IEC TS 60364-7-725:2026

IEC TS 60364-7-725 ®
Edition 1.0 2026-01
TECHNICAL
SPECIFICATION
Low-voltage electrical installations -
Part 7-725: Requirements for special installations or locations - Resilient power
supply system
ICS 29.020  ISBN 978-2-8327-1021-0

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CONTENTS
FOREWORD . 3
INTRODUCTION . 5
725 Resilient power supply system . 6
725.1 Scope . 6
725.2 Normative references. 6
725.3 Terms and definitions . 6
725.31 Purposes, supplies and structure . 7
725.312 Conductor arrangement and system earthing . 7
725.313 Supplies . 7
725.314 Division of installation . 7
725.36 Continuity of service . 7
725.5 Selection and erection of electrical equipment . 7
725.51 Common rules . 7
725.512 Operational conditions and external influences . 7
725.52 Wiring systems. 9
725.522 Selection and erection of wiring systems in relation to external
influences . 9
725.55 Other equipment . 9
725.6 Verification . 10
Annex A (informative) Reference for non-specific disaster . 11
A.1 Examples of systems . 11
A.2 Example of connected loads . 14
Annex B (informative) Reference for earthquake-specific disaster . 16
B.1 Calculation of seismic force of electrical equipment and method to support
and fix it . 16
B.2 Installation example of a wiring installation . 20
Annex C (informative) Reference for flood damage-specific disaster . 23
C.1 Power supplies and switchboards . 23
C.2 Electrical equipment. 23
C.3 Wiring systems . 23
Annex D (informative) List of notes concerning certain countries . 24
Bibliography . 25

Figure A.1– Example of a system that switches from TT to the TN system during
independent operation . 12
Figure A.2 – Example of a system where supply diversity has been improved . 13
Figure B.1 – Example of calculating anchor bolts loads . 19
Figure B.2 – Example of seismic support for horizontal piping, etc. . 20
Figure B.3 – Example of installation of underground service cable to a building . 22
Figure B.4 – Example of wiring installation at an expansion joint . 22

Table A.1 – ‘Communication sheet’ to decide a specification of respective rooms in a
building in normal times and a performance in time of disaster . 15
Table B.1 – Standard seismic intensity for design (K ) . 16
s
Table B.2 – Correlation table of zone factor (Z) for peak ground acceleration (PGA) . 17
Table B.3 – Examples of specific facilities . 18
Table B.4 – Guideline of seismic class to importance of facility and equipment . 18
Table B.5 – Horizontal conduits, application of seismic support . 21
Table D.1 – Notes concerning certain countries . 24

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Low-voltage electrical installations -
Part 7-725: Requirements for special installations or locations -
Resilient power supply system
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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IEC TS 60364-7-725 has been prepared by IEC technical committee 64: Electrical installations
and protection against electric shock. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
64/2772/DTS 64/2816A/RVDTS
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 Specification 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.
A list of all parts in the IEC 60364 series, published under the general title Low voltage electrical
installations, can be found on the IEC website.
The reader's attention is drawn to the fact that Annex D lists all of the "in-some-country" clauses
on differing practices of a less permanent nature relating to the subject of this document.
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
For the purpose of this part of IEC 60364 (IEC 60364-7-725) the requirements of the general
Parts 1, 4, 5, 6 and 8 of IEC 60364 apply.
The IEC 60364-7-7XX parts of IEC 60364 contain particular requirements for special
installations or locations which are based on the requirements of the general parts of IEC 60364
(IEC 60364-1 to IEC 60364-6 and IEC 60364-8). These IEC 60364-7-7XX parts are considered
in conjunction with the requirements of the general parts.
The particular requirements of this part of IEC 60364 supplement, modify or replace certain of
the requirements of the general parts of IEC 60364 being valid at the time of publication of this
part. The absence of reference to the exclusion of a part or a clause of a general part means
that the corresponding clauses of the general part are applicable (undated references).
Requirements of other 7XX parts being relevant for installations covered by this document also
apply. This document can therefore also supplement, modify or replace certain of these
requirements valid at the time of publication of this document.
The clause numbering of this document follows the pattern and corresponding references of
IEC 60364. The numbers following the particular number of this document are those of the
corresponding parts, or clauses of the other parts of the IEC 60364 series, valid at the time of
publication of this document, as indicated in the normative references of this document (dated
references).
If requirements or explanations additional to those of the other parts of the IEC 60364 series
are needed, the numbering of such items appears as 725.101, 725.102, 725.103, etc. In the
case where new or amended general parts with modified numbering were published after this
document was issued, the clause numbers referring to a general part in this document will
possibly no longer align with the latest edition of the general part. Dated references should be
observed.
The clause numbers following 725 are those of the corresponding parts or clauses of IEC 60364.
The absence of reference to a part or a clause means that all parts of IEC 60364 are applicable.

