EN 61557-8:2007

SLOVENSKI STANDARD
01-december-2007
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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 8:
Insulation monitoring devices for IT systems
Elektrische Sicherheit in Niederspannungsnetzen bis AC 1 000 V und DC 1 500 V -
Geräte zum Prüfen, Messen oder Überwachen von Schutzmaßnahmen - Teil 8:
Isolationsüberwachungsgeräte für IT-Systeme
Sécurité électrique dans les réseaux de distribution basse tension de 1 000 V c.a. et 1
500 V c.c. - Dispositifs de contrôle, de mesure ou de surveillance de mesures de
protection - Partie 8: Contrôleurs d'isolement pour réseaux IT
Ta slovenski standard je istoveten z: EN 61557-8:2007
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
29.080.01 (OHNWULþQDL]RODFLMDQD Electrical insulation in
VSORãQR general
29.240.01 2PUHåMD]DSUHQRVLQ Power transmission and
GLVWULEXFLMRHOHNWULþQHHQHUJLMH distribution networks in
QDVSORãQR general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 61557-8
NORME EUROPÉENNE
July 2007
EUROPÄISCHE NORM
ICS 17.220.20; 29.080.01; 29.240.01 Supersedes EN 61557-8:1997

English version
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 8: Insulation monitoring devices for IT systems
(IEC 61557-8:2007 + corrigendum May 2007)

Sécurité électrique dans les réseaux  Elektrische Sicherheit
de distribution basse tension in Niederspannungsnetzen
de 1 000 V c.a. et 1 500 V c.c. - bis AC 1 000 V und DC 1 500 V -
Dispositifs de contrôle, de mesure Geräte zum Prüfen,
ou de surveillance de mesures Messen oder Überwachen
de protection - von Schutzmaßnahmen -
Partie 8: Contrôleurs d'isolement Teil 8: Isolationsüberwachungsgeräte
pour réseaux IT für IT-Systeme
(CEI 61557-8:2007 (IEC 61557-8:2007
+ corrigendum May 2007) + corrigendum May 2007)

This European Standard was approved by CENELEC on 2007-04-11. 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 Central Secretariat 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 Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Cyprus, the
Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2007 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61557-8:2007 E
Foreword
The text of document 85/296/FDIS, future edition 2 of IEC 61557-8, prepared by IEC TC 85, Measuring
equipment for electrical and electromagnetic quantities, was submitted to the IEC-CENELEC parallel vote
and was approved by CENELEC as EN 61557-8 on 2007-04-11.
This European Standard supersedes EN 61557-8:1997.
The following changes were made with respect to EN 61557-8:1997:
– definitions complemented;
– revision of some requirements;
– addition of information on operating instructions;
– sections “type tests” and “routine tests” complemented;
– modification of Table 1;
– addition of Annexes A and B.
This standard is to be used in conjunction with EN 61557-1.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2008-02-01
– latest date by which the national standards conflicting
(dow) 2010-05-01
with the EN have to be withdrawn
Annexes ZA and ZB have been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61557-8:2007, including the corrigendum May 2007, 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 standards indicated:
IEC 60364-4-41 NOTE  Harmonized as HD 60364-4-41:2007 (modified).
IEC 61140 NOTE  Harmonized as EN 61140:2002 (not modified).
__________
- 3 - EN 61557-8:2007
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

IEC 60364-7-710 2002 Electrical installations of buildings - - -
(mod) Part 7-710: Requirements for special
installations or locations - Medical locations

1) 2)
IEC 60664-1 - Insulation coordination for equipment within EN 60664-1 2007
low-voltage systems -
Part 1: Principles, requirements and tests

1) 2)
IEC 60664-3 - Insulation coordination for equipment within EN 60664-3 2003
low-voltage systems -
Part 3: Use of coating, potting or moulding for
protection against pollution
IEC 60691 2002 Thermal-links - Requirements and application EN 60691 2003
guide
1) 2)
IEC 60721-3-1 - Classification of environmental conditions - EN 60721-3-1 1997
Part 3: Classification of groups of
environmental parameters and their
severities - Section 1: Storage

