – Examples of one-port SPDs . 45
Figure A.2 – Examples of two-port SPDs . 46
Figure A.3 – Response of one-port and two-port SPDs to a combination wave impulse . 47
Figure B.1 – Test setting . 50
Figure C.1 – Simple calculation of the sum of partial lightning currents into the power
distribution system . 52
Figure D.1 – Domestic installation . 55
Figure D.2 – Industrial installation . 58
Figure D.3 – Industrial installation circuitry . 59
Figure D.4 – Example for a lightning protection system . 60
Figure E.1 – HV and LV overhead lines . 62
Figure E.2 – HV overhead line and buried LV lines . 63
Figure E.3 – HV and LV buried lines . 63
Figure E.4 – HV line overhead . 63
Figure F.1 – General distribution of lightning current . 66

– 5 – CLC/TS 61643-12:2009
Figure H.1 – Wiring diagram of an SPD connected on the load side of the main incoming
isolator via a separate isolator (which could be included in SPD enclosure) . 69
Figure H.2 – SPD connected to the nearest available outgoing way (MCB) to the incoming
supply (TNS installation typically seen in the UK) . 70
Figure H.3 – Single line-wiring diagram of an SPD connected in shunt on the first outgoing way
of the distribution panel via a fuse (or MCB) . 71
Figure J.1 – SPDs arrangement for the coordination test . 77

Tables
Table 1 – Maximum TOV values as given in IEC 60364-4-44 . 18
Table 2 – Preferred values of I . 24
imp
Table 3 – Possible modes of protection for various LV systems. 31
Table 4 – Minimum required U of the SPD dependent on supply system configuration. 36
c
Table 5 – Typical TOV test values . 37
Table I.1 – Examples of ratio between single shot withstand and full preconditioning/operating
duty test . 74
Table J.1 – Test procedure for coordination . 78
Table K.1 – Determination of the value of I on the AC side of PV generators . 80
imp
0 Introduction
0.1 General
This Technical Specification is to be used with EN 61643-11:2002.
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 in accordance with their environmental conditions and the acceptable failure
rate of the equipment and the SPDs.
This Technical Specification provides information :
• to the user about characteristics useful for the selection of an SPD.
• to evaluate, with reference to EN 62305-1 to EN 62305-4 and HD 384/60364 series, the need for
using SPDs in low-voltage systems.
• on selection and co-ordination of SPDs, while taking into account the entire environment in which
they are applied. Some examples are: equipment to be protected and system characteristics,
insulation levels, overvoltages, method of installation, location of SPDs, co-ordination of SPDs,
failure mode of SPDs and equipment failure consequences.
• and provides guidance to perform a risk analysis.
The HD 384/60364 series of harmonised documents provides direct information for contractors on the
installation of SPDs.
For the purpose of having a usable and complete working document, parts from existing documents
have been duplicated where necessary. Such parts are explicitly mentioned in the text and attention is
drawn to the reader that these parts may change in future.
0.2 Keys to understanding the structure of this Technical Specification
The list below summarizes the structure of this Technical Specification and provides a summary of the
information covered in each clause and annex. The main clauses provide basic information on the
factors used for SPD selection. Readers who wish to obtain more detail on the information provided in
Clauses 4 to 7 should refer to the relevant annexes.
Clause 1 describes the scope of this Technical Specification.
Clause 2 lists the normative references where additional information may be found.
Clause 3 provides definitions useful for the comprehension of this Technical Specification.
Clause 4 addresses the parameters of systems and equipment relevant to SPDs. In addition to the
stresses created by lightning, those created by the network itself as temporary overvoltages and
switching surges are described.
Clause 5 lists the electrical parameters used in the selection of an SPD and gives some explanation
regarding these parameters. These are related to the data given in EN 61643-11.

– 7 – CLC/TS 61643-12:2009
Clause 6 is the core of this Technical Specification. It relates the stresses coming from the network (as
discussed in Clause 4) to the characteristics of the SPD (as discussed in Clause 5). It outlines how the
protection given by SPDs may be affected by its installation. The different steps for the selection of an
SPD are presented including the problems of co-ordination when more than one SPD is used in an
installation (details about co-ordination may be found in Annex F).
