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IEC 61557-3
Edition 3.0 2019-07
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Electrical safety in low voltage distribution systems up to 1 000 V a.c. and
1 500 V d.c. – Equipment for testing, measuring or monitoring of protective
measures –
Part 3: Loop impedance
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IEC 61557-3
Edition 3.0 2019-07
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Electrical safety in low voltage distribution systems up to 1 000 V a.c. and
1 500 V d.c. – Equipment for testing, measuring or monitoring of protective
measures –
Part 3: Loop impedance
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.20; 29.080.01; 29.240.01 ISBN 978-2-8322-7233-6
– 2 – IEC 61557-3:2019 RLV © IEC 2019
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms and definitions. 5
4 Requirements . 6
4.1 General . 6
4.2 Measurement of loop impedance . 6
4.3 External resistance . 7
4.4 Fault voltage exceeding U . 7
L
4.5 Overvoltage . 7
5 Marking and operating instructions . 7
5.1 Marking . 7
5.2 Operating instructions . 8
6 Tests . 8
6.1 General . 8
6.2 Operating uncertainty . 8
6.3 External resistance . 10
6.4 Fault voltage . 10
6.5 Overvoltage . 10
Bibliography . 11
Table 1 – Calculation of operating uncertainty . 9
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL SAFETY IN LOW VOLTAGE DISTRIBUTION SYSTEMS
UP TO 1 000 V AC AND 1 500 V DC –
EQUIPMENT FOR TESTING, MEASURING OR MONITORING
OF PROTECTIVE MEASURES –
Part 3: Loop impedance
FOREWORD
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– 4 – IEC 61557-3:2019 RLV © IEC 2019
International Standard IEC 61557-3 has been prepared by IEC technical committee 85:
Measuring equipment for electrical and electromagnetic quantities.
This third edition cancels and replaces the second edition published in 2007. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) addition of equirements as regards the measurement category;
b) addition of new requirements for operating instructions;
c) alignment of the structure with that of the whole IEC 61557 series.
The text of this International Standard is based on the following documents:
FDIS Report on voting
85/687/FDIS 85/694/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.
This International Standard is to be used in conjunction with IEC 61557-1:2019.
A list of all parts in the IEC 61557 series, published under the general title Electrical safety in
low voltage distribution systems up to 1 000 V AC and 1 500 V DC – Equipment for testing,
measuring or monitoring of protective measures, 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.
ELECTRICAL SAFETY IN LOW VOLTAGE DISTRIBUTION SYSTEMS
UP TO 1 000 V AC AND 1 500 V DC –
EQUIPMENT FOR TESTING, MEASURING OR MONITORING
OF PROTECTIVE MEASURES –
Part 3: Loop impedance
1 Scope
This part of IEC 61557 specifies the requirements applicable to equipment for measuring the
loop impedance between a phase line conductor and protective conductor or; between a phase
line conductor and neutral; or between two phase line conductors by using the voltage drop
when the circuit under test is loaded.
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 61010-1:20012010, Safety requirements for electrical equipment for measurement, control,
and laboratory use – Part 1: General requirements
IEC 61010-1:2010/AMD1:2016
IEC 61010-2-030:2017, Safety requirements for electrical equipment for measurement, control,
and laboratory use – Part 2-030: Particular requirements for equipment having testing or
measuring circuits
IEC 61557-1:2019, Electrical safety in low voltage distribution systems up to 1 000 V AC and
1 500 V DC – Equipment for testing, measuring or monitoring of protective measures – Part 1:
General requirements
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61557-1 and the
following 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
loading method
method of loading applying a load to a circuit within a distribution system to cause a voltage
drop
__________
A consolidated version of this publication exists, comprising IEC 61010-1:2010 and
IEC 61010-1:2010/AMD1:2016.
– 6 – IEC 61557-3:2019 RLV © IEC 2019
3.2
loading equipment
equipment causing a voltage drop in a circuit
part of the measuring equipment to load the circuit being tested
3.3
test current
current that causes a voltage drop in a circuit
electric current controlled by the measuring device to cause a voltage drop in a circuit being
tested
3.4
system phase angle
angle between loop impedance and loop resistance of the distribution system
3.5
loop impedance
Z Z
s L
sum of the impedances in a current loop comprising the impedance of the source of the current,
...