1) 2)
IEC 60721-3-2 - Classification of environmental conditions - EN 60721-3-2 1997
Part 3: Classification of groups of
environmental parameters and their
severities - Section 2: Transportation

1) 2)
IEC 60721-3-3 - Classification of environmental conditions - EN 60721-3-3 1995
Part 3: Classification of groups of
environmental parameters and their
severities - Section 3: Stationary use at
weatherprotected locations
1) 2)
IEC 60947-5-1 - Low-voltage switchgear and controlgear - EN 60947-5-1 2004
Part 5-1: Control circuit devices and switching + corr. July 2005
elements - Electromechanical control circuit
devices
1) 2)
IEC 60947-5-4 - Low-voltage switchgear and controlgear - EN 60947-5-4 2003
Part 5-4: Control circuit devices and switching
elements - Method of assessing the
performance of low-energy contacts - Special
tests
1)
Undated reference.
2)
Valid edition at date of issue.

Publication Year Title EN/HD Year
IEC 61010-1 2001 Safety requirements for electrical equipment EN 61010-1 2001
for measurement, control, and + corr. June 2002
laboratory use -
Part 1: General requirements
1) 2)
IEC 61326-2-4 - Electrical equipment for measurement, EN 61326-2-4 2006
control and laboratory use - EMC
requirements -
Part 2-4: Particular requirements - Test
configurations, operational conditions and
performance criteria for insulation monitoring
devices according to IEC 61557-8 and for
equipment for insulation fault location
according to IEC 61557-9
1) 2)
IEC 61557-1 - Electrical safety in low voltage distribution EN 61557-1 2007
systems up to 1 000 V a.c. and 1 500 V d.c. -
Equipment for testing, measuring or
monitoring of protective measures -
Part 1: General requirements
1) 2)
IEC 61810-2 - Electromechanical elementary relays - EN 61810-2 2005
Part 2: Reliability
1) 2)
CISPR 11 (mod) - Industrial scientific and medical (ISM) radio- EN 55011 2007
frequency equipment - Electromagnetic
disturbance characteristics - Limits and
methods of measurement
- 5 - EN 61557-8:2007
Annex ZB
(informative)
A-deviations
A-deviation: National deviation due to regulations, the alteration of which is for the time being outside the
competence of the CENELEC member.
This European Standard falls under Directive 2006/95/EC.
NOTE (from CEN/CENELEC IR Part 2:2006 , 2.17)  Where standards fall under EC Directives, it is the view of the Commission of
the European Communities (OJ No C 59, 1982-03-09) that the effect of the decision of the Court of Justice in case 815/79
Cremonini/Vrankovich (European Court Reports 1980, p. 3583) is that compliance with A-deviations is no longer mandatory and that
the free movement of products complying with such a standard should not be restricted except under the safeguard procedure
provided for in the relevant Directive.
A-deviations in an EFTA-country are valid instead of the relevant provisions of the European Standard in
that country until they have been removed.
Clause Deviation
A.3.5 Spain
(REBT ITC-BT-38)
The device shall include monitoring of the isolation value to verify the alarm and the test
device.
__________
NORME CEI
INTERNATIONALE
IEC
61557-8
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2007-01
Sécurité électrique dans les réseaux
de distribution basse tension de 1 000 V c.a.
et 1 500 V c.c. –
Dispositifs de contrôle, de mesure ou de
surveillance de mesures de protection –

Partie 8: Contrôleurs d'isolement pour réseaux IT

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 8: Insulation monitoring devices
for IT systems
© IEC 2007 Droits de reproduction réservés ⎯ Copyright - all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in any
utilisée sous quelque forme que ce soit et par aucun procédé, form or by any means, electronic or mechanical, including
électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from
microfilms, sans l'accord écrit de l'éditeur. the publisher.
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Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
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Pour prix, voir catalogue en vigueur
For price, see current catalogue

