Cascading; Startup Testing - Siemens SIRIUS 3SK1 Manual

4.3.11

Cascading

Cascading of safety relays is used for tripping safety relays in series.
Several safety functions can then be logically connected to a shared shutdown path. Several
safety-related outputs can be created for selective shutdown of drive elements.
The connection between the individual modules must be arranged on one side only, because
cascading from the last relay to the first one would create a loop which would prevent
starting.
Cascading is implemented within a control cabinet in a single-channel configuration; this is
even permissible with SIL 3 / PL e, because cable routing within a control cabinet is
protected against short-circuits and short-circuiting to P potential (fault exclusion in
accordance with ISO 13849-2).
The 3SK1 Advanced device series offers an extremely convenient solution for cascading.
Input expansions can be easily connected to the evaluation unit by means of device
connectors.
4.3.12

Startup testing

The sensor or protection equipment must be opened and closed again after the supply
voltage is restored before the enables for the 3SK1 safety relay can be switched through.
Startup testing ensures that any errors in the sensors are detected (again), because safety
relays lose their ability to store errors at zero voltage.
Unauthorized manipulation of the protection equipment can also be detected through startup
testing.
The plant operator decides whether startup testing should be performed (risk assessment).
No general statements apply.
Note
In the delivery state of 3SK1 safety relays, startup testing is deactivated.
SIRIUS 3SK1 safety relays
Manual, 06/2018, A5E02526190021A/RS-AD/004
Safety systems - General information
4.3 Basic terminology
39