SIST EN 61557-8:2015

SLOVENSKI STANDARD
01-junij-2015
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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 (IEC 61557-8:2014)
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 (IEC 61557-8:2014)
Ta slovenski standard je istoveten z: EN 61557-8:2015
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
EUROPÄISCHE NORM February 2015
ICS 17.220.20; 29.240.01; 29.080.01 Supersedes EN 61557-8:2007
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 61557-8:2014)
Sécurité électrique dans les réseaux de distribution basse Elektrische Sicherheit in Niederspannungsnetzen bis AC 1
tension de 1 000 V c.a. et 1 500 V C:C - Dispositifs de
000 V und DC 1 500 V - Geräte zum Prüfen, Messen oder
contrôle, de mesure ou de surveillance de mesures de Überwachen von Schutzmaßnahmen - Teil 8:
protection - Partie 8: Contrôleur permanent d'isolement Isolationsüberwachungsgeräte für IT-Systeme
pour réseaux IT (IEC 61557-8:2014)
(CEI 61557-8:2014)
This European Standard was approved by CENELEC on 2015-01-15. 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2015 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 61557-8:2015 E
Foreword
The text of document 85/485/FDIS, future edition 3 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 approved by CENELEC as EN 61557-8:2015.

The following dates are fixed:
(dop) 2015-10-15
 latest date by which the document has to be
implemented at national level by
publication of an identical national
standard or by endorsement
 latest date by which the national (dow) 2018-01-15
standards conflicting with the
document have to be withdrawn
This document supersedes EN 61557-8:2007.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent rights.

This standard covers the Principle Elements of the Safety Objectives for Electrical Equipment Designed for
Use within Certain Voltage Limits (LVD).

Endorsement notice
The text of the International Standard IEC 61557-8:2014 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.
IEC 60664-1 NOTE Harmonized as EN 60664-1.
IEC 60664-3 NOTE Harmonized as EN 60664-3.
IEC 61140 NOTE Harmonized as EN 61140.
IEC 60027-7 NOTE Harmonized as EN 60027-7.
IEC 61557-9 NOTE Harmonized as EN 61557-9.
IEC 60364-7-712 NOTE Harmonized as HD 60364-7-712.

- 3 - EN 61557-8:2015
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
NOTE 1 When 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.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60068-2-1 -  Environmental testing -- Part 2-1: Tests - Test EN 60068-2-1 -
A: Cold
IEC 60068-2-2 -  Environmental testing -- Part 2-2: Tests - Test EN 60068-2-2 -
B: Dry heat
IEC 60068-2-6 -  Environmental testing -- Part 2-6: Tests - Test EN 60068-2-6 -
Fc: Vibration (sinusoidal)
IEC 60068-2-27 -  Environmental testing -- Part 2-27: Tests - EN 60068-2-27 -
Test Ea and guidance: Shock
IEC 60364-7-710 2002 Electrical installations of buildings -- Part 7- HD 60364-7-710 2012
(mod) 710: Requirements for special installations or
locations - Medical locations
+AC 2013
IEC 60691 -  Thermal-links - Requirements and application - -
guid
IEC 60721-3-1 -  Classification of environmental conditions -- EN 60721-3-1 -
Part 3: Classification of groups of
environmental parameters and their severities
-- Section 1: Storage
IEC 60721-3-2 -  Classification of environmental conditions -- EN 60721-3-2 -
Part 3: Classification of groups of
environmental parameters and their severities
-- Section 2: Transportation
IEC 60721-3-3 -  Classification of environmental conditions -- EN 60721-3-3 -
Part 3: Classification of groups of
environmental parameters and their severities
-- Section 3: Stationary use at
weatherprotected locations
IEC 60947-5-1 -  Low-voltage switchgear and controlgear -- EN 60947-5-1 -
Part 5-1: Control circuit devices and switching
elements - Electromechanical control circuit
devices
+EN 60947-5- 2005
1:2004/corrigendum
Jul. 2005
+EN 60947-5- 2004
1:2004/corrigendum
Nov. 2004
IEC 60947-5-4 -  Low-voltage switchgear and controlgear -- EN 60947-5-4 -
Part 5-4: Control circuit devices and switching
elements - Method of assessing the
performance of low-energy contacts - Special
tests
IEC 61010-1 2010 Safety requirements for electrical equipment EN 61010-1 2010
for measurement, control and laboratory use -
- Part 1: General requirements
IEC 61010-2- -  Safety requirements for electrical equipment - -
030:2010/corrigendu for measurement, control and laboratory use -
m May 2011 - Part 2-030: Particular requirements for
testing and measuring circuits
IEC 61326-2-4 -  Electrical equipment for measurement, control EN 61326-2-4 -
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 61557-8
IEC 61557-1 -  Electrical safety in low voltage distribution EN 61557-1 -
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 EN 61810-2 -
2: Reliability
IEC 62109-2 2011 Safety of power converters for use in EN 62109-2 2011
photovoltaic power systems -- Part 2:
Particular requirements for inverters
CISPR 11 -  Industrial, scientific and medical equipment - EN 55011 -
Radio-frequency disturbance characteristics -
Limits and methods of measurement