61557-8 © IEC:2007 – 3 –
CONTENTS
FOREWORD.5

1 Scope.9
2 Normative references .9
3 Terms and definitions .11
4 Requirements .15
5 Marking and operating instructions .19
5.1 Marking .19
5.2 Operating instructions .21
6 Tests .21
6.1 Type tests .21
6.2 Routine tests .25

Annex A (normative) Medical insulation monitoring devices (IMDs) .29
Annex B (informative) Monitoring of overload and high temperature.37

Bibliography.41

Table 1 – Requirements applicable to insulation monitoring devices .17
Table A.1 – Additional requirements applicable to medical insulation monitoring
devices (IMDs).33
Table A.2 – Emission test for medical insulation monitoring devices (IMDs) .35

61557-8 © IEC:2007 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
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 8: Insulation monitoring devices for IT systems

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
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
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 61557-8 has been prepared by IEC technical committee 85:
Measuring equipment for electrical and electromagnetic quantities.
This second edition cancels and replaces the first edition published in 1997. This edition
constitutes a technical revision.
The following changes were made with respect to the previous edition:
a) definitions complemented;
b) revision of some requirements;
c) addition of information on operating instructions;
d) sections “type tests” and “routine tests” complemented;

61577-8 © IEC:2007 – 7 –
e) modification of Table 1;
f) addition of Annexes A and B.
The text of this standard is based on the following documents:
FDIS Report on voting
85/296/FDIS 85/306/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
This part of IEC 61557 shall be used in conjunction with Part 1.
A list of all parts of the IEC 61557 series, published under the general title 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, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
The contents of the corrigendum of May 2007 have been included in this copy.

61557-8 © IEC:2007 – 9 –
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 8: Insulation monitoring devices for IT systems

1 Scope
This part of IEC 61557 specifies the requirements for insulation monitoring devices (IMD)
which permanently monitor the insulation resistance to earth of unearthed IT a.c. systems, for
IT a.c. systems with galvanically connected d.c. circuits having nominal voltages up to
1 000 V a.c., as well as of unearthed IT d.c. systems with voltages up to 1 500 V d.c.
independent from the method of measuring.
NOTE 1 IT systems are described in IEC 60364-4-41 amongst other literature. Additional data for a selection of
devices in other standards should be noted.
NOTE 2 Various standards specify the use of insulation monitoring devices in IT systems. In such cases, the
objective of the equipment is to signal a drop in insulation resistance below a minimum limit.
NOTE 3 Insulation monitoring devices according to this part of IEC 61557 may also be used for de-energized
electrical systems.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60364-7-710:2002, Electrical installations of buildings – Part 7-710: Requirements for
special installations or locations – Medical locations
IEC 60664-1, Insulation co-ordination for equipment within low-voltage systems – Part 1:
Principles, requirements and tests
IEC 60664-3, Insulation coordination for equipment within low voltage systems – Part 3: Use
of coating, potting or moulding for protection against pollution.
IEC 60691:2002, Thermal-links – Requirements and application guide
IEC 60721-3-1, Classification of environmental conditions – Part 3: Classification of groups of
environmental parameters and their severities – Section 1: Storage
IEC 60721-3-2, Classification of environmental conditions – Part 3: Classification of groups of
environmental parameters and their severities – Section 2: Transportation
IEC 60721-3-3, Classification of environmental conditions – Part 3: Classification of groups of
environmental parameters and their severities – Section 3: Stationary use at
weatherprotected locations
61557-8 © IEC:2007 – 11 –
IEC 60947-5-1, Low-voltage switchgear and controlgear – Part 5-1: Control circuit devices
and switching elements – Electromechanical control circuit devices
IEC 60947-5-4, Low-voltage switchgear and controlgear – Part 5-4: Control circuit devices
and switching elements – Method of assessing the performance of low-energy contacts –
Special tests
IEC 61010-1:2001, Safety requirements for electrical equipment for measurement, control,
and laboratory use – Part 1: General requirements
IEC 61326-2-4, Electrical equipment for measurement, control and laboratory use – EMC
requirements – Part 2-4: Particular requirements – Test configurations, operational conditions
and performance criteria for insulation monitoring devices according to IEC 61557-8 and for
equipment for insulation fault location according to IEC 61557-9
IEC 61557-1, 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 1: General
requirements
IEC 61810-2, Electromechanical elementary relays – Part 2: Reliability
CISPR 11, Industrial, scientific and medical (ISM) radio-frequency equipment –
Electromagnetic disturbance characteristics – Limits and methods of measurement
3 Terms and definitions
For the purposes of this document, the definitions given in IEC 61557-1 and the following
definitions apply.
3.1
extraneous d.c. voltage
U
fg
d.c. voltage occurring in a.c. systems between the a.c. conductors and earth (derived from d.c.
parts)
3.2
insulation resistance
R
F
resistance in the system being monitored, including the resistance of all the connected
appliances to earth
3.3
specified response value
R
an
value of the insulation resistance, permanently set or adjustable, on the device and monitored
if the insulation resistance falls below this limit
3.4
response value
R
a
value of the insulation resistance at which the device responds under specified conditions

