Using PHOENIX CONTACT relays (2961105) 24V DC with contact 6 A rating with socket (2966016) at output of Siemens PLC. Very unfortunately we are facing problem of the relay getting stuck up many times. I would like your expert opinion to know the reason behind it. I read, it could be because of leakage current. Other reasons? Any other phoenix relay to kill either leakage current if any?
It is hard to give you much in the way of good advice w/o better information. However, I can make these general comments.
I have had some of this style of relay fail on me in the past. Sometimes they fail open, sometimes the contacts weld closed. I don't like to use them for that reason. Sometimes brand new they come in non-functional.
The contacts themselves do not seem to be very robust.
I am not sure what you mean by leakage current or by "stuck up". Is the leakage current coming from the Siemens output module and keeping the relay on when it should shut off? If so, a simple resistor in parallel with the relay coil should fix that.
Depending on your cable run for those relays, the cable will pick up inductive voltage from AC wires within the run and cause those to switch erratically. They are very sensitive I guess.
You can determine if it's leakage by disconnecting the PLC output from the relay when the output is stuck on, but you must do so at the PLC. Any physical disturbance of the relay may un-stick it, and this can be another test (though not as definitive as the leakage test). If the relay itself is sticking, the load characteristics have most likely welded the contacts.