E-Stop Circuits In US Food and Beverage Industry

Not to be overly complicated but a little more costly I use a Dual Loop safety relay one each for each E-stop button. each e-stop button safety relay is dual looped to a master safety relay. I monitor both channels of all safety relays to the PLC . The master Safety relay is set for manual reset while individual e-stop Safety relays are set as auto reset.
This lets me determine if an e-stop is triggered or if I have a bad contact on one of the loops. being an end user I am not trying to cut costs on safety while keeping my Safety Manager happy.

40 years ago it was just a red maintained PB to a relay and you had to check every red button on the machine when the call came in "my machine wont start"
Now it tells you status on HMI so all you have to do is keep telling them to read what it says!

My preference is for all E-Stop PB’s to be illuminated (PB depressed & light is on). The thought being if you see a red light then that points to the location.

Also, E-Stop PB’s should be maintained.

theColonel26 said:

• Safety Circuit, power right after the fuse
• E-Stop NC (E-Stop Output)
• E-Stop NO going only to the PLC

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Which of those are required for safety? Which are for troubleshooting? What are the relative costs of a down-time automotive vs. a bakery or brewery.

The first only detects a power failure, because (presumably) power is required to the safety relay or safety PLC, loss of power will not result in a hazard because the system will stop.

The second is what provides safety, if the button is pressed, or wiring cut this will cause the safety relay or safety PLC to stop process.

The third only tells you which button has been pressed. This makes finding and resetting easier but doesn't provide any additional safety. (In theory if you use a combination of two and three it would be a little bit safer in the event a contact welded closed but two NC contacts would be much better for that purpose, so I'm assuming this is for detection only).

You have better diagnostics with those three but safety is essentially the same.

theColonel26 said:

Really the purpose of the NO is as an extra layer of protection so that if the NC on the E-STOP welds at least the PLC can stop the process.

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Using an NO contact is probably not giving you the boost in safety you think it is. How often is the required testing of each E-STOP switch? Since it is NO the only time you can detect a failure is when the switch is pressed. If (like many places) E-STOP switches are only 'tested' when they are needed you could have a broken wire in the NO circuit for years and not know it. That is why modern, high integrity safety systems use two NC contacts (with periodic testing).