IEC 61557-8 ®
Edition 3.0 2014-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
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

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: Contrôleur permanent d’isolement pour réseaux IT

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX X
ICS 17.220.20; 29.080.01; 29.240.01 ISBN 978-2-8322-1973-7

– 2 – IEC 61557-8:2014 © IEC 2014
CONTENTS
FOREWORD . 6
1 Scope . 8
2 Normative references . 8
3 Terms, definitions and abbreviations . 9
3.1 Terms and definitions . 9
3.2 Abbreviations . 13
4 Requirements . 13
4.1 General requirements . 13
4.2 Types of IMDs . 14
4.2.1 General . 14
4.2.2 Mandatory functions provided by IMDs . 14
4.2.3 Mandatory service function provided by the IMD – Test function . 15
4.3 Optional functions provided by IMD . 15
4.3.1 General . 15
4.3.2 Local transformer monitoring warning (LTMW) . 15
4.3.3 Remote transformer monitoring warning (RTMW) . 15
4.3.4 Remote enabling and disabling command (REDC) . 16
4.4 Performance requirements . 16
4.4.1 Specified response value R . 16
an
4.4.2 System leakage capacitance C . 16
e
4.4.3 Relative percentage uncertainty A of the specified response value R . 16
an
4.4.4 Response time t . 17
an
4.4.5 Measuring voltage U and measuring current I . 17
m m
4.4.6 Internal d.c. resistance R and internal impedance Z . 17
i i
4.4.7 Indication of the value of the insulation resistance R . 18
F
4.4.8 Permanently admissible nominal voltage U . 18
n
4.4.9 Permanently admissible extraneous d.c. voltage U . 18
fg
4.4.10 Supply voltage U . 18
S
4.5 Electromagnetic compatibility (EMC) . 18
4.6 Safety requirements . 18
4.6.1 General . 18
4.6.2 Clearances and creepage distances . 19
4.6.3 Protection class and earth connection of an IMD . 19
4.7 Climatic environmental conditions . 19
4.8 Mechanical requirements . 19
4.8.1 General . 19
4.8.2 Product mechanical robustness . 19
4.8.3 IP protection class requirements . 20
5 Marking and operating instructions . 21
5.1 Marking . 21
5.2 Operating instructions . 22
6 Tests . 23
6.1 General . 23
6.2 Type tests . 23
6.2.1 General . 23
6.2.2 Test of response values . 23

