Application 2: Wiring External Contactors: Separate P And M Controlled Contactors; Application 3: Wiring External Contactors: Parallel Connected Between P And M - Siemens SIMATIC S7 Functional Safety Manual

Fail-Safe signal module (SM) applications
3.2 Digital output applications
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

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S7-1200 Functional Safety Manual
Manual, 02/2015, A5E03470344-AA