Clause 7 is an introduction to the risk analysis (considerations of when the use of SPDs is beneficial).
Clause 8 deals with co-ordination between signalling and power lines (under consideration).
Annex A gives examples of various SPD technologies.
Annex B deals with explanations of testing procedures used in EN 61643-11.
Annex C deals with the calculation of the sharing of lightning current between different earthing
systems.
Annex D provides specific examples on the use of this Technical Specification.
Annex E provides specific examples of the use of the risk analysis.
Annex F deals with consideration when Type 1 SPDs are to be applied.
Annex G discusses differences between immunity level and insulation withstand of equipments.
Annex H provides practical examples of SPD installation as used in some countries.
Annex I deals with surge withstand of fuses.
Annex J provides SPD coordination tests principles.
Annex K provides simple calculation of I for Type 1 SPDs in case of a building protected by a LPS.
imp
1 Scope
This Technical Specification describes the principles for selection, operation, location and
co-ordination of SPDs to be connected to 50 Hz to 60 Hz a.c. power circuits and equipment rated up
to 1 000 V r.m.s.
NOTE 1 This Technical Specification deals only with SPDs and not with SPDs components integrated inside equipment.
NOTE 2 Additional requirements may be necessary for special applications such as electrical traction, etc.
NOTE 3 It should be remembered that IEC 60364 series and EN 62305-4 are also applicable.
2 Normative references
The following referenced documents are indispensable for the application 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.
HD 384/60364 series, Electrical installations of buildings/Low-voltage electrical installations
(IEC 60364 series, mod.)
HD 60364-4-41, Low-voltage electrical installations – Part 4-41: Protection for safety – Protection
against electric shock (IEC 60364-4-41, mod.)
HD 60364-4-443:2006, Electrical installations of buildings – Part 4-44: Protection for safety –
Protection against voltage disturbances and electromagnetic disturbances – Clause 443: Protection
against overvoltages of atmospheric origin or due to switching (IEC 60364-4-44:2001/A1:2003, mod.)
HD 60364-5-534:2008, Low-voltage electrical installations – Part 5-53: Selection and erection of
electrical equipment – Isolation, switching and control – Clause 534: Devices for protection against
overvoltages (IEC 60364-5-53:2001/A1:2002 (Clause 534), mod.)
EN 60529, Degrees of protection provided by enclosures (IP Code) (IEC 60529)
EN 60664-1, Insulation coordination for equipment within low-voltage systems – Part 1: Principles,
requirements and tests (IEC 60664-1)
EN 61000-4-5, Electromagnetic compatibility (EMC) – Part 4-5: Testing and measurement
techniques – Surge immunity test (IEC 61000-4-5)
EN 61008-1, Residual current operated circuit-breakers without integral overcurrent protection for
household and similar uses (RCCB's) – Part 1: General rules (IEC 61008-1, mod.)
EN 61009-1, Residual current operated circuit-breakers with integral overcurrent protection for
household and similar uses (RCBO's) – Part 1: General rules (IEC 61009-1, mod.)
EN 61643-11:2002 + A11:2007, Low-voltage surge protective devices – Part 11: Surge protective
devices connected to low-voltage power systems – Requirements and tests (IEC 61643-1:1998, mod.
+ corrigendum Dec. 1998, mod.)
EN 62305-1:2006, Protection against lightning – Part 1: General principles (IEC 62305-1:2006)
EN 62305-2, Protection against lightning – Part 2: Risk management (IEC 62305-2)
EN 62305-3, Protection against lightning – Part 3: Physical damage to structures and life hazard
(IEC 62305-3, mod.)
EN 62305-4, Protection against lightning – Part 4: Electrical and electronic systems within structures
(IEC 62305-4)
– 9 – CLC/TS 61643-12:2009
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE These definitions are for the most part reproduced from EN 61643-11 (the definition number being indicated within
square brackets). Where necessary a note has been added for better understanding regarding application of SPDs.