IEC 61557-8:2014 © IEC 2014 – 3 –
6.2.3 Test of response time t . 24
an
6.2.4 Test of peak value of the measuring voltage U . 24
m
6.2.5 Test of the peak value of the measuring current I . 24
m
6.2.6 Test of internal d.c. resistance R and internal impedance Z . 25
i i
6.2.7 Test of facilities for indicating the insulation resistance R . 25
F
6.2.8 Test of effectiveness of the test device . 25
6.2.9 Test of permanently admissible nominal voltage U . 25
n
6.2.10 Test of permanently admissible extraneous d.c. voltage U . 25
fg
6.2.11 Test of supply voltage U . 26
S
6.2.12 Test of optional functions . 26
6.2.13 Voltage tests . 26
6.2.14 Test of electromagnetic compatibility (EMC) . 26
6.2.15 Inspection of the marking and operating instructions . 26
6.2.16 Mechanical tests . 26
6.3 Routine tests. 27
6.3.1 General . 27
6.3.2 Test of response values . 27
6.3.3 Test of effectiveness of the test function . 27
6.3.4 Test of facility for indicating the insulation resistance R . 27
F
6.3.5 Voltage tests . 27
6.3.6 Compliance with tests of 6.3 . 27
7 Overview of requirements and tests for IMDs . 27
Annex A (normative) Medical insulation monitoring devices (MED-IMD) . 29
A.1 Scope and object . 29
A.2 Requirements . 29
A.2.1 General . 29
A.2.2 Types of MED-IMDs . 29
A.2.3 Mandatory functions provided by MED-IMD . 29
A.2.4 Performance requirements . 30
A.2.5 Electromagnetic compatibility (EMC) . 31
A.3 Marking and operating instructions . 31
A.4 Tests . 32
A.4.1 General . 32
A.4.2 Type tests . 32
A.5 Overview of requirements and tests for MED-IMDs . 32
Annex B (informative)  Monitoring of overload current and over-temperature . 34
B.1 Scope and object . 34
B.2 Requirements . 34
B.2.1 General . 34
B.2.2 Local transformer monitoring warning (LTMW) and/or remote
transformer monitoring warning (RTMW). 34
B.2.3 Monitoring of overload current . 34
B.2.4 Monitoring of over-temperature of the IT system transformer . 34
B.3 Operating instructions . 35
B.4 Tests . 35
B.4.1 General . 35
B.4.2 Test of overload current and over-temperature monitoring . 35
Annex C (normative) Insulation monitoring devices for photovoltaic systems (PV-IMD) . 36
C.1 Scope and object . 36

– 4 – IEC 61557-8:2014 © IEC 2014
C.2 Requirements for PV-IMDs for PV installations . 36
C.2.1 General . 36
C.2.2 Types of PV-IMDs . 37
C.2.3 Mandatory functions provided by PV-IMDs . 37
C.2.4 Performance requirements . 37
C.3 Marking and operating instructions . 38
C.3.1 Marking . 38
C.3.2 Operating instructions . 39
C.4 Tests . 39
C.4.1 General . 39
C.4.2 Additional type tests . 39
C.4.3 Additional routine tests . 40
C.5 Overview of requirements and tests for PV-IMDs . 40
Annex D (normative) Insulation monitoring function of a photovoltaic inverter (PV-IMF)
or in a charge controller . 41
D.1 Scope and object . 41
D.2 Requirements for PV-IMFs . 41
D.2.1 General requirements for PV-IMFs . 41
D.2.2 Types of PV-IMFs . 42
D.2.3 Mandatory functions provided by PV-IMFs . 42
D.2.4 Performance requirements for PV-IMFs . 43
D.2.5 Electromagnetic compatibility (EMC) . 44
D.2.6 Safety requirements. 44
D.2.7 Climatic environmental conditions . 44
D.2.8 Mechanical requirements . 44
D.3 Marking and operating instructions . 44
D.3.1 Marking . 44
D.3.2 Operating instructions . 44
D.4 Tests . 45
D.4.1 General . 45
D.4.2 Type tests . 45
D.4.3 Routine tests . 46
D.5 Overview of requirements and tests for PV-IMF . 46
Bibliography . 47

Figure A.1 – Pictogram for marking a MED-IMD . 32
Figure C.1 – Dynamic reference characteristics of d.c. PV system voltage . 38
Figure C.2 – Pictogram for marking a PV-IMD . 39

