IEC 61892-1:2019

IEC 61892-1 ®
Edition 4.0 2019-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Mobile and fixed offshore units – Electrical installations –
Part 1: General requirements and conditions

Unités mobiles et fixes en mer – Installations électriques –
Partie 1: Exigences générales et conditions

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IEC 61892-1 ®
Edition 4.0 2019-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Mobile and fixed offshore units – Electrical installations –

Part 1: General requirements and conditions

Unités mobiles et fixes en mer – Installations électriques –

Partie 1: Exigences générales et conditions

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 47.020.60 ISBN 978-2-8322-6663-2

– 2 – IEC 61892-1:2019 © IEC 2019
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 General requirements and conditions . 13
4.1 General . 13
4.2 Acceptance of substitutes or alternatives . 14
4.3 Additions and alterations . 14
4.4 Environmental conditions . 14
4.4.1 General . 14
4.4.2 Ambient temperature . 14
4.5 Power supply system characteristics . 14
4.5.1 General . 14
4.5.2 AC distribution systems . 15
4.5.3 DC distribution systems . 18
4.6 Clearance and creepage distances . 19
4.7 Insulation . 19
4.8 Precautions against vibration and mechanical shock . 19
4.9 Location of electrical equipment in units. 19
4.10 Mechanical protection . 20
4.11 Protection against heat, water, steam and oil . 20
4.12 Protection against electrical shock . 21
4.13 Enclosures . 21
4.14 Ignition source control . 21
4.14.1 General . 21
4.14.2 Emergency shutdown (ESD) – General . 22
4.14.3 Emergency conditions due to drilling operations – Mobile drilling units . 23
4.14.4 Manual electrical shutdown . 23
4.15 Degree of protection of equipment by enclosures . 23
4.16 Environmental impact. 26
Annex A (informative) Degree of protection . 27
Annex B (informative) Cold climate precautions . 29
B.1 General . 29
B.2 Emergency power source . 29
B.3 Equipment – General . 29
B.4 Cables and cable installations . 29
B.5 Electrical trace heating systems . 29
B.6 Lighting systems . 30
B.6.1 General . 30
B.6.2 Emergency lights . 30
B.7 Electrical rotating machines . 30
B.8 Explosion protected equipment . 30
Annex C (informative) Specification of surface treatment and protective painting
system . 31
C.1 Objectives . 31

C.2 General and specification. 31
C.2.1 General . 31
C.2.2 Atmospheric corrosivity categories for protective painting systems . 31
C.2.3 Durability performance of a protective painting system . 32
Bibliography . 34

Table 1 – Voltage characteristics . 16
Table 2 – Frequency characteristics . 17
Table 3 – Tolerances for DC system . 18
Table 4 – Fast transients . 19
Table 5 – Minimum requirements for the degree of protection for mobile and fixed

offshore units . 24
Table A.1 – Degrees of protection against foreign objects indicated by the first
characteristic numeral . 27
Table A.2 – Degrees of protection against water indicated by the second characteristic
numeral . 28
Table C.1 – Description of typical atmospheric environments related to the estimation

of corrosivity categories . 32

– 4 – IEC 61892-1:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MOBILE AND FIXED OFFSHORE UNITS –
ELECTRICAL INSTALLATIONS –
Part 1: General requirements and conditions