3.1
surge protective device
SPD
device that is intended to limit transient overvoltages and divert surge currents. It contains at least one
non-linear component
[EN 61643-11:2002, Definition 3.1]
3.2
continuous operating current
I
c
current flowing through each mode of protection of the SPD when energized at the maximum
continuous operating voltage (U ) for each mode
c
3.3
maximum continuous operating voltage
U
c
maximum r.m.s. voltage which may be continuously applied to the SPD's mode of protection. This is
equal to the rated voltage
[EN 61643-11:2002, Definition 3.11]
3.4
voltage protection level
U
p
parameter that characterizes the performance of the SPD in limiting the voltage across its terminals,
which is selected from a list of preferred values. This value is greater than the highest value of the
measured limiting voltages
[EN 61643-11:2002, Definition 3.15]
3.5
measured limiting voltage
maximum magnitude of voltage that is measured across the terminals of the SPD during the
application of impulses of specified waveshape and amplitude
[EN 61643-11:2002, Definition 3.16]
3.6
residual voltage
U
res
peak value of voltage that appears between the terminals of an SPD due to the passage of discharge
current
[EN 61643-11:2002, Definition 3.17]

3.7
temporary overvoltage test value
U
T
test voltage applied for a specific duration, to the SPD to simulate the stress under TOV conditions
NOTE 1 Adapted from EN 61643-11:2002, Definition 3.18, by adding the following note.
NOTE 2 It is a characteristic declared by the manufacturer that gives information about the behaviour of the SPD when
stressed with voltages U above U for a given specific duration t (this behaviour may either be no change in the performance
T c T
after application of the temporary overvoltage or a defined failure without hazard for either personnel, equipment or facility).
3.8
temporary overvoltage of the network
U
TOV
power frequency overvoltage occurring on the network at a given location, of relatively long duration.
TOVs may be caused by faults inside the LV system (U ) or inside the HV system (U )
TOV,LV TOV,HV
NOTE Temporary overvoltages, typically lasting up to several seconds, usually originate from switching operations or faults
(for example, sudden load rejection, single-phase faults, etc.) and/or from non-linearity (ferroresonance effects, harmonics, etc.).
3.9
nominal discharge current
I
n
crest value of the current through the SPD having a current waveshape of 8/20. This is used for the
classification of the SPD for class II test and also for preconditioning of the SPD for class I and II tests
[EN 61643-11:2002, Definition 3.8]
3.10
impulse current
I
imp
it is defined by three parameters, a current peak value I , a charge Q and a specific energy W/R.
peak
Tested in accordance with the test sequence of the operating duty test. This is used for the
classification of the SPD for class I test
[EN 61643-11:2002, Definition 3.9]
3.11
thermal runaway
operational condition when the sustained power dissipation of an SPD exceeds the thermal dissipation
capability of the housing and connections, leading to a cumulative increase in the temperature of the
internal elements culminating in failure
[EN 61643-11:2002, Definition 3.25]
3.12
thermal stability
an SPD is thermally stable if after the operating duty test causing temperature rise, the temperature of
the SPD decreases with time when the SPD is energized at specified maximum continuous operating
voltage and at specified ambient temperature conditions
[EN 61643-11:2002, Definition 3.26]
3.13
SPD disconnector
device (internal and/or external) required for disconnecting an SPD from the power system
NOTE This disconnecting device is not required to have isolating capability. It is to prevent a persistent fault on the system and
is used to give indication of the SPD failure.
There may be more than one disconnector function for example, an overcurrent protection function and a thermal protection
function. These functions may be integrated into one unit or performed in separate units.
[EN 61643-11:2002, Definition 3.29]

– 11 – CLC/TS 61643-12:2009
3.14
short-circuit withstand
maximum prospective short-circuit current that the SPD is able to withstand
[EN 61643-11:2002, Definition 3.28]
3.15
one-port SPD
SPD connected in shunt with the circuit to be protected. A one-port device may have separate input
and output terminals without a specified series impedance between these terminals
NOTE 1 Adapted from EN 61643-11:2002, Definition 3.2, by adding the following note.
