EN IEC 60688:2024

Electrical measuring transducers for converting AC and DC electrical quantities to analogue or digital signals

IEC 60688:2024 applies to transducers (TRD) with electrical inputs and outputs for making measurements of AC or DC electrical quantities. The output signal can be in the form of an analogue or digital signal. This document applies to measuring transducers used for converting electrical quantities such as: – current, – voltage, – active power, – reactive power, – power factor, – phase angle, – frequency, – harmonics or total harmonic distortion, – apparent power, and – DC power to an output signal. This document applies a) if the fundamental frequency of the input(s) lies between 0 Hz and 1 500 Hz, b) to the electrical measuring transducer if it is part of a system for the measurement of an electrical or non-electrical quantity, c) to transducers for use in a variety of applications such as telemetry and process control and in one of a number of defined environments. This document is not applicable for: – instrument transformers that comply with IEC 61869 (all parts), – transmitters for use in an industrial process application that comply with IEC 60770 (all parts), – power metering and monitoring devices (PMD) that comply with IEC 61557-12, – meters that comply with the IEC 62053 series, – handheld sensors, – residual current monitoring devices (RCMs) that comply with IEC 62020-1, – residual current detecting devices (RDC-DD) that comply with IEC 62955, – in-cable control and protection devices (IC-CPDs) that comply with IEC 62752, – modular residual current devices (MRCDs) that comply with IEC 60947 2:2016/AMD1:2019, Annex M. Within the measuring range, the output signal is a function of the measurand. An auxiliary supply can be required. This document is intended: – to specify the terminology and definitions relating to transducers whose main application is in industry, – to unify the test methods used in evaluating transducer performance, – to specify accuracy limits and output values for transducers. IEC 60688:2024 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.

Elektrische Messumformer zur Umwandlung von elektrischen Wechselstromgrößen und Gleichstromgrößen in analoge oder digitale Signale

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

L'IEC 60688:2024 s’applique aux transducteurs (TRD) à grandeurs d’entrées et de sorties électriques destinés à mesurer des grandeurs électriques alternatives ou continues. Le signal de sortie peut être sous la forme d’un signal analogique ou numérique. Le présent document s’applique aux transducteurs de mesure destinés à convertir des grandeurs électriques, telles que: – le courant; – la tension; – la puissance active; – la puissance réactive; – le facteur de puissance; – le déphasage; – la fréquence; – les harmoniques ou la distorsion harmonique totale; – la puissance apparente; et – la puissance en courant continu, en signal de sortie. Le présent document s’applique: a) si la fréquence fondamentale de la ou des grandeurs d’entrée est comprise entre 0 Hz et 1 500 Hz; b) à un transducteur de mesure électrique appartenant à une chaîne de mesure d’une grandeur électrique ou non électrique; c) aux transducteurs destinés à une utilisation générale, par exemple à la télémesure, à la commande de processus et dans un des nombreux environnements spécifiés. Le présent document ne s’applique pas: – aux transformateurs de mesure conformes à la série IEC 61869; – aux transmetteurs utilisés dans un processus industriel conforme à la série IEC 60770; – aux dispositifs de comptage et de surveillance du réseau électrique (PMD) conformes à l’IEC 61557-12; – aux compteurs conformes à la série IEC 62053; – aux capteurs portatifs; – aux contrôleurs d’isolement à courant différentiel résiduel (RCM) conformes à l’IEC 62020-1; – aux dispositifs de détection de courant résiduel (RDC-DD) conformes à la série IEC 62955; – aux dispositifs de contrôle et de protection intégrés au câble (IC-CPD) conformes à la série IEC 62752; – aux dispositifs modulaires à courant résiduel (MRCD) conformes à l’IEC 60947-2:2016/AMD1:2019, Annexe M. Dans l’étendue de mesure, le signal de sortie varie en fonction du mesurande. Une alimentation auxiliaire peut être exigée. Le présent document a pour objet: – de spécifier la terminologie et les définitions relatives aux transducteurs dont l’application principale relève du domaine de l’industrie; – d’unifier les méthodes d’essai utilisées pour évaluer les performances des transducteurs; – de spécifier les limites de précision et les valeurs de sortie des transducteurs. L'IEC 60688:2024 annule et remplace la quatrième édition parue en 2021. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l’édition précédente: a) mise à jour des références normatives; b) mise à jour des définitions; c) mise à jour de la structure; d) ajout du mesurage de la puissance en courant continu.

