IEC 61643-331:2020

IEC 61643-331 ®
Edition 3.0 2020-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Components for low-voltage surge protective devices protection –
Part 331: Performance requirements and test methods for metal oxide varistors
(MOV)
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IEC 61643-331 ®
Edition 3.0 2020-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Components for low-voltage surge protective devices protection –

Part 331: Performance requirements and test methods for metal oxide varistors

(MOV)
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 31.040.20 ISBN 978-2-8322-8023-2

– 2 – IEC 61643-331:2020 RLV © IEC 2020
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, symbols and abbreviated terms . 8
3.1 Terms and definitions . 8
3.1.1 Ratings . 8
3.1.2 Characteristics. 9
3.2 Symbols and abbreviated terms used in this document . 11
3.2.1 Symbols . 11
3.2.2 Abbreviated terms . 11
4 Service conditions . 12
4.1 Operating and storage temperature ranges . 12
4.2 Altitude or atmospheric pressure range . 12
4.3 Relative Humidity . 12
5 Mechanical requirements and materials . 12
5.1 Robustness of terminations . 12
5.2 Solderability . 12
5.3 Marking . 12
6 General . 13
6.1 Failure rates . 13
6.2 Test standard atmospheric conditions . 13
7 Electrical requirements . 13
7.1 Nominal Varistor voltage (V ) . 13
V
7.2 Maximum AC (DC) continuous operating voltage (V / V ) . 13
M(AC) M(DC)
7.3 Standby current I (I ) . 13
DC
D
7.4 Capacitance (C ) . 13
V
7.5 Clamping voltage (V ) . 13
C
7.6 Electrostatic discharge (ESD) (for SMD type MOV only). 15
7.7 Rated impulse energy (W ) . 15
TM
7.8 Nominal discharge current (I ) . 15
n
7.9 Endurance . 15
7.10 Limited current temporary overvoltage . 16
8 Standard design test criteria . 16
8.1 General . 16
8.2 Ratings . 16
8.2.1 Single-impulse maximum current (I ) . 16
TM
8.2.2 Next impulse . 17
8.2.3 Maximum Continuous rated voltage (V ) . 17
M
8.3 Electrical Characteristics . 17
8.3.1 Clamping voltage (V ) . 17
C
8.3.2 Standby current (I ) . 17
D
8.3.3 Nominal Varistor voltage (V ) (V ) . 18
N V
8.3.4 Capacitance (C ) . 18
V
8.3.5 Rated energy . 18
8.4 Endurance Varistor Rating Assurance Testing . 18

8.5 ESD test Method . 19
9 Nominal discharge current and limited current temporary overvoltage. 19
9.1 Thermally protected varistors – Sequence of tests . 19
9.2 Temperature and humidity cycle conditioning . 20
9.3 Nominal discharge current I(n) (I ) test description . 20
n
9.3.1 General . 20
9.3.2 Pass/fail criteria . 22
9.4 Limited current temporary overvoltage test description and procedure for
thermally protected varistors . 22
9.4.1 General . 22
9.4.2 Sample preparation . 23
9.4.3 Test conditions . 23
9.4.4 Pass/fail criteria . 23
9.5 Dielectric testing . 24
9.5.1 Test conditions for thermally protected MOV . 24
9.5.2 Setup from foil to leads . 25
9.5.3 Pass criteria . 25
9.6 Insulation Resistance . 25
Annex A (informative) MOV testing according to the IEC 61643-11:2011 Surge
protective devices for the Class I, II and III . 26
A.1 General . 26
A.2 MOV selection . 26
A.3 Cross reference list of abbreviations, descriptions and definitions . 26
A.4 Operating duty test . 27
A.4.1 General . 27
A.4.2 Class I and II operating duty tests (8.3.4.3) . 32
A.4.3 Additional duty test for test class I . 33
A.4.4 Class III operating duty tests . 33
A.4.5 Pass criteria for all operating duty tests and for the additional duty test
for test class I . 34
A.4.6 Preferred parameters of impulse discharge current I used for Class I
imp
additional duty tests . 34
A.4.7 Preferred values of impulse discharge current I used for Class I and
n
Class II residual voltage and operating duty tests . 35
A.4.8 Preferred values of combination generator waveshape used for Class III
tests . 36
Annex B (informative) IEC 61051 Varistors for use in electronic equipment . 38
Annex C (informative normative) Accelerated Endurance screening test . 39
C.1 Accelerated endurance screening test . 39
C.2 Preparation of sample . 39
C.3 Test conditions . 39
C.4 Refer to test circuit diagram as shown in Figure C.1. . 39
C.5 Pass criteria . 40
Annex D (informative) Proposed test method for determination of MTTF – Mean time
to failure (MTTF) . 41
D.1 Sampling plans . 41
D.2 Total test hours . 41
D.3 Samples. 41
D.4 Test set-up . 42
D.5 Intermediate measurements . 42

– 4 – IEC 61643-331:2020 RLV © IEC 2020
D.6 Failure criteria . 42
D.7 Acceptance criteria . 42
Bibliography .

Figure 1 – V-I characteristic of an MOV . 10
Figure 2 – Symbol for MOV . 11
Figure 3 – Symbol for thermally protected MOV . 11
Figure 4 – Test circuit for single-impulse maximum current . 16
Figure 5 – Test circuit for measuring leakage standby current . 17
Figure 6 – Test circuit for measuring nominal varistor voltage (V ) (V ) . 18
N V
Figure 7 – Varistor rating assurance test setup . 18
Figure 8 – Nominal discharge current test flowchart . 21
Figure 9 – Sequence of the I Test . 22
n
Figure 10 – Temporary overvoltage limited current test procedure flowchart . 24
Figure A.1 – Flow chart of the operating duty test . 28
Figure A.2 – Test set-up for operating duty test . 29
Figure A.3 – Flow chart of testing to determine the measured limiting voltage . 31
Figure A.4 – Operating duty test timing diagram for test classes I and II . 32
Figure A.5 – Additional duty test timing diagram for test class I . 33
Figure A.6 – Operating duty test timing diagram for test class III . 34
Figure C.1 – Circuit of accelerated ageing test . 39
Figure D.1 – Test Circuit of MTTF . 42

Table 1 – Typical Voltage ratings for disc types . 14
Table 2 – Typical Voltage Ratings for SMD types . 14
Table 3 – Test voltages for dielectric strength Between Test voltage . 25
Table A.1 – Comparison of IEC 61643-11 and IEC 61643-311 Abbreviations,
descriptions and definitions . 27
Table A.2 – Preferred parameters for class I test . 34
Table A.3 – Preferred values for class I and class II tests . 35
Table A.4 – Preferred values for class III tests . 36
Table C.1 – Current in V measurement . 39
T
Table D.1 – Sampling plans . 41

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
COMPONENTS FOR LOW-VOLTAGE SURGE PROTECTIVE DEVICES
PROTECTION –
Part 331: Performance requirements and test methods
for metal oxide varistors (MOV)

FOREWORD
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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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.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.

