IEC 61225:2019

IEC 61225 ®
Edition 3.0 2019-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear power plants – Instrumentation, control and electrical power systems –
Requirements for static uninterruptible DC and AC power supply systems

Centrales nucléaires de puissance – Systèmes d'instrumentation, de contrôle-
commande et d'alimentation électrique – Exigences pour les systèmes
d'alimentation en courant alternatif et en courant continu statiques sans
interruption
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IEC 61225 ®
Edition 3.0 2019-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Nuclear power plants – Instrumentation, control and electrical power systems –

Requirements for static uninterruptible DC and AC power supply systems

Centrales nucléaires de puissance – Systèmes d'instrumentation, de contrôle-

commande et d'alimentation électrique – Exigences pour les systèmes

d'alimentation en courant alternatif et en courant continu statiques sans

interruption
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.120.20 ISBN 978-2-8322-6382-2

– 2 – IEC 61225:2019 © IEC 2019
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Abbreviated terms . 11
5 System requirements . 11
5.1 General . 11
5.2 Function and description . 12
5.2.1 Preamble . 12
5.2.2 Designations . 14
5.2.3 Direct current systems . 14
5.2.4 Alternating current systems . 14
5.3 System divisions . 15
5.4 System boundaries . 15
6 Functional requirements for static uninterruptible power supplies . 15
6.1 Static uninterruptible power supplies for systems important to safety . 15
6.2 Batteries and battery chargers . 16
6.3 Inverters and bypass switches . 17
6.4 UPS . 18
6.5 Converters used for voltage stabilization . 18
6.6 I&C power supply using DC/DC-converters and AC/DC-converters . 19
7 Requirements for distribution systems . 19
7.1 System aspects . 19
7.2 Load allocation . 19
7.3 Electrical aspects . 21
7.4 Earthing . 22
8 Effects of loads on supply quality. 22
8.1 General . 22
8.2 Electromagnetic interference. 22
8.3 Transients . 22
8.4 Load current . 23
8.5 Power supplies to loads of lower safety classification. 23
9 Monitoring and protection . 23
9.1 General . 23
9.2 Monitoring . 24
9.3 Electrical protection . 24
10 Qualification of equipment . 25
11 Design to cope with ageing . 25
12 Testing . 25
13 Maintenance . 26
Annex A (informative)  Examples of voltage input variations . 27
Annex B (informative) Examples of specifications . 29
B.1 Example 1: Specification for an DC power supply for equipment requiring a
non-interruptible supply. 29

B.2 Example 2: Specification for AC power supply for equipment requiring a non-
interruptible supply . 30
B.3 Example 3: Specification for DC power supply with DC/DC converter for
equipment . 31
B.4 Human factor engineering programme . 31
Bibliography . 33

Figure 1 – System boundary . 13
Figure 2 – Example of one division of an uninterruptible power supply system . 20
Figure 3 – Example of I&C uninterruptible AC power supply system . 21
Figure A.1 – Example of voltage variations on the on-site AC power system during
clearing of a transmission system fault . 27
Figure A.2 – Example of on-site voltage profile after loss of load (transfer to house
load operation). 27
Figure A.3 – Example of simulated safety bus voltages, double open phase condition

in the 400 kV line to the unit transformer . 28

Table B.1 – Example 1 . 29
Table B.2 – Example 2 . 30
Table B.3 – Example 3 . 31

– 4 – IEC 61225:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
NUCLEAR POWER PLANTS – INSTRUMENTATION, CONTROL AND
ELECTRICAL POWER SYSTEMS – REQUIREMENTS FOR STATIC
UNINTERRUPTIBLE DC AND AC POWER SUPPLY 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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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International Standard IEC 61225 has been prepared by subcommittee 45A: Instrumentation,
control and electrical power systems of nuclear facilities, of IEC technical committee 45:
Nuclear instrumentation.
This third edition cancels and replaces the second edition published in 2005. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) the principal objective of this edition is to address the requirements on the static
uninterruptible power supplies in nuclear power plants;
b) in addition to Instrumentation and Control (I&C) power supplies include all static
uninterruptible power supplies;