61557-8 © IEC:2007 – 13 –
3.5
relative (percentage) uncertainty
A[ %]
response value minus the specified response value, divided by the specified response value,
multiplied by 100 and stated as a percentage
R − R
a an
A [%] = × 100 %
R
an
3.6
system leakage capacitance
C
e
maximum permissible value of the total capacitance to earth of the system to be monitored,
including any connected appliances, up to which value the insulation monitoring device can
work as specified
3.7
rated contact voltage
voltage for which a relay contact is rated to open and close under specified conditions
3.8
response time
t
an
time required by an insulation monitoring device to respond under the conditions specified in 6.1.2
3.9
measuring voltage
U
m
voltage present at the measuring terminals during the measurement
NOTE Additionally to the definition given in IEC 61557-1, the measuring voltage (U ) is the voltage present in a
m
fault-free and de-energized system between the terminals of the system to be monitored and the terminals of the
protective conductor
3.10
measuring current
I
m
maximum current that can flow between the system and earth, limited by the internal
resistance R from the measuring voltage source of the insulation monitoring device
i
NOTE Measuring current is designated as injected current in IEC 60364-7-710.
3.11
internal impedance
Z
i
total impedance of the insulation monitoring device between the terminals to the system being
monitored and earth, measured at the nominal frequency
3.12
internal d.c. resistance
R
i
resistance of the insulation monitoring device between the terminals to the system being
monitored and earth
3.13
functional earthing
FE
earthing a point or points in a system or in an installation or in equipment for purposes other
than electrical safety
NOTE For insulation monitoring devices this is the measuring connection to earth.

61557-8 © IEC:2007 – 15 –
4 Requirements
The following requirements as well as those given in IEC 61557-1 shall apply.
4.1 Insulation monitoring devices shall be capable of monitoring the insulation resistance of
IT systems including symmetrical and asymmetrical components and to give a warning if the
insulation resistance between the system and earth falls below a predetermined level.
NOTE 1 A symmetrical insulation deterioration occurs when the insulation resistance of all conductors in the
system to be monitored decreases (approximately) similarly. An asymmetrical insulation deterioration occurs when
the insulation resistance of, for example, one conductor decreases substantially more than that of the other
conductor(s).
NOTE 2 So-called earth fault relays using a voltage asymmetry (voltage shift) in the presence of an earth fault as
the only measurement criterion, are not insulation monitoring devices in the interpretation of this part of IEC 61557.
NOTE 3 A combination of several measurement methods, including asymmetry monitoring, may become
necessary for fulfilling the task of monitoring under special conditions on the system.
4.2 Insulation monitoring devices shall comprise a test device, or be provided with means for
the connecti
...