– 6 – IEC 61643-331:2020 RLV © IEC 2020
International Standard IEC 61643-331 has been prepared by subcommittee 37B: Components
for low-voltage surge protection, of IEC technical committee 37: Surge arresters.
This third edition cancels and replaces the second edition published in 2017. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) a Varistor MCOV rating assurance test;
b) an energy rating test (2ms);
c) revised Dielectric strength and insulation resistance tests.
The text of this International Standard is based on the following documents:
FDIS Report on voting
37B/211/FDIS 37B/214/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of IEC 61643 series, under the general title Components for low-voltage
surge protective devices, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
COMPONENTS FOR LOW-VOLTAGE SURGE PROTECTIVE DEVICES
PROTECTION –
Part 331: Performance requirements and test methods
for metal oxide varistors (MOV)

1 Scope
This part of IEC 61643 is a test specification for metal oxide varistors (MOV), which are used
for applications up to 1 000 V AC or 1 500 V DC in power lines, or telecommunication, or
signalling circuits. They are designed to protect apparatus or personnel, or both, from high
transient voltages.
This document applies to MOVs having two electrodes and hybrid overvoltage surge
protection components. This document also does not apply to mountings and their effect on
the MOV’s characteristics. Characteristics given apply solely to the MOV mounted only in the
ways described for the tests.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 60068-1:2013, Environmental testing – Part 1: General and guidance
IEC 60068-2-6:2007, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-14:2009, Environmental testing – Part 2-14: Tests – Test N: Change of
temperature
IEC 60068-2-20:2008, Environmental testing – Part 2-20: Tests – Test T: Test methods for
solderability and resistance to soldering heat of devices with leads
IEC 60068-2-21:2006, Environmental testing – Part 2-21: Tests – Test U: Robustness of
terminations and integral mounting devices
IEC 60068-2-27:2008, Environmental testing – Part 2-27: Tests – Test Ea and guidance:
Shock
IEC 60068-2-52:2017 Environmental testing – Part 2-52: Tests – Test Kb: Salt mist, cyclic
(sodium chloride solution)
IEC 60068-2-78:2012, Environmental testing – Part 2-78: Tests – Test Cab: Damp heat,
steady state
IEC 61643-11:2011, Low-voltage surge protective devices – Part 11: Surge protective devices
connected to low-voltage power systems – Requirements and test methods
IEC 61000-4-2:2008, Electromagnetic compatibility (EMC) – Part 4-2: Testing and
measurement techniques – Electrostatic discharge immunity test

– 8 – IEC 61643-331:2020 RLV © IEC 2020
3 Terms, definitions, symbols and abbreviated terms
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 Terms and definitions
3.1.1 Ratings
3.1.1.1
absolute maximum ratings
limiting values of operating and environmental conditions applicable to a component, device,
equipment or machine as defined by its published specification data, which should not be
exceeded under the worst possible conditions
Note 1 to entry: A limiting condition may be either a maximum or a minimum or both.
[SOURCE: MODIFIED: IEC 62240-1:2013, 3.1.1, modified ("any semiconductor device of a
specific type" replaced by "a component, device, equipment or machine", addition of Note 1 to
entry)]
3.1.1.2
single-impulse [transient] maximum current
I
TM
rated maximum value of current which may be applied for a single impulse of specified
waveform
Note 1 to entry: For power distribution surge protective devices ( SPDs), IEC 61643-11, Maximum Discharge
Current I is used.
MAX
3.1.1.3
nominal discharge current
I
n
crest value of the current through the MOV having a current waveshape of 8/20
3.1.1.4
impulse life characteristic
graphical representation between impulse current peak (I), equivalent rectangular pulse width
(T), and impulse numbers (n) for which the varistor MOV can withstand
Note 1 to entry: Unless otherwise specified, the range of T shall be 20 µs to 10 ms, the range of n shall be 10 ,
5 4 3 2 1 0
10 ,10 , 10 , 10 , 10 and 10 temperature derating curve.
3.1.1.5
temperature derating curve
graphical representation of parameter derating against temperature
Note 1 to entry: Typical parameters are rated voltage, impulse current, energy and average power dissipation.
3.1.1.6
single-pulse [transient] maximum energy
W
TM
rated maximum value which may be absorbed for a single pulse of a specified waveform
Note 1 to entry: Unless otherwise specified, 2 ms rectangular pulse is used (IEC 60060).

3.1.1.7
maximum continuous voltage
V
M
voltage that may be applied continuously at a specified temperature
Note 1 to entry: May also be called U or maximum continuous operating voltage (MCOV).
C
Note 2 to entry: See Figure 1.
3.1.1.8
maximum continuous AC voltage
V
M(AC)
value of RMS power frequency voltage (less than 5 % total harmonic distortion) that may be
applied continuously at a specified temperature
3.1.1.9
maximum continuous DC voltage
V
M(DC)
DC voltage that may be applied continuously at a specified temperature
3.1.1.10
mean time to failure
MTTF
basic measure of reliability for non-repairable items, the total number of life units of an item
divided by the total number of failures within that population ,during a particular measurement
interval under stated conditions
3.1.2 Characteristics
3.1.2.1
characteristic
inherent and measurable property properties of an MOV
3.1.2.2
standby current
I
D
current passing through MOV at maximum continuous voltage V
M
Note 1 to entry: The current passing through the MOV at less than V is called leakage current.
M
3.1.2.3
nominal varistor voltage
V V
N V
voltage across the MOV measured at a specified current (typically 1 mA) for a specific
duration
Note 1 to entry: See Figure 1.
3.1.2.4
varistor test current
I
N
test current (typically 1 mA) to determine the varistor voltage V
V
Note 1 to entry: See Figure 1.
3.1.2.5
clamping voltage
V
C
peak voltage across the MOV measured under conditions of a specified peak pulse current
) and specified waveform
(I
P
– 10 – IEC 61643-331:2020 RLV © IEC 2020
Note 1 to entry: See Figure 1.
Note 2 to entry: Unless otherwise specified, a typical value of this parameter is measured with a pulsed current
8/20 waveform.
Note 3 to entry: Clamping voltage, V , is referred to as measured limiting voltage in IEC 61643-11.
C
Figure 1 – V-I characteristic of an MOV
3.1.2.6
capacitance
C
V
capacitance across the MOV measured at a specified frequency, voltage and time
3.1.2.7
metal oxide varistor (MOV)
component whose conductance during static state, at a given temperature, increases rapidly
with increasing voltage
Note 1 to entry: This is also known as a voltage dependant resistor (VDR).
3.1.2.8
thermally protected metal oxide varistor
varistor which includes a series non-resettable element that will disconnect the MOV when it
is overheated due to excessive dissipation