Električni merilni pretvorniki za pretvarjanje izmeničnih električnih veličin v analogne ali digitalne signale (IEC 60688:2024)

Ta dokument se uporablja za pretvornike (TRD) z električnimi vhodi in izhodi za izvajanje meritev izmeničnih ali enosmernih električnih veličin. Izhodni signal je lahko v obliki analognega ali digitalnega signala.
Ta dokument se uporablja za merilne pretvornike, ki se uporabljajo za pretvarjanje električnih veličin, kot so:
– tok,
– napetost,
– delovna moč,
– jalova moč,
– faktor moči,
– fazni kot,
– frekvenca,
– harmonika ali skupno harmonsko popačenje,
– navidezna moč in
– enosmerni tok
v izhodni signal.
OPOMBA: Zgoraj navedene električne veličine vključujejo izmenične in/ali enosmerne komponente.
Ta dokument se uporablja:
a) če je osnovna frekvenca vhoda/vhodov med 0 Hz in 1500 Hz;
b) za električni merilni pretvornik, če je del sistema za merjenje električne ali neelektrične veličine;
c) za pretvornike, ki se uporabljajo za različne namene, kot sta telemetrija in vodenje procesa, ter v enem od številnih opredeljenih okolij.
Ta dokument se ne uporablja za:
– instrumentne transformatorje, ki so skladni s standardom IEC 61869 (vsi deli);
– oddajnike za uporabo v industrijskih procesih, ki so skladni s standardom IEC 60770 (vsi deli);
– naprave za merjenje in nadzorovanje moči (PMD), ki so skladne s standardom IEC 61557-12;
– merilnike, ki so skladni s skupino standardov IEC 62053;
– ročne senzorje;
– naprave za nadzorovanje preostalega toka (RCM), ki so skladne s standardom IEC 62020-1;
– naprave za zaznavanje preostalega toka (RDC-DD), ki so skladne s standardom IEC 62955;
– integrirane zaščite kablov in zaščitne naprave (IC-CPD), ki so skladne s standardom IEC 62752;
– modularne naprave s preostalim tokom (MRCD), ki so skladne s standardom IEC 60947-2:2016/AMD1:2019, dodatek M.
V okviru merilnega razpona je izhodni signal funkcija merjene veličine. Morda je potrebno pomožno napajanje.
Ta dokument je namenjen:
– določanju izrazov in definicij v zvezi s pretvorniki, ki se uporabljajo predvsem v industriji;
– poenotenju preskusnih metod za ocenjevanje lastnosti pretvornikov;
– opredelitvi mejnih vrednosti točnosti in izhodnih vrednosti za pretvornike.

General Information

• Status: Published
• Publication Date: 19-Dec-2024
• ICS: 17.220.20 - Measurement of electrical and magnetic quantities
• Technical Committee: CLC/TC 85X - Measuring equipment for electrical and electromagnetic quantities
• Current Stage: 6060 - Document made available - Publishing
• Start Date: 20-Dec-2024
• Completion Date: 20-Dec-2024
• Directive: 2014/30/EU - Directive 2014/30/EU of the European Parliament and of the Council of 26 February 2014 on the harmonisation of the laws of the Member States relating to electromagnetic compatibility (recast)
• Directive: 2014/35/EU - Directive 2014/35/EU of the European Parliament and of the Council of 26 February 2014 on the harmonisation of the laws of the Member States relating to the making available on the market of electrical equipment designed for use within certain voltage limits
• Mandate: M/511 - Mandate to CEN, CENELEC and ETSI relating to harmonised standards in the field of the Low Voltage Directive
• Mandate: M/552 - [C(2016) 7641 final] Standardisation request as regards harmonised standards in support of Directive 2014/30/EU of the European Parliament and of the Council of 26 February 2014 on the harmonisation of the laws of the Member States relating to electromagnetic compatibility
• Ref Project: SIST EN IEC 60688:2025 - Electrical measuring transducers for converting AC and DC electrical quantities to analogue or digital signals (IEC 60688:2024)