c) emphasize that the static uninterruptible power supplies shall protect the connected
equipment (loads) from transients on the on-site AC distribution system (the immunity
concept);
d) in accordance with the defence-in-depth concept, this standard applies to static
uninterruptible power supplies for all equipment, not only for equipment important to
safety, with a graded approach to verification and validation;
e) addition of the requirement that, when batteries are connected in parallel under abnormal
operating conditions, they shall be properly protected with isolation devices to avoid any
failure that may impair more than one division of the uninterruptible power supply.
The text of this International Standard is based on the following documents:
FDIS Report on voting
45A/1235/FDIS 45A/1250/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.
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.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC 61225:2019 © IEC 2019
INTRODUCTION
a) Technical background, main issues and organization of the standard
The 1993 issue of IEC 61225 was developed for specifying the requirements relevant to
the design of electrical supplies for I&C systems in nuclear power plants. Considering the
experience gathered worldwide on this subject, in 2003 working group A2 recommended a
revision to this standard so that a new revision, IEC 61225 Ed. 2 (2005), could be
consistently integrated into the SC 45A standard series. In 2015, working group A11
recommended a revision to this standard following the publication of the revision of IAEA
SSG-34 and that the scope of the standard should cover static uninterruptible power
supplies for all types of connected equipment.
International operating experience with electrical supply systems in nuclear power plants
has highlighted a number of supply voltage variations and malfunctions, such as:
– voltage perturbations due to disturbances on the internal AC distribution system (with
origin off-site or on-site);
– voltage overshoot on loss of grid;
– open phase conditions (one or two phases);
– asymmetrical faults.
These types of perturbations can degrade the performance of static uninterruptible power
supplies and ultimately result in failure of connected equipment.
One of the objectives of the uninterruptible power supplies is to protect the connected
equipment from voltage variations on the on-site AC distribution system (the immunity
concept). The power supplies shall also guarantee an output voltage with specified
magnitude and waveform (in case of AC) to connected loads. The power supplies shall
have the capacity to supply the relevant loads during a specified time regardless of any
voltage variations on the on-site AC distribution system.
Examples of voltage and frequency variations in the incoming feeder to the supplies can
be found in informative Annex A. Examples of specifications for static uninterruptible
power supplies can be found in informative Annex B.
This standard is applicable to the design of static uninterruptible electrical power supplies
in new nuclear power plants, when design work is initiated after the publication of this
standard. It also serves as a reference for upgrading and modernizing existing nuclear
power plants.
b) Situation of the current standard in the structure of the SC 45A standard series
IEC 61225 is a second level document specifically addressing the particular topic of
requirements for electrical supplies.
For more details on the structure of the SC 45A standard series, see item d) of this
introduction.
c) Recommendations and limitations regarding the application of this standard
This standard is to be applied in conjunction with IEC 61513, IEC 60709, IEC 60880,
IEC 62138, IEC 62855 and IEC 63046 (to be published).
d) Description of the structure of the IEC SC 45A standard series and relationships
with other IEC documents and other bodies documents (IAEA, ISO)
The top-level documents of the IEC SC 45A standard series are IEC 61513 and
IEC 63046. IEC 61513 provides general requirements for I&C systems and equipment that
are used to perform functions important to safety in NPPs. IEC 63046 provides general
requirements for electrical power systems of NPPs; it covers power supply systems
including the supply systems of the I&C systems. IEC 61513 and IEC 63046 are to be
considered in conjunction and at the same level. IEC 61513 and IEC 63046 structure the
IEC SC 45A standard series and shape a complete framework establishing general
requirements for instrumentation, control and electrical systems for nuclear power plants.
IEC 61513 and IEC 63046 refer directly to other IEC SC 45A standards for general topics
related to categorization of functions and classification of systems, qualification,
separation, defence against common cause failure, control room design, electromagnetic

