IEC 61643-21:2000+AMD1:2008 CSV

IEC 61643-21
Edition 1.1 2009-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Low voltage surge protective devices –
Part 21: Surge protective devices connected to telecommunications and
signalling networks – Performance requirements and testing methods

Parafoudres basse tension –
Partie 21: Parafoudres connectés aux réseaux de signaux et de
télécommunications – Prescriptions de fonctionnement et méthodes d’essais
IEC 61643-21:2000+A1:2008
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IEC 61643-21
Edition 1.1 2009-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Low voltage surge protective devices –
Part 21: Surge protective devices connected to telecommunications and
signalling networks – Performance requirements and testing methods

Parafoudres basse tension –
Partie 21: Parafoudres connectés aux réseaux de signaux et de
télécommunications – Prescriptions de fonctionnement et méthodes d’essais

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CS
CODE PRIX
ICS 29.240; 29.240.10 ISBN 2-8318-9836-6

– 2 – 61643-21 © IEC:2000+A1:2008
CONTENTS
FOREWORD.5
INTRODUCTION.7
1 General .8
1.1 Scope.8
1.2 SPD configurations.8
1.3 Use of this standard .10
2 Normative references .13
3 Definitions .14
4 Service and test conditions.17
4.1 Service conditions .17
4.1.1 Normal service conditions.17
4.1.2 Abnormal service conditions .18
4.2 Test temperature and humidity .18
4.3 SPD testing .18
4.4 Waveform tolerances.19
5 Requirements .19
5.1 General requirements.19
5.1.1 Identification and documentation .19
5.1.2 Marking .19
5.2 Electrical requirements.20
5.2.1 Voltage-limiting requirements .20
5.2.2 Current-limiting requirements .21
5.2.3 Transmission requirements.22
5.3 Mechanical requirements.22
5.3.1 Terminals and connectors.23
5.3.2 Mechanical strength (mounting).24
5.3.3 Resistance to ingress of solid objects and to harmful ingress of water .24
5.3.4 Protection against direct contact.24
5.3.5 Fire resistance.24
5.4 Environmental requirements .24
5.4.1 High temperature and humidity endurance.24
5.4.2 Environmental cycling with impulse surges .25
5.4.3 Environmental cycling with a.c. surges .25
6 Type test .25
6.1 General tests.25
6.1.1 Identification and documentation .25
6.1.2 Marking .25
6.2 Electrical tests.26
6.2.1 Voltage-limiting tests .26
6.2.2 Current-limiting tests .32
6.2.3 Transmission tests .35
6.3 Mechanical tests .37
6.3.1 Terminals and connectors.37
6.3.2 Mechanical strength (mounting).39
6.3.3 Resistance to ingress of solid objects and to harmful ingress of water .39
6.3.4 Protection against direct contact.39

61643-21 © IEC:2000+A1:2008 – 3 –
6.3.5 Fire resistance.40
6.4 Environmental tests.41
6.4.1 High temperature and humidity endurance.41
6.4.2 Environmental cycling with impulse surges .41
6.4.3 Environmental cycling with a.c. surges .42
6.5 Acceptance tests.42

Annex A (informative) Devices with current-limiting components only .56
Annex B (Void) .57
Annex C (Void) .58
Annex D (informative) Measurement accuracy .59
Annex E (informative) Determination of let-through current (I ).60
p
Bibliography.63

