PLC Control and Stop, not E-Stop, buttons

I have starting work at a new place and the stop buttons will stop the machinery as long as the stop button is pushed in. Releasing the stop button allows the PLC to restart the machine. While this seems inherently wrong, bad, and unsafe I cannot find any regulations that state this is a no-no. Can anyone help?

It seems like a cycle pause button. If it is only stopping a machine cycle rather than motors start/stop circuits or something, I don't think it's violating any rules (I would never do it though)

There shouldn't be anything unsafe about it ever. Because if they let go of the button and the machine starts up, the machine should be safe guarded to the point where they cannot gain access to moving machinery. Be it through the use of two-hand safety devices, physical guarding, or safety light curtains, grids, fencing or mats.

If the operator is in danger of getting hurt after letting go of the "pause" button, then they are going to be in danger of being hurt before they even hit the "pause" button.

As you noted, it's not the EStop which is covered in regs. This is like the inverse of a Jog mode. Depending on appropriate warnings and the needs of the process it may be ok. Is there a safety concern?

Stephen3776 said:

I have starting work at a new place and the stop buttons will stop the machinery as long as the stop button is pushed in. Releasing the stop button allows the PLC to restart the machine. While this seems inherently wrong, bad, and unsafe I cannot find any regulations that state this is a no-no. Can anyone help?

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What color is the button, how is it labelled, and what type of operator?

I have always believed (not 100% sure) that a red mushroom head button labelled stop, must not automatically restart the machine when released, and that another deliberate button press is required to meet safety regulations.

If it's labelled E-STOP or EMERGENCY STOP then it must be in violation (I can't prove it, but I am sure one of the code gurus on here with access to the latest regs. can confirm this statement.)

I have worked in a plant that had some controls that didn't meet current codes, but were grandfathered in because they were unmodified since the late 1970s

Even they would never label a button STOP and allow auto restart. Now if the button is momentary or maintained might make a difference as well, but I don't think we're allowed to use a maintained stop button cause equipment to restart when pulled out anymore, although I do have some small old simple machines wired that way.

I would accept it only if it is labelled appropriately, any color other than red, and has a flush momentary operator (or shrouded), just not a raised head PB, or a mushroom operator.

Those labels in combination with certain operator types, I believe to be reserved for emergency stop devices which require separate deliberate restart via a different.

Are my understandings within the rules?

Yeah, make it a yellow lighted shrouded momentary operator and have it blink all the paused buttons when it's in pause mode, plus time limit the operation in PLC code if possible, buy legend plates that say "HOLD" or "PAUSE", use a normally open contact, so a wire break doesn't halt automatic operation.

Heck I wouldn't even use the word "STOP" on a button unless it was red and did exactly that, requiring a separate, deliberate "START" command.

"If it seems inherently wrong, it probably is."

Paul

EDIT: I left the most important factor. Hazard Analysis. If this machine can't break your skin if you fall into it, then that's different than one which can sever limbs.

Be Safe!

If the button was yellow or any color except red and not labeled stop I probably would not see much harm; however, the buttons are part of the start/stop circuit and the PLC maintained output does not turn off when the stop button is pushed, thus the equipment, ranging from pumps to screw conveyors, turns back on when the stop button is released. Come to think of it, I have not checked to verify the equipment does not turn back on when the E-Stops are reset, a point for me to examine on Monday.
I am unsure if an operator can be harmed; however, my gut tells me if the button is red and labeled stop it should not start again when I release the button. This is not my code as I cannot ever imagine writing something that did not drop the output when the stop button is pushed. Heck, most of my code mirror three start/stop and the output is only momentary and latched by the auxiliary contact input.
Does anyone know of any regulations concerning a red button labeled stop that permits the equipment to restart when it is released?

Several have given you good practices. There advice is good and solid. Good practice and good design override Code any day of the week. Code is bare minimum in all too many cases.

Dan Bentler

At our plant Printing ,when any stop button is pushed whether it is a maintained or momentary set of contacts a start button being pushed is required to restart any piece of machainery

leitmotif said:

Good practice and good design override Code any day of the week. Code is bare minimum in all too many cases.

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I think our European colleagues may find this statement quite amusing.

A little reading of the clear as mud NFPA has several sections that suggest this is no good. I am refering to 9.2.5.1.2, 9.2.5.3.2, 9.2.5.3.3, and 9.2.5.5.2; however, none of these directly state that tis is forbidden as stated in E-stop circuits and PLC interaction (or lack of interaction). It would be nice to have some secure footing before I make a stink against the bosses pet and stress safety in a productive manner.

Stephen3776 said:

A little reading of the clear as mud NFPA has several sections that suggest this is no good. It would be nice to have some secure footing before I make a stink against the bosses pet and stress safety in a productive manner.

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OH that battle and bosses pet to boot. You have my sincere sympathy.

Right now I am sure you know NFPA better than I - sounds like you been doing some studying especially from how aggravated you sound.

IF
1. The machine has a RED stop switch / pushbutton that requires independent action to restart ie move from OFF to ON or hit the start button,,
2 The switch is labeled anything BUT stop and is not red. Could be labeled HOLD or PAUSE or ?? Could be pink with green and yellow polka dots maybe??
3. Poses no additional hazard to operator(s) by operation

Then I see nothing wrong with it. As Bernie said "a JOG in reverse" uh quoted you correct Bernie??

Think recessing switch to prevent inadvertent operation would be a good idea.

Dan Bentler

CYA with code as the ace up your sleeve. Assess the hazard inform the executives of the danger, and offer a quick solution including rough cost.

Back that up with tour lock out hasp!

If that doesn't get results, then threaten them with code.

They can't ignore warnings of missing body parts.

You will be respected for taking a firm stance on safety.

Thanks everyone for the input. I am thinking from memory (means iffy) that the machinery will restart if the E-Stop is reset. If this is true this is a clear code violation that must be fixed. If this is true then I will piggy back the "stop" button issue on top if it and kill two birds with one stone. Will know more on Monday and post my discover.

Bottom line is that when someone gets hurt, OSHA will reference any and all codes THEY deem applicable to your machines. If it is an industrial machine you can bet NFPA 79 will be looked at along with others that may apply to specific types of machinery.

One other little tidbit when it comes to codes is that the word "shall" is the magic phrase that means this is not optional. When you see that you have to provide the described circuit or operation to be in compliance with the code.

Sounds like you are on the right track technically. If only company pollute were clear cut you'd be home free.

Not sure what the regulations are in the US, but in the UK you would not have to change.

The safety regulations are only enforced on new machinery or if you make changes to or move old equipment.

If the equipment passed whatever was the safety regs at the time it was installed then you do not have to change, can you imagine having to go through everything in your plant every time the laws change.

E/Stops

Well here in the UK that would be considered as poor practice. Any safety devices that have been operated should not automatically restart, when reset, There should be a separate reset!! I.E through a pilz relay or the plc.