IEC 62991:2022

IEC 62991 ®
Edition 1.0 2022-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Particular requirements for source switching equipment (SSE)

Exigences particulières relatives au matériel de commutation de source (SSE)

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IEC 62991 ®
Edition 1.0 2022-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Particular requirements for source switching equipment (SSE)

Exigences particulières relatives au matériel de commutation de source (SSE)

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 03.100.70; 27.015; 29.020 ISBN 978-2-8322-6198-9

– 2 – IEC 62991:2022 © IEC 2022
CONTENTS
FOREWORD . 8
INTRODUCTION . 10
1 Scope . 12
2 Normative references . 13
3 Terms and definitions . 15
3.1 General definitions . 15
3.2 Additional definitions for NC-SSE and SSE control units (controllers) of
C-SSE . 25
3.3 Additional definitions dedicated to C-SSE . 26
4 Classification . 27
4.1 According to the method of operation . 27
4.2 According to the construction . 27
4.3 According to the kind of current . 28
4.4 According to the number of switched poles . 28
4.5 According to the type of terminals . 28
4.6 According to the SSE's intended application . 28
4.7 According to coupling method . 28
4.7.1 SSE with synchronization . 28
4.7.2 SSE with interlock . 28
4.7.3 SSE with synchronization and interlock . 28
4.8 According to the transition type . 28
4.9 According to the possibility to select sources . 28
4.10 According to the utilization category . 28
4.11 According to the possibility to provide an OFF position . 28
4.12 According to the method of mounting . 29
4.13 According to the protection against external influences . 29
4.14 According to functional categories . 29
5 Characteristics . 31
5.1 General . 31
5.2 Type and characteristics of the equipment . 32
5.3 Characteristics of NC-SSE . 32
5.3.1 General . 32
5.3.2 Characteristics of main circuits . 32
5.3.3 Utilization categories . 35
5.3.4 Characteristics of control circuits, including electrical interlocks . 35
5.3.5 Characteristics of auxiliary circuits . 37
5.4 Characteristics of C-SSE . 37
5.4.1 General . 37
5.4.2 Characteristics of main circuits . 37
5.4.3 Utilization categories . 38
5.4.4 Characteristics of control circuits, including electrical interlocks . 38
5.4.5 Characteristics of auxiliary circuits . 39
6 Markings and product information . 39
7 Standard conditions for operation in service . 40
7.1 General . 40
7.2 Ambient temperature range in normal use . 41

7.3 Relative humidity . 41
7.4 Altitude . 41
7.5 Conditions of installation . 41
7.6 Pollution degree . 41
8 Requirements for construction and operation . 41
8.1 General . 41
8.2 Mechanical design . 42
8.2.1 General . 42
8.2.2 Constructional requirements . 42
8.2.3 Mechanism and operating means. 44
8.2.4 Clearances and creepage distances and distances through sealing
compound . 46
8.2.5 Screws, current-carrying parts and connections . 49
8.2.6 Terminals for external conductors . 50
8.3 Protection against electric shock . 52
8.4 Dielectric properties . 52
8.4.1 General . 52
8.4.2 Dielectric properties . 52
8.5 Temperature-rise . 52
8.6 Making and breaking capacity . 53
8.7 Performances . 54
8.7.1 General . 54
8.7.2 Operating conditions . 55
8.7.3 Operational performance . 57
8.8 Resistance to heat . 58
8.9 Resistance of insulating material to abnormal heat and to fire . 58
8.10 Resistance to rusting . 59
8.11 Coordination with short-circuit protective devices (SCPDs) . 59
8.12 EMC . 59
8.13 Resistance to abnormal conditions . 59
8.14 Components . 59
8.14.1 General . 59
8.14.2 Fuses . 60
8.14.3 Capacitors . 60
8.14.4 Resistors . 61
8.14.5 Transformers . 61
9 Type tests . 61
9.1 General requirements . 61
9.1.1 Type tests and test sequences . 61
9.1.2 Test conditions . 61
9.1.3 Test procedure . 63
9.2 Tests of indelibility of markings . 63
9.3 Tests of the mechanical strength . 63
9.3.1 Tests of the resistance to mechanical stresses of insulating means . 63
9.3.2 Verification of installation and connections . 73
9.3.3 Tests of fixings of covers, cover plates and actuating members . 75
9.3.4 Tests of attachment of knobs . 76
9.3.5 Tests of covers, cover plates or actuating members – Accessibility to
live parts. 77