compatibility, cybersecurity, software and hardware aspects for programmable digital
systems, coordination of safety and security requirements and management of ageing.
The standards referenced directly at this second level should be considered together with
IEC 61513 and IEC 63046 as a consistent document set.
At a third level, IEC SC 45A standards not directly referenced by IEC 61513 or by
IEC 63046 are standards related to specific equipment, technical methods, or specific
activities. Usually these documents, which make reference to second-level documents for
general topics, can be used on their own.
A fourth level extending the IEC SC 45 standard series, corresponds to the Technical
Reports which are not normative.
The IEC SC 45A standards series consistently implements and details the safety and
security principles and basic aspects provided in the relevant IAEA safety standards and
in the relevant documents of the IAEA nuclear security series (NSS). In particular this
includes the IAEA requirements SSR-2/1, establishing safety requirements related to the
design of nuclear power plants (NPPs), the IAEA safety guide SSG-30 dealing with the
safety classification of structures, systems and components in NPPs, the IAEA safety
guide SSG-39 dealing with the design of instrumentation and control systems for NPPs,
the IAEA safety guide SSG-34 dealing with the design of electrical power systems for
NPPs and the implementing guide NSS17 for computer security at nuclear facilities. The
safety and security terminology and definitions used by SC 45A standards are consistent
with those used by the IAEA.
IEC 61513 and IEC 63046 have adopted a presentation format similar to the basic safety
publication IEC 61508 with an overall life-cycle framework and a system life-cycle
framework. Regarding nuclear safety, IEC 61513 and IEC 63046 provide the interpretation
of the general requirements of IEC 61508-1, IEC 61508-2 and IEC 61508-4, for the
nuclear application sector. In this framework IEC 60880, IEC 62138 and IEC 62566
correspond to IEC 61508-3 for the nuclear application sector. IEC 61513 and IEC 63046
refer to ISO as well as to IAEA GS-R part 2 and IAEA GS-G-3.1 and IAEA GS-G-3.5 for
topics related to quality assurance (QA). At level 2, regarding nuclear security, IEC 62645
is the entry document for the IEC/SC 45A security standards. It builds upon the valid high
level principles and main concepts of the generic security standards, in particular
ISO/IEC 27001 and ISO/IEC 27002; it adapts them and completes them to fit the nuclear
context and coordinates with the IEC 62443 series. At level 2, IEC 60964 is the entry
document for the IEC/SC 45A control rooms standards and IEC 62342 is the entry
document for the ageing management standards.
NOTE 1 It is assumed that for the design of I&C systems in NPPs that implement conventional safety
functions (e.g. to address worker safety, asset protection, chemical hazards, process energy hazards)
international or national standards would be applied.
NOTE 2 IEC/SC 45A domain was extended in 2013 to cover electrical systems. In 2014 and 2015 discussions
were held in IEC/SC 45A to decide how and where general requirements for the design of electrical systems
were to be considered. IEC/SC 45A experts recommended that an independent standard be developed at the
same level as IEC 61513 to establish general requirements for electrical systems. Project IEC 63046 is now
launched to cover this objective. When IEC 63046 is published, this NOTE 2 of the introduction of IEC/SC 45A
standards will be suppressed.
– 8 – IEC 61225:2019 © IEC 2019
NUCLEAR POWER PLANTS – INSTRUMENTATION, CONTROL AND
ELECTRICAL POWER SYSTEMS – REQUIREMENTS FOR STATIC
UNINTERRUPTIBLE DC AND AC POWER SUPPLY SYSTEMS

