IEC TR 63436:2026

IEC TR 63436 ®
Edition 1.0 2026-01
TECHNICAL
REPORT
Insulation monitoring device - Marine AC application example

ICS 47.020.60  ISBN 978-2-8327-0994-8

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CONTENTS
FOREWORD . 2
INTRODUCTION . 4
1 Scope . 5
2 Normative references . 5
3 Terms, definitions, symbols and abbreviated terms . 5
3.1 Terms and definitions . 5
3.2 List of symbols and abbreviations . 7
4 General considerations . 8
5 IT system in marine application . 9
6 Touch voltage . 11
7 Application example . 12
8 Setting of IMD . 18
9 IMD injection method: AC/DC . 19
10 Insulation resistance tests . 19
11 Conclusion . 19
Bibliography . 21

Figure 1 – General schematic principle at first fault . 9
Figure 2 – System impedance . 10
Figure 3 – Simplified schematic and fault current equation . 11
Figure 4 – Fault current I (A) versus R (Ω) with R = 0,01 Ω. 13
F N F
Figure 5 – Touch voltage V (V) versus R (Ω) with R = 0,2 Ω, R = 1 MΩ and
c F A N
1 500 Ω . 14
Figure 6 – Touch voltage V versus R (Ω) with R = 2 Ω, C and R = 1 MΩ,
c F A 1max N
1 500 Ω, 100 Ω, and 10 Ω, voltage system at 690 V. 15
Figure 7 – Touch voltage V (V) versus R (Ω) with R = 2 Ω or 0,2 Ω with limit of 50 V
c F A
and 25 V on Y axis . 15
Figure 8 – Fault current I (A) versus R (Ω) for different low values of R (0,1 Ω,
F N F
1 500 Ω, 13,2 kΩ, 100 kΩ) and 30 mA in Y axis at 690 V . 16
Figure 9 – Setting of IMD (Ω) . 17

Table 1 – List of abbreviations . 7
Table 2 – Minimum values of insulation resistances . 8
Table 3 – Example of ship contribution and situations . 12
Table 4 – Example of ship leakage capacitance . 12
Table 5 – Summary of results . 19

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Insulation monitoring device - Marine AC application example

FOREWORD
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IEC TR 63436 has been prepared by IEC technical committee 18: Electrical installations of
ships and of mobile and fixed offshore units. It is a Technical Report.
The text of this Technical Report is based on the following documents:
Draft Report on voting
18/2010/DTR 18/2019/RVDTR
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Report is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
INTRODUCTION
The purpose of this document is to determine the values of the alarm thresholds of the insulation
controller resulting from a loss of insulation of a device or a group of devices installed in an IT
electrical system.
IEC 60364-4-41:2005 and IEC 60364-4-41:2005/AMD1:2017 is dedicated to the safety of
people, i.e. protection against electric shock. Subclause 411.6 is dedicated to the IT system.
In cases where an IT system is used for reasons of continuity of supply, also in the event of an
earth fault, an insulation monitoring device is used to indicate the occurrence of that first fault
from a live part to exposed-conductive-parts or to earth.
For onshore applications, the exposed-conductive-parts are connected to earth, either
individually, in groups, or collectively to R (see Figure 1). R is the sum of the resistance in
A A
ohms of the earth electrode and protective earthing conductor PE (see IEC 60364-4-41:2005
and IEC 60364-4-41:2005/AMD1:2017, 411.6, and IEC 60364-1:2025, Figure 19).
For marine applications, the exposed-conductive-parts are connected, either individually, in
groups, or collectively to the hull. The protective conductors are either connected to the earthing
bar of the switchboard or directly to the hull.
For the purpose of this study of the alarm thresholds and touch voltage, the following is
presumed:
is the parameter to calculate at the fault point to find the touch voltage between exposed-
a) R
A
conductive-parts of a faulty equipment and to the hull (not including R ). The basic
B
schematics are not changed. See Figure 1.
b) R is not used in the calculations, because this is a very low value which does not influence
B
the current within the impedance if fitted on the neutral point and this value is not easily
identified.
c) R and R are estimated in Clause 6.
A B
Low voltage rotating machines, transformers, switchgear and controlgear assemblies, cables,
loads, etc., are subject to insulation resistance measurements during production, installation,
commissioning and periodic maintenance of equipment and systems. These values give the
operators information regarding the operational quality of a product or a sub-assembly, but do
not make it possible to conclude on the operational quality of an entire electrical network.
Insulation monitoring devices (IMDs) measure the insulation resistance, including the
resistance of all the connected loads to one voltage system to earth.
These two types of measurements have generally different values and cannot be compared.

