Siemens SIMATIC MV550 S Operating Instructions Manual page 27

Connecting the 24 V DC power supply
Requirement: Safe extra low voltage
The device should only be connected to a 24 V DC power supply which satisfies the
requirements of safe extra low voltage (SELV).
When the device is operated on a wall, in an open rack or other similar locations, an NEC
Class 2 current source is needed for compliance with UL requirements (according to
UL 60950-1). In all other cases (according to IEC/EN/DlN EN 60950-1), a current source
with limited power (LPS = Limited Power Source) is required.
24 V DC power supply (19.2 to 28.8 V)
The generation of the 24 V DC supply voltage by the line-side power supply must be
implemented as functional extra-low voltage with safe electrical isolation (floating)
according to IEC 80364-4-41, or as SELV according to IEC/EN/DlN EN 60950-1 and
LPS/NEC class 2.
Overvoltage protection
NOTICE
Protection of the external power supply
If the optical reader is supplied via extensive supply lines or networks, interference by
strong electromagnetic pulses on the supply lines is possible, e.g. from lightning or the
switching of large loads.
The connection of the external power supply is not protected against strong
electromagnetic pulses. An external overvoltage protection module is required for this
purpose. The requirements according to EN 61000-4-5, Surge test on power supply lines,
are only met when a suitable protective element is used. A suitable device would be, for
example, the Dehn Blitzductor BVT AVD 24, article number 918 422, or a comparable
protective element.
Manufacturer:
DEHN+SOEHNE GmbH+Co.KG, Hans-Dehn-Str.1, P.O. Box 1640, D-92306 Neumarkt,
Germany
SIMATIC MV500
Operating Instructions, 05/2019, C79000-G8976-C494-02
WARNING
Safety notes
27