IEC 60364-5-53:2001/AMD2:2015

IEC 60364-5-53 ®
Edition 3.0 2015-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
A MENDMENT 2
AM ENDEMENT 2
Electrical installations of buildings –
Part 5-53: Selection and erection of electrical equipment – Isolation, switching
and control
Installations électriques des bâtiments –
Partie 5-53: Choix et mise en oeuvre des matériels électriques – Sectionnement,
coupure et commande
IEC 60364-5-53:2001-08/AMD2:2015-09(en-fr)

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IEC 60364-5-53 ®
Edition 3.0 2015-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
A MENDMENT 2
AM ENDEMENT 2
Electrical installations of buildings –

Part 5-53: Selection and erection of electrical equipment – Isolation, switching

and control
Installations électriques des bâtiments –

Partie 5-53: Choix et mise en oeuvre des matériels électriques – Sectionnement,

coupure et commande
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.130; 91.140.50 ISBN 978-2-8322-2883-8

– 2 – IEC 60364-5-53:2001/AMD2:2015

© IEC 2015
FOREWORD
This amendment has been prepared by IEC technical committee 64: Electrical installations

and protection against electric shock.

The text of this amendment is based on the following documents:

FDIS Report on voting
64/2031/FDIS 64/2072/RVD
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the stability date indicated on the IEC website under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication 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• withdrawn,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.

_______
FOREWORD
Replace the existing text, including the text provided in Amendment 1:2002 that reads:
"This publication has been drafted, as close as possible, in accordance with the ISO/IEC

Directives, Part 3"
by the following new sentence:
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
Delete, from both IEC 60364-5-53:2001 and from Amendment 1:2002, the sentence that reads
"Annexes A, B, C and D are for information only."

530.2 Normative references
Add the following new references:
IEC 60038, IEC standard voltages
IEC 60364-5-54, Low-voltage electrical installations – Part 5-54: Selection and erection of
electrical equipment – Earthing arrangements and protective conductors

© IEC 2015
IEC 61643-11:2011, Low-voltage surge protective devices – Part 11: Surge protective devices

connected to low-voltage power systems – Requirements and test methods

IEC 62305 (all parts), Protection against lightning

IEC 62305-1, Protection against lightning – Part 1: General principles

IEC 62305-2, Protection against lightning – Part 2: Risk management

IEC 62305-4, Protection against lightning – Part 4: Electrical and electronic systems within

structures
Replace the current reference to "IEC 61643-12" by the following:
IEC 61643-12:2008, Low-voltage surge protective devices – Part 12: Surge protective devices
connected to low-voltage power distribution systems – Selection and application principles
Replace the existing date "2001" for IEC 60364-4-41 by "2005"
Replace the existing date "2001" for IEC 60364-4-43 by "2008"
Replace the existing date "2001" for IEC 60364-4-44 by "2007"
Replace the existing date "1996" for IEC 61008-1 by "2010"

534 Devices for protection against electromagnetic and voltage disturbances
Replace the existing title and text of Clause 534, including the text provided in Amendment
1:2002, by the following new title and text:
534 Devices for protection against transient overvoltages
534.1 General
This clause contains provisions for the application of voltage limitation in order to obtain
insulation coordination in the cases described in IEC 60364-4-44, IEC 60664-1, IEC 62305-1,
IEC 62305-4 and IEC 61643-12.
This clause focuses mainly on the requirements for the selection and erection of SPDs for
protection against transient overvoltages where required by Clause 443 of IEC 60364-4-
44:2007, the IEC 62305 series, or as otherwise specified.
This clause does not take into account:

– surge protective components which may be incorporated in the appliances connected to
the installation;
– portable SPDs.
NOTE Further information can be found in IEC 61643-12.
This clause applies to a.c. power circuits. As far as it is applicable, the requirements of this
clause may be followed for d.c. power circuits.
534.2 Void
534.3 Terms and definitions
534.3.1
SPD assembly
one SPD or a set of SPDs, in both cases including all SPD disconnectors required by the SPD
manufacturer, providing the required overvoltage protection for a type of system earthing

