ISO/IEC 22237-3:2021

INTERNATIONAL ISO/IEC
STANDARD 22237-3
First edition
2021-10
Information technology — Data centre
facilities and infrastructures —
Part 3:
Power distribution
Technologie de l’information — Installation et infrastructures de
centres de traitement de données —
Partie 3: Distribution de puissance
Reference number
© ISO/IEC 2021
© ISO/IEC 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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© ISO/IEC 2021 – All rights reserved

Contents Page
Foreword .v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 2
3.1 Terms and definitions . 2
3.2 Abbreviated terms . 6
3.3 Symbols . 6
4 Conformance . 7
5 Power supply and distribution within data centres . 7
5.1 Functional elements. 7
5.1.1 General . 7
5.1.2 Power supply to the data centre . 8
5.1.3 Power distribution within the data centre . 9
5.2 Dimensioning of power distribution systems . 10
6 Availability .11
6.1 General requirements . 11
6.2 Power supply . 11
6.2.1 Capacity planning . 11
6.2.2 Availability of the utility supply . 13
6.2.3 Power quality . 14
6.2.4 Load presented to the utility supply. 15
6.2.5 Equipment . 15
6.2.6 Availability Class design options . 17
6.3 Power distribution .23
6.3.1 Capacity planning . 23
6.3.2 Power quality . 24
6.3.3 Equipment . 25
6.3.4 Availability Class design options . 25
6.4 Incorporation of low voltage direct current distribution .29
6.5 Additional considerations . 29
6.5.1 Residual current measurement .29
6.5.2 Lightning and surge protection .29
6.5.3 Segregation of power distribution cabling and information technology
cabling . 30
6.6 Emergency power off (EPO). 30
6.6.1 Requirements .30
6.6.2 Recommendations.30
7 Physical security .30
7.1 General .30
7.2 Access. 30
7.2.1 Power supply . .30
7.2.2 Power distribution .30
7.2.3 Attachment of unauthorized end-equipment .30
7.3 Internal environmental events . 31
7.3.1 Power supply . . 31
7.3.2 Power distribution . 31
7.4 External environmental events . 31
8 Energy efficiency enablement and power distribution .31
8.1 General . 31
8.2 Granularity Level 1 . 32
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8.2.1 Requirements . 32
8.2.2 Recommendations.33
8.3 Granularity Level 2 . 33
8.3.1 Requirements . 33
8.3.2 Recommendations. 33
8.4 Granularity Level 3 .34
8.4.1 Requirements .34
8.4.2 Recommendations.34
8.5 Cabling infrastructure to support energy efficiency enablement .34
Bibliography .35
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Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are
members of ISO or IEC participate in the development of International Standards through technical
committees established by the respective organization to deal with particular fields of technical
activity. ISO and IEC technical committees collaborate in fields of mutual interest. Other international
organizations, governmental and non-governmental, in liaison with ISO and IEC, also take part in the
work.
The procedures used to develop this document and those intended for its further maintenance
are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria
needed for the different types of document should be noted. This document was drafted in
accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives or
www.iec.ch/members_experts/refdocs).
Attention is drawn to the possibility that some of the elements of this document may be the subject
of patent rights. ISO and IEC shall not be held responsible for identifying any or all such patent
rights. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents) or the IEC
list of patent declarations received (see patents.iec.ch).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www.iso.org/iso/foreword.html. In the IEC, see www.iec.ch/understanding-standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 39, Sustainability, IT & Data Centres.
This first edition cancels and replaces the first edition (ISO/IEC TS 22237-3:2018), which has been
technically revised.
The main changes are as follows:
— availability requirements have been aligned with ISO/IEC 22237-1 and ISO/IEC 22237-4;
— figures have been updated.
A list of all parts in the ISO/IEC 22237 series can be found on the ISO and IEC websites.
Any feedback or questions on this document should be directed to the user’s national standards
body. A complete listing of these bodies can be found at www.iso.org/members.html and
www.iec.ch/national-committees.
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Introduction
The unrestricted access to internet-based information demanded by the information society has led to
an exponential growth of both internet traffic and the volume of stored/retrieved data. Data centres
are housing and supporting the information technology and network telecommunications equipment
for data processing, data storage and data transport. They are required both by network operators
(delivering those services to customer premises) and by enterprises within those customer premises.
Data centres need to provide modular, scalable and flexible facilities and infrastructures to easily
accommodate the rapidly changing requirements of the market. In addition, energy consumption
of data centres has become critical, both from an environmental point of view (reduction of carbon
footprint), and with respect to economic considerations (cost of energy) for the data centre operator.
The implementation of data centres varies in terms of:
a) purpose (enterprise, co-location, co-hosting or network operator facilities);
b) security level;
c) physical size; and
d) accommodation (mobile, temporary and permanent constructions).
NOTE Cloud services can be provided by all data centre types mentioned.
The needs of data centres also vary in terms of availability of service, the provision of security and
the objectives for energy efficiency. These needs and objectives influence the design of data centres in
terms of building construction, power distribution, environmental control, telecommunications cabling
and physical security. Effective management and operational information are required to monitor
achievement of the defined needs and objectives.
The ISO/IEC 22237 series specifies requirements and recommendations to support the various parties
involved in the design, planning, procurement, integration, installation, operation and maintenance of
facilities and infrastructures within data centres. These parties include:
1) owners, operators, facility managers, ICT managers, project managers, main contractors;
2) consultants, architects, building designers and builders, system and installation designers, auditors
and commissioning agents;
3) suppliers of equipment; and
4) installers, maintainers.
At the time of publication of this document, the ISO/IEC 22237 series comprises the following
documents:
— ISO/IEC 22237-1, Information technology — Data centre facilities and infrastructures — Part 1:
General concepts;
— ISO/IEC TS 22237-2, Information technology — Data centre facilities and infrastructures — Part 2:
Building construction;
— ISO/IEC 22237-3 (this document), Information technology — Data centre facilities and infrastructures —
Part 3: Power distribution;
— ISO/IEC 22237-4, Information technology — Data centre facilities and infrastructures — Part 4:
Environmental control;
— ISO/IEC TS 22237-5, Information technology — Data centre facilities and infrastructures — Part 5:
Telecommunications cabling infrastructure;
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— ISO/IEC TS 22237-6, Information technology — Data centre facilities and infrastructures — Part 6:
Security systems;
— ISO/IEC TS 22237-7: Information technology — Data centre facilities and infrastructures — Part 7:
Management and operational information.
The inter-relationship of the specifications within the ISO/IEC 22237 series is shown in Figure 1.
Figure 1 — Schematic relationship between the ISO/IEC 22237 series of documents
ISO/IEC TS 22237-2 to ISO/IEC TS 22237-6 specify requirements and recommendations for particular
facilities and infrastructures to support the relevant classification for “availability”, “physical security”
and “energy efficiency enablement” selected from ISO/IEC 22237-1.
This document, ISO/IEC 22237-3, addresses facilities and infrastructures for power supplies to, and
power distribution within, data centres together with the interfaces for monitoring the performance
of those facilities and infrastructures in line with ISO/IEC TS 22237-7 (in accordance with the
requirements of ISO/IEC 22237-1). The line diagrams used in certain figures are not intended to replace
the more familiar electrical circuit diagrams associated with power supply and distribution systems,
which are included where relevant.
ISO/IEC TS 22237-7 addresses operational and management information (in accordance with the
requirements of ISO/IEC 22237-1).
This document is intended for use by and collaboration between architects, building designers and
builders, and system and installation designers.
The ISO/IEC 22237 series does not address the selection of information technology and network
telecommunications equipment, software and associated configuration issues.
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© ISO/IEC 2021 – All rights reserved