– 4 – IEC 62991:2022 © IEC 2022
9.3.6 Tests of covers, cover plates or actuating members – Accessibility to
non-earthed metal parts separated from live parts . 78
9.3.7 Tests of covers, cover plates or actuating members – Accessibility to
insulating parts, earthed metal parts, the live parts of SELV ≤ 25 V AC
or metal parts separated from live parts . 78
9.3.8 Tests of covers, cover plates or actuating members – Application of
gauges . 78
9.3.9 Tests of grooves, holes and reverse tapers. 80
9.4 Measurements of clearances and creepage distances. 81
9.5 Test of reliability of screws, current-carrying parts and connections . 82
9.6 Test of reliability of screw-type terminals for external copper conductors . 82
9.7 Tests for the protection against electric shock . 84
9.8 Tests of dielectric properties . 86
9.8.1 General . 86
9.8.2 Tests of the resistance to humidity. 87
9.8.3 Tests of the insulation resistance of the main circuits . 87
9.8.4 Tests of the dielectric strength of main circuits . 88
9.8.5 Tests of the insulation resistance and dielectric strength of other circuits . 90
9.8.6 Verification of impulse withstand voltages (across clearances and
through solid insulations) . 91
9.9 Tests of temperature-rise . 92
9.9.1 General . 92
9.9.2 Test setup . 92
9.9.3 Test procedure . 94
9.10 Tests of making and breaking capacity . 94
9.11 Verification of performances . 95
9.11.1 General . 95
9.11.2 Verification of interlocking function . 95
9.11.3 Verification of controls, sequences and limits of operations . 98
9.11.4 Verification of the operational performance capability . 102
9.12 Tests of heat resistance . 103
9.12.1 Basic heating test . 103
9.12.2 Ball-pressure test on parts of insulating material necessary to retain
current-carrying parts and parts of the earthing circuit in position . 104
9.12.3 Ball-pressure test on parts of insulating material not necessary to retain

current-carrying parts and parts of the earthing circuit in position . 104
9.13 Tests of the resistance of insulating material to abnormal heat and to fire . 104
9.14 Resistance to rusting . 106
9.15 Tests of coordination with short-circuit protective devices (SCPDs) . 107
9.15.1 General . 107
9.15.2 Test conditions . 107
9.15.3 Tests of coordination between the SSE and the SCPDs . 112
9.16 EMC tests . 113
9.16.1 General . 113
9.16.2 Electromagnetic emission . 113
9.16.3 Electromagnetic immunity . 113
9.17 Tests under abnormal conditions . 117
9.17.1 General . 117
9.17.2 Tests under fault conditions . 119
9.17.3 Overload tests . 121

9.18 Tests of components . 121
Annex A (informative) Examples of possible use of SSE . 125
A.1 General concept of prosumer's low-voltage electrical installation . 125
A.2 Examples of SSE use . 128
Annex B (informative) Correspondence between ISO and AWG copper conductors . 133
Annex C (normative) Determination of clearances and creepage distances . 134
C.1 General . 134
C.2 Orientation and location of a creepage distance . 134
C.3 Creepage distances where more than one material is used . 134
C.4 Creepage distances split by floating conductive part . 134
C.5 Measurement of creepage distances and clearances . 134
Annex D (normative) Test sequences and number of specimens . 137
Annex E (normative) Arrangement for the detection of the emission of ionized gases
during short-circuit tests . 139
Bibliography . 142