– 4 – IEC 60364-5-53:2001/AMD2:2015

© IEC 2015
534.3.2
SPD disconnector
disconnector
device for disconnecting an SPD, or part of an SPD, from the power system

Note 1 to entry: This disconnecting device is not required to have isolating capability for safety purposes. It is to

prevent a persistent fault on the system and is used to give an indication of an SPD’s failure. Disconnectors can be

internal (built in) or external (required by the manufacturer). There may be more than one disconnector function, for
example an over-current protection function and a thermal protection function. These functions may be in separate
units.
[SOURCE: IEC 61643-11:2011, 3.1.28]

534.3.3
mode of protection of an SPD
intended current path, between terminals that contains protective components, e.g. line-to-
line, line-to-earth, line-to-neutral, neutral-to-earth
[SOURCE: IEC 61643-11:2011, 3.1.8]
534.3.4
follow current interrupt rating
I
fi
prospective short-circuit current that an SPD is able to interrupt without operation of a
disconnector
[SOURCE: IEC 61643-11:2011, 3.1.39]
534.3.5
short-circuit current rating
I
SCCR
maximum prospective short-circuit current from the power system for which the SPD, in
conjunction with the disconnector specified, is rated
[SOURCE: IEC 61643-11:2011, 3.1.27]
534.3.6
voltage protection level
U
P
maximum voltage to be expected at the SPD terminals due to an impulse stress with defined
voltage steepness and an impulse stress with a discharge current with given amplitude and
waveshape
Note 1 to entry: The voltage protection level is given by the manufacturer and may not be exceeded by:
– the measured limiting voltage determined for front-of-wave sparkover (if applicable) and the measured limiting
voltage determined from the residual voltage measurements at amplitudes corresponding to I and/or I
n imp
respectively for test classes II and/or I;
– the measured limiting voltage at the open circuit voltage of the combination wave generator (U ), determined
OC
for the combination wave for test class III.
[SOURCE: IEC 61643-11:2011, 3.1.14]
534.3.7
rated impulse voltage
U
W
impulse withstand voltage value assigned by the manufacturer to the equipment or to a part of
it, characterizing the specified withstand capability of its insulation against transient
overvoltages
[SOURCE: IEC 60664-1:2007, 3.9.2 MOD]

© IEC 2015
534.3.8
maximum continuous operating voltage

U
C
maximum r.m.s. voltage, which may be continuously applied to the SPD's mode of protection

Note 1 to entry: The U value covered by this standard may exceed 1 000 V.
C
[SOURCE: IEC 61643-11:2011, 3.1.11]

534.3.9
nominal discharge current for class II test

I
n
crest value of the current through the SPD having a current waveshape of 8/20
[SOURCE: IEC 61643-11:2011, 3.1.9]
534.3.10
impulse discharge current for class I test
I
imp
crest value of a discharge current through the SPD with specified charge transfer Q and
specified energy W/R in the specified time
[SOURCE: IEC 61643-11:2011, 3.1.10]
534.3.11
two-port SPD
SPD having specific series impedance connected between separate input and output
connections
[SOURCE: IEC 61643-11:2011, 3.1.3]
534.4 Selection and erection of SPDs
534.4.1 SPD location and SPD test class
SPDs shall at least be installed as close as possible to the origin of the installation. For
protection against effects of lightning and against switching overvoltages, class II tested
SPDs shall be used.
Where the structure is equipped with an external lightning protection system or protection
against effects of direct lightning is otherwise specified, class I tested SPDs shall be used.
Where the structure is not equipped with an external lightning protection system and where
the occurrence of direct lightning strike to the overhead lines between the last pole and the
entrance of the installation is to be taken into consideration, class I tested SPDs at or near
the origin of the electrical installation may be also selected according to Annex B.