INTERNATIONAL STANDARD ISO/IEC 22237-3:2021(E)
Information technology — Data centre facilities and
infrastructures —
Part 3:
Power distribution
1 Scope
This document addresses power supplies to, and power distribution within, data centres based upon
the criteria and classifications for “availability”, “physical security” and “energy efficiency enablement”
within ISO/IEC 22237-1.
This document specifies requirements and recommendations for the following:
a) power supplies to data centres;
b) power distribution systems to all equipment within data centres;
c) telecommunications infrastructure bonding;
d) lightning protection;
e) devices for the measurement of the power consumption and power quality characteristics at points
along the power distribution system and their integration within management tools.
Safety and electromagnetic compatibility (EMC) requirements are outside the scope of this document
and are covered by other standards and regulations. However, information given in this document can
be of assistance in meeting these standards and regulations.
Conformance of data centres to the present document is covered in Clause 4.
The use of the data centre stored energy or alternate sources to be used by the grid is not in the scope of
this document and is for consideration in future specifications.
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.
EN 13160 (all parts), Leak detection systems
IEC 60076-11, Power transformers — Part 11: Dry-type transformers
IEC 60364 (all parts), Low-voltage electrical installations
IEC 60947 (all parts), Low-voltage switchgear and controlgear
IEC 61000-2-4, Electromagnetic compatibility (EMC) — Part 2-4: Environment — Compatibility levels in
industrial plants for low-frequency conducted disturbances
IEC 61439 (all parts), Low-voltage switchgear and controlgear assemblies
© ISO/IEC 2021 – All rights reserved

