Siemens SIMATIC ET 200SP System Manual page 88

24 V DC supply
Below you will find a description of what you need to pay attention to with 24 V DC supply:
● For buildings: In the event of danger through overload, you must provide lightning
protection measures for external lightning protection (e.g. lightning protection elements).
● For 24 V DC supply lines and signal lines: If there is a risk of overvoltages, you need to
take precautions to ensure internal lightning protection (e.g. lightning protection elements,
refer to section Accessories/spare parts (Page 291)).
● For 24 V DC supply: Ensure protection by electrical separation and separate cable
routing or increased insulation of circuits with dangerous potentials from extra low voltage
(SELV/PELV) in accordance with IEC 61131-2 / IEC 61010-2-201.
Requirements for power supplies in the event of voltage interruption
Note
To ensure adherence to IEC 61131-2 and NAMUR Recommendation NE 21, only use power
packs/power supply units (230 V AC → 24 V DC) with a mains buffering time of at least
20 ms. Observe the relevant requirement in your product standards (e.g. 30 ms for "burners"
pursuant to EN 298) as regards possible voltage interruptions. The latest up-to-date
information on PS components is available on the Internet
(https://mall.industry.siemens.com).
These requirements, of course, also apply to power packs/power supply units not
constructed using ET 200SP or S7-300-/400-/1500 technology.
Protection against outside electrical influences
Below is a description of what you must pay attention to in terms of protection against
electrical impacts and/or faults:
● Make sure that the system for discharging electromagnetic interference is connected to a
functional earth or to protective conductor with a sufficient cross-section for all plants with
an ET 200SP distributed I/O system.
● For supply, signal and bus lines, you must ensure that the laying of the lines and the
installation is correct.
● For signal and bus lines, you must ensure that a wire/cable break or a cross-circuit does
not lead to undefined states of the plant or system.
Reference
You can find more information in the Designing interference-free controllers
(http://support.automation.siemens.com/WW/view/en/59193566) function manual.
Distributed I/O system
System Manual, 09/2019, A5E03576849-AJ
6.1 Rules and regulations for operation
Wiring
87