Figure 1 – SPD configurations .9
Figure 16 – Examples of multi-line SPDs with a common protective element.28
Figure 2 – Test circuits for impulse reset time.43
Figure 3 – Test circuits for a.c. durability and overstressed fault mode .44
Figure 4 – Test circuits for impulse durability and overstressed fault mode .45
Figure 5 – Test circuits for rated current, series resistance, response time,
current reset time, maximum interrupting voltage and operating duty test .46
Figure 6 – Test circuits for a.c. durability .47
Figure 7 – Test circuits for impulse durability .48
Figure 8 – Test circuits for insertion loss.49
Figure 9 – Test circuit for return loss .49
Figure 10 – Test circuits for longitudinal balance .50
Figure 11 – Test circuit for bit error ratio test .51
Figure 12 – Test circuit for near-end crosstalk .52
Figure 13 – Test circuits for high temperature/humidity endurance
and environmental cycling.53
Figure 14 – Environmental cycling schedule A with RH ≥ 90 % .54
Figure 15 – Environmental cycling B .55
Figure A.1 – Configurations of devices with current-limiting component(s) only.56
Figure E.1 – Determination of differential mode let-through current.60
Figure E.2 – Determination of common mode let-through current .61
Figure E.3 – Determination of differential mode let-through current.61
Figure E.4 – Determination of differential mode let-through current.61
Figure E.5 – Determination of common mode max. let-through current .61
Figure E.6 – Determination of common mode max. let-through current
at multi-terminal SPDs .62

– 4 – 61643-21 © IEC:2000+A1:2008
Table 1 – General SPD requirements.11
Table 2 – Waveform tolerances.19
Table 3 – Voltage and current waveforms for impulse-limiting voltage.27
Table 4 – Source voltages and currents for impulse reset test .29
Table 5 – Preferred values of currents for a.c. durability test .30
Table 6 – Test currents for response time.32
Table 7 – Preferred values of current for operating duty tests .34
Table 8 – Preferred values of a.c. test currents.34
Table 9 – Preferred values of impulse current.35
Table 10 – Standard parameters for figure 8 .35
Table 11 – Impedance values for longitudinal balance test.36
Table 12 – Test times for BER test .37
Table 13 – Connectable cross-sectional areas of copper conductors
for screw-type terminals or screwless-type terminals .38
Table 14 – Pulling force (screwless terminals) .38
Table 15 – Preferred values of test-time duration for high temperature
and humidity endurance.41
Table 16 – Preferred values of temperature and duration for environmental cycling tests.42

61643-21 © IEC:2000+A1:2008 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
–––––––––––
LOW VOLTAGE SURGE PROTECTIVE DEVICES –

Part 21: Surge protective devices connected to telecommunications
and signalling networks –
Performance requirements and testing methods

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
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6) All users should ensure that they have the latest edition of this publication.
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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.
International Standard IEC 61643-21 has been prepared by subcommittee 37A: Low-voltage
surge protective devices, of IEC technical committee 37: Surge arresters.
This consolidated version of IEC 61643-21 consists of the first edition (2000) [documents
37A/101/FDIS and 37A/104/RVD], its amendment 1 (2008) [documents 37A/200/FDIS and
37A/201/RVD] and its corrigendum of March 2001.
The technical content is therefore identical to the base edition and its amendment and has
been prepared for user convenience.
It bears the edition number 1.1.
A vertical line in the margin shows where the base publication has been modified by
amendment 1.
– 6 – 61643-21 © IEC:2000+A1:2008
The committee has decided that the contents of the base publication and its amendments 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.
61643-21 © IEC:2000+A1:2008 – 7 –
INTRODUCTION
The purpose of this International Standard is to identify the requirements for Surge Protective
Devices (SPDs) used in protecting telecommunication and signalling systems, for example,
low-voltage data, voice, and alarm circuits. All of these systems may be exposed to the
effects of lightning and power line faults, either through direct contact or induction. These
effects may subject the system to overvoltages or overcurrents or both, whose levels are
sufficiently high to harm the system. SPDs are intended to provide protection against
overvoltages and overcurrents caused by lightning and power line faults. This standard
describes tests and requirements which establish methods for testing SPDs and determining
their performance.
The SPDs addressed in this International Standard may contain overvoltage protection
components only, or a combination of overvoltage and overcurrent protection components.
Protection devices containing overcurrent protection components only are not within the
coverage of this standard. However, devices with only overcurrent protection components are
covered in annex A.
An SPD may comprise several overvoltage and overcurrent protection components. All SPDs
are tested on a "black box" basis, i.e., the number of terminals of the SPD determines the
testing procedure, not the number of components in the SPD. The SPD configurations are
described in 1.2. In the case of multiple line SPDs, each line may be tested independently of
the others, but there may also be a need to test all lines simultaneously.
This standard covers a wide range of testing conditions and requirements; the use of some of
these is at the discretion of the user. How the requirements of this standard relate to the
different types of SPD is described in 1.3. Whilst this is a performance standard and certain
capabilities are demanded of the SPDs, failure rates and their interpretation are left to the
user. Selection and application principles are covered in IEC 61643-22.
If the SPD is known to be a single component device, it has to meet the requirements of the
relevant standard as well as those in this standard.