IEC 61557-12, Electrical safety in low voltage distribution systems up to 1 000 V a.c. and 1 500 V d.c. —
Equipment for testing, measuring or monitoring of protective measures — Part 12: Performance measuring
and monitoring devices (PMD)
IEC 61869-2:2012, Instrument transformers — Part 2: Additional requirements for current transformers
IEC 62040 (all parts), Uninterruptible power systems (UPS)
IEC 62053-21, Electricity metering equipment (a.c.) — Particular requirements — Part 21: Static meters
for active energy (classes 1 and 2)
IEC 62053-22, Electricity metering equipment (a.c.) — Particular requirements — Part 22: Static meters
for active energy (classes 0,2 S and 0,5 S)
IEC 62271-200, High-voltage switchgear and controlgear — Part 200. AC metal-enclosed switchgear and
controlgear for rated voltages above 1 kV and up to and including 52 kV
IEC 62305 (all parts), Protection against lightning
IEC 62586-1, Power quality measurement in power supply systems — Part 1: Power quality instruments
(PQI)
IEC 62586-2, Power quality measurement in power supply systems — Part 2: Functional tests and
uncertainty requirements
IEC 62974-1, Monitoring and measuring systems used for data collection, gathering and analysis — Part 1:
Device requirements
IEC 88528-11, Reciprocating internal combustion engine driven alternating current generating sets —
Part 11: Rotary uninterruptible power systems — Performance requirements and test methods
IEC/TS 62749, Assessment of power quality — Characteristics of electricity supplied by public networks
ISO/IEC 22237-1, Information technology — Data centre facilities and infrastructures — Part 1: General
concepts
ISO/IEC 22237-4, Information technology — Data centre facilities and infrastructures — Part 4:
Environmental control
ISO/IEC/TS 22237-6, Information technology — Data centre facilities and infrastructures — Part 6:
Security systems
ISO/IEC 30129, Information technology — Telecommunications bonding networks for buildings and other
structures
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 22237-1 and the following
apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
© ISO/IEC 2021 – All rights reserved

3.1.1
active power
P
under periodic conditions, mean value, taken over one period, T, of the instantaneous power, p:
T
P = ∫ ptd
T
Note 1 to entry: Under sinusoidal conditions, the active power is the real part of the complex power S, thus
P = Re S.
Note 2 to entry: The coherent SI unit for active power is watt, W.
[SOURCE: IEC 60050-131:2002, 131-11-42]
3.1.2
additional supply
power supply that provides power in the event of failure of primary (3.1.22) and/or secondary supply
(3.1.24)
3.1.3
apparent power
product of the r.m.s. voltage U between the terminals of a two-terminal element or two-terminal circuit
and the r.m.s. electric current I in the element or circuit S = UI
Note 1 to entry: Under sinusoidal conditions, the apparent power is the modulus of the complex power S,
thus S = |S|.
Note 2 to entry: The coherent SI unit for apparent power is voltampere, VA.
[SOURCE: IEC 60050-131:2002, 131-11-41]
3.1.4
capacitive load
load that is capacitive, so that the alternating current is out of phase with and leads the voltage
3.1.5
catenary
wire hung at a specific tension between supporting structures of power cabling
3.1.6
diverse route
alternative separate pathway intended to provide adequate segregation from another pathway, in order
to maintain service provision in the event of physical damage to one of the pathways
3.1.7
dual-corded equipment
equipment served by multiple power supply input interfaces
3.1.8
emergency power off
EPO
designated device to provide emergency switching which disconnects power from one or more data
centre facilities, infrastructures or spaces
Note 1 to entry: The configuration and function of emergency power off devices can be subject to national or
local regulations.
3.1.9
fire compartment
discrete zone designed to contain a fire within that zone
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3.1.10
high voltage
HV
voltage whose nominal r.m.s. value is 35 kV < U ≤ 230 kV
N
Note 1 to entry: Because of existing network structures, in some countries the boundary between MV and HV can
be different.
3.1.11
inductive load
load that is inductive, so that the alternating current is out of phase with and lags behind the voltage
3.1.12
IT load
electrical consumption of all the information technology equipment, providing data storage, processing
and transport services, measured at its input terminals including all on-board integrated power
supplies and cooling fans
3.1.13
load factor
ratio, expressed as a numerical value or as a percentage, of the consumption within a specified period
(year, month, day, etc.), to the consumption that would result from continuous use of the maximum or
other specified demand occurring within the same period
Note 1 to entry: This term should not be used without specifying the demand and the period to which it relates.
Note 2 to entry: The load factor for a given demand is also equal to the ratio of the utilization time to the time in
hours within the same period.
[SOURCE: IEC 60050-691:1973, 691-10-02]
3.1.14
locally protected socket
sockets (3.1.26) which continue to deliver power to connected equipment for a defined period following
failure of power supply and distribution equipment by means of a battery supply or UPS adjacent to, or
co-located with, those sockets (e.g. emergency lighting)
3.1.15
low voltage
LV
voltage whose nominal r.m.s. value is U ≤ 1 kV
N
3.1.16
Main-Tie-Tie-Main
electrical connection between two power supply or power distribution circuits which allows current
to flow in either direction and containing two circuit breakers enabling maintenance while one of the
circuits is active
3.1.17
medium voltage
MV
voltage whose nominal r.m.s. value is 1 kV < U ≤ 35 kV
N
Note 1 to entry: Because of existing network structures, in some countries the boundary between MV and HV can
be different.
3.1.18
pathway
defined route for cables between termination points
[SOURCE: ISO/IEC 14763-2:2019, 3.1.34]
© ISO/IEC 2021 – All rights reserved