NOTE 2 Annex A shows some typical one-port SPDs and the generic drawing for a one-port SPD. A one-port SPD may be
connected in shunt, Figure A.1 a), or in line with the power supply. In the first case the load current is not flowing through the
SPD. In the second case, the load current is flowing through the SPD and the temperature rise under load current and the
associated maximum admissible load current may be determined as for a two-port SPD. Figure A.3 shows the response of
various types of one-port SPD to an 8/20 impulse applied via a combination wave generator.
3.16
two-port SPD
SPD with two sets of terminals, input and output. A specific series impedance is inserted between
these terminals
NOTE 1 Adapted from EN 61643-11:2002, Definition 3.3, by adding the following note.
NOTE 2 The measured limiting voltage may be higher at the input terminals than at the output terminals. Therefore, equipment
to be protected shall be connected to the output terminals. Figure A.2 shows typical two-port SPDs. Figure A.3 shows the
response of a two-port SPD to an 8/20 impulse applied via a combination wave generator.
3.17
voltage switching type SPD
SPD that has a high impedance when no surge is present, but can have a sudden change in
impedance to a low value in response to a voltage surge. Common examples of components used as
voltage-switching devices are spark-gaps, gas discharge tubes (GDT), thyristors (silicon-controlled
rectifiers) and triacs. These SPDs are sometimes called "crowbar type"
NOTE 1 Adapted from EN 61643-11:2002, Definition 3.4, by adding the following note.
NOTE 2 A voltage-switching device has a discontinuous U versus I characteristic. Figure 3c shows the response of a typical
voltage switching SPD to an impulse applied via a combination wave generator.
3.18
voltage limiting type SPD
SPD that has a high impedance when no surge is present, but will reduce it continuously with
increased surge current and voltage. Common examples of components used as non-linear devices
are: varistors and suppressor diodes. These SPDs are sometimes called "clamping type"
NOTE 1 Adapted from EN 61643-11:2002, Definition 3.5, by adding the following note.
NOTE 2 A voltage-limiting device has a continuous U versus I characteristic. Figure 3b shows the response of a typical
voltage-limiting SPD to an impulse applied via a combination wave generator.
3.19
combination type SPD
SPD that incorporates both voltage switching type components and voltage limiting type components
may exhibit voltage-switching, voltage-limiting, or both voltage-switching and voltage-limiting
behaviour depending upon the characteristics of the applied voltage
NOTE 1 Adapted from EN 61643-11:2002, Definition 3.6, by adding the following note.
NOTE 2 Figure A.3 shows the response of various typical combination type SPDs to a combination wave impulse.
3.20
modes of protection
SPD protective components may be connected line to line or line to earth or line to neutral or neutral
to earth and combination thereof. These paths are referred to as modes of protection
[EN 61643-11:2002, Definition 3.7]

3.21
follow current
I
f
current supplied by the electrical power system and flowing through the SPD after a discharge current
impulse. The follow current is significantly different from the continuous operating current (I )
c
[EN 61643-11:2002, Definition 3.13]
3.22
maximum discharge current for class II test
(I )
max
crest value of a current through the SPD having an 8/20 waveshape and magnitude in accordance
with the test sequence of the class II operating duty test. I is greater than I
max n
[EN 61643-11:2002, Definition 3.10]
3.23
degradation
change of original performance parameters as a result of exposure of the SPD to surge, service or
unfavourable environment
NOTE 1 Adapted from 3.27 of EN 61643-11 by adding the following note.
NOTE 2 Degradation is a measure of the ability of an SPD to withstand the conditions for which it is designed throughout its
service life. Two type tests are applied to provide confidence with respect to degradation. The first one is the operating duty test
and the second is the ageing test. However, these two tests may be combined.
The operating duty test is conducted by applying a specified number of defined current waveshapes to the SPD. Permitted
changes in the SPD characteristics are given in EN 61643-11.
The ageing test is carried out at a specified temperature with a voltage of specified magnitude and duration applied to the SPD.