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
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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
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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 61892-1 has been prepared by IEC technical committee 18:
Electrical installations of ships and of mobile and fixed offshore units.
This fourth edition cancels and replaces the third edition published in 2015. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) voltage limitations have been removed;
b) definitions for fixed offshore units and mobile offshore units have been included;
c) tables for ambient air temperature and relative humidity have been removed, as this
information will normally be given in owner's/operator's documentation for specific
projects;
d) the requirement as to ignition source control has been moved from IEC 61892-7 to this
document;
e) tables for voltage characteristics have been updated;
f) requirements for a minimum degree of protection for equipment have been moved from
IEC 61892-2 to this document.
The text of this International Standard is based on the following documents:
FDIS Report on voting
18/1649/FDIS 18/1664/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 61892 series, published under the general title Mobile and fixed
offshore units – Electrical installations, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – IEC 61892-1:2019 © IEC 2019
INTRODUCTION
IEC 61892 forms a series of International Standards for safety in the design, selection,
installation, maintenance and use of electrical equipment for the generation, transmission,
storage, distribution and utilization of electrical energy for all purposes in offshore units which
are used for the purpose of exploration or exploitation of petroleum resources.
This part of IEC 61892 incorporates and coordinates, as far as possible, existing rules and
forms a code of interpretation, where applicable, of the requirements of the International
Maritime Organization (IMO), and constitutes a guide for future regulations which may be
prepared and a statement of practice for offshore unit owners, designers, installers and
appropriate organizations.
This document is based on solutions and methods which are in current use, but it is not
intended to impede the development of new or improved techniques.
In this revision, voltage limitations have been removed. However, voltage limitations may be
given in the referenced equipment standards. The removal of voltage limitations is considered
necessary due to the interconnection of, and supply from shore to offshore units. In such
cases, transmission voltages up to 132 kV AC and 150 kV DC are used and higher voltages
are being planned.
The IEC 61892 series aims to constitute a set of International Standards for the offshore
petroleum industry, but it is not intended to prevent their use beyond petroleum installations.

MOBILE AND FIXED OFFSHORE UNITS –
ELECTRICAL INSTALLATIONS –
Part 1: General requirements and conditions

