IEC 61557-8:2014
(Main)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
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 specifies the requirements for insulation monitoring devices (IMD) which permanently monitor the insulation resistance RF to earth of unearthed a.c. IT systems, 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. IMDs according to this part of IEC 61557 can also be used for de-energized TT, TN and IT systems or appliances. This third edition cancels and replaces the second edition published in 2007. This edition constitutes a technical revision which includes the following significant technical changes with respect to the previous edition:
- terms and definitions have been complemented;
- abbreviations are listed and explained;
- requirements have been revised;
- mandatory and optional functions and their terminology have been adapted from IEC 61557-15;
- mechanical requirements have been added;
- information on operating instructions has been added;
- type tests and routine tests have been complemented;
- an Annex C: 'Insulation monitoring devices for photovoltaic systems (PV-IMD)' has been added; and
- an Annex D: 'Insulation monitoring function of a photovoltaic inverter (PV-IMF) or in a charge controller' has been added.
This publication is to be read in conjunction with IEC 61557-1:2007. The contents of the corrigendum of May 2016 have been included in this copy.
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
L'IEC 61557-8:2014 spécifie les exigences applicables aux contrôleurs d'isolement (CPI) destinés à surveiller en permanence, et quelle que soit la méthode de mesure, la résistance d'isolement RF par rapport à la terre de réseaux IT à courant alternatif non mis à la terre, ou de réseaux IT à courant alternatif comprenant des circuits à courant continu reliés galvaniquement dont les tensions nominales sont au plus égales à 1 000 V en courant alternatif, et de réseaux IT à courant continu non mis à la terre dont les tensions nominales sont au plus égales à 1 500 V en courant continu. Les réseaux IT sont décrits entre autres dans l'IEC 60364-4-41. Il convient de noter que, pour le choix des appareils, des indications supplémentaires sont données dans d'autres normes. Les CPI conformes à la présente partie de l'IEC 61557 peuvent également être utilisés dans des systèmes ou appareils hors tension du type TT, TN et IT. Cette troisième édition annule et remplace la deuxième édition parue en 2007. Cette édition constitue une révision technique qui inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- les termes et définitions ont été complétés;
- énumération et explication des abréviations;
- révision des exigences;
- adaptation des fonctions obligatoires et facultatives et leur terminologie à l'IEC 61557-15;
- ajout d'exigences mécaniques;
- ajout d'informations relatives aux instructions de fonctionnement;
- les essais de type et essais individuels de série ont été complétés;
- ajout de l'Annexe C: 'Contrôleurs d'isolement pour systèmes photovoltaïques (PV-CPI)'; et
- ajout de l'Annexe D: 'Fonction de surveillance de défaut d'isolement d'un onduleur photovoltaïque (PV-IMF) ou dans un contrôleur de charge'.
Cette publication doit être lue conjointement avec la CEI 61557-1:2007. Le contenu du corrigendum de mai 2016 a été pris en considération dans cet exemplaire.
General Information
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Standards Content (Sample)
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 au plus
égale à 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
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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 au plus
égale à 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
X
CODE PRIX
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
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
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
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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;
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.
The contents of the corrigendum of May 2016 have been included in this copy.
– 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 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
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 installation of a PV system starts from a PV module or a set of PV modules
connected in series with their own cables, up to a distribution network or to a customer
installation
3.1.27
d.c. side
part of a PV installation from the PV modules to the d.c. terminals of the PV inverter
3.1.28
a.c. side
part of a PV installation from the a.c. terminals of the PV inverter to the point of connection of
the PV supply cable to the electrical installation
3.1.29
PV inverter
device which converts d.c. voltage and d.c. current of the PV generator into a.c. voltage and
a.c. current
3.1.30
system leakage capacitance of the PV installation
sum of the leakage capacitances C of the individual PV modules to earth including the
e
leakage capacitances C of the complete PV installation
e
3.1.31
insulation monitoring device for photovoltaic systems
PV-IMD
insulation monitoring device suitable to monitor the insulation resistance of photovoltaic
electrical installations to earth
3.1.32
insulation monitoring function of a PV inverter
PV-IMF
function integrated in the PV inverter to monitor the insulation resistance R of the PV input
F
(array) to earth
3.2 Abbreviations
For the purposes of this document, the terms and abbreviations given in Table 1 apply.
Table 1 – Abbreviations
Abbreviation Term Clause/Subclause Referenced
standard
EMC Electromagnetic compatibility 4.5 IEC 60050-
161:1990,161-01-
IMD Insulation monitoring device 3.1.14 IEC 61557-8
LIW Local insulation warning 4.2.2.2 IEC 61557-8
LTMW Local transformer monitoring warning 4.3.2 IEC 61557-8
MED-IMD Medical insulation monitoring device Annex A IEC 61557-8
PTC Positive temperature coefficient Annex B IEC 61557-8
PV-IMD Photovoltaic IMD (IMD for photovoltaic systems) Annex C IEC 61557-8
PV-IMF Photovoltaic insulation monitoring function Annex D IEC 61557-8
RIW Remote insulation warning 4.2.2.3 IEC 61557-8
REDC Remote enabling / disabling command 4.3.4 IEC 61557-8
RTMW Remote transformer monitoring warning 4.3.3 IEC 61557-8
4 Requirements
4.1 General requirements
In addition to the requirements of Clause 4 of IEC 61557-1:2007, the requirements of
Clause 4 shall apply.
IMDs shall be capable of monitoring the insulation resistance R of IT systems including
F
symmetrical and asymmetrical allocation of the insulation resistance R and to give an
F
insulation warning if the insulation resistance R between either the system and earth or the
F
– 14 – IEC 61557-8:2014 © IEC 2014
system and the PE-connection or the system and another reference point for equipotential
bonding falls below the specified response value R including the relative uncertainty of R .
,
an an
So-called earth fault relays using a voltage asymmetry (voltage shift) in the presence of an
earth fault as the only measurement criterion and, as a consequence, detecting only
asymmetrical insulation faults, are not insulation monitoring devices according to this
standard.
A combination of several measurement methods, including asymmetry monitoring, may
become necessary for fulfilling the task of monitoring under special conditions on the IT
system.
NOTE These requirements are independent from the method of measurement. The methods of measurement can
use a measuring voltage or measuring current source which is independent from the system to be monitored or
they can use a measuring voltage or measuring current which is driven directly from the voltage of the system to be
monitored.
4.2 Types of IMDs
4.2.1 General
The measuring principle of IMDs shall have the ability to monitor the insulation resistance R
F
of IT systems for which they a
...
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