Relations

• Replaces: EN 60688:2013 - Electrical measuring transducers for converting A.C. and D.C. electrical quantities to analogue or digital signals
• Effective Date: 17-Oct-2023
• Revises: prEN IEC 60688:2021 - Electrical measuring transducers for converting AC and DC electrical quantities to analogue or digital signals
• Effective Date: 13-Feb-2024

Overview

EN IEC 60688:2024 (IEC 60688:2024) defines requirements, terminology and test methods for electrical measuring transducers that convert AC and DC electrical quantities into analogue or digital signals. It covers transducers measuring current, voltage, active/reactive/apparent power, power factor, phase angle, frequency, harmonics/THD and DC power, for input fundamentals from 0 Hz to 1 500 Hz. The standard consolidates performance criteria, accuracy limits and unified type/routine tests for industrial applications such as telemetry and process control.

Key topics and technical requirements

• Scope & exclusions: Applies to standalone and system‑embedded transducers but excludes instrument transformers (IEC 61869), process transmitters (IEC 60770), power metering devices (IEC 61557‑12), energy meters (IEC 62053 series), handheld sensors and several residual‑current and in‑cable protection devices.
• Terminology and classification: Unified definitions for transducer types, measurands, accuracy classes and nominal values.
• Performance & accuracy: Specifies accuracy limits, class indices and how output signals must relate to the measurand across the measuring range.
• Design & safety: Requirements for mechanical, electrical and safety design including protection against electric shock, temperature limits and component selection.
• EMC, climatic and mechanical requirements: Immunity and emission limits, environmental conditioning and mechanical stress guidelines.
• Testing regime: Detailed type tests and routine tests covering variations due to supply voltage/frequency, temperature, input distortion, unbalance, magnetic interference, self‑heating, impulse/high‑frequency disturbances and permissible excessive inputs.
• Marking & documentation: Required product markings, ratings and user documentation that support safe installation and verification.

Applications and who uses the standard

EN IEC 60688:2024 is used by:

• Manufacturers of electrical measuring transducers and power sensors for product design, verification and CE/market compliance.
• Test laboratories and certification bodies performing type and routine testing, EMC and environmental qualification.
• System integrators, utilities and OEMs specifying transducers for telemetry, process control, power monitoring and protection systems.
• Procurement and compliance teams ensuring devices meet accuracy, safety and environmental requirements.

Practical benefits include consistent performance benchmarking, clearer procurement specs, and reduced integration risk when transducers feed control, SCADA or power‑quality instruments.

Related standards

Relevant referenced standards include (but are not limited to): IEC 61869, IEC 60770, IEC 61557‑12, IEC 62053 series, IEC 61010, IEC 61326‑1, IEC 60664‑1 and environmental/EMC test standards (IEC 60068 series, IEC 61000‑4‑7). These should be consulted for complementary safety, metering or EMC requirements.

Standards Content (Sample)

SLOVENSKI STANDARD
01-marec-2025
Električni merilni pretvorniki za pretvarjanje izmeničnih električnih veličin v
analogne ali digitalne signale (IEC 60688:2024)
Electrical measuring transducers for converting AC and DC electrical quantities to
analogue or digital signals (IEC 60688:2024)
Elektrische Messumformer zur Umwandlung von elektrischen Wechselstromgrößen und
Gleichstromgrößen in analoge oder digitale Signale (IEC 60688:2024)
Transducteurs électriques de mesure convertissant les grandeurs électriques
alternatives ou continues en signaux analogiques ou numériques (IEC 60688:2024)
Ta slovenski standard je istoveten z: EN IEC 60688:2024
ICS:
17.220.20 Merjenje električnih in Measurement of electrical
magnetnih veličin and magnetic quantities
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60688