Permitted changes in the SPD characteristics are given in this Technical Specification (this test is under consideration).
This can be used to determine the SPD prospective installed life which should also consider the following:
– replacement policy;
– location and accessibility;
– acceptable failure rate;
– operating practices.
3.24
residual current device
RCD
mechanical switching device or association of devices intended to cause the opening of the contacts
when the residual or unbalanced current attains a given value under specified conditions
[EN 61643-11:2002, Definition 3.37]
3.25
nominal voltage of the system phase to earth
U
n
voltage by which a system or equipment is designated and to which certain operating characteristics
are referred (for example, 230/400 V).
Under normal system conditions, the voltage at the supply terminals may differ from the nominal
voltage as determined by the tolerances of the supply systems. In this Technical Specification a
tolerance of ± 10 % is used
3.26
line to neutral voltage of the system
U
o
line to neutral voltage (r.m.s. value of the a.c. voltage) of the system, derived from the nominal system
voltage (the voltage by which the system is designated)
[EN 61643-11:2002, Definition 3.46]

– 13 – CLC/TS 61643-12:2009
3.27
rated load current (I )
L
maximum continuous rated r.m.s. current that can be supplied to a load connected to the protected
output of an SPD
NOTE 1 Adapted from EN 61643-11:2002, Definition 3.14, by adding the following note.
NOTE 2 This is only relevant to SPD(s) having separate input and output terminals.
3.28
overcurrent protection
overcurrent device (e.g. circuit breaker or fuse), which could be part of the electrical installation
located externally up-stream of the SPD
[EN 61643-11:2002, Definition 3.36]
3.29
maximum continuous operating voltage of the power system at the SPD location
U
cs
maximum r.m.s. voltage to which the SPD may be permanently subjected at the point of application of
the SPD
NOTE 1 Adapted from EN 61643-11:2002, Definition 3.49, by adding the following notes
NOTE 2 This takes into account only voltage regulation and/or voltage drop or increase. It is also called actual maximum
system voltage (see Figure 6) and is directly linked to U
NOTE 3 This voltage does not take into account harmonics, faults, TOVs or transient conditions.
3.30
sparkover voltage of a voltage-switching SPD
maximum voltage value before disruptive discharge between the electrodes of the gap of a SPD
NOTE 1 Adapted from EN 61643-11:2002, Definition 3.38, by adding the following note.
NOTE 2 A voltage-switching SPD may be based on components other than gaps (for example, silicon-based components).
3.31
lightning protection system
LPS
complete system used to protect a structure and its contents against the effects of lightning
3.32
multiservice SPD
surge protective device providing protection for two or more services such as power,
telecommunication and signalling in a single enclosure in which a reference bond is provided between
services during surge conditions
3.33
residual current
I
PE
current flowing through the PE terminal, when the SPD is energized at the maximum continuous
operating voltage (U ) when connected in accordance with the manufacturer instructions
c
[EN 61643-11:2002, Definition 3.42]
3.34
prospective short-circuit current of a power supply
I
p
current which would flow at a given location in a circuit if it were short-circuited at that location by a link
of negligible impedance
[EN 61643-11:2002, Definition 3.40]

3.35
follow current interrupting rating
I
fi
prospective short-circuit current that an SPD is able to interrupt by itself
[EN 61643-11:2002, Definition 3.41]
3.36
specific energy for class I test
(W/R)
energy dissipated by a unit resistance of 1 Ω with the impulse discharge current I
imp
3.37
rated impulse withstand voltage
(U )
W
impulse withstand voltage assigned by the manufacturer to the equipment or to a part of it,
characterizing the specified withstand capability of its insulation against overvoltages
NOTE For the purpose of this Technical Specification only withstand voltages between live conductors and earth is
considered.