3.1.2.9
DC standby current
I
DC
current passing through MOV at maximum continuous voltage DC V
M(DC)
3.2 Symbols and abbreviated terms used in this document
3.2.1 Symbols
Figure 2 and Figure 3 represent the IEC 60617 symbols for MOV and thermally protected
MOV, respectively.
Figure 2 – Symbol for MOV
Figure 3 – Symbol for thermally protected MOV
NOTE IEC 60027 recommends the letters V and v only as reserve symbols for voltage; however, in the field of
MOV components, these are so widely used that in this document they are preferred to U and u.
3.2.2 Abbreviated terms
CUT Component Under Test
DUT Device Under Test
ESD Electrostatic Discharge
MCOV Maximum Continuous Operating Voltage
MOV Metal Oxide Varistor
MTTF Mean Time To Failure
SMD Surface Mount Device
SPD Surge Protective Device
VDR Voltage Dependent Resistor

– 12 – IEC 61643-331:2020 RLV © IEC 2020
4 Service conditions
4.1 Operating and storage temperature ranges
Operating range
– Normal: –5 °C to +55 °C
– Extended: −40 °C to +85 °C
Storage range MOV
– Normal: –40 °C to +85 °C
– Extended: −40 °C to +125 °C
Storage range Thermally protected MOV
– Normal: –40 °C to +85 °C
– Extended: −40 °C to +85 °C
NOTE Temperature range (operating or storage) could be different than the normal or extended values shown
above.
4.2 Altitude or atmospheric pressure range
The altitude of air pressure is within 80 kPa to 106 kPa (refer to IEC 60068-1).
4.3 Relative Humidity
Normal range: 5 % to 95 % at 25 °C (refer to IEC 60068-1 and IEC 60068-2-78).
5 Mechanical requirements and materials
5.1 Robustness of terminations
If applicable, the user shall specify a suitable test from IEC 60068-2-21.
5.2 Solderability
Solder terminations shall meet the requirements of IEC 60068-2-20, test Ta, method 1.
5.3 Marking
Legible and permanent marking shall be applied to the MOV as necessary to ensure that the
user can determine the following information by inspection.
Each MOV shall be marked with the following information:
– Date of manufacture or batch number
– Manufacturer name or trademark
– part number
– safety approval markings
NOTE 1 The necessary information can also be coded.
NOTE 2 When the space is not sufficient for printing this data, it should be provided in the technical
documentation after agreement between the manufacturer and the purchaser it could be provided on the smallest
unit container in which the product is packaged or as agreed upon between the manufacturer and the purchaser.

6 General
6.1 Failure rates
Sampling size, electrical characteristics to be tested, etc. should be covered by the quality
assurance requirements, which are not covered by this document.
6.2 Test standard atmospheric conditions
The following tests shall be performed on the MOVs as required by the application. Unless
otherwise specified, ambient test conditions shall be as follows:
• Temperature: 15 °C to 35 °C;
• Relative humidity 25 % to 75 %;
MOVs of various types should have the characteristics listed in Table 1 when tested in
accordance with Clause 8.
7 Electrical requirements
7.1 Nominal Varistor voltage (V )
V
When tested according to 8.3.3, varistor voltage should be within the specified manufacturer’s
specified limits. Table 1 shows the nominal varistor voltages of high voltage and low voltage
disc types that are commonly used; their allowable tolerances are ±10 %.
The nominal varistor voltages and tolerances listed in Table 2 are typical for surface mount
Device ( SMD) types.
7.2 Maximum AC (DC) continuous operating voltage (V / V )
M(AC) M(DC)
Unless otherwise specified, MOVs shall have a maximum AC (DC) continuous voltage
V / (V ) as given in Table 1 and Table 2, the conformity shall be evaluated according
M(AC) M(DC)
to 8.2.3.
NOTE Maximum AC (DC) continuous operating voltage V / (V ) is sometimes referred to as U .
M(AC) M(DC) C
7.3 Standby current I (I )
DC
D
When tested according to 8.3.2, the standby current DC I under maximum continuous DC
DC
voltage V V , shall be less than the maximum value specified by the manufacturer and
DC M(DC)
there shall be no upward drifting during the application of the test voltage V V .
DC M(DC)
7.4 Capacitance (C )
V
When tested according to 8.3.4, the measured value of capacitance shall not exceed the
value specified by the manufacturer.
7.5 Clamping voltage (V )
C
The measured clamping voltage (see 8.3.1) at a specified impulse current shall be no more
than the specified values or the values indicated in Table 1 and 2. Unless otherwise specified,
an 8/20 impulse current having the peak as specified shall be used.
NOTE Clamping voltage V is referred to as Measured Limiting Voltage in IEC 61643-11.
C
– 14 – IEC 61643-331:2020 RLV © IEC 2020
Table 1 – Typical Voltage ratings for disc types
Nominal Max. continuous voltage (V ) Clamping voltage (NOTE), V (V)
M C
Varistor
AC (RMS)
voltage V V
N V DC V V 8/20, V
DC M(DC) C
V /VM(DC
(V) )
M(AC)
18 11 14 36
22 14 18 43
27 17 22 53
33 20 26 65
39 25 31 77
47 30 38 93
56 35 45 110
68 40 56 135
82 50 65 135
100 60 85 165
120 75 100 200
150 95 125 250
180 115 150 300
200 130 170 340
220 140 180 360
240 150 200 395
275 175 225 455
300 195 250 505
330 210 270 545
360 230 300 595
390 250 320 650
430 275 350 710
470 300 385 775
510 320 410 845
560 350 450 930
620 385 505 1 025
680 420 560 1 120
715 440 585 1 180
750 460 615 1 240
820 510 670 1 355
910 550 745 1 500
1 000 625 825 1 650
1 100 680 895 1 815
1 200 750 970 2 000
1 600 1 000 1 280 2 650
1 800 1 100 1 465 2 970
NOTE Clamping voltage V is referred to as measured limiting voltage in IEC 61643-11.
C
During the tests, there shall be no flashover or puncture of the samples, the MOV clamping
voltage (V ) of the samples shall be tested prior to and after the tests, the change of which
C
shall not exceed ±10 %, when tested according to 8.3.31.

