IEC 60688:2024

IEC 60688 ®
Edition 5.0 2024-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical measuring transducers for converting AC and DC electrical quantities
to analogue or digital signals

Transducteurs électriques de mesure convertissant les grandeurs électriques
alternatives ou continues en signaux analogiques ou numériques

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IEC 60688 ®
Edition 5.0 2024-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical measuring transducers for converting AC and DC electrical quantities

to analogue or digital signals

Transducteurs électriques de mesure convertissant les grandeurs électriques

alternatives ou continues en signaux analogiques ou numériques

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 17.220.20  ISBN 978-2-8322-9547-2

– 2 – IEC 60688:2024 © IEC 2024
CONTENTS
FOREWORD . 9
INTRODUCTION . 11
1 Scope . 12
2 Normative references . 13
3 Terms and definitions . 14
3.1 General terms . 14
3.2 Terms describing transducers . 15
3.3 Terms describing transducers according to the measurand . 17
3.4 Terms describing transducers according to their output load . 18
3.5 Nominal values . 19
3.6 Terms describing transducers with provisions to be adjusted by users . 19
3.7 Influence quantities and reference conditions. 20
3.8 Errors and variations . 20
3.9 Accuracy, accuracy class, class index. 21
3.10 Terms related to primary of transducers . 21
3.11 Terms related to secondary output of transducers . 22
4 Environmental conditions . 22
5 Ratings . 22
6 Requirements for design and construction . 23
6.1 General . 23
6.1.1 Transducer general architecture . 23
6.1.2 Classification of transducers (TRD) . 23
6.2 Safety requirements . 24
6.2.1 General . 24
6.2.2 Protection against electric shocks . 24
6.2.3 Protection against mechanical hazards . 25
6.2.4 Resistance to mechanical stress . 25
6.2.5 Protection against the spread of fire . 25
6.2.6 Equipment temperature limits and resistance to heat . 25
6.2.7 Protection against hazards from fluids . 26
6.2.8 Protection against radiation, including laser sources, and against sonic
and ultrasonic pressure . 26
6.2.9 Protection against liberated gases and substances, explosion and
implosion . 26
6.2.10 Components and subassemblies. 26
6.2.11 Protection by interlocks . 26
6.2.12 Hazards resulting from application . 26
6.2.13 Risk assessment . 27
6.3 EMC requirements . 27
6.3.1 General . 27
6.3.2 Immunity requirements . 27
6.3.3 Emission requirements . 28
6.4 Climatic requirements . 28
6.5 Mechanical requirements . 28
6.6 Functional requirements . 28
6.7 Marking requirements . 28
6.8 Documentation requirements . 28

7 Type tests . 29
8 Routine tests . 29
Annex A (normative) Requirements for TRD1 . 30
A.1 General . 30
A.2 References for the purposes of this Annex A . 30
A.3 Terminology for the purposes of this Annex A . 30
A.4 Environmental conditions . 30
A.5 Ratings . 30
A.6 Requirements for design and construction of TRD1 . 31
A.6.1 General . 31
A.6.2 Safety requirements. 31
A.6.3 EMC requirements . 31
A.6.4 Climatic requirements . 31
A.6.5 Mechanical requirements . 31
A.6.6 Functional requirements . 31
A.6.7 Marking requirements . 39
A.6.8 Documentation requirements . 42
A.7 Type tests for TRD1 . 42
A.7.1 General . 42
A.7.2 General additional requirements for type tests for TRD1 . 42
A.7.3 Variations due to auxiliary supply voltage . 43
A.7.4 Variations due to auxiliary supply frequency . 44
A.7.5 Variations due to ambient temperature . 44
A.7.6 Variations due to the frequency of the input quantity(ies) . 45
A.7.7 Variations due to the input voltage . 46
A.7.8 Variations due to the input current . 46
A.7.9 Variations due to power factor . 47
A.7.10 Variation due to output load . 48
A.7.11 Variations due to distortion of the input quantity(ies). 49
A.7.12 Variation due to magnetic field of external origin. 49
A.7.13 Variation due to unbalanced currents . 50
A.7.14 Variation due to interaction between measuring elements . 51
A.7.15 Variation due to self-heating . 52
A.7.16 Variation due to continuous operation . 52
A.7.17 Variation due to common mode interference . 53
A.7.18 Variation due to series mode interference . 53
A.7.19 Permissible excessive inputs . 54
A.7.20 Impulse voltage tests . 54
A.7.21 High frequency disturbance test . 55
A.7.22 Test for temperature rise . 55
A.7.23 Other tests . 55
Annex B (normative) Requirements for TRD2 . 56
B.1 General . 56
B.2 References for the purposes of this Annex B . 56
B.3 Terminology for the purposes of this Annex B . 56
B.4 Environmental conditions . 56
B.4.1 General . 56
B.4.2 Normal environmental conditions . 56

