Siemens SIMATIC ET 200SP System Manual page 50

Wiring
5.1 Rules and regulations for operation
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 245)).
● For 24 V DC supply: Make sure there is safe (electrical) isolation and separate cable
routing or increased insulation of the low voltage (SELV/PELV) to electric circuits with
dangerous potentials in accordance with IEC 60364-4-41.
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
protective conductor with 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.
50
Distributed I/O system
System Manual, 12/2015, A5E03576849-AF