IEC 60364-5-55:2011/AMD1:2012

IEC 60364-5-55 ®
Edition 2.0 2012-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
AMENDMENT 1
AMENDEMENT 1
Electrical installations of buildings –
Part 5-55: Selection and erection of electrical equipment – Other equipment

Installations électriques des bâtiments –
Partie 5-55: Choix et mise en oeuvre des matériels électriques – Autres matériels

IEC 60364-5-55:2011/A1:2012
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IEC 60364-5-55 ®
Edition 2.0 2012-10
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
AMENDMENT 1
AMENDEMENT 1
Electrical installations of buildings –

Part 5-55: Selection and erection of electrical equipment – Other equipment

Installations électriques des bâtiments –

Partie 5-55: Choix et mise en oeuvre des matériels électriques – Autres matériels

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX L
ICS 91.140 ISBN 978-2-83220-395-8

– 2 – 60364-5-55 Amend.1 © IEC:2012
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
64/1831/FDIS 64/1863/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 web site 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• withdrawn,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.
_____________
Insert the following new references into Clause 550.2, Normative references:
IEC 60038, IEC standard voltages
IEC 60364-4-44:2007, Low-voltage electrical installations – Part 4-44: Protection for safety –
Protection against voltage disturbances and electromagnetic disturbances
IEC 60364-5-52:2009, Low-voltage electrical installations – Part 5-52: Selection and erection
of electrical equipment – Wiring systems
IEC 61439-1:2011, Low-voltage switchgear and controlgear assemblies – Part 1: General
rules
IEC 61508 (all parts), Functional safety of electrical/electronic/programmable electronic
safety-related systems
IEC 61557-8, 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 8:
Insulation monitoring devices for IT systems
IEC 61557-9, 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 9:
Equipment for insulation fault location in IT systems
Replace "IEC 60364-4-43" by "IEC 60364-4-43:2008.
Insert the following new Clause 557 after Clause 551.8 and before Clause 559:

60364-5-55 Amend.1 © IEC:2012 – 3 –
557 Auxiliary circuits
557.1 Scope
This clause applies to auxiliary circuits, except those covered by specific product or system
standards.
557.2 Terms and definitions
For the purposes of this document, the following definitions apply.
NOTE For general definitions, see IEC 60050-826.
557.2.1
auxiliary circuit
circuit for transmission of signals intended for control, detection, supervision or measurement
of the functional status of a main circuit
557.2.2
main circuit
circuit containing electrical equipment for generation, conversion, distribution or switching of
electrical power or current-using equipment
557.2.3
current-limiting signal output
signal output provided by a device which serves to limit the current
557.2.4
inherently short-circuit and earth fault proof
state of an electric equipment or assembly protected against short-circuits and earth faults by
suitable design and erection provisions
[SOURCE: IEC 60050-826:2004, definition 826-14-15]
557.2.5
safety integrity level
SIL
discrete level for specifying the safety integrity requirements of the safety functions to be
allocated to the electrical/electronic/programmable electronic safety-related systems, where
safety integrity level 4 has the highest level of safety integrity and safety integrity level 1 has
the lowest
[SOURCE: IEC 61508-4:2010, 3.5.8, modified]
557.3 Requirements for auxiliary circuits
557.3.1 General
The power supply a.c. or d.c. for an auxiliary circuit may be either dependent or independent
of the main circuit according to its required function. If the status of the main circuit has to be
signaled, then the signaling circuit shall be able to operate independently of that main circuit.
NOTE In extensive installations the use of a d.c. auxiliary supply may be preferred.
557.3.2 Power supply for auxiliary circuits dependent on the main circuit
557.3.2.1 General
Auxiliary circuits with a power supply dependent on the main a.c. circuit shall be connected to
the main circuit:
– 4 – 60364-5-55 Amend.1 © IEC:2012
– directly (see Figure 557.1); or
– via a rectifier (see Figure 557.2); or
– via transformer (see Figure 557.3).
It is recommended that auxiliary circuits supplying primarily electronic equipment or systems
should not be supplied directly but at least via simple separation from the main circuit.
L1
L2
L3
N
Terminals for the
auxiliary circuit
IEC  1802/12
Figure 557.1 – Auxiliary circuit supplied directly from the main circuit

L1
L2
L3
N
Terminals for the
auxiliary circuit
+ –
IEC  1803/12
Figure 557.2 – Auxiliary circuit supplied via rectifier from the main circuit

L1
L2
L3
N
Terminals for the
auxiliary circuit
IEC  1804/12
Figure 557.3 – Auxiliary circuit supplied from the main circuit via transformer
NOTE In the case of an auxiliary circuit supplied from the main circuit, directly or via the rectifier, the auxiliary
circuit begins at the connection point to the main circuit, see Figure 557.1. When via the rectifier, see Figure 557.2,
or by a transformer supply, see Figure 557.3, the auxiliary circuit begins on the d.c. side of the rectifier or on the
secondary side of the transformer.
557.3.2.2 Auxiliary circuit supplied from the main circuit via transformer
Where an auxiliary circuit is supplied by more than one transformer, they shall be connected
in parallel both on primary and secondary sides.

