Safety Relay Monitoring

In a guardlogix system, are the feedback inputs for monitoring a failed relay suppose to be safety inputs? We just got a new line where all the feedbacks were just standard inputs and then mapped into the safety PLC. They said this is sufficient and meets regulations.

To me that kind of worries me. Everyone has access to the standard logic in our facility. I wouldn't put it past a maintenance guy to be having a problem with a relay sticking and just tieing the output signal to the input signal in standard logic. Hence, disabling any monitoring for failed relays.

Thoughts?

my opinion.
is the relays controlled by the safety controller? if yes, then you can't wire them into a standard plc. what if the plc dies? what if a maintenance guy programs the input to be true all the time? if someone modifies the code, the safety plc integrity is compromised and someone can get hurt.

that's why you have the safety plc.
I don't know the system design, so I really can't say for sure.

james

According to KB article 624460, it is acceptable to wire the feedback to a standard input, but if you want cat 4, then they 'suggest' using a safety input if possible.

https://rockwellautomation.custhelp.com/app/answers/detail/a_id/624460/page/1

Wiring an output to an input to bypass the functionality won't work if negative feedback is being used.

If you are just monitoring the feedback of the safety relay and the equipment is connected directly to the safety relay, then its still doing its job, all is well.

If the output of the safety relay is going into the PLC and then that is controlling the equipment, then that is a no no.

As you have a GuardLogix, ditch the safety relay and bring that safety function into the PLC so its all under the same roof.

Password the safety logic also if the maintenance guys do this sort of thing also.

lanman said:

According to KB article 624460, it is acceptable to wire the feedback to a standard input, but if you want cat 4, then they 'suggest' using a safety input if possible.

https://rockwellautomation.custhelp.com/app/answers/detail/a_id/624460/page/1

Wiring an output to an input to bypass the functionality won't work if negative feedback is being used.

Click to expand...

Thanks, this is most helpful. This IS suppose to be a category 4 system. I finally convinced them to buy more safety modules and wire them up as safety inputs.

My fear was they bypass it in the standard PLC logic, not acctually hard wire bypassing. Everyone has access to standard logic in our facility, multiple computers on plant floor. Safety logic is passworded and only I can access it. I wouldn't put it past a maintenance guy to do XIO (Relay Output) -> OTE (feedback).

janner_10 said:

If you are just monitoring the feedback of the safety relay and the equipment is connected directly to the safety relay, then its still doing its job, all is well.

If the output of the safety relay is going into the PLC and then that is controlling the equipment, then that is a no no.

As you have a GuardLogix, ditch the safety relay and bring that safety function into the PLC so its all under the same roof.

Password the safety logic also if the maintenance guys do this sort of thing also.

Click to expand...

Most everything is done is in the safety PLC, but there are still some required relays. For example valve power, motor power,etc...Safety output pulls in 2 seperate safety relays then we monitor feedback to verify they both performed correctly.