Siemens Industry Online Support
Siemens AG
Entry type: FAQ Entry ID: 77282496, Entry date: 08/18/2016

SIRIUS Safety Integrated: Cascading of safety relays to SIL 3 or PL e

  • Entry
  • Associated product(s)



Cascading of safety relays is used for tripping several safety relays in series. Multiple safety functions can then be logically connected to a shared shutdown path. At the same time, several enabling circuits can be created for selective shutdown of drive elements.


The two safety relays represented are logically connected via the cascading input. If the emergency stop is triggered at the first safety relay, both safety relays then switch their actuators off. By contrast, if the protective hood shown is opened, only the associated actuators are switched off, for example.
If an emergency stop has been triggered by the higher-level safety relay, the lower-level safety relay must be switched on again manually using the Start button. A global Start button is only possible if all danger zones are visible from this Start button.



Content of Downloads


Wiring diagrams    Cascading_SIL3_3SK1_wiring.zip ( 3197 KB )
Project for Safety Evaluation Tool Cascading_SIL3_3SK1_set.zip ( 52 KB )



Filter criteria: 

Hardware platform:  Safety, SIRIUS
Software:  none
Entry contens:  Application Examples