60364-5-55 Amend.1 © IEC:2012 – 5 –
557.3.3 Auxiliary circuit supplied by an independent source
Where an independent source is used, a loss of supply or undervoltage of the main circuit
source should be detected. An independent auxiliary circuit shall not create a hazardous
situation.
NOTE Batteries and a power supply system independent of the mains are examples of independent sources.
557.3.4 Auxiliary circuits with or without connection to earth
General
557.3.4.1
An auxiliary circuit shall comply with the earthing requirements in IEC 60364, except as
modified by 557.3.4.2 or 557.3.4.3.
NOTE It depends on the requirements for an auxiliary circuit as to whether it is operated earthed or unearthed.
For example, in earthed auxiliary circuits an earth fault in a non-earthed conductor leads to a switching off of the
power supply of the auxiliary circuit. In unearthed auxiliary circuits, an earth fault in a conductor leads only to a
signal from the IMD (see 557.3.4.3).
The use of unearthed auxiliary circuits should be considered, where high reliability is required.
557.3.4.2 Earthed auxiliary circuit
Earthed auxiliary circuits supplied via a transformer shall be connected to earth only at one
point on the secondary side of the transformer. The connection to earth shall be situated
close to the transformer. The connection shall be easily accessible and capable of being
isolated for insulation measurement.
557.3.4.3 Unearthed auxiliary circuit
If an auxiliary circuit is operated unearthed via a transformer, an insulation monitoring device
(IMD) according to IEC 61557-8 shall be installed on the secondary side.
NOTE Depending on a risk assessment it should be determined if the signal of the IMD is to initiate an acoustic
and/or flash alarm or transmit it to a monitoring system.
557.3.5 Power supplies for auxiliary circuits
557.3.5.1 General
The rated voltage of the auxiliary circuit and the components used in the circuit shall be
compatible with the supply to that circuit.
NOTE If the supply voltage is too low for the design of the circuit, then the operation will not be reliable, e.g. for
the proper function of relays.
Consideration should be given to the effects of voltage drop on the correct function of the
electrical equipment of the auxiliary circuit, e.g.:
– for an a.c. supply, relays and solenoid valves may have an inrush current of 7 to 8 times of
the holding current;
– for a d.c. supply, the inrush current is equal to the steady current;
– in the case of motors starting direct-on-line, the starting current could reduce the supply
voltage of an auxiliary circuit dependent on the main circuit below the minimum operating
voltage of the associated switchgear.
557.3.5.2 Standby power supply or power supply for safety services
Where a standby power supply or a power supply from a generating set is used to supply
auxiliary circuits, the frequency variation shall be taken into account.