NOTE 1 The origin of the installation could be the location where the supply enters the building or the main
distribution board.
NOTE 2 Following the product standard, the marking of the product is as follows:
- for test class I: either “test class I” and/or “T1“ (T1 in a square);
- for test class II: either “test class II” and/or “T2“ (T2 in a square);
- for test class III: either “test class III, and/or “T3“(T3 in a square).
Additional class II tested or class III tested SPDs may be needed to sufficiently protect the
installation according to 534.4.4.2 and shall be located downstream in the fixed electrical
installation, for example in the sub-distribution boards or at the socket outlets. These SPDs
shall not be used without SPDs being installed at the origin of the installation and shall be
coordinated with SPDs located upstream (see 534.4.4.5).
If a class I tested SPD is not able to provide protection according to 534.4.4.2, it shall be
accompanied by a coordinated class II tested or class III tested SPD to ensure the required
voltage protection level.
– 6 – IEC 60364-5-53:2001/AMD2:2015

© IEC 2015
Additional class II tested SPDs or class III tested SPDs may be needed close to sensitive

equipment to sufficiently protect the equipment according to Table 534.1 and shall be

coordinated with SPDs located upstream.

NOTE 3 Such additional SPDs may be part of the fixed electrical installation or may be portable SPDs.

Additional SPDs may be necessary to provide transient overvoltage protection regarding

threats coming from other sources such as:

– switching overvoltages produced by current using equipment located within the

installation;
– overvoltages on other incoming services such as telephone lines, internet connections;

– overvoltages on other services feeding other structures such as secondary buildings,
external installations/lighting, power lines feeding external sensors;
in which case one should consider installing SPDs located as close as possible to the origin
of such threats. More information may be found in IEC 61643-12.

Figure 534.1 – Example of installation of class I, class II and class III tested SPDs
The presence of SPDs installed downstream of a distribution board (e.g. in a socket-outlet)
shall be permanently indicated (e.g. by a label) in this distribution board.
534.4.2 Transient overvoltage protection requirements
Protection against transient overvoltages may be provided:

– between live conductors and PE (common mode protection);
– between live conductors (differential mode protection)
NOTE 1 Connection type CT1 provides primarily common mode protection. If differential mode protection is also
necessary, this will in most cases require additional SPDs between live conductors.
NOTE 2 Connection type CT2 provides a combination of common mode protection and differential mode
protection.
Protection between live conductors and PE (including neutral to PE if there is a neutral
conductor) is compulsory.
Protection between line conductors and neutral (if there is a neutral conductor) is
recommended to ensure equipment protection.
Protection between line conductors (in the case of multiple phases) is optional.

© IEC 2015
Some equipment may require both common mode protection (for impulse withstand) and

differential mode protection (for impulse immunity).

NOTE 3 For example, electronic class I equipment or class II equipment with FE-connection requires common
mode as well as differential mode protection to ensure overall protection against transient overvoltages due to

switching or from atmospheric origin.

534.4.3 Connection types
Connection type CT1 (e.g. 3+0 or 4+0-configuration): SPD assembly providing a mode of

protection between each live conductor (line and neutral conductors, if available) and PE or
between each line conductor and PEN.

Two examples of connection type CT1 for application in a three-phase system are

represented in Figure 534.2 and in Figure 534.3.
Connection type CT2 (e.g. 3+1-configuration): SPD assembly providing a mode of protection
between each line conductor and the neutral conductor, and between the neutral conductor
and PE.
An example of connection type CT2 for application in a three-phase system is represented in
Figure 534.4
L1 L2 L3 N
SS SS
SS SS
PP PP
PP PP
DD DD DD
DD
PE
Figure 534.2 – Connection type CT1 (4+0-configuration) for a three-phase system with
neutral
L1 L2 L3
S
SS SS SS
PP P
PP PP
DD DD D
DD
PEN
Figure 534.3 – Connection type CT1 (3+0-configuration) for a three-phase system