1 Scope
This part of IEC 61892 is applicable to electrical installations and equipment in mobile and
fixed offshore units, including pipeline, pumping or "pigging" stations, compressor stations
and single buoy moorings, used in the offshore petroleum industry for drilling, production,
accommodation, processing, storage and offloading purposes.
It applies to all installations, whether permanent, temporary, transportable or hand-held, to AC
installations and DC installations without any voltage level limitation. Referenced equipment
standards may give voltage level limitations.
This document specifies requirements such as those concerning
– environmental conditions,
– power supply characteristics,
– location of electrical equipment in units,
– protection against external influences,
– protection against electrical shock, and
– ignition source control.
This document gives information and guidance on topics such as
– cold climate protection, and
– surface treatment and protective painting system.
This document does not apply to
– fixed equipment for medical purposes,
– electrical installations of tankers, and
– control of ignition sources other than those created by electrical equipment.
NOTE 1 For medical rooms, IEC 60364-7-710 provides specific requirements. Requirements for tankers are given
in IEC 60092-502.
NOTE 2 Guidance on protection of non-electrical equipment can be found in ISO 80079-36, ISO 80079-37 and
IMO 2009 MODU Code, 6.7.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 60364-4-41, Low-voltage installations – Part 4-41: Protection for safety – Protection
against electric shock
– 8 – IEC 61892-1:2019 © IEC 2019
IEC 61000-2-4:2002, Electromagnetic compatibility (EMC) – Part 2-4: Environment –
Compatibility levels in industrial plants for low-frequency conducted disturbances
IEC 61892-2:2019, Mobile and fixed offshore units – Electrical installations – Part 2: System
design
IEC 61892-3, Mobile and fixed offshore units – Electrical installations – Part 3: Equipment
IEC 61892-5, Mobile and fixed offshore units – Electrical installations – Part 5: Mobile units
IEC 61892-6:2019, Mobile and fixed offshore units – Electrical installations – Part 6:
Installation
IEC 61892-7:2019, Mobile and fixed offshore units – Electrical installations – Part 7:
Hazardous areas
ISO 8468, Ships and marine technology – Ship's bridge layout and associated equipment –
Requirements and guidelines
ISO 11064 (all parts), Ergonomic design of control centres
IMO, International Convention for the Safety of Life at Sea (SOLAS), consolidated edition
IMO, 2009 MODU Code, Code for the Construction and Equipment of Mobile Offshore Drilling
Units, 2009, 2010 Edition
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
NOTE The terms and definitions included in this document are those that have general application in the
IEC 61892 series. Terms and definitions applying to particular apparatus or equipment are included in the other
parts of the IEC 61892 series.
3.1
offshore unit
construction, buoyant or non-buoyant, designed and built for installation or operation at an
offshore location
Note 1 to entry: Topside interface of subsea installed equipment which is an integral part of production and
transport systems assigned to fixed and floating offshore units, as well as a temporary interface to mobile offshore
units, are also considered as part of the offshore unit.
3.2
unmanned offshore unit
offshore unit normally unmanned, remote controlled without need of human presence for
operability and without living quarter facilities
Note 1 to entry: An unmanned offshore unit may also contain a survival shelter to support occasional site
maintenance.
3.3
fixed offshore unit
buoyant or non-buoyant construction engaged in offshore operations including drilling,
production, storage or support functions, and which is designed and built for installation at a
particular offshore location
Note 1 to entry: LNG production units and LNG storage and regasification unit terminals are also considered to be
fixed offshore units. FPSO/FSO on location is also considered as a fixed offshore unit. Floating LNG terminals and
FPSOs with detachable arrangements are also considered to be fixed offshore units.
3.4
mobile offshore unit
buoyant construction engaged in offshore operations including drilling, production, storage,
accommodation or support functions, not intended for service at one particular offshore site
and which can be relocated without major dismantling or modification, for example barges,
semisubmersible or jack-up unit and drill-ships
3.5
manned unit
offshore unit with need of human presence for operation and maintenance, and provided with
living quarter facility
3.6
satellite unit
small offshore unit, normally unmanned, connected to a larger unit by means of a pipeline,
power cable and/or umbilical
3.7
appropriate authority
governmental body and/or classification society with whose rules a unit is required to comply
3.8
equipment
single apparatus or set of devices or apparatuses, or the set of main devices of an
installation, or all devices necessary to perform a specific task
EXAMPLE Power transformer, measuring equipment.
[SOURCE: IEC 60050-151:2001, 151-11-25, modified – The words "the equipment of a
substation" have been removed from the example.]
3.9
apparatus
device or assembly of devices which can be used as an independent unit for specific functions
[SOURCE: IEC 60050-151:2001, 151-11-22, modified – The note has been deleted.]
3.10
IP
degree of protection of enclosure
numerical classification according to IEC 60529 preceded by the symbol IP applied to the
enclosure of electrical apparatus to provide:
– protection of persons against contact with, or approach to, live parts and against contact
with moving parts (other than smooth rotating shafts and the like) inside the enclosure,
– protection of the electrical apparatus against ingress of solid foreign objects, and
– where indicated by the classification, protection of the electrical apparatus against harmful
ingress of water
– 10 – IEC 61892-1:2019 © IEC 2019
Note 1 to entry: Explanation of the numerals used for classification of degree of protection is given in Tables A.1
and A.2.
[SOURCE: IEC 60050-426:2008, 426-04-02, modified – Note 1 to entry has been added.]
3.11
primary distribution system
system which is galvanically connected to the generator or, in offshore units with power
supply from another unit or shore via cable, connected to the switchboard where the voltage
regulation takes place
3.12
secondary distribution system
system without galvanic connection to the generator or to the switchboard where the voltage
regulation takes place
3.13
distribution board
assembly containing different types of switchgear and controlgear associated with one or
more outgoing electric circuits fed from one or more incoming electric circuits, together with
terminals for the neutral and protective conductors, if required
[SOURCE: IEC 60050-826:2004, 826-16-08, modified – The words "if required" have been
added.]
3.14
earth
ground, US, CA
general mass of the metal structure or hull of the unit
3.15
earthed
connected to the general mass of the metal structure or hull of the unit in such a manner as to
ensure at all times an immediate discharge of electrical energy without danger
3.16
emergency service
services required to allow safe shutdown of the unit and provide safety oriented services for
the personnel on the unit during an emergency situation for a defined time
EXAMPLE Emergency shutdown system, emergency lighting, firefighting, alarm and telecommunication systems
are examples of emergency services.
3.17
essential service
services required to maintain the unit in a defined state of readiness and habitation for a
period defined by the user for situations other than normal operation and without recourse to
the emergency source of power except than in an emergency situation
EXAMPLE Services required to maintain the unit in a minimum comfortable condition of habitability, maintaining
heading control thrusters for turret moored floating units and fuel transfer/bunkering operations are examples of
essential services.
3.18
frequency
3.18.1
cyclic frequency variation
periodic deviation in frequency during normal operation such as might be caused by regularly
repeated loading
± ( f − f )× 100
max. min.
%
2 f
nominal
3.18.2
frequency tolerance
maximum departure from nominal frequency during normal operation conditions excluding
transient and cyclic frequency variations
Note 1 to entry: Frequency tolerance is a steady state tolerance and includes variations caused by loads and
governor characteristics.
3.18.3
frequency transient
sudden change in frequency which goes outside the frequency tolerance limits and returns to
and remains inside these limits within a specified recovery time after initiation of the
disturbance (time range: seconds)
3.19
live part
conductor or conductive part intended to be energized in normal operation, including a neutral
conductor, but by convention not a PEN conductor or PEM conductor or PEL conductor
Note 1 to entry: This concept does not necessarily imply a risk of electric shock.
[SOURCE: IEC 60050-195:1998, 195-02-19]
3.20
PEN conductor
conductor combining the functions of both a protective earthing conductor and a neutral
conductor
[SOURCE: IEC 60050-195:1998, 195-02-12]
3.21
PEM conductor
conductor combining the functions of both a protective earthing conductor and a mid-point
conductor
[SOURCE: IEC 60050-195:1998, 195-02-13]
3.22
PEL conductor
conductor combining the functions of both a protective earthing conductor and a line
conductor
[SOURCE: IEC 60050-195:1998, 195-02-14]
3.23
petroleum
complex mixture of hydrocarbons that occurs in the earth in liquid or gaseous forms
3.24
point
termination of the fixed wiring intended for the attachment of a luminaire or for
connecting to the supply of a current-using appliance

