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?
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!