1 Scope
This document specifies the performance and the functional characteristics of the low voltage
static uninterruptible power supply (SUPS) systems in a nuclear power plant and, for
applicable parts, in general for nuclear facilities. An uninterruptible power supply is an
electrical equipment which draws electrical energy from a source, stores it and maintains
supply in a specified form by means inside the equipment to output terminals. A static
uninterruptible power supply (SUPS) has no rotating parts to perform its functions.
The specific design requirements for the components of the power supply system are covered
by IEC standards and standards listed in the normative references and are otherwise outside
the scope of this document.
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 60038, IEC standard voltages
IEC 60146-1-1, Semiconductor converters – General requirements and line commutated
converters – Part 1-1: Specification of basic requirements
IEC 60146-2, Semiconductor converters – Part 2: Self-commutated semiconductor converters
including direct d.c. converters
IEC 60364-4-41, Low voltage electrical installations – Part 4.41: Protection for safety –
Protection against electric shock
IEC 60709, Nuclear power plants – Instrumentation, control and electrical power systems
important to safety – Separation
IEC/IEEE 60780-323, Nuclear power plants – Electrical equipment important to safety –
Qualification
IEC 60880, Nuclear power plants – Instrumentation and control systems important to safety –
Software aspects for computer-based systems performing category A functions
IEC 60980, Recommended practices for seismic qualification of electrical equipment of the
safety system for nuclear generating stations
IEC 61000 (all parts), Electromagnetic compatibility (EMC)
IEC 61508 (all parts), Functional safety of electrical/electronic/programmable electronic
safety-related systems
IEC 61513, Nuclear power plants – Instrumentation and control important to safety – General
requirements for systems
IEC 62003, Nuclear power plants – Instrumentation and control important to safety –
Requirements for electromagnetic compatibility testing
IEC 62040 (all parts), Uninterruptible power systems (UPS)
IEC 62138, Nuclear power plants – Instrumentation and control systems important to safety –
Software aspects for computer-based systems performing category B or C functions
IEC 62566, Nuclear power plants – Instrumentation and control important to safety –
Development of HDL-programmed integrated circuits for systems performing category A
functions
IEC 62566-2, Nuclear power plants – Instrumentation and control important to safety –
Development of HDL-programmed integrated circuits – Part 2: HDL-programmed integrated
circuits for systems performing category B or C functions (to be published)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE Other terms not defined below are defined in IAEA Safety Guides SSG-34 and SSG-39.
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
3.1
anticipated operational occurrence
AOO
deviation of an operational process from normal operation that is expected to occur at least
once during the operating lifetime of a facility but which, in view of appropriate design
provisions, does not cause any significant damage to items important to safety or lead to
accident conditions
[SOURCE: Source IAEA Safety Glossary, 2016 edition]
3.2
battery charger
electrical item used to convert AC into DC to charge batteries and to supply power to DC
loads during normal operation
Note 1 to entry: The battery charger provides transformer isolation of the DC output from the AC input and is
equipped with regulation and monitoring.
[SOURCE: IEEE 946, 2004]
3.3
common cause failure
CCF
failures of two or more structures, systems and components due to a single specific event or
cause
[SOURCE: IAEA Safety Glossary, 2016 edition]

– 10 – IEC 61225:2019 © IEC 2019
3.4
diversity
the presence of two or more independent (redundant) systems or components to perform an
identified function, where the different systems or components have different attributes so as
to reduce the possibility of common cause failure, including common mode failure
[SOURCE: IAEA Safety Glossary, 2016 edition]
3.5
division
collection of items, including their interconnections, that form one redundancy of a redundant
system or safety group
Note 1 to entry: Divisions may include multiple channels.
Note 2 to entry: Designation that enables the establishment and maintenance of physical, electrical, and
functional independence from other redundant sets of items.
[SOURCE: IAEA SSG-39, 2016]
3.6
plant states
Operational states Accident conditions
Normal operation Anticipated Design basis Design extension conditions
operational accidents
Without significant fuel With core melting
occurrences
degradation
[SOURCE: IAEA Safety Glossary, 2016 edition]
3.7
redundancy
provision of alternative (identical or diverse) structures, systems and components, so that any
one can perform the required function regardless of the state of operation or failure of any
other
[SOURCE: IAEA Safety Glossary, 2016 edition]
3.8
safety related system
system important to safety that is not part of a safety system
[SOURCE: IAEA Safety Glossary, 2016 edition]
3.9
safety system
system important to safety, provided to ensure the safe shutdown of the reactor or residual
heat removal from the core, or to limit the consequences of anticipated operational
occurrences and design basis accidents
[SOURCE: IAEA Safety Glossary, 2016 edition]
3.10
single failure
failure which results in the loss of capability of a single system or component to perform its
intended safety function(s), and any consequential failure(s) which result from it

