Siemens SIMATIC S7 Functional Safety Manual page 189

Unsuppressed inductive loads can lead to failures.
The following failures can result from unsuppressed inductive loads:
• Unsuppressed inductive loads can lead to early "stuck-on'" failures of F-DQ and F-relay
• Unsuppressed inductive load switching generates an EMI hazard to the PLC system
Death or serious personal injury and damage to machines and equipment may result if
proper precautions are not taken.
You should use suppressor circuits with inductive loads to limit the voltage rise when a
control output turns off and to limit the electrical noise generated when switching inductive
loads.
S7-1200 Functional Safety Manual
Manual, 02/2015, A5E03470344-AA
WARNING
outputs.
and correct processing of the safety function.
A.3 Fail-Safe signal module (SM) technical specifications
Technical specifications
189