725 Resilient power supply system
725.1 Scope
This part of IEC 60364 provides additional requirements for the design, erection and verification
of electrical installations applicable for resilient power supply systems that must be operational
in a time of disaster. It specifies additional requirements for
– generating sets,
– a circuit concerning external generating sets, and
– circuits of an installation to be supplied
so as to prevent or limit the effects of a natural disaster such as
– earthquake,
– flood damage, or
– wind hazard (e.g. tropical cyclone such as hurricane, typhoon).
725.2 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 60364-1:2005, Low-voltage electrical installations - Part 1: Fundamental principles,
assessment of general characteristics, definitions
IEC 60364-5-51, Electrical installations of buildings - Part 5-51: Selection and erection of
electrical equipment - Common rules
IEC 60364-5-52, Electrical installations of buildings - Part 5-52: Selection and erection of
electrical equipment - Wiring systems
IEC 60364-5-55, Electrical installations of buildings - Part 5-55: Selection and erection of
electrical equipment - Other equipment
IEC 60364-6, Low-voltage electrical installations - Part 6: Verification
725.3 Terms and definitions
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
725.3.1
essential load
current-using equipment intended to be supplied even during or after a natural disaster
725.31 Purposes, supplies and structure
725.312 Conductor arrangement and system earthing
725.312.2 Type of system earthing
725.312.2.101 Electric system according to operating modes
Where the type of earthing system of the network is different from the type of system earthing
of the local source, protection for safety shall be effective for each operational source.
NOTE An example of the transition from grid connected mode supplied by a TT system to island mode supplied by
a local source in a TN system is given in Figure A.1.
725.313 Supplies
725.313.101 Connection of external supplies
In addition to the provision of a suitable means of earthing, consideration should be given to
the provision of connections which allow the rapid connection of external supplies.
725.314 Division of installation
725.314.101
For the division of installation, the following requirements shall be fulfilled.
– The power supply shall achieve the reliability required in island mode operation, e.g. by
having multiple distributed power sources connected in parallel.
– The installation shall be configured so that a fault of one or more of its power sources will
not likely result in an entire failure of the power supply.
– The current-using equipment, devices and supplies of the installation intended to be used
during a disaster shall be installed in such a way that they can be quickly maintained,
repaired or replaced.
– The circuits to be supplied in the event of a natural disaster shall be identified.
NOTE Annex A provides examples of systems which satisfy the requirements.
725.36 Continuity of service
After a disaster occurs, circuits supplying essential loads shall be re-energized within a time
that is decided according to the nature of each essential load.
725.5 Selection and erection of electrical equipment
725.51 Common rules
NOTE Requirements for electrical and mechanical characteristics for the selection and erection of electrical
equipment against wind hazard and floods are under consideration.
725.512 Operational conditions and external influences
725.512.2 External influences
725.512.2.101 Installed electrical equipment shall have an AP rating of at least that required
by the location at which it is installed. For electrical equipment installed in a building, the storey
level where the electrical equipment is installed shall also be taken into account. Otherwise,
the minimum required AP level shall be assumed to be AP3.
Where the acceleration factor is known, the minimum AP level shall be selected according to
the place where the resilient power supply system is installed. Otherwise, the minimum AP level
shall be AP3.
NOTE The symbol AP (seismic effects) as in Table 51A is considered.
725.512.2.102 Where the installation is required to be resilient to seismic effect, equipment
shall be selected to withstand the values of F and F .
V H
and F are already determined, e.g. by special analysis, seismic
Except where the value of F
H V
force applied to electrical equipment by an earthquake shall be calculated as shown below. The
acceleration of the ground arising from the earthquake is transmitted to the electrical equipment
through its mountings. The force is equal to the ground acceleration multiplied by the mass of
the equipment acting through its centre of gravity. The ground acceleration, which can be in
any direction, is often expressed as a submultiple of the acceleration due to gravity.
a) Seismic force is the combined force of horizontal seismic design force (F ) and vertical
H
seismic design force (F ).
V
b) In principle, the point of action shall be the centre of gravity of the electrical equipment.
c) The value of horizontal seismic design force (F ), in kilonewtons (kN), shall be calculated
H
by the formulae below:
F KW⋅
H H
K ZK⋅
HS
where
K is the coefficient to estimate the horizontal force from the horizontal acceleration from
H
the local force of gravity;
W is the weight of the equipment (kN);
K is a constant decided according to the floor and the type of the building, according to
S
B.1.1.2;
Z is the zone factor, according to B.1.1.3 (shall be 1,0 for a normal condition).
The value of vertical seismic design force (F ) shall be calculated by the formulae below:
V
F KW⋅
VV
KK= 2
VH
where
K is the vertical seismic design intensity.
V
NOTE Annex B provides tables of the constants referenced in the above formulas.
725.512.2.103 Loads intended to be used in island mode shall be selected in advance. The
system shall have a power supply which can deliver sufficient power to operate the selected
loads intended to be used in island mode.
The size of the building, its purpose and required functions in case of disaster shall be taken
into consideration to determine the loads.
NOTE An example of determination of loads in island mode operation is shown in Clause A.2.
725.512.2.104 Electrical equipment shall be securely fixed to a structure of a building or to
the base of an anti-seismic device by an ancho
...