Siemens SIMATIC S7 - Application 2: Wiring External Contactors: Separate P and M Controlled Contactors; Application 3: Wiring External Contactors: Parallel Connected between P and M

Fail-Safe signal module (SM) applications
3.2 Digital output applications
S7-1200 Functional Safety Manual
76 Manual, 02/2015, A5E03470344-AA
3.2.3
Application 2: Wiring external contactors: Separate P and M controlled
contactors
A short-circuit between the P and the M output can immediately lead to dangerous failure.
You must prevent this failure mode by proper separation and protection of conductors.
3.2.4
Application 3: Wiring external contactors: Parallel connected between P and M