Non-latching em stops

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Phoenix

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I know theres a few on here who do machinery safety systems.... more a curiosity question than anything... are non latching EM stops every allowed, and if so, under what conditions?

I always thought they had to be of a latching type, but it seems not all that are fitted are. When working near those industrial speed doors I've got in the habbit of popping the EM stop in so the door can't move, but came across one that was a non-latching EM stop. Surely it cannot be right, that after the door has been stopped on the EM stop, that it can be be commanded to move again from the remote up/down controls without having to go to the EM stop and unlatch it?

 
Sidewinder is  the goto  person on that I'd say .    But I'm thinking the non latching  remote stops are the older  installs .

As you rightly say ,  latching forces someone to go and investigate  at the position of the stop .  

 
those doors will have their own safety detection etc to 12453/12445  so an emergency stop is not actually required in the first place, although id expect it to be latching if one is there an intended to be used as an emergency stop.

note that many are just a stop button, i.e GFA control units have an up / stop / down button on them, neither are latching and the stop is just that, stop. it can then move on another command without unlatching it

your best option is to either isolate it, or cover the photocell if present. that will stop it going down, but not up

 
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The mechanism that "latches" the stop is electrical (a relay of some sort drops out until reset) so should not rely on the actuator head to keep it stopped.

A latching button, sometimes with a key release is an extra measure to ensure it can't re start without investigation, but the latching mechanism of the button should NOT be the thing that latches the stop.

As already pointed out, what you have is a "stop" button, not an "emergency stop" button.

 
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If it is not-latching, it is not an emergency stop.


Thats interesting to know... it looks like it was intended as one... the panel has a standard red push button with a stop legend in addition to the non-latching mushroom head style em stop button

 
The mechanism that "latches" the stop is electrical (a relay of some sort drops out until reset) so should not rely on the actuator head to keep it stopped.

A latching button, sometimes with a key release is an extra measure to ensure it can't re start without investigation, but the latching mechanism of the button should NOT be the thing that latches the stop.
Wrong Dave an emergency stop button must, have a trigger operation latching actuator.

The remainder of the circuit is something else.

Key release buttons are no longer de rigeur.  They are not to be used as a normal emergency stop button.

 
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those doors will have their own safety detection etc to 12453/12445  so an emergency stop is not actually required in the first place, although id expect it to be latching if one is there an intended to be used as an emergency stop.

note that many are just a stop button, i.e GFA control units have an up / stop / down button on them, neither are latching and the stop is just that, stop. it can then move on another command without unlatching it

your best option is to either isolate it, or cover the photocell if present. that will stop it going down, but not up


Correct Andy, an emergency stop is not a replacement for safeguarding, and is not to be relied upon as such.

Also, equipment should be isolated prior to work, how do you know that the PL of the equipment is adequate to protect you with just the e-stop depressed.

LOTO.

 
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On a similar subject I think the lock off calipers are important .    

  I date back to pre H&S   ...I worked on overhead cranes for a while  ,  the other electrical guy with us  once stepped off a crane ,    onto the  crane track  ,  (Don't know why)   .    The crane on the next track  went past and knocked him off ,    worse  , he fell onto the conduit pipe vice below,  & worse again , he had a long , thin screwdriver in his  overall top pocket  which was driven up through his neck  , pierced his eardrum  but missed his brain .  

He recovered  but could only work in the workshop as he had a limp , deaf in that ear and a morbid fear of heights .   

Following that we carried calipers and padlocks and would have isolated BOTH cranes if we needed to go onto the track .   If the fitters were with us  they would also  attach padlocks to the caliper.    

Have to say , it was not unusual for the fitters  to isolate the crane by raising the  three pick-ups  off the downshop rails ....  then to use a drill  they had an extension lead , tied the socket to the handrail,   crocodile clip  the neutral  to the metalwork of the crane  and drape the bare end of the flex across the top rail   :C  

 
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yep, always lock everything off. few factories i work at have overhead cranes. i dont work on them directly, but if i need to be within their path (i.e fixing lights above them) then they get isolated and locked off, even if they say they are working away from me

even put a lock through a fused spur often, get a few looks when people realise you can do that

 
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You gotta watch yer back  all the time Mate  !!

One of the assessors irritated me , one of those who fire questions at you for 4 hours  until you just wish they'd ****** off ..... he started on about "Safe isolation "   etc    Domestically speaking  I suppose ....    wanted to see my MCB locks I produced some  , I only have four ,    so he  comes back with "What if you need more "     I say we often disconnect in the board , but thats not good enough for them ,   " What if someone  re- connects them ? "       

Well in my opinion  the circuit now becomes their responsibility  ,    but that wasn't good enough either  , I  just said well thats it , I can do no more ....  how far do go  ? FFS  !!  

On industrial work we do indeed disconnect at the board  and label  the ends ...if you leave the fuses around some twonk will shove them back in .  

 
Non-latching emergency stop buttons will work safely as long as it operates a contactor, either at the mains point 

(or on a machine,  say a lathe). The contactor should then only be possible to reset with a key held by someone in charge.

This is  how the workshops I've worked in over the years in schools & colleges worked. Any stop button placed around

the work-shop would be able to kill all the power straight away, in an emergency. Same thing after any power-cut.

Southsparks.

 
Non-latching emergency stop buttons will work safely as long as it operates a contactor, either at the mains point 

(or on a machine,  say a lathe). The contactor should then only be possible to reset with a key held by someone in charge.

This is  how the workshops I've worked in over the years in schools & colleges worked. Any stop button placed around

the work-shop would be able to kill all the power straight away, in an emergency. Same thing after any power-cut.

Southsparks.


There is no such thing recognised any longer as an non-latching emergency stop button.

Emergency stops are now covered by BS EN 13850, they must be latching and the performance level of the emergency stop system must be as a minimum of PLc.

The emergency switching system you describe for schools & colleges is defined in BS 4163, this calls on the other harmonised safety standards.

 

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