– 8 – 61643-21 © IEC:2000+A1:2008
LOW VOLTAGE SURGE PROTECTIVE DEVICES –

Part 21: Surge protective devices connected to telecommunications
and signalling networks –
Performance requirements and testing methods

1 General
1.1 Scope
This International Standard is applicable to devices for surge protection of telecommunications
and signalling networks against indirect and direct effects of lightning or other transient
overvoltages.
The purpose of these SPDs is to protect modern electronic equipment connected to
telecommunications and signalling networks with nominal system voltages up to 1 000 V
(r.m.s.) a.c. and 1 500 V d.c.
1.2 SPD configurations
The SPD configurations described in this standard are shown in figure 1. Each SPD
configuration is composed of one or more voltage-limiting components and may include
current-limiting components.
61643-21 © IEC:2000+A1:2008 – 9 –

X1
SPD
(V)
X2
IEC  549/08
Figure 1a – Two-terminal SPD
X1
SPD SPD
X1 Y1
C
(V, I)
(V)
C X2
IEC  550/08 IEC  551/08
Figure 1b – Three-terminal SPD Figure 1c – Three-terminal SPD

X1 Y1
SPD
(V, I)
X2 Y2
X1 Y1
SPD
(V, I)
Y2
X2
C
IEC  552/08
IEC  553/08
Figure 1d – Four-terminal SPD Figure 1e – Five-terminal SPD

Y1
X1
X2
Y2
SPD
(V, I )
Yn
Xn
a
C
IEC  554/08
a
The common terminal C may not be provided.
Figure 1f – Multi-terminal SPD
Key
V voltage-limiting component
V, I voltage-limiting components or a combination of voltage-limiting and current-limiting components
X1, X2.Xn line terminals
Y1, Y2…Yn protected line terminals
C common terminal
Figure 1 – SPD configurations
– 10 – 61643-21 © IEC:2000+A1:2008
1.3 Use of this standard
This standard considers two basic types of SPD.
The first type of SPD contains at least one voltage-limiting component and no current-limiting
component(s) in a housing. All the SPD configurations of figure 1 can be of this type. These
SPDs shall satisfy the requirements of 5.1, 5.2.1 and 5.3 (see table 1). The SPDs shown in
figures 1b, 1d, 1e and 1f may contain a linear component between the line terminal and
the corresponding protected line terminal. These SPDs shall also satisfy the applicable
requirements of 5.2.2.
The second type of SPD contains both voltage-limiting and current-limiting components in a
housing. SPD configurations shown in figures 1b, 1d, 1e, and 1f are applicable for SPDs with
both voltage-limiting and current-limiting components. This type of SPD shall satisfy the
requirements of 5.1, 5.2.1, 5.2.2 and 5.3 (see table 1). Configurations of protective devices
having only current-limiting components are covered in annex A.
SPDs may need to satisfy additional requirements depending on the application. The
additional requirements are described in 5.2.3 and 5.4 (see table 1).
Subclause 5.2.3 provides transmission tests that SPDs may need to conform to, depending on
their communication and signalling application. Selection of the applicable transmission tests
from 5.2.3 shall be made, based on the intended application of the SPDs. Table 1 provides
general guidance on how to select the applicable transmission tests.
Subclause 5.4 provides the environmental requirements when the SPDs are intended only for
use in uncontrolled environments as described in 4.1. SPDs shall satisfy these requirements
after an agreement between the user and the manufacturer. Table 1 provides examples of
what requirements different types of SPD shall satisfy.