– 12 – IEC 61892-1:2019 © IEC 2019
3.25
voltages
3.25.1
voltage tolerance
maximum departure from nominal user voltage during normal operating conditions, excluding
transient and cyclic voltage variations
Note 1 to entry: Voltage tolerance is a steady state tolerance and includes voltage drop in cables and voltage
regulator characteristics. It also includes variations due to environmental conditions.
3.25.2
voltage unbalance tolerance
maximum permissible unbalance, expressed in percent of nominal voltage, between the
highest and lowest phase voltage
3.25.3
cyclic voltage variation
periodic voltage deviation (max. to min. RMS values) of the nominal voltage, such as might be
caused by regularly repeated loading
±(UU −× ) 100
max. min.
%
2 U
nominal
3.25.4
voltage transient
sudden change in voltage (excluding spikes) which goes outside the nominal voltage
tolerance limits and returns to and remains inside those limits within a specified recovery time
after the initiation of the disturbance (time range: seconds)
3.26
recovery time
3.26.1
voltage transient recovery time
time elapsed from exceeding the steady state voltage tolerance until the voltage recovers and
remains within the steady state tolerance limits
3.26.2
frequency transient recovery time
time elapsed from exceeding the steady state frequency tolerance until the frequency
recovers and remains within the steady state tolerance limits
3.27
waveform
3.27.1
THD
total harmonic distortion
ratio of the RMS value of the sum of all the harmonic components up to a specified order
(recommended notation "H") to the RMS value of the fundamental component
hH=
Q
( )
h
THD = ∑
h= 2
Q
( )
where
Q represents either current or voltage;
Q is the RMS value of the fundamental component;
h is the harmonic order;
Q is the RMS value of the harmonic component of order h;
h
H is 50 for the purpose of the compatibility levels in this document.
Note 1 to entry: THD takes account of harmonics only. For the case where interharmonics are to be included,
reference is made to IEC 61000-2-4:2002, A.3.1.
Note 2 to entry: This note applies to the French language only.
[SOURCE: IEC 61000-2-4:2002, 3.2.7, modified – Note 1 to entry has been rephrased, and
Note 2 to entry has been added.]
3.27.2
single harmonic content
ratio of the effective RMS value of the harmonic to the RMS value of the fundamental,
expressed as a percentage
3.28
umbilical
group of functional components, such as electrical cables, optical fibre cables, hoses and
tubes, laid up or bundled together or in combination with each other, that generally provides
hydraulics, fluid injection, power and/or communication services
[SOURCE: ISO 13628-5:2009, 3.1.47, modified – Note 1 to entry has been omitted.]
3.29
equipment protection level
EPL
level of protection assigned to equipment based on its likelihood of becoming a source of
ignition and distinguishing the differences between explosive gas atmospheres, explosive dust
atmospheres, and the explosive atmospheres in mines susceptible to firedamp
Note 1 to entry: This note applies to the French language only.
[SOURCE: IEC 60079-0:2017, 3.33, modified – The note to entry has been added in English.]
4 General requirements and conditions
4.1 General
This clause contains requirements and conditions which are common to all equipment and
electrical installations in the IEC 61892 series.
Electrical installations shall be such that:
a) the safety of the unit and any people present onboard is ensured;
b) the requirements with respect to safety in this document are followed;
c) the requirements of the International Convention for the Safety of Life at Sea (SOLAS) are
met as far as applicable;
d) the requirements of the IMO MODU Code are met as far as applicable.
For buoyant units, all machinery and equipment shall operate satisfactorily under the static
and dynamic inclination limits according to IEC 61892-5.
The appropriate authority may have additional requirements which have to be complied with.