– 8 – IEC 60364-5-53:2001/AMD2:2015

© IEC 2015
L1 L2 L3 N
SS SS
SS
PP
PP
PP
DD
DD DD
SS
PP
DD
PE
Figure 534.4 – Connection type CT2 (e.g. 3+1-configuration)
for a three-phase system with neutral
When assembling SPDs, attention should be drawn to the selection of parameters for SPDs
connected between N and PE, depending on the connection type.
In TN-S or TN-C-S systems, the SPD between neutral and PE may be omitted if the distance
between the separation point of PE to N and the location of the installed SPDs is less than 0,5
m or if the separation point and the SPDs are located in the same distribution board.
If a line conductor is earthed, it is considered to be technically equivalent to a neutral
conductor for the application of this subclause. However correct choice of the SPD
parameters requires special considerations in such case.
534.4.4 Selection of SPDs
534.4.4.1  General
The selection of SPDs shall be based on the following parameters:
– voltage protection level (U ) and rated impulse voltage (U ) of equipment to be protected
p W
(see 534.4.4.2);
– continuous operating voltage (U ), i.e. supply system (TT, TN, IT) (see 534.4.4.3);
c
– nominal discharge current (I ) and impulse discharge current (I ) (see 534.4.4.4);
n imp
– SPD coordination (see 534.4.4.5);
– expected short-circuit current (see 534.4.4.6);
– follow current interrupting rating (see 534.4.4.7).
SPDs shall comply with the requirements of IEC 61643-11.
NOTE Additional information regarding selection and application is given in IEC 61643-12.
534.4.4.2 Selection of voltage protection level (U ) as a function of equipment rated
p
impulse voltage (U )
W
The voltage protection level U of SPDs shall be selected in accordance with required rated
p
impulse voltage according to overvoltage category II of Table 534.1. In order to provide
adequate protection of equipment, the voltage protection level between live conductors and
PE shall in no case exceed the required rated impulse voltage of the equipment according to
Table 534.1.
NOTE 1 Where only overvoltage category III or IV equipment is to be protected, reference is made to the required
rated impulse voltage of Table 443.2.
Where protection between line conductors and PE is provided by a series connection of SPD
protection modes (e.g. single mode SPDs, line–to-neutral + neutral-to-PE, according CT2),
this series connection shall fulfill the above voltage protection level requirement.

© IEC 2015
Where such combined voltage protection level between line conductor and PE is not provided

in the data sheet of the manufacturer, it shall be calculated by addition of the voltage

protection levels given for the individual SPDs modes of protection, which are connected in

series.
It is recommended that the voltage protection level provided by SPDs does not exceed 80 %
of the required rated impulse voltage for equipment according to Table 534.1 and

corresponding to overvoltage category II, but shall in no case exceed the required rated

impulse voltage of the equipment.

This safety margin is not necessary where one of the following cases applies:

– where the equipment is connected directly to the SPD terminals;
– where a protection scheme according Figure 534.9 is already applied;
– where the voltage drop across the overcurrent protection in the SPD branch circuit is
already taken into account for the voltage protection level U ;
p
– where protection according to overvoltage category II is provided but only overvoltage
category III or IV equipment is installed at this location.
NOTE 2 IEC 61643-12 gives additional information about the rated impulse voltage of equipment and the given U
p
for the SPD.
Table 534.1 – Required rated impulse voltage of equipment
c
Required rated impulse voltage (U ) of
W
equipment for
Voltage line to
Nominal voltage Nominal
neutral from
of the supply voltage of the
Overvoltage category Overvoltage
a a nominal a.c. or
system supply system
II (equipment with category I
d.c. voltages
Three-phase Single -phase
up to and normal rated impulse (equipment with
systems systems
including voltage) reduced rated
impulse voltage)
V V V kV kV
50 0,5 0,33
100 0,8 0,5
120/240 150 1,5 0,8
230/400 300 2,5 1,5
277/480
400/690 600 4 2,5
1 000 1 000 6 4
b b
1 500 d.c.
8 6
a
According to IEC 60038;
b
Recommended values based on Annex D of IEC 60664-2-1:2011;
c
The rated impulse voltage applies between live conductor and PE.