– 6 – 60364-5-55 Amend.1 © IEC:2012
557.3.5.3 AC supply
The nominal voltage of control circuits should preferably not exceed
– 230 V for circuits with 50 Hz nominal frequency,
– 277 V for circuits with 60 Hz nominal frequency,
respectively, taking into account voltage tolerances according to IEC 60038.
The dimensioning of cable length with respect to the conductor capacitances, e.g. connection
to a limit switch, needs to be coordinated with the selected relays or solenoid valves.
The standing voltage caused by high conductor capacitances may impair the switching off of
the relay or solenoid valve.
557.3.5.4 DC supply
557.3.5.4.1 Supply by a power system
The nominal voltage of control circuits should preferably not exceed 220 V.
557.3.5.4.2 Supply by batteries
Where batteries are used as a power supply for auxiliary circuits, the voltage fluctuation due
to charging or discharging shall not exceed voltage tolerances specified in IEC 60038, unless
the auxiliary circuit is specifically designed to compensate for such voltage fluctuation.
Compensation of the voltage fluctuation may be achieved by counter cells.
557.3.6 Protective measures
557.3.6.1 Protection of wiring systems
In the case of extended auxiliary circuits it is necessary to ensure that the required tripping
current of the protective device will be achieved also at the far end of the respective cables or
conductors, see IEC 60364-4-43:2008, Clause 433.1.
Single-phase earthed a.c. or d.c. auxiliary circuits supplied on the secondary side of the
transformer for an auxiliary supply are permitted to be protected by single-pole switching
devices. The protective devices shall only be inserted in conductors which are not connected
directly to the earth.
Unearthed a.c. or d.c. auxiliary circuits shall be protected against short-circuit current by
protective devices interrupting all line conductors. Single-pole protection is permitted if the
rated voltage and the time-current characteristic of the related short-circuit protective device
are such that the conductor with the smallest cross-sectional area is protected.
NOTE 1 The use of protective devices which disconnect all lines of an unearthed auxiliary circuit will aid fault
diagnosis and maintenance activities.
If the short-circuit protective device on the primary side of the transformer for an auxiliary
circuit is selected so that it also protects against short-circuit current on the secondary side, a
protective device on the secondary side of the transformer may be omitted.
NOTE 2 The magnitude of the short-circuit current on the primary side depends also on the impedance of the
transformer.
60364-5-55 Amend.1 © IEC:2012 – 7 –
557.3.6.2 Protection against short-circuit
Switching contacts of electrical switching devices of the auxiliary circuit shall be protected
against damage caused by short-circuit currents, according to the manufacturer's instructions.
557.4 Characteristics of cables and conductors – Minimum cross-sectional areas
In order to ensure adequate mechanical strength, the following minimum cross-sectional
areas indicated in Table 557.1 shall be met. If there are special mechanical strength
requirements for cables or conductors, then a larger cross-sectional area of the conductors
should be selected in accordance with IEC 60364-5-52:2009, 522.6.
Table 557.1 – Minimum cross-sectional area of copper conductors in mm
Type of cable
Single-core Two-core Multi-core
Application
Single-wire Stranded Screened Unscreened Screened or
unscreened
a
Control circuits 0,5 0,5 0,5 0,5 0,1
Data transfer – – – – 0,1
a
Other auxiliary circuits may need a larger cross-sectional area of copper conductor, e.g. for measuring.

NOTE The cross-sectional area of copper conductors is derived from IEC 60364-5-52:2009.

557.5 Requirements for auxiliary circuits used for measurement
557.5.1 General
Measuring circuits are auxiliary circuits with dedicated requirements which are given in the
following subclauses.
557.5.2 Auxiliary circuits for direct measurement of electrical quantities
Where there is direct contact of a measurement device with the main circuit, the following
measures for protection of cables against overheating shall be applied:
– requirements according IEC 61439-1:2011. 8.6.2 and 8.6.4; and/or
– use of short-circuit protective devices.
If an interruption of the measurement circuit by disconnection of the short-circuit protective
device could lead to a hazardous situation, the short-circuit protective device shall also
disconnect the related main circuit.
For a measurement device with direct contact between the measurement circuit and the
auxiliary source attention should be given to phase coincidence and correct polarity.
557.5.3 Auxiliary circuits for measurement of electrical quantities via a transformer
557.5.3.1 Current transformer
Where a measurement device is connected to the main circuit via a current transformer, the
following requirements shall be taken into account:
– the secondary side of the transformer in a low voltage installation shall not be earthed,
except where the measurement can only be carried out with a connection to earth;
– protective devices interrupting the circuit shall not be used on the secondary side of the
transformer;
– 8 – 60364-5-55 Amend.1 © IEC:2012
– conductors on the secondary side of the transformer shall be insulated for the highest
voltage of any live parts or shall be installed such that their insulation cannot come into
contact with other live parts, e.g. contact with busbars;
– terminals for temporary measurements shall be provided.
To reduce the influence of conductor impedance on the measuring result, the transformer
should preferably have a secondary nominal current of 1 A.
The above requirements do not apply to summation current transformers where hazardous
voltages do not occur, e.g. equipment for insulation fault location according to IEC 61557-9.
557.5.3.2 Voltage transformer
The secondary side of a voltage transformer shall be protected by a short-circuit protective
device.
557.6 Functional consideration
557.6.1 Voltage supply
Where loss of voltage, i.e. voltage fluctuation, overvoltage or undervoltage, could cause the
auxiliary circuit to be unable to perform its intended function, means to ensure continued
operation of the auxiliary circuit shall be provided.
557.6.2 Quality of signals depending on the cable characteristics
The operation of an auxiliary circuit shall not be adversely affected by the characteristics,
including impedance and length, of the cable between operational components.
The capacitance of the cable shall not impair the proper operation of an actuator in the
auxiliary circuit. The cable characteristics and length shall be taken into account for the
selection of switchgear and controlgear or electronic circuits.
For an extensive auxiliary circuit, the use of a d.c. power supply or bus-system is
recommended.
557.6.3 Measures to avoid the loss of functionality
An auxiliary circuit serving a special function where reliability is a concern will require
additional design considerations to minimize the likelihood of wiring faults. These wiring faults
could result in loss of function and/or loss of signal. Among the design considerations are
– selection of appropriate installation methods of cables (see 557.4),
– selection of equipment where a short-circuit to exposed-conductive-parts is not possible,
e.g. Class II equipment.
– use of inherently short-circuit and earth fault proof installation and equipment
For the use of inherently short-circuit and earth fault proof installation and equipment, the
following shall be considered:
a) Arrangements of single wires if measures are provided which prevent mutual contact and
contact to exposed-conductive-parts, e.g. with basic insulation and where short-circuits by
external influences are not expected. This may be achieved by, e.g.
– installation in cable trunking systems, or
– installation in conduit.
b) Arrangements of
– single-core cables, or
60364-5-55 Amend.1 © IEC:2012 – 9 –
– single-core, non-metallic-sheathed cables, or
– rubber-insulated flexible cables.
c) Provision of protection against mechanical damage and of safe distance from flammable
material for non-metallic sheathed cables.
d) Arrangements of non-metallic-sheathed cables with nominal voltage U /U at least 0,6/1 kV
(U = conductor to earth voltage, U = conductor-to-conductor voltage).

