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Rc Circuit On Siemens S7 Relay Outputs


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If you use the Siemens S7 card SM 322 DO 8 relay AC250V/5A, when can you use the RC circuit in the card, and when can you not?


If you controll another 230VAC motor relay that already have a RC circuit paralell to the coil, can you still use it. Is it necessary, and why? To protect the Simens-card or to protect the other relay/coil?


There was one time when I connected the RC circuit in the card on a 230V relay, and the relay went on/off at a very high speed. And when i took the connection to the RC circuit in the card away it worked fine.



Se page 168 in https://support.automation.siemens.com/WW/l...&viewreg=WW


or search for 6ES7322-5HF00-0AB0 in the document.

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For minimizing the arcing between relay contacts in AC supply, it is necessary to use "Snubbers/Spark Quenchers/RC Circuit" parrallul with output coils. This increases the life of relay in output card. But keep it in mind that where the high speed switching applications, this RCC creates problem and INCREASE the ON time of related coil. Though this ON time is very short (in mili seconds) but not good in high speed applications. For such high speed switching applications , we use Solid State Relay or Transistor type output cards.


Here in my plant, I installed every where the RCC and in DC supply case, the reverse biased Diodes.


"Don't assume any thing, always check/ask and clear yourself".

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