Additional SPDs between live conductors may be needed to avoid equipment malfunctions.
An appropriate voltage protection level needs to be evaluated based on equipment immunity
and availability requirements (see IEC 61643-12).
Where the required voltage protection level cannot be met with a single SPD assembly,
additional coordinated SPDs shall be applied to ensure the required voltage protection level.
534.4.4.3 Selection of SPDs with regard to continuous operating voltage (U )
c
In a.c., the maximum continuous operating voltage U of SPDs shall be equal to or higher than
c
required in Table 534.2.
– 10 – IEC 60364-5-53:2001/AMD2:2015

© IEC 2015
Table 534.2 – U of the SPD dependent on supply system configuration
c
SPD connected System configuration of distribution network

between
TN system TT system IT system
(as applicable)
1,1 U 1,1 U 1,1 U
Line conductor
√3 √3 √3
and neutral conductor
or (0,64 × U) or (0,64 × U) or (0,64 × U)

1,1 U 1,1 U
Line conductor and PE conductor √3 √3 1,1 × U

or (0,64 × U) or (0,64 × U)
1,1 U
Line conductor and PEN conductor √3 N/A N/A
or (0,64 × U)
1,1 U
U U
a  a
Neutral conductor and PE conductor √3

√3 √3
or (0,64 × U)
Line conductors 1,1 U 1,1 U 1,1 U
NOTE 1 N/A: not applicable.
NOTE 2 U is the line-to-line voltage of the low-voltage system.

a
These values are related to worst-case fault conditions, therefore the tolerance of 10 % is not taken into
account.
534.4.4.4 Selection of SPDs with regard to nominal discharge current (I ) and impulse
n
discharge current (I )
imp
At or near the origin of the installation, SPDs shall comply with one of the following cases, as
applicable:
– where the building is protected against direct lightning strike, SPDs at the origin of the
installation shall be selected according to 534.4.4.4.2 and Table 534.4;
– in other cases, SPDs shall be selected according to 534.4.4.4.1.
Further SPDs installed downstream of the SPDs at or near the origin of the installation shall
also comply with the coordination requirements in 534.4.4.5.
Overvoltages due to switching can be longer in duration and can contain more energy than
the transient overvoltages of atmospheric origin. This has to be considered for the selection of
SPDs with regard to nominal discharge current and impulse discharge current
534.4.4.4.1 Class II tested SPDs

Where class II tested SPD are required at or near the origin of installation, their nominal
discharge current shall be not less than that given in Table 534.3.
Table 534.3 – Nominal discharge current (I ) in kA depending on supply system and
n
connection type
Connection Supply system
Single-phase Three-phase
CT1 CT2 CT1 CT2
5 5
L − N
L − PE 5 5
N – PE 5 10 5 20
© IEC 2015
534.4.4.4.2 Class I tested SPDs

Where class I tested SPDs are required at or near the origin of the installation, one of the

following cases applies:
a) Where no risk analysis according to IEC 62305-2 has been carried out, the impulse

discharge current (I ) shall be not less than as given in Table 534.4:
imp
Table 534.4 – Selection of impulse discharge current (I ) where the building is

imp
protected against direct lightning strike

I in kA
imp
Supply system
Connection
Single phase Three phase
CT1 CT2 CT1 CT2
L − N 12,5 12,5
12,5 12,5
L − PE
12,5 25 12,5 50
N − PE
NOTE This table refers to lightning protection levels (LPL) III and IV.

b) Where the risk analysis according to IEC 62305-2 has been carried out, the impulse
discharge current (I ) shall be determined according to the IEC 62305 series.
imp
534.4.4.5 Coordination of two or several SPDs
Coordination of SPDs in the installation needs to be ensured. The manufacturer's instructions
on how to achieve coordination between SPDs shall be followed with reference IEC 61643-12.
534.4.4.6 Selection of SPDs with regard to the short-circuit current rating I
SCCR
In general, the short-circuit current rating I of the SPD, as stated by the manufacturer,
SCCR
shall be not lower than the maximum prospective short-circuit current at the connection points
of the SPD assembly. See Figure 534.5
This requirement does not apply to SPDs connected between neutral conductor and PE in TN
or TT systems, for which this is already covered by the product standard IEC 61643-11.
For SPDs connected between the neutral conductor and PE in IT systems, the short-circuit
current rating I of the SPD shall not be lower than the maximum prospective short-circuit
SCCR
current at the connection points of this SPD in case of a double earth fault under worst case
conditions.
534.4.4.7 Selection of SPDs with regard to the follow current interrupting rating
In general, the follow current interrupting rating I of the SPD, if declared by the manufacturer,
fi
shall not be lower than the maximum prospective short-circuit current at the connection points
of the SPD assembly. See Figure 534.5.
This requirement does not apply to SPDs connected between neutral conductor and PE
conductor in TN or TT systems, for which this is already covered by the product standard IEC
61643-11.
For SPDs connected between the neutral conductor and PE in IT systems, the follow current
interrupting rating I of the SPD if declared by the manufacturer shall not be lower than the
fi
maximum prospective short-circuit current at the connection points of this SPD in case of a
double earth fault under worst case conditions.