1 Scope
This document explains the setting parameters of insulation monitoring devices (IMDs) and how
to interpret these measurements through plotted curves. Some examples of injection methods
are also proposed.
NOTE 1 Requirements for IMDs are specified by IEC 61557-8.
The examples given in this document consider the situation of an insulation fault in an
installation or equipment (motors, enclosure, cables, etc.) creating a resistive path to earth and
calculate the touch voltage. It does not consider a person making direct contact with a live
conductor in an IT grid.
NOTE 2 This document is informative and cannot contain requirements, in accordance with the ISO/IEC Directives,
Part 2, for technical reports.
2 Normative references
There are no normative references in this document.
3 Terms, definitions, symbols and abbreviated terms
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.1 Terms and definitions
3.1.1
isolated neutral system
system where the neutral point is not intentionally connected to earth, except for high
impedance connections for protection or measurement purposes
[SOURCE: IEC 60050-601:1985, 601-02-24]
3.1.2
insulation monitoring devices
IMD
device which permanently monitors the insulation resistance to earth of unearthed AC IT
systems, AC IT systems with galvanically connected DC circuits having nominal voltages up to
1 000 V AC, as well as monitoring the insulation resistance of unearthed DC IT systems with
voltages up to 1 500 V DC, independent from the method of measuring
[SOURCE: IEC 61557-8:2014, 3.1.14]
3.1.3
insulation resistance
R
F
resistance in the system being monitored, including the resistance of all the connected
appliances to earth
[SOURCE: IEC 61557-8:2014, 3.1.2]
3.1.4
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 61557-8:2014, 3.1.18]
3.1.5
insulation resistance meter
instrument intended to measure insulation resistance
[SOURCE: IEC 60050-313:2001, 313-01-11]
3.1.6
touch voltage,
voltage between conductive parts when touched simultaneously by a human being or livestock
Note 1 to entry: The value of the touch voltage is influenced by the impedance of the human being or the livestock
in electric contact with these conductive parts.
[SOURCE: IEC 60050-195:2021, 195-05-11]
3.1.7
exposed-conductive-part
conductivepart of equipment that can be touched and that is not live under normal conditions,
but that can become live when basic insulation fails
[SOURCE: IEC 60050-195:2021, 195-06-10]
3.1.8
non-conducting environment
environment with high impedance to earth and without any earthed conductive parts
3.1.9
protective earthing conductor
PE conductor
protective grounding conductor, US
protective conductor provided for protective earthing
[SOURCE: IEC 60050-195:2021, 195-02-11]
3.1.10
PEN conductor
conductor combining the functions of both a protective earthing conductor and a neutral
conductor
[SOURCE: IEC 60050-195:2021, 195-02-12]
3.1.11
line-to-line voltage
voltage between two line conductors at a given point in an electric circuit
[SOURCE: IEC 60050-195:2021, 195-05-01]
3.1.12
line-to-neutral voltage
voltage between a line conductor and the neutral conductor at a given point in an AC circuit
[SOURCE: IEC 60050-195:2021, 195-05-02]
3.1.13
line-to-earth voltage
voltage between a line conductor and reference earth at a given point in an electric circuit
[SOURCE: IEC 60050-195:2021, 195-05-03]
3.2 List of symbols and abbreviations
Table 1 – List of abbreviations
R = R = R = R
The insulation resistance between each phase and ground
1 2 3
C = C = C = C
The capacitor between each phase and ground
1 2 3
R
The neutral resistance to the earth
N
R
Fault resistance of a resistive path between a phase and earth
F
The hull resistance including the connection resistance at the neutral point. See
R
B
Figure 1
R
One or more group earthing resistance and PE conductor. See Figure 1.
A
I
Current through the earthing resistance
R
I
Capacitive currents to ground mainly due to cables and filters
C
I Vectorial sum of I + I
F C N
Line-to-neutral voltages (V )
V , V , V
1 2 3 (i)
V Line to line voltage
ph-ph
V
Line to neutral voltage
ph-n
V
Line to earth voltage at the point of fault V V V /3
F
F ph-gnd ph-ph
V
Voltage between neutral point and earth
N
V
Touch voltage
c
Z
Positive sequence or direct impedance of the generation system
ds
Z
Negative sequence or inverse impedance of the generation system
is
Zero sequence or homopolar impedance of the generation system,
Z
0s
Z equal ∞ for insulated neutral or R if resistance earthed.
0s N
Synchronous generated voltage with V : the positive sequence voltage, Z : the
d d
E = V + Z I
direct impedance, I : the positive sequence current of the generation system (see
d d d
d
Figure 2 b),
The zero sequence of neutral resistor and the distributed zero sequence
z =R // (1/3Cω)
0 N
capacitance in parallel,
Z = z + R
Zero sequence or homopolar impedance of the fault,
0 0 F
==
4 General considerations
Low voltage electric systems are normally characterized by:
– a leakage current of the resistance between phases and phases to earth. For a network
properly insulated, the insulation resistance is balanced between phases to earth;
R = R = R = R;
1 2 3
– a leakage current of the capacitance between each phase and earth, including mainly cables
but also EMC/EMI filters, rotating machines, transformers, etc. For a network properly
insulated, the capacitance is balanced between phases to earth; C = C = C = C;
1 2 3
– whether a neutral point is earthed directly or through an impedance or resistance. The
earthing resistance R is close to zero;
B
– that the earthing conductors PE or PEN are generally interconnected or can be
interconnected per group or individually, each group will have a resistance R not eq
...