7.6 Electrostatic discharge (ESD) (for SMD type MOV only)
The SMD MOVs shall be subjected to electrostatic discharge (ESD) contact discharge test of
8 kV for 10 applications with an interval of 1 s according to 8.5.
During the tests, there shall be no evidence of flashover or puncture of the samples, and the
Varistor voltage of the samples shall be tested prior to and after the tests, the change of
which shall not exceed ±30 %.
The requirement of Table 2 is only applicable for surface mount devices (for SMD varistors
ONLY). SMD MOV shall be tested as in 8.5.
Table 2 – Typical Voltage Ratings for SMD types
Maximum continuous voltage (V )
Nominal Varistor
M
Voltage V V (V) AC (RMS) V DC V
N V AC DC
5,6 ±20 % 2,5 4
6,8±20 % 3,5 4,5
8,2 ±20 % 4 5,5
10 ± 20 % 5 7
12± 20 % 6 8,5
15± 20 % 7,5 10,5
18 ± 20 % 9 13
22 ± 10 % 14 18
27 ± 10 % 17 22
33 ± 10 % 20 26
39 ± 10 % 25 31
47 ± 10 % 30 38
56 ± 10 % 35 45
68 ± 10 % 40 56
82 ± 10 % 50 65
NOTE Clamping voltage V is referred to as Measured Limiting Voltage in
C
IEC 61643-11.
7.7 Rated impulse energy (W )
TM
The MOV shall be capable of absorbing the impulse energy specified by the manufacturer
when subjected to one impulse current of 2 ms rectangular pulse or 10/1000 wave or 8/20 and
tested according to 8.2.1.
7.8 Nominal discharge current (I )
n
The MOV shall be subjected to 15 applications of impulse currents of 8/20 wave with the peak
specified by the manufacturer, and tested according to 9.3.
7.9 Endurance
The MOV used for power supply circuitry shall be subjected to an endurance test under the
conditions of maximum operating specified temperature and maximum continuous operating
voltage for 1 000 h and tested according to 8.4. If all concerned parties agree, the optional
accelerated endurance screening test in Annex C may be used.

– 16 – IEC 61643-331:2020 RLV © IEC 2020
7.10 Limited current temporary overvoltage
This is an AC step stress test to evaluate thermally protected MOVs components for potential
ignition sources when the component thermally protected MOV is subjected to AC overload
(see 9.4).
8 Standard design test criteria
8.1 General
The design tests described in 8.3 provide standardized methods for measuring specified
characteristics parameters of an MOV for the purpose of component selection for a surge
protective device (SPD). These characteristics parameters may vary from MOV to MOV,
making it necessary to measure all components to be selected for a SPD. MOVs are bi-
directional and they shall be tested with both positive and negative voltages.
8.2 Ratings
8.2.1 Single-impulse maximum current (I )
TM
In the absence of specified requirements, the test current shall be an 8/20 waveshape. An
oscilloscope is used to record the clamping voltage (V ) of the CUT. Rated voltage, V
c M(AC)
or V as appropriate, shall be applied continuously for a minimum of 2 s before impulse
M(DC)
and a minimum of 30 s after the impulse.
Measurement techniques for high-current and high-frequency testing should be observed,
such as four-point Kelvin contact, differential oscilloscope, short leads, etc.
NOTE See Figure 4.
Components
C Energy storage capacitor R3 Impulse-shaping resistor
L Impulse-shaping inductor R2 Impulse-shaping and current-limiting resistor
MOV Device Component under test (MOV) R4 Current-sensing resistor (coaxial).
Alternatively, a current transformer probe of
adequate rating may be used
OSC Oscilloscope for observing current and S1 Charging switch
voltage
PS DC charging power supply S2 Discharge switch
R1 Charging resistor
NOTE Caution: The circuit shown is for description only. Measurement techniques for high-current and high-
frequency testing should be observed, such as four-point Kelvin contact, differential oscilloscope, short leads, etc.
Figure 4 – Test circuit for single-impulse maximum current

8.2.2 Next impulse
The next impulse shall be applied after the device under test (DUT) CUT has returned to
thermal equilibrium (for example, the initial conditions before the impulses were applied). In
the absence of specified requirements, the test current shall be an 8/20 waveshape.
NOTE 1 MOVs intended for service in IEC 61643-11 surge protective devices require special class I, class II and
class III testing procedures and waveforms. These tests are covered in Annex A.
NOTE 2 See Figure 4.
8.2.3 Maximum Continuous rated voltage (V )
M
This rating is verified in 8.3.2.
8.3 Electrical Characteristics
8.3.1 Clamping voltage (V )
C
Maximum Clamping voltage shall be measured during the single impulse current (I ) (I ),
C P
clause 8.2.1. The peak clamping voltage and peak test current are not necessarily coincident
in time. In the absence of specified requirements, the test current shall be an 8/20
waveshape.
NOTE 1 MOVs intended for service in IEC 61643-11 surge protective devices require special class II or class III
testing procedures and waveforms. These tests are covered in Annex A.
NOTE 2 See Figure 4.
8.3.2 Standby current (I )
D
In this measurement, voltage should be maintained at a steady value regardless of the load
impedance. A power supply of constant voltage source should shall be used. It is not
recommended that the voltmeter be connected across the DUT CUT due to the current
bleeding through the meter. The leakage standby current reading would be inaccurate. The
Voltage supplied power supply PS should be set to the specified Maximum Continuous
Operating Voltage V of the MOV under test.
M(DC)
NOTE 1 See Figure 5.
NOTE 2 The test duration of standby current depends mainly on the electrode area of the MOV; the larger the
electrode area, the longer the test duration needs to be if other conditions remain the same. The test duration can
be sufficiently long for the standby current to stabilize.

