2 Different Machines Estops on the Same Panel?

spaceacealpha

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I've did a Google search on this and the NFPA79 guide to estops. I have one machine that shares an additional estop with a nearby machine. Is this legit? Basically there is an HMI and below it are two estops. One labeled 'Emergency Stop' and the other is not labeled at all (I know this is wrong). They are using the host HMI cabinet as a very fancy push button box so the operator can respond when the other machine acts up. Anybody else run into this? To me it seems sketchy. Thanks, Darren
 
Not 100% positive how your layout is.... but I have worked on many large machines that have several control systems running them and they all have one safety/estop circuit that are interlocked so if something happens on one machine the other machine will also stop

Edit: Maybe one of yours should be a Stop and not a EStop??
 
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They have these split. It will only stop the one that they pressed for. Perhaps they should have a stop there instead of a e-stop. To me if there is an emergency, there would be confusion as to which to hit. I've asked the control technicians to look into what this bonus e-stop is tied into (since they have been around it longer).
 
They have these split. It will only stop the one that they pressed for. Perhaps they should have a stop there instead of a e-stop. To me if there is an emergency, there would be confusion as to which to hit. I've asked the control technicians to look into what this bonus e-stop is tied into (since they have been around it longer).

So a easy way to test in my opinion, push it and if the control power drops out its a estop, if it just stops the process and you can restart it then it's just a stop and needs to be relabeled as stop machine A and stop machine B
 
All rules aside, having two estops is confusing and confusion is dangerous in an emergency.

This sort of thing happens when a machine with its own safety is integrated into a larger safety system. If both buttons perform safety functions then the simplest thing to do is to put the switches all onto one button and blank out one. If one is not a safety function then it should not be using an estop button type.
 
we have several lines which consist of machines feeding a process machine to machine,(Food packaging)each machine has its own machine stop and an e stop for the complete line
 
All rules aside, having two estops is confusing and confusion is dangerous in an emergency.

This sort of thing happens when a machine with its own safety is integrated into a larger safety system. If both buttons perform safety functions then the simplest thing to do is to put the switches all onto one button and blank out one. If one is not a safety function then it should not be using an estop button type.

This is the real factor that a lot of people don't factor in. I've worked in a system where the operator had 4 e-stops to deal with and worst of all the overall e-stop didn't stop one of the machines, it only cut operator input to it (mission critical equipment).
Well, during commissioning with someone very inexperienced, the position controller went wild, the guy reacted and hit the overall e-stop which didn't stop the machine and by the time he hit the right one all hell had broken loose. No one died, two people were taken to hospital with a broken arm.

I left the industry since, but wouldn't surprise me if that contributes to problems in the future with that design.
 
There must never be a case where one has to guess which E-stop button to press.

Here is how we do it:

Each machine has its own E-stop safety relay. This safety relay requires reset with a dedicated reset button.
Additionally there is a safety relay for "e-stops from external machines". This safety relay has automatic reset. The externally connected e-stops must have their own safety relay with their own reset buttons. The connection between the machines is by dual channels from safety relay to safety relay.
The machines own E-stop stops everything on the machine. The external E-stop may only have to stop the parts of the plant or machine that can be considered part of the "zone" or area of the other machine. This goes both ways.
In other words, not everything needs to be stopped. And zones may overlap.
In this way, each e-stop button stops everything within vicinity. But it may well be that a machine isnt stopped when it doesnt need to be.
 

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