Figure 1 – Energy efficiency management system (EEMS). 10
Figure 2 – Principle of management of two sources with source switching equipment
(SSE) . 11
Figure 3 – Example of A-SSE . 30
Figure 4 – Example of R-SSE . 31
Figure 5 – Example of M-SSE . 31
Figure 6 – Pendulum impact test apparatus . 65
Figure 7 – Pendulum impact test apparatus (striking element) . 66
Figure 8 – Mounting support of specimens . 67
Figure 9 – Mounting block for a flush type SSE . 68
Figure 10 – Example of mounting support of panel board type SSE . 69
Figure 11 – Example of mounting support for a rear fixed SSE. 70
Figure 12 – Application of forces on a rail-mounted SSE . 72
Figure 13 – Determination of the direction of the forces to be applied . 74
Figure 14 – Direction for the conductor pull of 30 N for 1 min . 75
Figure 15 – Gauge (thickness: about 2 mm) for the verification of the outline of covers,
cover plates or actuating members . 78
Figure 16 – Example of application of the gauge of Figure 15 on covers fixed without
screws on a mounting surface or supporting surface . 79
Figure 17 – Examples of applications of the gauge of Figure 15 . 80
Figure 18 – Gauge for verification of grooves, holes and reverse tapers . 81
Figure 19 – Sketch showing the direction of application of the gauge of Figure 18 . 81
Figure 20 – Jointed test finger (test probe B according to IEC 61032:1997) . 85
Figure 21 – Test pin for checking the protection against electric shock . 86
Figure 22 – Actuator test force . 97
Figure 23 – Test circuit for connection to source 1 and source 2 . 99
Figure 24 – Ball-pressure test apparatus. 104
Figure 25 – Diagrammatic representation . 105
Figure 26 – Typical diagram for all coordination tests . 108

– 6 – IEC 62991:2022 © IEC 2022
Figure 27 – Detail of impedances Z and Z . 109
Figure 28 – Minimum clearances and creepage distances on printed boards . 120
Figure 29 – Surge test – Test circuit . 122
Figure 30 – Surge test – Example of a switch to be used in the test circuit. 123
Figure A.1 – Example of PEI . 126
Figure A.2 – Example of an individual PEI . 127
Figure A.3 – Example of a shared PEI with a distribution system within the PEI in
parallel to the DSO distribution system . 128
Figure A.4 – Example of SSE use in an individual PEI with PV production and storage

on the DC side . 129
Figure A.5 – Example of SSE use in an individual PEI with PV production and storage
on the AC side . 130
Figure A.6 – Example of SSE use for power backup with storage or a generating set . 131
Figure A.7 – Example of SSE use for power backup with storage only . 132
Figure C.1 – Example 1 . 135
Figure C.2 – Example 2 . 135
Figure C.3 – Example 3 . 135
Figure C.4 – Example 4 . 135
Figure C.5 – Example 5 . 136
Figure C.6 – Example 6 . 136
Figure C.7 – Example 7 . 136
Figure E.1 – Test arrangement . 140
Figure E.2 – Grid . 141
Figure E.3 – Grid circuit . 141

Table 1 – Source switching functional categories . 29
Table 2 – Preferred values of rated voltages . 33
Table 3 – Rated impulse voltage as a function of the nominal voltage of the installation . 34
Table 4 – Utilization categories . 35
Table 5 – Requirements and position for markings and other product information . 39
Table 6 – Cross-sectional areas (S) of test copper conductors corresponding to the
rated currents . 43
Table 7 – Minimum clearances and creepage distances . 47
Table 8 – Connectable cross-sections of copper conductors for screw-type terminals . 50
Table 9 – Temperature-rise values . 53
Table 10 – Making and breaking conditions for tests of making and breaking capacities . 54
Table 11 – OFF-time durations for the verification of making and breaking capacities

for utilization categories . 54
Table 12 – Making and breaking conditions for the operational performance . 58
Table 13 – Number of operations for operational performance . 58
Table 14 – Capacitors . 61
Table 15 – Tightening torque for the verification of the mechanical strength of screw-
type terminals . 62
Table 16 – Height of fall for impact test . 71

Table 17 – Forces to be applied to covers, cover plates or actuating members whose
fixing is not dependent on screws . 76
Table 18 – Test values for pulling out test . 83
Table 19 – Test voltage, points of application and minimum values of insulating
resistance for the verification of dielectric strength . 89
Table 20 – Test voltages of auxiliary circuits . 90
Table 21 – Test voltage for verification of impulse withstand voltage . 92
Table 22 – Temperature-rise test currents and cross-sectional areas of copper
conductors . 93
Table 23 – Actuator test force . 97
Table 24 – Minimum values of I t and I . 110
p
Table 25 – Power factors for short-circuit tests . 111
Table 26 – Immunity tests (overview) . 114
Table 27 – Performance criteria . 114
Table 28 – Voltage dip test values . 115
Table 29 – Short-interruption test values . 115
Table 30 – Surge test voltages . 115
Table 31 – Fast transient test values . 116
Table 32 – Permissible temperature rise values . 118
Table B.1 – Correspondence between ISO and AWG copper conductors . 133
Table D.1 – Test sequences and number of specimens for tests . 138