Components
A Current meter
PS voltage source (DC) Power Supply (shall
be a DC voltage source)
V Voltmeter
Figure 5 – Test circuit for measuring leakage standby current

– 18 – IEC 61643-331:2020 RLV © IEC 2020
8.3.3 Nominal Varistor voltage (V ) (V )
N V
In this measurement, current should be maintained at a steady value regardless of the load
impedance. A power supply of constant current source should be used. The time of applied
test current (I ) shall be between 10 20 ms to 100 ms. Unless otherwise specified, the test
N
current shall be 1 mA DC.
NOTE 1 See Figure 6.
NOTE 2 The test duration cannot be too long in order to avoid a thermal effect when the temperature of the MOV
rises appreciably during the measurement. However, for very large varistor sizes, it may be necessary to go above
100 ms.
Components
A Current meter
P Bipolar pulsed current source
V Voltmeter
Figure 6 – Test circuit for measuring nominal varistor voltage (V ) (V )
N V
8.3.4 Capacitance (C )
V
This should be measured at a specified sinuso
...

IEC 61643-331 ®
Edition 3.0 2020-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Components for low-voltage surge protection –
Part 331: Performance requirements and test methods for metal oxide varistors
(MOV)
Composants pour parafoudres basse tension –
Partie 331: Exigences de performance et méthodes d'essai pour les varistances
à oxyde métallique (MOV)
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IEC 61643-331 ®
Edition 3.0 2020-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Components for low-voltage surge protection –

Part 331: Performance requirements and test methods for metal oxide varistors

(MOV)
Composants pour parafoudres basse tension –

Partie 331: Exigences de performance et méthodes d'essai pour les varistances

à oxyde métallique (MOV)
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 31.040.20 ISBN 978-2-8322-8558-9

– 2 – IEC 61643-331:2020 © IEC 2020
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, symbols and abbreviated terms . 8
3.1 Terms and definitions . 8
3.1.1 Ratings . 8
3.1.2 Characteristics. 9
3.2 Symbols and abbreviated terms used in this document . 11
3.2.1 Symbols . 11
3.2.2 Abbreviated terms . 11
4 Service conditions . 12
4.1 Operating and storage temperature ranges . 12
4.2 Altitude or atmospheric pressure range . 12
4.3 Relative Humidity . 12
5 Mechanical requirements and materials . 12
5.1 Robustness of terminations . 12
5.2 Solderability . 12
5.3 Marking . 12
6 General . 13
6.1 Failure rates . 13
6.2 Test standard atmospheric conditions . 13
7 Electrical requirements . 13
7.1 Varistor voltage (V ) . 13
V
7.2 Maximum AC (DC) continuous voltage (V / V ) . 13
M(AC) M(DC)
7.3 Standby current (I ) . 13
D
7.4 Capacitance (C ) . 13
V
7.5 Clamping voltage (V ) . 13
C
7.6 Electrostatic discharge (ESD) (for SMD type MOV only). 15
7.7 Rated impulse energy . 15
7.8 Nominal discharge current (I ) . 15
n
7.9 Endurance . 15
7.10 Limited current temporary overvoltage . 15
8 Standard design test criteria . 16
8.1 General . 16
8.2 Ratings . 16
8.2.1 Single-impulse maximum current (I ) . 16
TM
8.2.2 Next impulse . 16
8.2.3 Maximum Continuous voltage (V ) . 17
M
8.3 Electrical Characteristics . 17
8.3.1 Clamping voltage (V ) . 17
C
8.3.2 Standby current (I ) . 17
D
8.3.3 Varistor voltage (V ) . 17
V
8.3.4 Capacitance (C ) . 18
V
8.3.5 Rated energy . 18
8.4 Varistor Rating Assurance Testing . 18
8.5 ESD test . 19

9 Nominal discharge current and limited current temporary overvoltage. 19
9.1 Thermally protected varistors – Sequence of tests . 19
9.2 Temperature and humidity cycle conditioning . 19
9.3 Nominal discharge current (I ) test description . 20
n
9.3.1 General . 20
9.3.2 Pass/fail criteria . 22
9.4 Limited current temporary overvoltage test description and procedure for
thermally protected varistors . 22
9.4.1 General . 22
9.4.2 Sample preparation . 23
9.4.3 Test conditions . 23
9.4.4 Pass/fail criteria . 23
9.5 Dielectric testing . 24
9.5.1 Test conditions for thermally protected MOV . 24
9.5.2 Setup from foil to leads . 25
9.5.3 Pass criteria . 25
9.6 Insulation Resistance . 25
Annex A (informative) MOV testing according to the IEC 61643-11:2011 Surge
protective devices for the Class I, II and III . 26
A.1 General . 26
A.2 MOV selection . 26
A.3 Cross reference list of abbreviations, descriptions and definitions . 26
A.4 Operating duty test . 27
A.4.1 General . 27
A.4.2 Class I and II operating duty tests (8.4.4.3) . 32
A.4.3 Additional duty test for test class I . 33
A.4.4 Class III operating duty tests . 33
A.4.5 Pass criteria for all operating duty tests and for the additional duty test
for test class I . 34
A.4.6 Preferred parameters of impulse discharge current I used for Class I
imp
additional duty tests . 34
A.4.7 Preferred values of impulse discharge current I used for Class I and
n
Class II residual voltage and operating duty tests . 35
A.4.8 Preferred values of combination generator waveshape used for Class III
tests . 36
Annex B (informative) IEC 61051 Varistors for use in electronic equipment . 38
Annex C (normative) Accelerated Endurance screening test . 39
C.1 Accelerated endurance screening test . 39
C.2 Preparation of sample . 39
C.3 Test conditions . 39
C.4 Refer to test circuit diagram as shown in Figure C.1. . 39
C.5 Pass criteria . 40
Annex D (informative) Proposed test method of MTTF – Mean time to failure (MTTF) . 41
D.1 Sampling plans . 41
D.2 Total test hours . 41
D.3 Samples. 41
D.4 Test set-up . 42
D.5 Intermediate measurements . 42
D.6 Failure criteria . 42
D.7 Acceptance criteria . 42