– 12 – IEC 60364-5-53:2001/AMD2:2015

© IEC 2015
A
OCPD1
E/I
OCPD2
SPD
SPD
SPDA
B
Key
OCPD1 overcurrent protective device in the installation
OCPD2 overcurrent protective device (SPD disconnector) required by the SPD manufacturer
SPD surge protective device
SPDA SPD assembly
A & B connection points of SPD assembly
E/I equipment or installation to be protected

Figure 534.5 – Connection points of an SPD assembly

534.4.5 Protection of the SPD against overcurrent
534.4.5.1 General
SPD installations shall be protected against overcurrent with respect to short-circuit currents.
This protection may be internal and/or external to the SPD according to the manufacturer’s
instructions.
The ratings and characteristics of external overcurrent protective device(s) (OCPD) for
protecting the SPD assembly shall be selected:

– according to Clause 434; and
– as high as possible, to ensure a high surge current capability for the complete assembly
but not exceeding the ratings and characteristics as required in the SPD manufacturer’s
installation instructions for the maximum overcurrent protection.
534.4.5.2 Arrangement of SPDs with relation to overcurrent protection
The location of overcurrent protective devices used to protect the SPDs may have an
influence on the continuity of supply of the installation and the effective voltage protection
level within the installation.
NOTE 1 National committees may decide which of the following arrangement is to be preferred, depending on the
type of installation.
a) If the overcurrent protective device for the SPD is located in the SPD branch circuit, the
continuity of the supply is unaffected in case of SPD failure, but neither the installation nor
the equipment is protected against possible further overvoltages (see Figure 534.6) after

© IEC 2015
tripping of such protective devices. In such an arrangement, the effective voltage

protection level within the installation is increased due to the voltage drop at the external

overcurrent protective device connected in series with the SPD.

NOTE 2 If the protection against overcurrent is internal to the SPD the voltage drop of the overcurrent protective

device is already included in the SPD’s voltage protection level U .
p
A
E/I
OCPD
SPD
B
Key
OCPD overcurrent protective device (SPD disconnector) required by the SPD manufacturer
SPD surge protective device
A and B connection points of SPD assembly
E/I equipment or installation to be protected

Figure 534.6 – Example of overcurrent protection in the SPD branch
by using a dedicated external overcurrent protective device

b) If the overcurrent protective device for the SPD is installed upstream of the SPD branch
circuit, continuity of the supply is not likely to be provided in the event of SPD failure (see
Figure 534.7). Nevertheless, in such an arrangement, the effective voltage protection level
within the installation is kept to a minimum.

However, protection according to Figure 534.6 shall also be applied whenever the rating of
the upstream overcurrent protective device (OCPD) is higher than the maximum
overcurrent protection recommended by the SPD manufacturer.