– 4 – IEC 60688:2024 © IEC 2024
B.5 Ratings for TRD2 . 57
B.5.1 General . 57
B.5.2 Input ratings . 57
B.5.3 Output ratings . 58
B.5.4 General ratings . 59
B.6 Requirements for design and construction of TRD2 . 61
B.6.1 General . 61
B.6.2 Safety requirements. 61
B.6.3 EMC requirements . 61
B.6.4 Climatic requirements . 61
B.6.5 Mechanical requirements . 62
B.6.6 Functional requirements . 66
B.6.7 Marking requirements . 73
B.6.8 Documentation requirements . 74
B.7 Type tests of TRD2 . 76
B.7.1 General . 76
B.7.2 Safety tests . 76
B.7.3 EMC tests . 76
B.7.4 Climatic tests . 77
B.7.5 Mechanical tests . 79
B.7.6 Functional tests . 89
B.7.7 Verification of markings and documentation . 96
B.7.8 Short-time currents tests. 96
B.7.9 Inter-turn overvoltage tests . 97
B.7.10 Anti-aliasing tests . 98
B.7.11 Test with harmonics and at low frequencies . 98
B.8 Routine tests for TRD2 . 99
B.8.1 General . 99
B.8.2 Accuracy tests . 99
B.8.3 Verification of markings . 99
B.8.4 Safety tests . 99
B.8.5 Inter-turn overvoltage tests . 99
Annex C (normative) Interface coding . 100
C.1 General . 100
C.2 Characteristics of interface connection . 100
C.3 Coding of rated output values for transducers . 100
C.4 Coding of auxiliary power supply for transducers . 102
C.5 Coding of transfer function curves for transducers . 103
C.6 Interface full coding for output of transducers . 103
C.6.1 General . 103
C.6.2 Examples of interface codes and most common interface codes . 104
Annex D (informative) Anti-aliasing guidance . 106
Annex E (normative) Requirements for the measurement of harmonics and low
frequencies . 109
E.1 General . 109
E.2 Requirements for accuracy class extension WBm0 . 109
E.3 Requirements for accuracy class extension WBm1 . 110
E.4 Requirements for accuracy class extension WBm2 . 110
E.5 Requirements for accuracy class extension WBm3 . 111

Annex F (normative) Markings of terminals of TRD2 . 112
F.1 Marking of terminals for TRD2 monitoring AC current . 112
F.2 Marking of terminals for TRD2 monitoring voltage . 112
Annex G (informative) Guidance related to cables, busbars and bare conductors within
an installation . 114
G.1 Insulation of cables . 114
G.2 Temperature of cables and busbars . 114
G.2.1 Cables . 114
G.2.2 Busbars . 114
Annex H (informative) Guidance related to overvoltage categories and measurement
categories . 115
H.1 Concept of overvoltage category . 115
H.2 Approach of IEC 60664-1 for primary circuits of TRD2 . 115
H.2.1 General . 115
H.2.2 Examples with IEC 60664-1:2020, for primary measuring circuits, OVC
III, PD 2, altitude under 2 000 m, inhomogeneous field . 115
H.3 Approach of IEC 61010 (all parts) for primary circuits of TRD2 . 116
H.3.1 General . 116
H.3.2 Example with IEC 61010-2-030:2023 for primary measuring circuits,
OVC III, PD 2, altitude under 2 000 m, inhomogeneous field . 116
H.4 Approach for secondary circuits of TRD2 . 117
Annex I (informative) Examples of clamping units and relationship between clamping
unit and connecting device. 118
I.1 Clamping unit in a connecting device . 118
I.2 Examples of clamping units . 118
Bibliography . 125