– 4 – IEC 61643-331:2020 © IEC 2020
Figure 1 – V-I characteristic of an MOV . 10
Figure 2 – Symbol for MOV . 11
Figure 3 – Symbol for thermally protected MOV . 11
Figure 4 – Test circuit for single-impulse maximum current . 16
Figure 5 – Test circuit for measuring standby current . 17
Figure 6 – Test circuit for measuring varistor voltage (V ) . 18
V
Figure 7 – Varistor rating assurance test setup . 19
Figure 8 – Nominal discharge current test flowchart . 21
Figure 9 – Sequence of the I Test . 22
n
Figure 10 – Temporary overvoltage limited current test procedure flowchart . 24
Figure A.1 – Flow chart of the operating duty test . 28
Figure A.2 – Test set-up for operating duty test . 29
Figure A.3 – Flow chart of testing to determine the measured limiting voltage . 31
Figure A.4 – Operating duty test timing diagram for test classes I and II . 32
Figure A.5 – Additional duty test timing diagram for test class I . 33
Figure A.6 – Operating duty test timing diagram for test class III . 34
Figure C.1 – Circuit of accelerated ageing test . 39
Figure D.1 – Test Circuit of MTTF . 42

Table 1 – Typical Voltage ratings for disc types . 14
Table 2 – Typical Voltage Ratings for SMD types . 15
Table 3 – Test voltages for dielectric strength Between Test voltage . 25
Table A.1 – Abbreviations, descriptions and definitions . 27
Table A.2 – Preferred parameters for class I test . 34
Table A.3 – Preferred values for class I and class II tests . 35
Table A.4 – Preferred values for class III tests . 36
Table C.1 – Current in V measurement . 39
T
Table D.1 – Sampling plans . 41

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
COMPONENTS FOR LOW-VOLTAGE SURGE PROTECTION –

Part 331: Performance requirements and test methods
for metal oxide varistors (MOV)

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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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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 61643-331 has been prepared by subcommittee 37B: Components
for low-voltage surge protection, of IEC technical committee 37: Surge arresters.
This third edition cancels and replaces the second edition published in 2017. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) a Varistor MCOV rating assurance test;
b) an energy rating test (2ms);
c) revised Dielectric strength and insulation resistance tests.

– 6 – IEC 61643-331:2020 © IEC 2020
The text of this International Standard is based on the following documents:
FDIS Report on voting
37B/211/FDIS 37B/214/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of IEC 61643 series, under the general title Components for low-voltage
surge protective devices, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
COMPONENTS FOR LOW-VOLTAGE SURGE PROTECTION –

Part 331: Performance requirements and test methods
for metal oxide varistors (MOV)

1 Scope
This part of IEC 61643 is a test specification for metal oxide varistors (MOV), which are used
for applications up to 1 000 V AC or 1 500 V DC in power lines, or telecommunication, or
signalling circuits. They are designed to protect apparatus or personnel, or both, from high
transient voltages.
This document applies to MOVs having two electrodes and hybrid surge protection
components. This document also does not apply to mountings and their effect on the MOV’s
characteristics. Characteristics given apply solely to the MOV mounted only in the ways
described for the tests.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 60068-1:2013, Environmental testing – Part 1: General and guidance
IEC 60068-2-6:2007, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-14:2009, Environmental testing – Part 2-14: Tests – Test N: Change of
temperature
IEC 60068-2-20:2008, Environmental testing – Part 2-20: Tests – Test T: Test methods for
solderability and resistance to soldering heat of devices with leads
IEC 60068-2-21:2006, Environmental testing – Part 2-21: Tests – Test U: Robustness of
terminations and integral mounting devices
IEC 60068-2-27:2008, Environmental testing – Part 2-27: Tests – Test Ea and guidance:
Shock
IEC 60068-2-52:2017 Environmental testing – Part 2-52: Tests – Test Kb: Salt mist, cyclic
(sodium chloride solution)
IEC 61643-11:2011, Low-voltage surge protective devices – Part 11: Surge protective devices
connected to low-voltage power systems – Requirements and test methods
IEC 61000-4-2:2008, Electromagnetic compatibility (EMC) – Part 4-2: Testing and
measurement techniques – Electrostatic discharge immunity test

– 8 – IEC 61643-331:2020 © IEC 2020
3 Terms, definitions, symbols and abbreviated terms
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1 Terms and definitions
3.1.1 Ratings
3.1.1.1
absolute maximum ratings
limiting values of operating and environmental conditions applicable to a component, device,
equipment or machine as defined by its published specification data, which should not be
exceeded under the worst possible conditions
Note 1 to entry: A limiting condition may be either a maximum or a minimum or both.
[SOURCE: IEC 62240-1:2013, 3.1.1, modified ("any semiconductor device of a specific type"
replaced by "a component, device, equipment or machine", addition of Note 1 to entry)]
3.1.1.2
single-impulse [transient] maximum current
I
TM
rated maximum value of current which may be applied for a single impulse of specified
waveform
Note 1 to entry: For power distribution SPDs, IEC 61643-11, Maximum Discharge Current I is used.
MAX
3.1.1.3
nominal discharge current
I
n
crest value of the current through the MOV having a current waveshape of 8/20
3.1.1.4
impulse life characteristic
graphical representation between impulse current peak (I), equivalent rectangular pulse width
(T), and impulse numbers (n) which the MOV can withstand
Note 1 to entry: Unless otherwise specified, the range of T shall be 20 µs to 10 ms, the range of n shall be 10 ,
5 4 3 2 1 0
10 ,10 , 10 , 10 , 10 and 10 .
3.1.1.5
temperature derating curve
graphical representation of parameter derating against temperature
Note 1 to entry: Typical parameters are rated voltage, impulse current, energy and average power dissipation.
3.1.1.6
single-pulse [transient] maximum energy
W
TM
rated maximum value which may be absorbed for a single pulse of a specified waveform
Note 1 to entry: Unless otherwise specified, 2 ms rectangular pulse is used (IEC 60060).

