I have been advised by contractor to use an interposing relay with the output card to give signals to external field elements such as actuators & valves. I have looked up wiring of interposing relay but haven't found anything specific related to how interposing relay should be wired within a panel.

Can somebody point me in the right direction as to how interposing relay should be wired with output card & field elements?

 

This is a very common practice. If you have not run across it before, maybe you should just ask someone with a little more experience.

The exact wiring will depending on what output card you are using and what you are trying to control, and where the control power is coming from.

 

Hi Thira,

did you mean how to wire relay to PLC digital output channel ? Following link should be helpful for you

http://www.thelearningpit.com/hj/plcs2.asp

 

Basically, it means that the PLC output drives the relay and the relay contacts actuate the field device, whether it be a solenoid, motor starter, etc. If you need more direction than that, then Bob is correct and you need to consult with someone more experienced.

 

Before going to the trouble of adding interposing relays, check you really need them.

Find out how much current the coils draw and compare it to the output module specs.

If your valves are 24 VDC use a flyback diode
If 120 VAC use a Metal Oxide Varistor rated for 130 Volts.

Roy

 

If the rating of the load even approaches, although still within the rating of the output module, I would still use interposing relays. Cheaper and easier to just pull a defective relay if an offending load coil decides to short (fuses are also a 'very good thing')! And as Roy pointed out, MOV's and reverse diodes are a must.

Gerald Beaudoin