61643-21 © IEC:2000+A1:2008 – 11 –
Table 1 – General SPD requirements
Test Sub-
Requirement – Test Type of SPD
series clause
1 General test 6.1
Identification and
documentation 6.1.1 A A A A A A
Marking 6.1.2 A A A A A A
Transmission tests 6.2.3
Capacitance 6.2.3.1 A O O O A O
Insertion loss 6.2.3.2 O A A A O A
Return loss 6.2.3.3 O O O A O O
Longitudinal balance 6.2.3.4 O O O A O O
Bit Error Ratio (BER) 6.2.3.5 O O O O O O
Near-end crosstalk (NEXT) 6.2.3.6 O O O A O O
Mechanical tests 6.3
Terminals and connectors 6.3.1 A A A A A A
General testing procedure 6.3.1.1 A A A A A A
Terminals with screws 6.3.1.2 A A A A A A
Screwless terminals 6.3.1.3 A A A A A A
Insulating pierced
connections 6.3.1.4 A A A A A A
Pull-out-test on SPD
terminals designed for
single-core conductors 6.3.1.4.1 A A A A A A
Pull-out-test on SPD
terminals designed for multi-
core cables and cords 6.3.1.4.2 A A A A A A
Mechanical strength
(mounting) 6.3.2 A A A A A A
Resistance to ingress of
solid objects and to harmful
ingress of water 6.3.3 A A A A A A
Protection against direct
contact 6.3.4 A A A A A A
Fire resistance 6.3.5 A A A A A A

SPD with only voltage-
limiting function
SPD with both voltage-
limiting and current-
limiting functions
SPD with voltage-
limiting function and
linear component
between its terminals
SPD having both
voltage-limiting and
current-limiting
functions with enhanced
transmission
capabilities
SPD having only
voltage-limiting function
but intended for use in
extended range
environment
SPD having both
voltage-limiting and
current-limiting
functions but intends for
use in extended range
environment
– 12 – 61643-21 © IEC:2000+A1:2008
Table 1 (continued)
Test
Sub-
4 Requirement – Test Type of SPD
series clause
Environmental tests 6.4
High temperature and
6.4.1 O O O O A A
humidity endurance
Environmental cycling with
impulse surges 6.4.2 O O O O A A
Environmental cycling with
a.c. surges 6.4.3 O O O O A A
2 Voltage limiting tests 6.2.1
Maximum continuous
operating voltage (Uc) 6.2.1.1 A A A A A A
Insulation resistance 6.2.1.2 A A A A A A
Impulse durability for
voltage limiting function 6.2.1.6 A A A A A A
Impulse-limiting voltage 6.2.1.3 A A A A A A
Impulse reset switching
types 6.2.1.4 A A A A A A
AC durability for voltage
limiting function 6.2.1.5 O O O O O O
Blind spot test multi stage
SPD 6.2.1.8 A A A A A A
Overstressed fault mode 6.2.1.7 A A A A A A
3 Current limiting tests 6.2.2
Rated current 6.2.2.1 N.A. A A A N.A. A
Series resistance 6.2.2.2 N.A. A A A N.A. A
A
Current response time 6.2.2.3 N.A. A N.A. A N.A.
A
Current reset time 6.2.2.4 N.A. A N.A. A N.A.
Maximum interrupting A
voltage 6.2.2.5 N.A. A N.A. A N.A.
A
Operating duty test 6.2.2.6 N.A. A N.A. A N.A.
AC durability for current A
1 3
limiting function 6.2.2.7 N.A. A N.A. A N.A.
Impulse durability for A
1 3
current limiting function 6.2.2.8 N.A. A N.A. A N.A.
4 Acceptance tests 6.5 O O O O O O
A Applicable.
N.A. Not applicable.
O Optional.
For each category of test impulse a new set of samples can be used.
It is admissible to measure the impulse-limiting voltage 6.2.1.3 while testing impulse durability 4.2.1.6.
Test not applicable if there is a linear component between its terminals.
Each test series is carried out on three samples.