3.1.1.7
maximum continuous voltage
V
M
voltage that may be applied continuously at a specified temperature
Note 1 to entry: May also be called U or MCOV.
C
Note 2 to entry: See Figure 1.
3.1.1.8
maximum continuous AC voltage
V
M(AC)
value of RMS power frequency voltage (less than 5 % total harmonic distortion) that may be
applied continuously at a specified temperature
3.1.1.9
maximum continuous DC voltage
V
M(DC)
DC voltage that may be applied continuously at a specified temperature
3.1.1.10
mean time to failure
MTTF
basic measure of reliability for non-repairable items, the total number of life units of an item
divided by the total number of failures within that population ,during a particular measurement
interval under stated conditions
3.1.2 Characteristics
3.1.2.1
characteristic
inherent and measurable properties of an MOV
3.1.2.2
standby current
I
D
current passing through MOV at maximum continuous voltage V
M
Note 1 to entry: The current passing through the MOV at less than V is called leakage current.
M
3.1.2.3
varistor voltage
V
V
voltage across the MOV measured at a specified current (typically 1 mA) for a specific
duration
3.1.2.4
varistor test current
I
N
test current (typically 1 mA) to determine the varistor voltage V
V
Note 1 to entry: See Figure 1.
3.1.2.5
clamping voltage
V
C
peak voltage across the MOV measured under conditions of a specified peak pulse current
(I ) and specified waveform
P
Note 1 to entry: See Figure 1.

– 10 – IEC 61643-331:2020 © IEC 2020
Note 2 to entry: Unless otherwise specified, a typical value of this parameter is measured with a pulsed current
8/20 waveform.
Note 3 to entry: Clamping voltage, V , is referred to as measured limiting voltage in IEC 61643-11.
C
Figure 1 – V-I characteristic of an MOV
3.1.2.6
capacitance
C
V
capacitance across the MOV measured at a specified frequency, voltage and time
3.1.2.7
metal oxide varistor (MOV)
component whose conductance during static state, at a given temperature, increases rapidly
with increasing voltage
Note 1 to entry: This is also known as a voltage dependant resistor (VDR).
3.1.2.8
thermally protected metal oxide varistor
varistor which includes a series non-resettable element that will disconnect the MOV when it
is overheated due to excessive dissipation
3.1.2.9
DC standby current
I
DC
current passing through MOV at maximum continuous voltage DC V
M(DC)
3.2 Symbols and abbreviated terms used in this document
3.2.1 Symbols
Figure 2 and Figure 3 represent the IEC 60617 symbols for MOV and thermally protected
MOV, respectively.
Figure 2 – Symbol for MOV
Figure 3 – Symbol for thermally protected MOV
NOTE IEC 60027 recommends the letters V and v only as reserve symbols for voltage; however, in the field of
MOV components, these are so widely used that in this document they are preferred to U and u.
3.2.2 Abbreviated terms
CUT Component Under Test
ESD Electrostatic Discharge
MCOV Maximum Continuous Operating Voltage
MOV Metal Oxide Varistor
MTTF Mean Time To Failure
SMD Surface Mount Device
SPD Surge Protective Device
VDR Voltage Dependent Resistor

– 12 – IEC 61643-331:2020 © IEC 2020
4 Service conditions
4.1 Operating and storage temperature ranges
Operating range
– Normal: –5 °C to +55 °C
– Extended: −40 °C to +85 °C
Storage range MOV
– Normal: –40 °C to +85 °C
– Extended: −40 °C to +125 °C
Storage range Thermally protected MOV
– Normal: –40 °C to +85 °C
– Extended: −40 °C to +85 °C
NOTE Temperature range (operating or storage) could be different than the normal or extended values shown
above.
4.2 Altitude or atmospheric pressure range
The altitude of air pressure is within 80 kPa to 106 kPa (refer to IEC 60068-1).
4.3 Relative Humidity
Normal range: 5 % to 95 % at 25 °C (refer to IEC 60068-1 and IEC 60068-2-78).
5 Mechanical requirements and materials
5.1 Robustness of terminations
If applicable, the user shall specify a suitable test from IEC 60068-2-21.
5.2 Solderability
Solder terminations shall meet the requirements of IEC 60068-2-20, test Ta, method 1.
5.3 Marking
Legible and permanent marking shall be applied to the MOV as necessary to ensure that the
user can determine the following information by inspection.
Each MOV shall be marked with the following information:
– Date of manufacture or batch number
– Manufacturer name or trademark
– part number
– safety approval markings
NOTE 1 The necessary information can also be coded.
NOTE 2 When the space is not sufficient for printing this data, it could be provided on the smallest unit container
in which the product is packaged or as agreed upon between the manufacturer and the purchaser.

6 General
6.1 Failure rates
Sampling size, electrical characteristics to be tested, etc. should be covered by the quality
assurance requirements, which are not covered by this document.
6.2 Test standard atmospheric conditions
The following tests shall be performed on the MOVs as required by the application. Unless
otherwise specified, ambient test conditions shall be as follows:
• Temperature: 15 °C to 35 °C;
• Relative humidity 25 % to 75 %;
MOVs of various types should have the characteristics listed in Table 1 when tested in
accordance with Clause 8.
7 Electrical requirements
7.1 Varistor voltage (V )
V
When tested according to 8.3.3, varistor voltage should be within the manufacturer’s specified
limits. Table 1 shows the varistor voltages of high voltage and low voltage disc types that are
commonly used; their allowable tolerances are ±10 %.
The varistor voltages and tolerances listed in Table 2 are typical for SMD types.
7.2 Maximum AC (DC) continuous voltage (V / V )
M(AC) M(DC)
Unless otherwise specified, MOVs shall have a maximum AC (DC) continuous voltage
V / (V ) as given in Table 1 and Table 2, the conformity shall be evaluated according
M(AC) M(DC)
to 8.2.3.
NOTE Maximum AC (DC) continuous voltage V / (V ) is sometimes referred to as U .
M(AC) M(DC) C
7.3 Standby current (I )
D
When tested according to 8.3.2, the standby current I under maximum continuous DC
DC
voltage V , shall be less than the maximum value specified by the manufacturer and there
M(DC)
shall be no upward drifting during the application of the test voltage V .
M(DC)
7.4 Capacitance (C )
V
When tested according to 8.3.4, the measured value of capacitance shall not exceed the
value specified by the manufacturer.
)
7.5 Clamping voltage (V
C
The measured clamping voltage (see 8.3.1) at a specified impulse current shall be no more
than the specified values or the values indicated in Table 1. Unless otherwise specified, an
8/20 impulse current having the peak as specified shall be used.
NOTE Clamping voltage V is referred to as Measured Limiting Voltage in IEC 61643-11.
C
– 14 – IEC 61643-331:2020 © IEC 2020
Table 1 – Typical Voltage ratings for disc types
Max. continuous voltage (V ) Clamping voltage (NOTE), V (V)
M C
Varistor
voltage V (V)
V AC (RMS) V DC V 8/20, V
M(AC) M(DC) C
18 11 14 36
22 14 18 43
27 17 22 53
33 20 26 65
39 25 31 77
47 30 38 93
56 35 45 110
68 40 56 135
82 50 65 135
100 60 85 165
120 75 100 200
150 95 125 250
180 115 150 300
200 130 170 340
220 140 180 360
240 150 200 395
275 175 225 455
300 195 250 505
330 210 270 545
360 230 300 595
390 250 320 650
430 275 350 710
470 300 385 775
510 320 410 845
560 350 450 930
620 385 505 1 025
680 420 560 1 120
715 440 585 1 180
750 460 615 1 240
820 510 670 1 355
910 550 745 1 500
1 000 625 825 1 650
1 100 680 895 1 815
1 200 750 970 2 000
1 600 1 000 1 280 2 650
1 800 1 100 1 465 2 970
NOTE Clamping voltage V is referred to as measured limiting voltage in IEC 61643-11.
C
During the tests, there shall be no flashover or puncture of the samples, the clamping voltage
(V ) of the samples shall be tested prior to and after the tests, the change of which shall not
C
exceed ±10 %, when tested according to 8.3.1.