– 14 – IEC 60364-5-53:2001/AMD2:2015

© IEC 2015
A
OCPD
E/I
SPD
B
Key
OCPD overcurrent protective device of the installation used to protect the SPD
SPD surge protective device
A and B connection points of SPD assembly
E/I equipment or installation to be protected

Figure 534.7 – Protective device, which is a part of the installation,
also used to protect the SPD
534.4.5.3 Selectivity between overcurrent protective devices
Where required, the need for selectivity between overcurrent protective devices shall be
considered according to the installation conditions at the point of installation of the SPD and
the information provided by the manufacturer (see Clause 535 of IEC 60364-5-53:2002).
534.4.5.4 Surge current withstand capability of upstream devices
For most installation devices (e.g. meters, terminals, protective devices, switches, etc.) which
are installed upstream of the SPD, there is no dedicated surge current withstand capability

required by the relevant product standards.
The installation of SPDs as close as possible to the origin of the installation, according to
534.4.1, reduces surge currents flowing through downstream installation devices.
For further information, see IEC 61643-12 as well as the manufacturer’s information.
534.4.6 Fault protection
Fault protection, as defined in IEC 60364-4-41, shall remain effective in the protected
installation even in the event of SPD failures.
In case of automatic disconnection of supply:
– in TN systems, this may generally be fulfilled by the overcurrent device on the supply side
of the SPD;
– in TT systems, this may be fulfilled by:
a) the installation of SPDs downstream of an RCD; or

© IEC 2015
b) the installation of SPDs upstream of the main RCD. Because of the possibility of a

failure of an SPD connected between neutral conductor and PE, the conditions of

411.4.1 of IEC 60364-4-41:2005 shall be met and the SPDs shall be installed in

accordance with connection type CT2.

– in IT systems, no additional measure is needed.

Surge protective devices at or near the origin of installation shall be connected according to

Table 534.5.
Table 534.5 – Connection of the SPD dependent on supply system

Supply system at the connection Connection type

point of the SPD assembly
CT1 CT2
TN system X X
TT system SPD only downstream of RCD X
IT system with neutral X X
IT system without neutral X N/A
NOTE 1 X = applicable.
NOTE 2 N/A = not applicable.
NOTE Additional requirements might apply for SPDs installed in the area of influence of applications such as
railway systems, HV power systems, mobile units, etc.

534.4.7 SPDs installation in conjunction with RCDs
If SPDs are installed in accordance with 534.4.1 and are located on the load side of a residual
current device, RCD(s) may be with or without a time delay but shall have an immunity to
surge currents of at least 3 kA 8/20.
NOTE 1 S-type RCDs in accordance with IEC 61008-1 and IEC 61009-1 satisfy this requirement.
NOTE 2 In the case of surge current higher than 3 kA 8/20, the RCD may trip causing interruption of the power
supply.
NOTE 3 This may not be applicable for RCDs installed upstream of additional SPDs provided to protect sensitive
equipment.
Installation of class I tested SPDs downstream of an RCD is not recommended.
534.4.8 Connections of the SPD
The effective voltage protection level within the installation depends significantly on the
connection and the wiring length and arrangement of the SPD itself and the required SPD
disconnectors.
All conductors and interconnections to the relevant line to be protected as well the

connections between the SPD and any external SPD disconnector shall be kept as short and
as straight as possible and any unnecessary cable loop shall be avoided.
The length of the connecting conductors is defined by the sum of the path length of
conductors used from the live conductor to the PE in between connection points A and B as
defined in Figure 534.8.
Consideration shall be given to limit the total wiring length of conductors between connection
points of the SPD assembly (see Figure 534.8 below) to a value not greater than 0,5 m.

– 16 – IEC 60364-5-53:2001/AMD2:2015

© IEC 2015
A
Live conductor
Length
a
OCPD
Length
b
SPD
Length
c
B PE
Key
OCPD  overcurrent protective device
SPD surge protective device
PE conductor protective earthing conductor
A and B connection points of SPD assembly

NOTE When OCPD is not present, length b is equal to 0.

Figure 534.8 – Connection of the SPD

To meet these requirements, the main protective conductor shall be connected to the earthing
terminal located as near as possible to the SPD by adding, if necessary, an intermediate
earthing terminal (see diagrams in Figure 534.9).
To determine the total length of the connecting conductors according to Figure 534.9, the

following cable lengths:
– from the main earthing terminal to the intermediate earthing terminal;
– from the intermediate earthing terminal to the PE-conductor;
shall not be taken into account.
The length (and therefore inductance) of the cables between the SPDs and the main earthing
terminal shall be kept to a minimum. SPDs may be connected to the main earthing terminal or
to the protective conductor via metallic parts e.g. the metallic enclosures of the assembly (see
543.4.2), provided it is connected to PE and meets the requirements for a protective
conductor in accordance with IEC 60364-5-54. Connection of the relevant SPD(s) to the main
earthing terminal, and in addition to the main protective conductor, may improve the voltage
protection level.
If the total wiring length (a +b +c) as defined in Figure 534.8 exceeds 0,5 m, at least one of
the following options shall be chosen:

