Digital modules
3.5 How to protect digital modules from inductive overvoltage
S7-300 Module data
Manual, 06/2017, A5E00105505-AJ
61
3.5 How to protect digital modules from inductive overvoltage
Inductive overvoltage
Overvoltage occurs when an inductance is deactivated. Examples of this are relay coils and
contactors.
Integrated overvoltage protection
The digital output modules of S7-300 have integrated overvoltage protection equipment.
Extra overvoltage protection
Inductances should only be configured with extra overvoltage protection equipment in the
following instances:
● If SIMATIC output current circuits can be deactivated by extra fitted contacts (e.g. relay
contacts).
● If the inductive reactances are not activated by SIMATIC modules.
Note: Ask the suppliers of inductive reactances what size of overvoltage protection
equipment should be used.
Example
The following diagram shows an output current circuit which make extra overvoltage
protection equipment necessary.
Contact in output current circuit
Inductive reactance needs a protective circuit
Figure 3-1 Relay contact for emergency stop in output current circuit
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