Siemens SINAMICS G120 Function Manual page 84

Interfaces
3.2 Activation via F-DI
Series-connected electromechanical sensors
You may connect emergency stop control devices in series because it is not possible for
these devices to fail and be actuated at the same time.
According to IEC 62061 (SIL) and ISO 13849-1 (PL), position switches of protective doors
may also connected in series.
Exception: If several protective doors are regularly opened at the same time, it is not
possible for faults to be detected, which means that the position switches must not be
connected in series.
The inverter provides the supply voltage
Connect the 24 V supply of the inverter to the sensors and connect the reference potentials
of the inputs used to GND.
Figure 3-6
82
Connecting electromechanical sensors to the inverter power supply in series
Safety Integrated Function Manual, SINAMICS G120 and G120C
Function Manual, 01/2011, FW 4.4, A5E03052391B AB