3.2 List of variables and abbreviations used in this Technical Specification
List of variables
Maximum energy withstand
E
MAX
Continuous operating current
I
c
Follow current
I
f
I Follow current interrupting rating
fi
I Impulse current for class I test
imp
Rated load current
I
L
Maximum discharge current for class II test
I
max
Nominal discharge current
I
n
Prospective short circuit current of the power supply
I
p
Current peak value of impulse current
I
peak
I Residual current
PE
I Short-circuit current of the CWG
sc
Inductance
L
Ground flash density
N
g
Keraunic level
N
k
Maximum continuous operating voltage
U
c
Maximum continuous operating voltage of the power system
U
cs
U Dynamic sparkover voltage of a gap
dyn
U Measured limiting voltage
m
Nominal voltage of the system phase to earth
U
n
Line-to-neutral voltage of the system
U
Open-circuit voltage for class III test
U
oc
– 15 – CLC/TS 61643-12:2009
Voltage protection level
U
p
Reference voltage of a varistor
U
ref
U Residual voltage
res
U Temporary overvoltage
T
Temporary overvoltage of the power system
U
TOV
Temporary overvoltage of the network inside the high-voltage system
U
TOV,HV
Temporary overvoltage of the network inside the low-voltage system
U
TOV,LV
Voltage withstand
U
W
Q Charge of impulse current
List of abbreviations
CWG Combination Wave Generator
EMC ElectroMagnetic Compatibility
GDT Gas Discharge Tubes
HV High Voltage
IP Degrees of protection provided by the enclosure
LPS Lightning Protection System
LPZ Lightning Protection Zone
LV Low Voltage
MEB Main Equipotential Bonding
MOV Metal Oxide Varistor
HVA High Voltage A (medium voltage, < 50 kV), called sometimes improperly MV
PE Protective Earth
RCD Residual Current Device
TOV Temporary OverVoltage
SPD Surge Protective Device
ZnO Zinc Oxide
4 Systems and equipment to be protected
When evaluating an installation with regard to the use of an SPD, two factors need to be considered:
• the characteristics of the low-voltage power distribution system on which it will be used,
including expected types and levels of overvoltage and current;
• the characteristics of the equipment requiring protection.
4.1 Low-voltage power distribution systems
Low-voltage power distribution systems are basically characterized by the type of system earthing
(TNC, TNS, TNC-S, TT, IT) and the nominal voltage (see 3.35). Various types of overvoltages and
currents may occur. In this Technical Specification, the overvoltages are classified into three groups:
• lightning;
• switching;
• temporary overvoltages.
4.1.1 Lightning overvoltages and currents
In most cases lightning stress is the main factor for the selection of an SPD’s class of test and
associated current or voltage values (I , I or U , in accordance with EN 61643-11).
imp max oc
Evaluation of the waveshape and current (or voltage) amplitude of the lightning surges is necessary
for the proper selection of an SPD. It is important to determine if the voltage protection level of the
SPD will be adequate to protect the equipment in such circumstances.
NOTE For example, areas prone to frequent lightning strikes may require an SPD suitable to withstand class I or class II tests.
Generally (for example, in the case of direct strike to the lines or induced surges on the lines), higher
stresses occur on the electrical installation external to the structure. Within the structure, the stresses
are decreased when moving from the installation’s entrance to internal circuits. The decrease is due to
the change of circuit configuration and impedances.
The need for protection against lightning surges depends on
• the local ground flash density N (average annual ground flash density, in lightning flashes per
g
km² per year, concerning the region where the structure is located). Modern lightning location
systems can provide information on N with reasonable accuracy;
g
• the exposure of the electrical installation, including incoming services. Underground systems
are generally considered to be less exposed than overhead systems;
• even if the supply is provided by an underground cable, the use of an SPD may be recom-
mended to provide protection. To determine if surge protection is needed, the following are
some items that should be considered:
– the installation has a lightning protection system in its vicinity;
– the length of the cable is not sufficient to provide adequate separation (attenuation) of the
installation from the overhead part of the network;
– high surges of atmospheric origin can be expected on the overhead line supplying the HV
(high voltage) side of the transformer connected to the installation;
– the underground cable may be affected by direct lightning in the presence of high soil
resistivity;
– the size or height of the building powered by the cable is large enough to significantly increase
the risk for direct strikes to the building. The risk for di
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