Table 1 – Abbreviations . 13
Table 2 – Product mechanical requirements . 20
Table 3 – Minimum IP requirements for IMDs . 21
Table 4 – Pictograms for marking the type of IMD . 22
Table 5 – Reference conditions for tests in operation . 23
Table 6 – Reference conditions for storage tests (product not powered) . 23
Table 7 – Requirements and tests applicable to IMD . 28
Table A.1 – Summary of additional requirements and tests applicable to MED-IMDs . 32

IEC 61557-8:2014 © IEC 2014 – 5 –
Table A.2 – Emission test for MED-IMDs . 33
Table C.1 – Requirements and tests for PV-IMDs . 40
Table D.1 – Requirements and tests for PV-IMF integrated in the inverter . 46

– 6 – IEC 61557-8:2014 © IEC 2014
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 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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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 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) Terms and definitions have been complemented;
b) Abbreviations are listed and explained;
c) Requirements have been revised;
d) Mandatory and optional functions and their terminology have been adapted from
IEC 61557-15;
IEC 61557-8:2014 © IEC 2014 – 7 –
e) Mechanical requirements have been added;
f) Information on operating instructions has been added;
g) Type tests and routine tests have been complemented;
h) An Annex C: ‘Insulation monitoring devices for photovoltaic systems (PV-IMD)’ has been
added;
i) An Annex D: ‘Insulation monitoring function of a photovoltaic inverter (PV-IMF) or in a
charge controller’ has been added.
The text of this standard is based on the following documents:
FDIS Report on voting
85/485/FDIS 85/502/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 in 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 stability 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.
– 8 – IEC 61557-8:2014 © IEC 2014
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 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 R to earth of unearthed a.c. IT systems,
F
of a.c. IT systems with galvanically connected d.c. circuits having nominal voltages up to
1 000 V a.c., as well as of unearthed d.c. IT systems with voltages up to 1 500 V d.c.
independent from the method of measuring.
IT systems are described in IEC 60364-4-41 amongst other literature. Additional data for the
selection of devices in other standards should be noted.
NOTE Various standards specify the use of IMDs in IT systems. In such cases, the objective of the equipment is
to signal a drop in insulation resistance R below a minimum limit.
F
IMDs according to this part of IEC 61557 can also be used for de-energized TT, TN and IT
systems or appliances.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60068-2-1, Environmental testing – Part 2-1: Tests – Test A: Cold
IEC 60068-2-2, Environmental testing – Part 2-2: Tests – Test B: Dry heat
IEC 60068-2-6, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-27, Environmental testing – Part 2-27: Tests – Test Ea and guidance: Shock
IEC 60364-7-710:2002, Electrical installations of buildings – Part 7-710: Requirements for
special installations or locations – Medical locations
IEC 60691, 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
IEC 61557-8:2014 © IEC 2014 – 9 –
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 61010-1:2010, Safety requirements for electrical equipment for measurement, control,
and laboratory use – Part 1: General requirements
IEC 61010-2-030, Safety requirements for electrical equipment for measurement, control, and
laboratory use –Part 2-030: Particular requirements for testing and measuring circuits
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
IEC 62109-2:2011, Safety of power converters for use in photovoltaic power systems – Part 2:
Particular requirements for inverters
CISPR 11, Industrial, scientific and medical equipment - Radio-frequency disturbance
characteristics - Limits and methods of measurement
3 Terms, definitions and abbreviations
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61557-1 and the
following apply.
3.1.1
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)
3.1.2
insulation resistance
R
F
resistance in the system being monitored, including the resistance of all the connected
appliances to earth
3.1.3
response value
R
a
value of the insulation resistance at which the device responds under specified conditions