3.1.19
power factor
λ
under periodic conditions, ratio of the absolute value of the active power (3.1.1), P, to the apparent power
(3.1.3), S: λ = |P|/S
Note 1 to entry: This is the ratio of the active (real) power flowing to the load to the apparent power (as a result of
the capacitive or inductive nature of the load) and is a dimensionless number between 0 and 1.
[SOURCE: IEC 60050-131:2002, 131-11-46, modified — new Note 1 to entry added.]
3.1.20
protected socket
socket (3.1.26) which continues to deliver power to connected equipment for a defined period following
failure of power supply and distribution equipment
3.1.21
primary distribution equipment
equipment which is required to manage, control and convert incoming power supplies (primary,
secondary and, where appropriate, additional) (3.1.22, 3.1.24, 3.1.2) in a form suitable for distribution
by secondary distribution equipment (3.1.23)
3.1.22
primary supply
principal power supply that provides power to the data centre under normal operating conditions
3.1.23
secondary distribution equipment
equipment which is required to manage, control and distribute the power provided by the primary
distribution equipment (3.1.21) to the short-break, protected and unprotected sockets (3.1.25, 3.1.20,
3.1.30) within the data centre and to the tertiary distribution equipment (3.1.27)
Note 1 to entry: The power supply can be single-phase AC, three-phase AC or DC. If there is a change from 3-phase
to 1-phase supply, this is generally achieved at the secondary distribution equipment that is served directly from
the primary distribution equipment.
3.1.24
secondary supply
power supply independent from, and that is continuously available to be used to provide power to the
data centre following the disruption of, the primary power supply
Note 1 to entry: A second feed to a separate transformer from the same grid is not a secondary supply.
3.1.25
short-break socket
sockets (3.1.26) which, upon failure of power supply and distribution equipment, will be provided with
power from an additional supply (3.1.2) after a defined period
3.1.26
socket
connection enabling the supply of power to attached equipment
Note 1 to entry: This can be a de-mateable or a hardwired connection.
3.1.27
tertiary distribution equipment
power supply equipment, typically accommodated within the cabinets, frames and racks of the data
centre spaces, which directly feeds the protected sockets (3.1.20) therein
© ISO/IEC 2021 – All rights reserved

3.1.28
total harmonic distortion of current
THD
i
measurement of the harmonic distortion present on a current level, defined as the ratio of the sum of
the powers of all harmonic components to the power of the fundamental frequency
3.1.29
total harmonic distortion of voltage
THD
u
measurement of the harmonic distortion present on a voltage level, defined as the ratio of the sum of
the powers of all harmonic components to the power of the fundamental frequency
3.1.30
unprotected socket
sockets (3.1.26) which fail to deliver power to connected equipment following failure in power supply or
distribution equipment
3.2 Abbreviated terms
For the purposes of this document, the abbreviated terms given in ISO/IEC 22237-1 and the following
apply.
AC alternating current
DC direct current
EPO emergency power off
HV high voltage
KPI key performance indicator
LV low voltage
MV medium voltage
PMD power metering and monitoring device
PSU power supply unit
r.m.s. root mean square
SPD surge protective device
THD total harmonic distortion of current
i
THD total harmonic distortion of voltage
u
3.3 Symbols
λ power factor
P real or active power
S complex power
S apparent power, the magnitude, or modulus, of complex power
T one time period
© ISO/IEC 2021 – All rights reserved