SPD with only voltage-
limiting function
SPD with both voltage-
limiting and current-
limiting functions
SPD with voltage-
limiting function and
linear component
between its terminals
SPD having both
voltage-limiting and
current-limiting
functions with enhanced
transmission
capabilities
SPD having only
voltage-limiting function
but intended for use in
extended range
environment
SPD having both
voltage-limiting and
current-limiting
functions but intends for
use in extended range
environment
61643-21 © IEC:2000+A1:2008 – 13 –
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.
IEC 60050(702):1992, International Electrotechnical Vocabulary – Chapter 702: Oscillations,
signals and related devices
IEC 60050(726):1982, International Electrotechnical Vocabulary – Chapter 726: Transmission
lines and waveguides
IEC 60060-1:1989, High-voltage test techniques – Part 1: General definitions and test
requirements
IEC 60068-2-30:1980, Environmental testing – Part 2: Tests – Test Db and guidance: Damp
heat, cyclic (12 + 12-hour cycle)
IEC 60529, Degrees of protection provided by enclosures (IP code)
IEC 60695-2-1/1:1994, Fire hazard testing – Part 2: Test methods – Section 1/sheet 1: Glow-
wire end-product test and guidance
IEC 60950:1999, Safety of information technology equipment
IEC 60999-1:1999, Connecting devices – Electrical copper conductors – Safety requirements
for screw-type and screwless-type clamping units – Part 1: General requirements and
2 2
particular requirements for clamping units for conductors from 0,2 mm up to 35 mm
(included)
IEC 61000-4-5, Electromagnetic compatibility (EMC) – Part 4: Testing and measurement
techniques – Section 5 – Surge immunity test
IEC 61083-1, Digital recorders for measurements in high voltage impulse tests – Part 1:
Requirements for digital recorders
IEC 61180-1:1992, High-voltage test techniques for low-voltage equipment – Part 1:
Definitions, test and procedure requirements
IEC 61643-1, Surge protective devices connected to low-voltage power distribution systems –
Part 1: Performance requirements and testing methods
IEC 61643-22:2004, Low-voltage surge protective devices – Part 22: Surge protection devices
connected to telecommunications and signalling networks – Selection and application
principles
ITU-T Recommendation K.30:1993, Positive temperature coefficient (PTC) thermistors
ITU-T Recommendation K.55:2002, Overvoltage and overcurrent requirements for insulation
displacement connectors (IDC) terminations
ITU-T Recommendation K.65:2004, Overvoltage and overcurrent requirements for termination
modules with contacts for test ports or SPDs
ITU-T Recommendation O.9:1999, Measuring arrangements to assess the degree of
unbalance about earth
– 14 – 61643-21 © IEC:2000+A1:2008
3 Definitions
For the purpose of this part of IEC 61643, the following definitions apply.
3.1
model number
code, either applied to the SPD or included in its documentation, that is used to identify the
SPD
3.2
preferred values
values for the parameters listed in the tables for the various tests, preferred in the sense that
their use promotes uniformity and provides a means of comparison among various protective
devices. They also provide a common engineering language beneficial to the user and
manufacturer of surge protectors used in telecommunications and signalling networks.
However, specific applications may require values other than the preferred values of the
tables
3.3
overstressed fault mode
mode 1 condition wherein the voltage-limiting part of the SPD has been disconnected. The
voltage-limiting function is no longer present, but the line is still operable
mode 2 condition wherein the voltage-limiting part of the SPD has been short-circuited by a
very low impedance within the SPD. The line is inoperable, but the equipment is still protected
by a short circuit
mode 3 situation wherein the SPD has undergone an internal open circuit on the network
side of the voltage-limiting part of the SPD. The line is inoperable but the equipment is still
protected by an open line
3.4
protection
application of methods and means to prevent the propagation of stressful electrical energy
beyond a designed interface
3.5
current response time
time required for a current-limiting component to operate at a specified current and a
specified temperature
3.6
maximum continuous operating voltage U
c
maximum voltage (d.c. or r.m.s.) which may be continuously applied to SPD terminals without
causing any degradation in the transmission characteristics of the SPD
3.7
maximum interrupting voltage
maximum voltage (d.c. or r.m.s.) that can be applied to the current-limiting components of an
SPD without degradation of the SPD. This voltage may be equal to the U of the SPD or may
c
be a higher value depending on the arrangement of the current-limiting component(s) within
the SPD
61643-21 © IEC:2000+A1:2008 – 15 –
3.8
surge protective device
SPD
device that restricts the voltage of a designated port or ports, caused by a surge, when it
exceeds a predetermined level
NOTE 1 Secondary functions may be incorporated, such as a current-limiting to restrict a terminal current.
NOTE 2 Typically the protective circuit has at least one non-linear voltage-limiting surge protective component.
NOTE 3 An SPD is a complete assembly, having terminals to connect to the circuit conductors.
3.9
voltage limiting
action of the SPD that causes all voltages exceeding a predetermined value to be reduced
3.10
current limiting
action of an SPD, containing at least one non-linear current-limiting component, that causes
currents exceeding a predetermined value to be restricted
3.11
non-resettable current limiting
action of an SPD that limits current only one time
3.12
resettable current limiting
action of an SPD that limits current and can be manually reset after operating
3.13
self-resetting current limiting
action of an SPD that limits current and will self-reset after the disturbing current is removed
3.14
voltage clamping type SPD
SPD that has high shunt impedance and will have a continuous reduction in impedance with
increasing current in response to a voltage surge exceeding the threshold level of the SPD
NOTE Examples of components used in voltage clamping type SPDs: varistors (e.g. MOV) and avalanche
breakdown diodes (ABD).
3.15
voltage switching type SPD
SPD that has a high shunt impedance and will have a sudden and large reduction in
impedance in response to a voltage surge exceeding the threshold level of the SPD
NOTE Examples of components used in voltage switching type SPDs: air gaps, gas discharge tubes (GDT) and
thyristor surge suppressors (TSS).
3.16
voltage protection level U
p
parameter that characterizes the performance of the SPD in limiting the voltage across its
terminals. This value of voltage is greater than the highest measured value of impulse-limiting
voltage and is specified by the manufacturer
3.17
multi-stage SPD
SPD which has more than one voltage-limiting component. These voltage-limiting components
may or may not be electrically separated by a series component. The voltage-limiting
components may be either switching or clamping types