[SOURCE: IAEA Safety Glossary, 2016 edition]
3.11
single failure criterion
criterion (or requirement) applied to a system such that it must be capable of performing its
task in the presence of any single failure
[SOURCE: IAEA Safety Glossary, 2016 edition]
3.12
station blackout
SBO
plant condition with complete loss of all AC power from off-site sources, from the main
generator and from standby AC power sources
Note 1 to entry: Uninterruptible DC and AC power supplies may be available as long as batteries can supply the
loads.é
Note 2 to entry: Alternate AC supplies according to IAEA SSG-34 are available.
[SOURCE: IAEA SSG-34, 2016]
4 Abbreviated terms
AC Alternating current
AOO Anticipated operational occurrence
CCF Common cause failure
DC Direct current
EMC Electromagnetic compatibility
I&C Instrumentation and control
IGBT Insulated-Gate Bipolar Transistor
NPP Nuclear Power Plant
SBO Station blackout
SSC Structures, systems and components
SUPS Static uninterruptible power supply
UPS Uninterruptible power supply
5 System requirements
5.1 General
This document defines requirements for reliable and robust SUPS systems in nuclear power
plants (NPPs). Even though more stringent criteria are applied to safety power supplies and
more verification is necessary, the entire onsite and off-site power systems contribute to the
reliability and robustness of the NPP power systems. It is recommended that the same
requirements are applied to SUPS systems regardless of safety classification with a graded
approach to verification and validation.
Robust power supply systems shall have sufficient margins and built-in conservatism to
ensure that:
• equipment ratings, capabilities and capacities required to meet intended goals are not
exceeded during all postulated conditions;

– 12 – IEC 61225:2019 © IEC 2019
• equipment protection set points are selected to accommodate anticipated perturbations in
the NPP electrical distribution system during all modes of operation;
• the equipment has the capacity and capability to support emergency operations.
The design of the power supplies shall include analysis of:
• transient, dynamic and quasi-stationary variations in voltage and frequency (in case of AC
power source);
• power interruptions (or voltage / frequency dips exceeding the allowed dynamic variation
range) lasting from milliseconds up to SBO conditions;
• asymmetrical conditions.
5.2 Function and description
5.2.1 Preamble
The SUPS system shall provide a continuous uninterruptible supply to each connected load
within the specified tolerances of voltage, and (for AC systems) waveform and frequency for
all input conditions.
SUPS generally consists of one or both of the following systems (see Figure 1):
• a DC power system with battery chargers and batteries, supplying DC loads;
• an AC power system with battery chargers, back-up batteries, static switches and
inverters, supplying AC loads.
In certain designs the battery chargers and batteries could be common to both the DC and AC
power system.
The functions and the classification of the power supplies should be designated according to
the safety classification scheme of the NPP. In general, the classification should be based on
the highest classification of the load supplied by the power supply as discussed in 7.2.
The constraints on connecting loads with different classifications are discussed in 8.5.