U root mean square (r.m.s.) voltage
I root mean square (r.m.s.) current
4 Conformance
For a data centre to conform to this document:
a) it shall feature a power supply and distribution design solution that meets both the general
requirements and the required Availability Class of Clause 6;
b) the environmental controls applied to the spaces accommodating the power supply and distribution
system within the premises and serving the data centre shall be in accordance with ISO/IEC 22237-
4;
c) it shall feature an approach to physical security in relation to the power supply and distribution
solution that meets the requirements of Clause 7;
d) it shall feature an energy efficiency enablement solution that meets the requirements of the
relevant Granularity Level of Clause 8;
e) the telecommunications bonding system within the computer room and telecommunications
spaces of the data centre shall be in accordance with the local mesh bonding requirements of ISO/
IEC 30129;
f) where lightning protection is required, it shall be in accordance with the IEC 62305 series applied
with reference to ISO/IEC 30129;
g) the design of low voltage (LV) power supply and distribution installations shall be in accordance
with the IEC 60364 series;
h) local regulations, including safety, shall be met.
The Availability Class of the power distribution infrastructure is based on the required Availability
Class of the data centre. The power supply infrastructure shall be of the same or higher Availability
Class.
5 Power supply and distribution within data centres
5.1 Functional elements
5.1.1 General
The distribution of electrical power is one of the most important aspects of data centre infrastructure.
Disturbances of power supply voltage, current and frequency have a direct effect on the operational
safety of the data centre infrastructure and its availability.
The functional elements of power supply and distribution to the data centre are described as:
— sources: e.g. primary, secondary or additional supplies;
— devices: e.g. supply transfer switchgear;
— paths: pathways, spaces and cabling.
Typical sources and devices of power supply to and distribution within data centres are described in
Table 1. The requirements and recommendations for the provision of physical security to the spaces
accommodating the functional elements are described in Clause 7.
© ISO/IEC 2021 – All rights reserved

Implementations need not include all of the elements listed in Table 1. Also, the types of equipment
comprising certain functional elements can exist in both the area of supply and distribution.
Table 1 — Typical functional elements of power supply and distribution
Typical accommodation
Area Functional element
(using spaces defined in ISO/IEC 22237-1)
Primary supply Transformer space
Secondary supply
Supply transfer equipment (where multiple Electrical space
Supply
supplies exists)
Additional supply (e.g. generator, uninter- Generator space or electrical space
ruptible power system [UPS])
Primary distribution equipment Electrical distribution space
Transformer space (if required)
UPS Electrical space (or computer room space)
Secondary distribution equipment Electrical space (but also present in many
Distribution
other areas)
Transformer space (if required)
Tertiary distribution equipment Computer room spaces or spaces requiring
provision of protected supplies
5.1.2 Power supply to the data centre
The power supply schematic of Figure 2 indicates two implementations. The upper diagram shows the
minimum implementation comprising a single source (primary power supply) only. The lower diagram
shows multiple sources and includes a secondary supply as well as an additional supply that provides
power to relevant equipment in the data centre.
The primary and secondary supplies are typically provided from transformers which can be within the
premises containing the data centre (and can be owned by either the utility or the data centre premises
owner) or external and owned by the utility (and not considered to be a functional element of the data
centre).
An additional supply is one of the possible functional elements for supplying the data centre with
power. The additional supply will provide energy in case the primary and secondary supplies are not
available. Therefore, parameters such as the sizing, the basic design as well as the availability of the
overall power supply concept have to be precisely planned.
While the additional supply is typically a locally managed supply, it can be provided by a separate
utility supply provided that it is protected from failures in the primary or secondary supplies. In such
cases, the concept of short-break (see 5.1.3) is not relevant. If the additional supply is a locally managed
supply, with no connection to the utility, it shall be designed to be able to replace the power supply(ies)
in case of their failure.
The primary distribution equipment can also contain transformers.
© ISO/IEC 2021 – All rights reserved