7.6 Electrostatic discharge (ESD) (for SMD type MOV only)
The requirement of Table 2 is only applicable for surface mount devices (for SMD varistors
ONLY). SMD MOV shall be tested as in 8.5.
Table 2 – Typical Voltage Ratings for SMD types
Varistor Maximum continuous voltage (V )
M
Voltage V (V)
AC (RMS) V DC V
V
AC DC
5,6 ± 20 % 2,5 4
6,8 ± 20 % 3,5 4,5
8,2 ± 20 % 4 5,5
10 ± 20 % 5 7
12 ± 20 % 6 8,5
15 ± 20 % 7,5 10,5
18 ± 20 % 9 13
22 ± 10 % 14 18
27 ± 10 % 17 22
33 ± 10 % 20 26
39 ± 10 % 25 31
47 ± 10 % 30 38
56 ± 10 % 35 45
68 ± 10 % 40 56
82 ± 10 % 50 65
7.7 Rated impulse energy
The MOV shall be capable of absorbing the impulse energy specified by the manufacturer
when subjected to one impulse current of 2 ms rectangular pulse or 10/1000 or 8/20 and
tested according to 8.2.1.
7.8 Nominal discharge current (I )
n
The MOV shall be subjected to 15 applications of impulse currents of 8/20 wave with the peak
specified by the manufacturer, and tested according to 9.3.
7.9 Endurance
The MOV shall be subjected to an endurance test under the conditions of specified
temperature and maximum continuous voltage for 1 000 h and tested according to 8.4. If all
concerned parties agree, the optional accelerated endurance screening test in Annex C may
be used.
7.10 Limited current temporary overvoltage
This is an AC step stress test to evaluate thermally protected MOVs for potential ignition
sources when the thermally protected MOV is subjected to AC overload (see 9.4).

– 16 – IEC 61643-331:2020 © IEC 2020
8 Standard design test criteria
8.1 General
The design tests described in 8.3 provide standardized methods for measuring specified
parameters of an MOV for the purpose of component selection. These parameters may vary
from MOV to MOV, making it necessary to measure all components. MOVs are bi-directional
and they shall be tested with both positive and negative voltages.
8.2 Ratings
8.2.1 Single-impulse maximum current (I )
TM
In the absence of specified requirements, the test current shall be an 8/20 waveshape. An
oscilloscope is used to record the clamping voltage (V ) of the CUT. Rated voltage, V
c M(AC)
or V as appropriate, shall be applied continuously for a minimum of 2 s before impulse
M(DC)
and a minimum of 30 s after the impulse.
Measurement techniques for high-current and high-frequency testing should be observed,
such as four-point Kelvin contact, differential oscilloscope, short leads, etc.
NOTE See Figure 4.
Components
C Energy storage capacitor R3 Impulse-shaping resistor
L Impulse-shaping inductor R2 Impulse-shaping and current-limiting resistor
MOV Component under test (MOV) R4 Current-sensing resistor (coaxial).
Alternatively, a current transformer probe of
adequate rating may be used
Oscilloscope for observing current and
OSC S1 Charging switch
voltage
PS DC charging power supply S2 Discharge switch
R1 Charging resistor
NOTE Caution: The circuit shown is for description only.
Figure 4 – Test circuit for single-impulse maximum current
8.2.2 Next impulse
The next impulse shall be applied after the CUT has returned to thermal equilibrium (for
example, the initial conditions before the impulses were applied). In the absence of specified
requirements, the test current shall be an 8/20 waveshape.
NOTE 1 MOVs intended for service in IEC 61643-11 surge protective devices require special class I, class II and
class III testing procedures and waveforms. These tests are covered in Annex A.
NOTE 2 See Figure 4.
8.2.3 Maximum Continuous voltage (V )
M
This rating is verified in 8.3.2.
8.3 Electrical Characteristics
8.3.1 Clamping voltage (V )
C
Clamping voltage shall be measured during the single impulse current (I ), clause 8.2.1. The
P
peak clamping voltage and peak test current are not necessarily coincident in time. In the
absence of specified requirements, the test current shall be an 8/20 waveshape.
NOTE 1 MOVs intended for service in IEC 61643-11 surge protective devices require special class II or class III
testing procedures and waveforms. These tests are covered in Annex A.
NOTE 2 See Figure 4.
8.3.2 Standby current (I )
D
In this measurement, voltage should be maintained at a steady value regardless of the load
impedance. A power supply of constant voltage source shall be used. It is not recommended
that the voltmeter be connected across the CUT due to the current bleeding through the
meter. The standby current reading would be inaccurate. The power supply PS should be set
to the specified Maximum Continuous Voltage V of the MOV under test.
M(DC)
NOTE 1 See Figure 5.
NOTE 2 The test duration of standby current depends mainly on the electrode area of the MOV; the larger the
electrode area, the longer the test duration needs to be if other conditions remain the same. The test duration can
be sufficiently long for the standby current to stabilize.

Components
A Current meter
PS Power Supply (shall be a DC voltage
source)
V Voltmeter
Figure 5 – Test circuit for measuring standby current
8.3.3 Varistor voltage (V )
V
In this measurement, current should be maintained at a steady value regardless of the load
impedance. A power supply of constant current source should be used. The time of applied
test current (I ) shall be between 20 ms to 100 ms. Unless otherwise specified, the tes
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