NORME EUROPÉENNE
EUROPÄISCHE NORM December 2024
ICS 17.220.20 Supersedes EN 60688:2013
English Version
Electrical measuring transducers for converting AC and DC
electrical quantities to analogue or digital signals
(IEC 60688:2024)
Transducteurs électriques de mesure convertissant les Elektrische Messumformer zur Umwandlung von
grandeurs électriques alternatives ou continues en signaux elektrischen Wechselstromgrößen und Gleichstromgrößen
analogiques ou numériques in analoge oder digitale Signale
(IEC 60688:2024) (IEC 60688:2024)
This European Standard was approved by CENELEC on 2024-10-16. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60688:2024 E
European foreword
The text of document 85/921/FDIS, future edition 5 of IEC 60688, prepared by TC 85 "Measuring
equipment for electrical and electromagnetic quantities" was submitted to the IEC-CENELEC parallel
vote and approved by CENELEC as EN IEC 60688:2024.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2025-12-31
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2027-12-31
document have to be withdrawn
This document supersedes EN 60688:2013 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 60688:2024 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 60051 (series) NOTE Approved as EN IEC 60051 (series)
IEC 60051-1 NOTE Approved as EN 60051-1
IEC 60068-2-30 NOTE Approved as EN 60068-2-30
IEC 60255-151 NOTE Approved as EN 60255-151
IEC 60359 NOTE Approved as EN 60359
IEC 60364-4-44 NOTE Approved as HD 60364-4-444
IEC 60381-1:1982 NOTE Approved as HD 452.1 S1:1984 (not modified)
IEC 60664-1 NOTE Approved as EN IEC 60664-1
IEC 61000-4-7 NOTE Approved as EN 61000-4-7
IEC 61010 (series) NOTE Approved as EN IEC 61010 (series)
IEC 61869 (series) NOTE Approved as EN IEC 61869 (series)
IEC 62052-11:2020 NOTE Approved as EN IEC 62052-11:2021 (not modified) + A11:2022
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60068-2-6 - Environmental testing - Part 2-6: Tests - Test EN 60068-2-6 -
Fc: Vibration (sinusoidal)
IEC 60068-2-11 - Environmental testing - Part 2-11: Tests - EN IEC 60068-2-11 -
Test Ka: Salt mist
IEC 60068-2-27 - Environmental testing - Part 2-27: Tests - EN 60068-2-27 -
Test Ea and guidance: Shock
IEC 60068-2-52 2017 Environmental testing - Part 2-52: Tests - EN IEC 60068-2-52 2018
Test Kb: Salt mist, cyclic (sodium chloride
solution)
IEC 60228 2023 Conductors of insulated cables EN IEC 60228 2024
IEC/TR 61000-2-3 - Electromagnetic compatibility (EMC) - Part 2: - -
Environment - Section 3: Description of the
environment - Radiated and non-network-
frequency-related conducted phenomena
IEC 61010-1 2010 Safety requirements for electrical equipment EN 61010-1 2010
for measurement, control, and laboratory use
- Part 1: General requirements
+ A1 (mod) 2016 + A1 2019
IEC 61010-2-030 2023 Safety requirements for electrical equipment - -
for measurement, control, and laboratory use
- Part 2-030: Particular requirements for
equipment having testing or measuring
circuits
IEC 61326-1 2020 Electrical equipment for measurement, EN IEC 61326-1 2021
control and laboratory use - EMC
requirements - Part 1: General requirements
Publication Year Title EN/HD Year
IEC 61557-12 2018 Electrical safety in low voltage distribution EN IEC 61557-12 2022
systems up to 1 000 V AC and 1 500 V DC. -
Equipment for testing, measuring or
monitoring of protective measures - Part 12:
Power metering and monitoring devices
(PMD)
+ A1 2021 + A1 2022
IEC 61558-1 2017 Safety of transformers, reactors, power EN IEC 61558-1 2019
supply units and combinations thereof - Part
1: General requirements and tests
IEC 60664-1 2020 Insulation coordination for equipment within EN IEC 60664-1 2020
low-voltage supply systems - Part 1:
Principles, requirements and tests
IEC 62586-1 2017 Power quality measurement in power supply EN 62586-1 2017
systems - Part 1: Power quality instruments
(PQI)
ISO 4628-3 - Paints and varnishes - Evaluation of - -
degradation of coatings - Designation of
quantity and size of defects, and of intensity
of uniform changes in appearance - Part 3:
Assessment of degree of rusting

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

IEC 60688:2024 © IEC 2024 – 3 –
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

IEC 60688:2024 © IEC 2024 – 5 –
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

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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

IEC 60688:2024 © IEC 2024 – 7 –
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

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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

IEC 60688:2024 © IEC 2024 – 9 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL MEASURING TRANSDUCERS FOR CONVERTING AC AND DC
ELECTRICAL QUANTITIES TO ANALOGUE OR DIGITAL SIGNALS

FOREWORD
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