– 10 – IEC 61557-8:2014 © IEC 2014
3.1.4
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
Note 1 to entry: R is the value declared by the manufacturer.
an
3.1.5
relative uncertainty
relative percentage uncertainty
A
response value R minus the specified response value R , divided by the specified response
a an
value R , multiplied by 100 and stated as a percentage
an
R −R
a an
A= ⋅100[%]
R
an
3.1.6
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 and within a response time t not exceeding 30 min
an
3.1.7
rated contact voltage
voltage for which a relay contact is rated to open and close under specified conditions
3.1.8
response time
t
an
time required by an insulation monitoring device to respond under specified conditions
3.1.9
measuring voltage
U
m
voltage present at the measuring terminals during the measurement
Note 1 to entry: In addition to the definition 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.
3.1.10
measuring current
I
m
maximum current that can flow between the system and earth, limited by the internal d.c.
resistance R from the measuring voltage source of the insulation monitoring device
i
Note 1 to entry: Measuring current I is designated as injected current in IEC 60364-7-710.
m
3.1.11
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 f
n
IEC 61557-8:2014 © IEC 2014 – 11 –
3.1.12
internal d.c. resistance
R
i
resistance of the insulation monitoring device between the terminals to the system being
monitored and earth
3.1.13
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 1 to entry: For IMDs this is the measuring connection to earth.
3.1.14
insulation monitoring device
IMD
device which permanently monitors the insulation resistance to earth of unearthed a.c. IT
systems, a.c. IT systems with galvanically connected d.c. circuits having nominal voltages up
to 1 000 V a.c., as well as monitoring the insulation resistance of unearthed d.c. IT systems
with voltages up to 1 500 V d.c., independent from the method of measuring
3.1.15
type AC IMD
device which permanently monitors the insulation resistance to earth of unearthed a.c. IT
systems
Note 1 to entry: Extraneous d.c. voltages which could occur when an insulation fault behind galvanically
connected rectifiers appears can influence the monitoring function in a way that the required uncertainty for the
measurement increases beyond the requirements or in some cases the monitoring process is even not guaranteed.
3.1.16
type DC IMD
device which permanently monitors the insulation resistance to earth of unearthed d.c. IT
systems
3.1.17
type AC/DC IMD
device which permanently monitors the insulation resistance to earth of unearthed a.c/d.c. IT
systems, d.c/a.c. IT systems or d.c. IT systems
Note 1 to entry: The insulation monitoring function is active for insulation faults in all parts of the IT system which
are galvanically connected.
3.1.18
insulation fault
defect in the insulation of an electrical installation or of an equipment which can create a
resistive path to earth
Note 1 to entry: The insulation fault can appear as a single fault from one line conductor or as a symmetrical fault
from all line conductors.
[SOURCE: IEC 60050-604:1987, 604-02-02, modified – Term definition has been adapted to
suit electrical installations which can result in another fault type. Note added.]
3.1.19
symmetrical insulation fault
defect in the insulation of an electric installation or equipment creating a resistive path to
earth having approximately the same resistance from all phase conductors to earth

– 12 – IEC 61557-8:2014 © IEC 2014
3.1.20
asymmetrical insulation fault
defect in the insulation of an electric installation or equipment creating a resistive path to
earth having different resistances from the phase conductors to earth
3.1.21
group 2 medical locations
medical locations where applied parts are intended to be used in applications such as
intracardiac procedures, operating theatres and vital treatment where discontinuity (failure) of
the supply can cause danger to life
Note 1 to entry: An intracardiac procedure is a procedure whereby an electrical conductor is placed within the
cardiac zone of a patient or is likely to come into contact with the heart, such conductor being accessible outside
the patient's body. In this context, an electrical conductor includes insulated wires, such as cardiac pacing
electrodes or intracardiac ECG-electrodes, or insulated tubes filled with conducting fluids.
[SOURCE: IEC 60364-7-710, 710.3.7, modified – Note to entry has been added.]
3.1.22
medical insulation monitoring device
MED-IMD
specific insulation monitoring device (IMD) dedicated to monitor medical IT systems of a
group 2 medical location
3.1.23
medical IT system
electrical IT system having specific requirements for medical applications
[SOURCE: IEC 60364-7-710:2002, 7.3.11]
3.1.24
overload current
overload current of an electrical circuit
overload current occurring in an electric circuit according to this standard is overload current
which is caused by connected loads
[SOURCE: IEC 60050-826:2004, 826-11-15, modified – The definition is about overload
current instead of overcurrent, which is not caused by a short-circuit or an earth fault.]
3.1.25
PV installation
erected equipment of a photovoltaic power (PV) supply system
3.1.26
PV electrical installation
the electrical
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