– 16 – 61643-21 © IEC:2000+A1:2008
3.18
blind spot
situation where voltages above the maximum continuous operating voltage U may cause
c
incomplete operation of the SPD. Incomplete operation of the SPD means not all of the stages
in a multi-stage SPD have operated during the impulse test. This may result in overstressing
of components in the SPD
3.19
a.c. durability
characteristic of an SPD which allows it to conduct alternating current of a specific magnitude
and duration for a specified number of times
3.20
impulse durability
characteristic of an SPD which allows it to conduct impulse current of a specified waveform
and peak value for a specified number of times
3.21
current reset time
time required for a self-resettable current limiter to revert to its normal or quiescent state
3.22
rated current
maximum current a current-limiting SPD can conduct continuously with no change in the
impedance of the current-limiting components
NOTE This is also applicable to linear series components.
3.23
insulation resistance
resistance between designated terminals of an SPD when U is applied to those terminals
c
3.24
return loss
modulus of the reciprocal of the reflection factor, generally expressed in decibels (dB)
NOTE When impedances can be defined, the return loss in dB is given by the formula:
20 log MOD [(Z +Z )/(Z –Z )]
10 1 2 1 2
where Z is the characteristic impedance of the transmission line ahead of the discontinuity, or the impedance of
the source, and Z is the impedance after the discontinuity or load impedance seen from the junction between the
source and the load [IEV 702-07-25, modified]
3.25
bit error ratio (BER)
ratio of the number of bit errors to the total number of bits transmitted in a given time interval
3.26
insertion loss
loss resulting from the insertion of an SPD into a transmission system. It is the ratio of the
power delivered to that part of the system following the SPD, before insertion of the SPD, to
the power delivered to that same part after insertion of the SPD. The insertion loss is
generally expressed in decibels [IEV 726-06-07, modified]
3.27
near-end crosstalk (NEXT)
crosstalk that is propagated in a disturbed channel in the direction opposite to the direction of
propagation of the current in the disturbing channel. The terminal of the disturbed channel at
which the near-end crosstalk is present is ordinarily near to, or coincides with, the energized
terminal of the disturbing channel