© IEC 2015
– select an SPD with a lower voltage protection level Up (a 1 m length of rectilinear cable

carrying a discharge current of 10 kA (8/20) adds a voltage drop of about 1 000 V);

– install a second coordinated SPD close to the equipment to be protected so as to adapt

the voltage protection level U to the rated impulse voltage of the equipment to be
p
protected;
– use the installation described in Figure 534.9.

Key
OCPD overcurrent protective device
SPD surge protective device
PE protective earthing
E/I equipment/installation
1 main earthing terminal
2 intermediate earthing terminal
3 length c (to be considered)
4 cable lengths need not be considered
5 cable lengths need not be considered
A and B connection points of the SPD assembly

Figure 534.9 – Example of installation of an SPD in order to decrease lead length of SPD
supply conductors
534.4.9 Effective protective distance of SPDs
Where the distance between the SPD and the equipment to be protected is greater than 10 m,
additional protective measures should be provided such as:
– an additional SPD installed as close as possible to the equipment to be protected; its
voltage protection level U shall in no case exceed the required rated impulse voltage U
P W
of the equipment; or
– the use of one-port SPDs at or near the origin of the installation; their voltage protection
level U shall in no case exceed 50 % of the required rated impulse voltage U of the
P W
equipment to be protected; This measure should be implemented together with other
measures such as the use of shielded wiring in the whole protected circuit(s); or
– the use of two-port SPDs at or near the origin of the installation; their voltage protection
level U shall in no case exceed the required rated impulse voltage U of the equipment
P W
to be protected. This measure should be implemented together with other measures such
as the use of shielded wiring in the whole protected circuit(s).

– 18 – IEC 60364-5-53:2001/AMD2:2015

© IEC 2015
534.4.10 Connecting conductors of SPDs

Conductors between the SPD and the main earthing terminal or the protective conductor shall

have a cross-sectional area not less than:

– 6 mm copper or equivalent for class II tested SPDs installed at or near the origin of the

installation;
– 16 mm copper or equivalent for class I tested SPDs installed at or near the origin of the

installation.
Referring to 433.3.1 b) of IEC 60364-4-43:2008, conductors connecting SPDs and the
overcurrent protective devices to live conductors shall be rated to withstand the prospective
short-circuit current to be expected and shall have a cross-sectional area not less than:
– 2,5 mm copper or equivalent for class II tested SPDs installed at or near the origin of the
installation;
– 6 mm copper or equivalent for class I tested SPDs installed at or near the origin of the
installation.
Annex A – Installation of surge protective devices in TN-systems
Replace the existing Annex A, including the title and the text provided in Amendment 1:2002,
by the following new Annex A and new title:

© IEC 2015
Annex A
(informative)
SPD installation –
Examples of installation diagrams according to system configurations

NOTE 1 National Committees may choose the preferred diagrams for their country.

NOTE 2 OCPDs may be single pole or multi pole devices according to IEC 60364.

A.1 TT system – 3 phase supply plus neutral

L1
L2
O
R
C
C
L3
P
D
D
N
OCPD2
S
P
SPD
D
PE conductor
Key
1 LV Switchboard
2 HV/LV transformer
3 Equipment/Installation
4 Main earthing terminal
5 Intermediate earthing terminal
6 SPDA
OCPD1 Overcurrent protective device(s) at the origin of the installation
SPD Surge protective device(s)
OCPD2 Overcurrent protective device(s) if required
RCD Residual current device
Figure A.1 – Example of SPDA installation with connexion type CT2
on the supply side (upstream) of the main RCD in TT system

– 20 – IEC 60364-5-53:2001/AMD2:
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