How To Protect Digital Output Modules Against Inductive Surge Voltage - Siemens SIMATIC S7-300 Hardware And Installation Manual

Appendix
12.3.5 1 How to protect digital output modules against inductive surge
voltage
Inductive surge voltage
Overvoltage occurs when inductive devices are switched off. Examples are relay
coils and contactors.
Integrated surge arrestor
S7-300 digital output modules are equipped with an integrated surge arrester.
Additional Overvoltage Protection
Inductive devices require additional surge arresters only in following cases:
• If SIMATIC output circuits can be switched off by additionally installed contacts
(e.g. relay contacts).
• If the inductive loads are not controlled by SIMATIC modules
Note: Request information on relevant surge protection rating from the supplier of
inductive devices.
Example:
The figure below shows an output circuit that requires additional surge arresters.
Figure 12-8 EMERGENCY-OFF relay contact in the output circuit
12-28
Contact in the output circuit
Iinductivity requires
circuiting
(See the following figures)
S7-300 Programmable Controller Hardware and Installation
A5E00105492-02