National foreword

This Published Document is the UK implementation of IEC TR 63436:2026.

The UK participation in its preparation was entrusted to Technical Committee JPEL/18, Electrical installations of ships and of mobile and fixed offshore units.

A list of organizations represented on this committee can be obtained on request to its committee manager.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

This publication is not to be regarded as a British Standard.

Compliance with a Published Document cannot confer immunity from legal obligations.

This Published Document was published under the authority of the Standards Policy and Strategy Committee on 28 February 2026.

FOREWORD

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.
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.
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.
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.
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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.
IEC draws attention to the possibility that the implementation of this document may involve the use of (a) patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which may be required to implement this document. However, implementers are cautioned that this may not represent the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC shall not be held responsible for identifying any or all such patent rights.

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:

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_A (see Figure 1). R_A is the sum of the resistance in 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:

R_A is the parameter to calculate at the fault point to find the touch voltage between exposed-conductive-parts of a faulty equipment and to the hull (not including R_B). The basic schematics are not changed. See Figure 1.
R_B is not used in the calculations, because this is a very low value which does not influence the current within the impedance if fitted on the neutral point and this value is not easily identified.
R_A and R_B are estimated in Clause 6.

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

3 Terms, definitions, symbols and abbreviated terms

3.1 Terms and definitions

3.2 List of symbols and abbreviations

4 General considerations

5 IT system in marine application

6 Touch voltage

7 Application example

8 Setting of IMD

9 IMD injection method: AC/DC

10 Insulation resistance tests

11 Conclusion

Bibliography

PD IEC TR 63436:2026

Insulation monitoring device — Marine AC application example

Current

Published:

28 Feb 2026