– 8 – IEC 62991:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PARTICULAR REQUIREMENTS FOR
SOURCE SWITCHING EQUIPMENT (SSE)

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 62991 has been prepared by subcommittee 23K: Electrical Energy Efficiency products, of
IEC technical committee 23: Electrical accessories. It is an International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
23K/78/FDIS 23K/79/RVD
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 International Standard 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
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– 10 – IEC 62991:2022 © IEC 2022
INTRODUCTION
The optimization of electrical energy usage can be facilitated by appropriate design and
installation considerations. An electrical installation can provide the required level of service
and safety for the lowest level of electrical consumption.
This is considered by designers as a general requirement of their design procedures to establish
the best use of electrical energy.
The optimization of the use of electricity is based on energy efficiency management taking into
consideration the price of electricity, electrical consumption of the loads and real-time
adaptation, as described in Figure 1, which is reproduced from IEC 60364-8-1:2019, Figure 1.

Figure 1 – Energy efficiency management system (EEMS)
This document applies to source switching equipment (SSE), for household and similar uses
(see Figure 2).
SSE is intended:
– to make transparent to the end-user the use of energy sources, taking into account local
generation or storage;
– to optimize the electrical energy originating either from the grid or from other local
sources/storage.
Figure 2 – Principle of management of two sources
with source switching equipment (SSE)
NOTE Examples of use of SSE are given Annex A.
As defined by IEC 60364-8-82:2022, the main operating modes of SSE are:
– direct feeding mode: corresponding to the normal source (supply from the grid). Storage
units can supply current-using-equipment or be charged by the grid or local power supplies;
– island mode: loads supplied by local energy sources and storage units, disconnected from
the grid;
– reverse feeding mode: corresponding to the supply of the grid. Storage units can supply
current-using-equipment and/or the grid or be charged by local power supplies.
Transfer from/to the direct feeding mode to island mode and vice versa can be achieved by the
operation of the SSE which can be either directly controlled (manually or remotely) or
automatically controlled.
Operation of SSE is to occur in safe conditions as described in IEC 60364‑8‑82:2022.
This document does not cover communication aspects such as protocols and interoperability
nor data security or other related aspects.
SSE switching operations are based on similar principles as transfer switching equipment
(TSE). For applications with higher currents, for example, for industrial applications, the reader
may refer to IEC 60947-6-1.
– 12 – IEC 62991:2022 © IEC 2022
PARTICULAR REQUIREMENTS FOR
SOURCE SWITCHING EQUIPMENT (SSE)

1 Scope
This International Standard applies to source switching equipment, hereafter referred to as
SSE, for household and similar uses, primarily intended to be used for energy efficiency (EE)
purposes with local production and/or storage of energy.
SSE is intended to be installed in low voltage prosumer electrical installations (PEI) to deliver
the electrical energy:
– either to current-using equipment (direct feeding mode or island mode);
– or to the grid (reverse feeding mode).
SSE is intended to select and/or combine two power sources (e.g. selected from among grid,
local power source, storage units) within an electrical energy management system (EEMS).
SSE can also be used for backup supply.
NOTE 1 "Switching device for islanding" (SDFI) function is under consideration as additional requirements can be
necessary. See also Figure 4 of IEC 60364-8-82:2022.
SSE is part of the fixed electrical installation.
This document applies to SSE for operation in AC single or multiphase main circuits with rated
voltages not exceeding 440 V AC, frequencies of 50 Hz, 60 Hz or 50/60 Hz and rated currents
not exceeding 125 A (40 A for screwless terminals). They are intended to be used in installations
with prospective short circuit currents not exceeding 25 000 A. DC operations are not covered
by this edition and are kept under consideration for a future revision of this document.
According to this document, SSE can be operated:
– manually (M-SSE), or
– remotely (R-SSE), or
– automatically (A-SSE), or
– a combination of the above methods of operation, e.g. manual and remote.
SSE is used to select two sources sequentially. SSE able to run two (or more) sources in parallel
are not covered by this edition and are
...