Figure 1 – Transducer (TRD) architecture example . 23
Figure A.1 – Transfer function curve A . 35
Figure A.2 – Transfer function curve B . 36
Figure A.3 – Transfer function curve C . 36
Figure A.4 – Transfer function curve D . 37
Figure A.5 – Transfer function curve E . 37
Figure B.1 – Relationship between ambient air temperature and relative humidity . 61
Figure B.2 – Dimensions . 63
Figure B.3 – Accuracy limits of a TRD2-IAC (a) and TRD2-IDC (b) . 68
Figure B.4 – Definition of the angle between primary conductor and the equipment . 71
Figure B.5 – Definition of the primary conductor position according to the position
factor . 72
Figure B.6 – Gauges of form A and form B . 83
Figure B.7 – Test equipment for flexion test . 85
Figure B.8 – Measurement of the step response time . 91
Figure B.9 – Temperature cycle accuracy test. 93
Figure B.10 – Test set up for impact of magnetic field from other phases – a) First
step – b) Second step . 94
Figure B.11 – Accuracy measurement test set up . 96
Figure D.1 – Digital data acquisition system example . 106

– 6 – IEC 60688:2024 © IEC 2024
Figure D.2 – Frequency response mask for metering accuracy class 1 (f = 60 Hz,
r
f = 4 800 Hz) . 108
s
Figure I.1 – Clamping unit in a connecting device . 118
Figure I.2 – Screw clamping units . 119
Figure I.3 – Pillar clamping units . 120
Figure I.4 – Stud clamping units . 121
Figure I.5 – Saddle clamping units . 122
Figure I.6 – Lug clamping units . 123
Figure I.7 – Mantle clamping units . 124

Table 1 – Functional classification of transducers with minimal required functions . 23
Table 2 – Definition of ports . 27
Table 3 – Performance criteria for EMC immunity tests . 28
Table A.1 – Usage groups. 30
Table A.2 – Relationship between the limits of intrinsic error, expressed as a
percentage of the fiducial value, and the class index . 31
Table A.3 – Pre-conditioning . 32
Table A.4 – Reference conditions of the influence quantities and tolerances for testing
purposes . 32
Table A.5 – Reference conditions relative to the measurand . 33
Table A.6 – Examples of marking relating to the reference conditions and nominal
range of use for temperature . 40
Table A.7 – Symbols for marking transducers . 41
Table A.8 – Permissible variations due to AC auxiliary supply . 43
Table A.9 – Permissible variations due to DC auxiliary supply . 44
Table A.10 – Permissible variations due to auxiliary supply frequency . 44
Table A.11 – Permissible variations due to ambient temperature . 45
Table A.12 – Permissible variations due to the frequency of input quantity . 46
Table A.13 – Permissible variations due to the input voltage . 46
Table A.14 – Permissible variations due to the input current . 47
Table A.15 – Permissible variations due to power factor . 48
Table A.16 – Permissible variations due to output load . 49
Table A.17 – Permissible variations due to distortion of input quantities . 49
Table A.18 – Permissible variations due to magnetic field of external origin . 50
Table A.19 – Permissible variations due to unbalance currents . 51
Table A.20 – Permissible variations due to interactions between measuring elements . 51
Table A.21 – Permissible variations due to self-heating . 52
Table A.22 – Permissible variations due to continuous operation . 53
Table A.23 – Permissible variations due to series mode interference . 54
Table B.1 – Environmental conditions parameters . 56
Table B.2 – Preferred rated burden for TRD2 with an AC or DC voltage output, or a
frequency output . 59
Table B.3 – Rated burden for TRD2 with an AC or DC current output . 59
Table B.4 – Rated temperatures for TRD2 . 60