Figure 2 — Power supply functional elements
The primary distribution equipment provides the interface between the supply and distribution areas.
The input to the primary distribution equipment can be LV and/or MV.
The output from the primary distribution equipment can be LV and/or MV depending upon the size
of the premises and the input requirements of any UPS or DC supply equipment installed between the
primary and secondary distribution equipment.
5.1.3 Power distribution within the data centre
The functional elements of the power distribution within the data centre are described as:
— devices: e.g. primary, secondary and tertiary distribution equipment, UPS;
— paths: pathways, spaces and cabling that connects the devices.
The distribution system is shown in Figure 3. The power is distributed via one or more instances of
secondary distribution equipment. These and subsequent figures adopt a system-level approach to the
implementation.
The input to the secondary distribution equipment can be LV and/or MV.
Equipment within the power distribution system may also contain transformers.
Within Figure 3, the power is provided to sockets in the distribution area that are categorized as:
1) unprotected sockets: suitable for equipment that is not critical to the function of the data centre
(e.g. powering of tools and equipment required for the maintenance of the facility);
2) protected sockets: intended for equipment that is critical to the function of the data centre (e.g.
information technology and network telecommunications equipment, certain elements of the
environmental control and security systems) and which cannot tolerate failure of supply, served by
solutions including UPS installed as part of the distribution system;
© ISO/IEC 2021 – All rights reserved

3) locally protected sockets: intended for equipment (e.g. emergency lighting) served by solutions
including UPS or local battery supplies installed at or close to the socket;
4) short-break sockets (available where the primary and/or secondary power supply is augmented
with an additional supply): intended for equipment (e.g. environmental control equipment and
certain lighting systems) that is critical to the function of the data centre but which can tolerate
a failure of supply for a defined period before the additional supply (e.g. generator) is brought into
service.
The output from the secondary distribution equipment is typically LV. Additional secondary distribution
equipment is typically installed where there is a need to change the current capacity of the power
supply cabling.
Figure 3 — Types of sockets served by the power distribution system
5.2 Dimensioning of power distribution systems
In small data centres, the data centre might only contain the functional elements within the distribution
area (the primary distribution equipment being elsewhere in the premises and serving the power
distribution in the remainder of the premises). In large data centres, primary distribution equipment
can be dedicated to the demands of the data centre itself.
The smallest data centres can comprise a single cabinet containing in-cabinet distribution equipment
providing protected power supplies to data processing, storage and transport equipment. In such cases
the functionality of the secondary distribution equipment is provided by the in-cabinet distribution
equipment. It is not necessary to provide any unprotected or short-break sockets within the cabinet.
In the small data centres comprising a limited number of cabinets, frames or racks, the UPS equipment
can be installed immediately adjacent to, or within, the tertiary distribution area.
As shown in Figure 2, a generator is included as an additional power supply. This is intended to deliver
short-break power supply and protected supply for an extended period in case of failures of the primary
and secondary power supply of the data centre.
The use of secondary power supplies and additional supplies and primary distribution equipment in
order to enhance levels of availability are addressed in 6.2.6.
© ISO/IEC 2021 – All rights reserved

6 Availability
6.1 General requirements
The power supply and distribution systems for a data centre comprise a complex sequence of functional
elements in a hierarchical structure. A series of serial and parallel systems convert the power from
the primary, secondary or additional supplies and, maintaining and/or improving its quality and
availability, deliver that power to a mix of end-equipment within the data centre.
The measurement of power supply parameters at the locations described in Clause 8 and the associated
monitoring of those parameters and their trends also enable the indication of conditions where demand
is threatened by the available capacity.
The power supply and distribution systems within the data centre shall be designed and/or selected in
order to provide the required availability of power supply to the end-equipment.
The Availability Class of the power supply and distribution systems shall be at least equal to that
required by the Availability Class of the overall set of facilities and infrastructures chosen in accordance
with ISO/IEC 22237-1.
Subclause 6.2 defines general requirements and recommendations for the design and selection of the
power supply system and in terms of Availability Class.
Subclause 6.3 defines general requirements and recommendations for the design of the power
distribution system and in terms of Availability Class.
6.2 Power supply
6.2.1 Capacity planning
6.2.1.1 Sizing
6.2.1.1.1 Requirements
The maximum capacity of the power supply system to the data centre shall be sized to accommodate:
a) the maximum planned IT load (typically, but not necessarily, based upon the published ‘start up’
power requirements supplied by the equipment manufacturers) taking into account allowance
for future growth and technology developments (including increased power density of the IT
equipment);
b) the maximum load associated with the environmental control systems serving the data centre
spaces taking into account:
1)
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