e) Use of cables with an insulation which is self-extinguishing and flame-retardant.
f) Use of cables that are afforded physical protection by being buried, e.g. installation of
cables in soil or concrete.
Lateral short-circuit proof means having provision for protection against the shorting of two
parallel conductors forming part of an assembly.
NOTE This may be achieved by use of cables with an earthed screen. In the case of pinching/shearing of a cable,
a possible short-circuit to earth via the cable screens should be considered. In earthed auxiliary circuits, designed
as closed-circuit working, a short-circuit may lead to tripping of the short-circuit protective device. In unearthed
auxiliary circuits, the short-circuit is detected by the IMD, see 557.3.4.3.
557.6.4 Current-limiting signal outputs
In earthed or unearthed auxiliary circuits with current-limiting signal outputs or electronically
controlled protection against short-circuit conditions, respectively, the signal circuit shall be
disconnected within 5 s if the respective measure operates. In special cases, a shorter
disconnection time may be required.
For current-limiting signal outputs or electronically controlled protection of the signal output,
respectively, automatic disconnection of supply may be omitted if a hazardous situation is not
likely to occur.
557.6.5 Connection to the main circuit
557.6.5.1 Auxiliary circuits without direct connection to the main circuit
Electrical actuators, e.g. actuating relays, contactors, signaling lights, electromagnetic locking
devices, shall be connected to the common conductor (see Figure 557.4):
a) in earthed auxiliary circuits, at the earthed (common) conductor;
b) in unearthed auxiliary circuits, at the common conductor.

Overcurrent protective
device
Switched conductor
Common conductor
IEC  1805/12
Figure 557.4 – Configuration of an auxiliary circuit
Exception: Switching elements of protective relays, e.g. overcurrent relays, which may be
installed between the earthed or the non-earthed conductor and a coil, provided that
– this connection is contained inside a common enclosure, or

– 10 – 60364-5-55 Amend.1 © IEC:2012
– it leads to a simplification of external control devices, e.g. conductor bars, cable drums,
multiple connectors, and taking into account the requirements of 557.3.6.2.
557.6.5.2 Auxiliary circuits with direct connection to the main circuit
If the auxiliary circuit
a) is supplied between two line conductors (e.g. L1 and L2 of an IT system), two-pole
switching contacts shall be used;
b) is connected to the earthed neutral of the main circuit, the requirements of
IEC 60364-4-43 apply.
557.6.6 Plug-in connections
Interchangeability between multiple plug-in connections is permitted only where it will not
result in mechanical damage or introduce a risk of fire, electric shock or injury to persons.
NOTE 1 These plug-in connections form a part of the auxiliary circuit(s) and may conduct different signals.
NOTE 2 Protection against interchangeability may be achieved by marking, polarization, design or electronic
interlocking.
The connectors shall be secured by a means to prevent unintended disconnection.
557.7 Functional safety
Where there is a safety related system in accordance with th
...