DC/DC converters, AC/DC converters and converters for voltage stabilization are not shown. Uninterruptible AC
power supply can also be provided by an UPS. An UPS is normally an integrated assembly of battery charger,
battery and inverter as shown on the right-hand side of the figure.
Figure 1 – System boundary
– 14 – IEC 61225:2019 © IEC 2019
5.2.2 Designations
Incoming feeder: The SUPS has an incoming feeder, generally from a low-voltage AC power
bus which is normally part of the electrical safety buses .
Outgoing feeder: The SUPS utilizes a set of battery charger/ battery or battery charger/
battery/ inverter system with an outgoing feeder that is connected to the distribution system.
The SUPS supplies the loads from a distribution system. (See Figure 1)
5.2.3 Direct current systems
Each division of an uninterruptible DC power supply system shall consist of at least:
• a battery;
• a battery charger;
• a distribution system.
In order to increase the availability and the robustness of the division, but also for increased
maintenance flexibility, the provision of internal redundancy in each division should be
considered. The provision of redundancy is discussed in 5.3.
The DC power supply system shall supply the DC loads during normal operation (including
outages), anticipated operational occurrences and accident conditions.
The DC power supply system shall supply the DC loads for a specified minimum duration
when power is lost on the incoming feeder with no perturbation of the outgoing feeder voltage
outside specified tolerances.
5.2.4 Alternating current systems
Each division of an uninterruptible AC power supply system shall consist of:
• a power supply from a DC power system to an inverter;
• alternatively, a power supply from an interruptible AC bus, a dedicated battery charger, a
battery and inverter;
• a distribution system.
A backup power supply to the distribution system from an interruptible AC bus shall be
installed together with a device for automatically switching between the power supply from the
inverter and the backup supply.
To increase the availability and the robustness of the division, but also for more flexibility for
maintenance, the provision of internal redundancy should be considered. The provision of
redundancy is discussed in 5.3.
The AC power supply system shall supply the AC loads during normal operation (including
outages), anticipated operational occurrences and accident conditions.
The AC power supply system shall supply the AC loads for a specified minimum time when
power is lost on the incoming feeder with no perturbation of the outgoing feeder voltage
outside specified tolerances.
___________
See figures in IAEA SSG-34.
Due to the higher reliability of DC systems, supplying a safety I&C system from the DC
system should be considered. If possible, a combination of DC and AC supply should be used
to minimize the risks of common mode failure. If only DC loads are supplied, the use of DC
supply should be the preferred solution. Such an approach eliminates a source of failure.
5.3 System divisions
The DC power supply system and the AC power supply system shall be divided into redundant
and independent divisions. The safety loads shall be supplied from at least one dedicated
supply source for each division, to ensure physical and functional separation. The required
number of redundant sources depends on the design of the reactor protection system and the
redundancy in the NPP design.
The power supplies for safety loads covered by this document shall be in accordance with the
single failure criterion as described in IEC 61513 and the requirements on separation and
failure tolerance described in IEC 60709.
The functional diversity of AC and DC systems shall be considered for I&C power supplies to
improve the availability of the overall power supply. The principle of independence and
diversity shall be applied to protect against credible common cause failures (CCF) that can
affect redundant parts which originate:
• in the equipment itself;
• from switching surges;
• from voltage and/or frequency excursions.
Examples of such events are given in Annex A.
The possibility of CCF shall be taken into account, e.g. by analysis and provision of defence
in depth, in the design, maintenance, testing and operation of the system.
5.4 System boundaries
The scope of this document covers the power supply system from the outgoing terminals of
the breaker to the battery charger up to the incoming breakers to each individual load (see
Figure 1).
Within the limits specified above, each system may include equipment such as transformers,
converters, battery chargers, inverters, cables, isolation devices, distribution boards,
switchover devices, central and local batteries, as well as switching, monitoring and protection
equipment.
If necessary, a load with lower safety classification within the same division may be supplied
from a bus supplying higher safety classified equipment subject to the provisions described
in 8.5.
6 Functional requirements for static uninterruptible power supplies
6.1 Static uninterruptible power supplies for systems important to safety
The SUPS may be subjected to electrical perturbations on the incoming feeder. These
transients should be identified and mitigated. Protection shall be provided to prevent
perturbations outside acceptable limits from affecting the outgoing feeder and distribution
system voltage (or frequency when applicable). The design of the SUPS shall make sure that
the connected equipment is shielded from these perturbations and variations.

– 16 – IEC 61225:2019 © IEC 2019
The output voltage to the loads (whether AC or DC) shall be maintained within specified limits
following a loss and restoration of power on the incoming feeder. The loads should be
assessed for their tolerance to short interruptions of supply during changeover operations.
The design of the SUPS shall ensure that interruptions and perturbations of the input feeder
voltage do not affect the connected equipment in fulfilling its safety function.
Electromagnetic compatibility (EMC) requirements shall be taken into account, e.g. by
analysis, and adequate immunity shall be demonstrated. Components being
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