– 14 – IEC 61892-1:2019 © IEC 2019
4.2 Acceptance of substitutes or alternatives
In the IEC 61892 series, where any special type of equipment, construction, or arrangement is
specified, the use of any other equipment, construction or arrangement is admissible,
provided it is at least of equal safety, effectiveness, and reliability.
4.3 Additions and alterations
An addition or alteration, temporary or permanent, shall not be made to an existing electrical
installation until it has been ascertained that the ratings and the condition of existing
accessories, conductors, switchgear, etc. affected, are adequate for the new situation.
Special attention is drawn to those factors affecting the existing system design such as
current-carrying capacity, short-circuit level, voltage drop, harmonics, stability and proper
discrimination of the protective devices.
4.4 Environmental conditions
4.4.1 General
Electrical equipment shall operate satisfactorily under various environmental conditions in the
location for which the unit is designed.
Environmental conditions are characterised by a number of variables:
a) one set including mainly climatic conditions, as well as conditions dependent upon
chemically and mechanically active substances and mechanical conditions;
b) another set dependent mainly upon locations within unit, operational patterns and
transient conditions.
NOTE 1 Environmental conditions will normally be specified in the overall design documentation for each project,
based on the place of operation.
NOTE 2 Guidance on of surface treatment and protective painting system is given in Annex C.
4.4.2 Ambient temperature
For a specific project, the project documentation may give specific information regarding
ambient temperature. In the absence of such information, the following shall apply.
In other parts of the IEC 61892 series, where no maximum ambient air temperature has been
specified as a design parameter for equipment, a value of 40 °C shall apply.
Mobile offshore units shall comply with IEC 61892-5.
NOTE 1 The Classification societies normally require an ambient air temperature of 45 °C. Other values of
ambient air temperature can be considered according to specific local conditions.
For a fixed unit, design temperature shall be based on the environmental condition of the
place of operation.
NOTE 2 For cold climate precautions, see Annex B.
4.5 Power supply system characteristics
4.5.1 General
Unless otherwise stated in other parts of this document, when supplied from general
distribution systems the equipment shall function with due regard to voltage and frequency
variations, harmonic distortion and conducted disturbances. The characteristics of general
distribution systems are given in the following subclauses of 4.5.

Where the power supply is obtained from the shore, due regard should be paid to the effect
that the quality of the supply, if different from that specified in 4.5, may have on the
performance of equipment.
For systems where semiconductors are connected and have a total rating which is a
significant portion of the total system rating, it may be feasible to suppress the harmonics.
Consideration should be given to taking appropriate measures to attenuate these effects of
the distribution system so that safe operation is assured. Care should be taken in selecting
consumers supplied from an electric power supply system with a higher harmonic content
than that specified in 4.5.2.3.
Electrical equipment which requires a higher quality power supply may need additional
provisions to be made locally. Where additional equipment is fitted to achieve this higher
quality power supply, it may be required to be duplicated and segregated to the same degree
as the electrical equipment it supplies.
4.5.2 AC distribution systems
4.5.2.1 General
The voltages referred to in 4.5.2.2 are measured at the point where the equipment is installed.
4.5.2.2 Voltage characteristics
Requirements for voltage characteristics are given in Table 1. Tolerances are expressed as a
percentage of the nominal voltage.