Table B.5 – Rated humidity classes . 60
Table B.6 – Examples of terminal lugs for equipment connected to copper conductors . 63
Table B.7 – Nominal cross-sections of round copper conductors and approximate
relationship between mm and AWG/kcmil sizes . 64
Table B.8 – Minimum values for maximum cross section of conductors up to 400 A
inclusive . 65
Table B.9 – Minimum values for maximum cross section of conductors from 400 A and
up to 800 A inclusive . 66
Table B.10 – Minimum values for maximum cross section for copper bars for currents
above 400 A and up to 3 150 A inclusive . 66
Table B.11 – Limits for relative error and phase error for TRD2-IAC . 67
Table B.12 – Limits of error for TRD2-IDC . 67
Table B.13 – Limits of relative error for TRD2-UAC . 69
Table B.14 – Limits of relative error for TRD2-UDC . 70
Table B.15 – Limits for the position of the primary conductor with respect to the
equipment . 71
Table B.16 – RJ45 connector pinout . 73
Table B.17 – Temperature tests . 78
Table B.18 – Tightening torques for the verification of the mechanical strength of
screw-type terminals . 80
Table B.19 – Maximum conductor cross-sections and corresponding gauges . 81
Table B.20 – Relationship between conductor cross-section and diameter . 82
Table B.21 – Test values for flexion and pull-out tests for round copper conductors . 84
Table B.22 – Test values for pull-out test for flat copper conductors . 86
Table B.23 – Test copper conductors for test currents up to 400 A inclusive . 87
Table B.24 – Test copper conductors for test currents above 400 A and up to 800 A
inclusive . 88
Table B.25 – Test copper bars for test currents above 400 A and up to 3 150 A
inclusive . 88
Table B.26 – Burden values for basic accuracy tests . 89
Table C.1 – Coding of interface connection . 100
Table C.2 – Rated AC RMS voltage output . 101
Table C.3 – Rated DC voltage output . 101
Table C.4 – Rated range of DC voltage output . 101
Table C.5 – Rated AC RMS current output less than 1A . 101
Table C.6 – Rated range of DC current output . 102
Table C.7 – Rated frequency output . 102
Table C.8 – Rated pulse density output. 102
Table C.9 – Coding of power supply for transducers supplied from a measuring
instrument via the connector . 103
Table C.10 – Coding of external power supply for transducers . 103
Table C.11 – Coding of transfer function curves for TRD1 . 103
Table C.12 – Interface full coding for output of transducers . 104
Table C.13 – Examples of interface codes and most common interface codes . 104
Table D.1 – Anti-aliasing filter . 107
Table E.1 – Limits of error for harmonics – Accuracy class extension WBm0 . 109

– 8 – IEC 60688:2024 © IEC 2024
Table E.2 – Limits of errors for harmonics – Accuracy class extension WBm1. 110
Table E.3 – Limits of errors for harmonics – Accuracy class extension WBm2. 111
Table E.4 – Limits of errors for supra-harmonics – Accuracy class extension WBm3 . 111
Table F.1 – Marking of terminals for TRD2 monitoring current . 112
Table F.2 – Marking of terminals for TRD2 monitoring voltage . 113
Table H.1 – Clearances according to IEC 60664-1:2020 . 115
Table H.2 – Creepage distances according to IEC 60664-1:2020 . 116
Table H.3 – Clearances according to IEC 61010-2-030:2017 . 117
Table H.4 – Creepage distances according to IEC 61010-2-030:2023 . 117

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL MEASURING TRANSDUCERS FOR CONVERTING AC AND DC
ELECTRICAL QUANTITIES TO ANALOGUE OR DIGITAL SIGNALS

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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IEC 60688 has been prepared by IEC technical committee 85: Measuring equipment for
electrical and electromagnetic quantities. It is an International Standard.
This fifth edition cancels and replaces the fourth edition published in 2021. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) updating normative references;
b) updating definitions;
c) updating structure;
d) adding DC power measurement.

– 10 – IEC 60688:2024 © IEC 2024
The text of this International Standard is based on the following documents:
Draft Report on voting
85/921/FDIS 85/932/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
In this document, the following print types are used:
– requirements and definitions: in roman t
...