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I/O protections devices

Created by: mohalomari at: 3/13/2012 3:20 PM (4 Replies)

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3/13/2012 3:20 PM	Rate (0)
mohalomari Posts: 10 Rating: (0)	HI ALL i have plc s7-1212 DC-DC-RELAY what is the protection devices(relays- fuses-diods-..etc) should i put on each input/output even it's digital or analoge thnx for your help
mohalomari Posts: 10 Rating: (0)
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3/13/2012 3:29 PM	Rate (0)
Marcjan Platinum Member Joined: 4/22/2010 Last visit: 12/15/2022 Posts: 5697 Rating: (702)	Hello, Inputs don't have to be protected unless there is a great risk that voltages above the max can occur (non isolated equipment) in that case optocoupler is recomended. Outputs you can fuse per group at the max current per group. In case of heavy inductive loads a diode antiparalel on the coil is recomended to extend the life of the relais contacts. Regards, Marcjan
	Problem solved? Please let us know! Please no technical questions by PM, use the forum sections for your questions.
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3/14/2012 6:55 AM	Rate (0)
mohalomari Posts: 10 Rating: (0)	thanks Mr.Marcjan but as i read in s7-1200 user manual p.58 (Guidelines for wiring the S7-1200) i found that we have to put fuse protection on every output circuit but what they mean with output circuit, is it every output or every group? -another thing what is the limit of inductive loads to be high 10kw, 30 kw or what? if i am using external power supply for the inputs and outputs and it is standard power supply from phonex do i have to put any fuses on the input maybe short circuit will occur then the plc will damage, maybe wrong modification in our panel will damage our plc please advise for the best solution. and thanks for you cooperation.
mohalomari Posts: 10 Rating: (0)
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3/14/2012 7:29 AM	Rate (0)
Marcjan Platinum Member Joined: 4/22/2010 Last visit: 12/15/2022 Posts: 5697 Rating: (702)	Hello, for inputs there is no need to fuse at plc side of course your wiring should be protected by a fuse, if there is a shortcut in the field, the wiring can be burned if not used a proper fuse, not the input. For the outputs fuse them per group (4). High inductive loads are i.e. Hydraulic valve coils most off the modern smaller pneumatic valves have build in diode to protect the relais/transistor outputs. If you have to switch lots of lamps or other heavy loads close to the rating of the relais, use external contactors. Regards, Marcjan
	Problem solved? Please let us know! Please no technical questions by PM, use the forum sections for your questions.
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3/8/2016 10:01 AM	Rate (0)
Min_Moderator Platinum Member Joined: 9/3/2014 Last visit: 3/13/2019 Posts: 4825 Rating: (123)	New question published by AlbretJuno is split to a separate thread with the subject PLC outputs with pneumatic solenoid valves. Best regards Min_Moderator

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