61643-21 © IEC:2000+A1:2008 – 17 –
3.28
longitudinal balance (analogue voice frequency circuits)
electrical symmetry of the two wires comprising a pair with respect to ground
3.29
longitudinal balance (data transmission)
measure of the similarity of impedance to ground (or common) for the two or more conductors
of a balanced circuit. This term is used to express the degree of susceptibility to common
mode interference
3.30
longitudinal balance (communication and control cables)
ratio of the disturbing common mode (longitudinal) r.m.s. voltage (V ) to ground and the
s
resulting differential mode (metallic) r.m.s. voltage (V ) of the SPD under test, expressed in
m
decibels (dB)
NOTE The longitudinal balance in dB is given by the formula:
20 log V /V
10 s m
where V and V are measured at the same frequency.
s m
3.31
longitudinal balance (telecommunications)
ratio of the disturbing common mode (longitudinal) voltage V and the resulting differential
s
mode (metallic) voltage V of the SPD under test, expressed in decibels (dB)
m
3.32
surge (telecommunications)
temporary excessive voltage or current, or both, coupled on a telecommunication line, from an
external electrical source
NOTE 1 Typical electrical sources are lightning and AC/DC power systems.
NOTE 2 Electrical source coupling can be one or more of the following; electric, magnetic, electromagnetic,
conductive.
4 Service and test conditions
4.1 Service conditions
4.1.1 Normal service conditions
4.1.1.1 Air pressure and altitude
Air pressure is 80 kPa to 106 kPa. These values represent an altitude of +2 000 m to –500 m
respectively.
4.1.1.2 Ambient temperature
• normal range: –5 °C to +40 °C
NOTE 1 This range normally addresses SPDs for indoor use. This corresponds to code AB4 in IEC 60364-5-51.
• extended range: –40 °C to +70 °C
NOTE 2 This range normally addresses SPDs for outdoor use in non weather-protected locations, class 3K7 in
IEC 60721-3-3.
• storage range: –40 °C to +70 °C
NOTE 3 All values beyond will be specified by the manufacturer.

– 18 – 61643-21 © IEC:2000+A1:2008
4.1.1.3 Relative humidity
• normal range: 5 % to 95 %
NOTE 1 This range normally addresses SPDs for indoor use. This corresponds to code AB4 in IEC 60364-5-51.
• extended range: 5 % to 100 %
NOTE 2 This range normally addresses SPDs for outdoor use in non weather-protected locations (e.g. SPD is
contained in a weather proofed enclosure).
4.1.2 Abnormal service conditions
Exposure of the SPD to abnormal service conditions may require special consideration in the
design or application of the SPD, and shall be called to the attention of the manufacturer.
4.2 Test tempe
...