– 16 – IEC 61892-1:2019 © IEC 2019
Table 1 – Voltage characteristics
System withstand requirements
Voltage characteristics Value Comments
Steady state voltage tolerance on switchboards
Voltage tolerance +6 %
and distribution panels which electrical system
−10 %
and consumers in general shall withstand.
Voltage transient variation +15 % Transient voltage tolerance on switchboards
and distribution panels which consumers in
−15 %
general shall withstand.
Max. voltage variation +20 % Voltage excursions (sum of transient and
steady state deviation) on switchboards and
−20 %
distribution panels which electrical system and
consumers in general shall withstand.
System operational requirements
Voltage characteristics Value Comments
Voltage tolerance in primary +2,5 % Steady state voltage tolerance on generator
distribution system switchboards.
−2,5 %
For offshore units with power supply from other
unit or shore via cable, this applies to the
switchboard were the voltage regulation takes
place.
Voltage tolerance in secondary +5 % Steady state voltage tolerance on switchboards
distribution system and distribution panels in secondary
−5 %
distribution system.
Voltage transients:
slow transients e.g. due to load +20 %
variation tolerance (deviation from
nominal voltage) −15 %
a
Maximum 1,5 s
voltage transients recovery time
Voltage unbalance 7 % Including phase voltage unbalance as a result
of unbalance of load.
Voltages are root mean square (RMS) unless otherwise stated.
a
After a transient condition has been initiated, the voltage in a main distribution system shall not differ from
the voltage before the transient was initiated by more than ±3 % within 1,5 s. In an emergency system the
limit is ±4% within 5 s.
The transient voltage drop at the point where equipment is installed can be up to −20 %. The
correct operating condition for a contactor is based upon a value of the control supply voltage
not less than 85 % of its rated value. The contactor shall not drop at a voltage above 75 % of
the rated control supply voltage.
The sum of voltage excursions at any point on the system (tolerances and transients) from
+20
nominal voltage should not exceed %.
−20
The requirements for voltage tolerances are valid for local generation (voltage controlled by
generator AVR). When power is supplied from sources external to the unit (voltage controlled
by transformer OLTC, on-load tap changer), it may not be possible to obtain these values.
4.5.2.3 Harmonic distortion (voltage waveform)
For voltage harmonic distortion, acceptance limits shall correspond to IEC 61000-2-4:2002,
Class 1.
Distorting equipment emission levels shall be such that the above limits shall not be exceeded
in normal operating conditions.

When operating with split sections (i.e. an open bus-tie breaker or an out-of-service
component such as a filter), the limits of IEC 61000-2-4:2002, Class 2 may be accepted.
For certain electrical installations, where it is confirmed by design study that it is not practical
to comply with the requirements of IEC 61000-2-4:2002, Class 1, higher values, as given in
Class 2 may be accepted, provided the generation and distribution equipment as well as
consumers are designed to operate at such higher limits.
IEC 61000-2-4:2002 (Table 2 and Table 5) Class 1, states that no single harmonic shall
exceed 3 % and the THD shall not exceed 5 %.
IEC 61000-2-4:2002 (Table 2 and Table 5) Class 2, states that no single harmonic shall
exceed 6 % and the THD shall not exceed 8 %.
4.5.2.4 Frequency characteristics
Requirements for frequency characteristics are given in Table 2. Tolerances are expressed as
a percentage of the nominal frequency.
Table 2 – Frequency characteristics
System withstand requirements
Frequency characteristics Value Comments
Frequency tolerance (continuous) +5 % Steady state frequency tolerance which
consumers in general shall withstand.
−5 %
Cyclic frequency variation 0,5 %
(continuous)
Frequency transient tolerance +10 % Transient frequency tolerance which
consumers in general shall
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