# E-Stops shuts off machine.



## telsa (May 22, 2015)

Sparkee said:


> The company I work for bought a very expensive brand new piece of machinery and the build shop wired it so when any E-stop or safety latch is opened it opens a 480 volt contactor wired below the main disconnect. So we lose the PLC, HMI and the dynamic brake that is supposed to stop a large spinning table. Hard to believe a company that builds machinery would wire a machine in such a way. How do I make my case that this is not the way it is supposed to be done?


The FACTORY.


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## JRaef (Mar 23, 2009)

Who says that's not the way it's supposed to be done? You? If so, why was it not done the way you think it should be? Nobody asked you? If not, why not?

What I'm really trying to get to is that although you might think it should be done differently, your opinion may be just that; your opinion. There may be some overriding safety regulation stating that ANY unauthorized access or E-stop must immediately remove all energy sources from the machine. It's not uncommon. Now I agree with what I believe you are thinking, that disabling the very thing that could stop the blade faster and allowing it to spin down for a long time is likely MORE hazardous. But I too have run this up a flagpole and had it shot down, numerous times. It has always boiled down to the removal of all sources of external energy if there is an emergency or unauthorized access. 

In one case with a bagel slicing machine I worked on, I at least convinced them to add a mechanical brake on the spinning blade motor. Normally they didn't use it, a normal shut down routine kept the brake coil energized while the D.C. Injection brake stopped the motor, then the brake coil dropped out, saving the wear and tear on the brake. But if anyone opened the access door without doing a normal shutdown, or didn't wait for the D.C. Brake to work, the main power dropped out and that released the brake coil, which stopped the blade. So it didn't violate the safety rule of removing all energy, but it did stop the blade. You might consider making that suggestion if you are concerned about it.


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## sbrn33 (Mar 15, 2007)

JRaef said:


> Who says that's not the way it's supposed to be done? You? If so, why was it not done the way you think it should be? Nobody asked you? If not, why not?
> 
> What I'm really trying to get to is that although you might think it should be done differently, your opinion may be just that; your opinion. There may be some overriding safety regulation stating that ANY unauthorized access or E-stop must immediately remove all energy sources from the machine. It's not uncommon. Now I agree with what I believe you are thinking, that disabling the very thing that could stop the blade faster and allowing it to spin down for a long time is likely MORE hazardous. But I too have run this up a flagpole and had it shot down, numerous times. It has always boiled down to the removal of all sources of external energy if there is an emergency or unauthorized access.
> 
> In one case with a bagel slicing machine I worked on, I at least convinced them to add a mechanical brake on the spinning blade motor. Normally they didn't use it, a normal shut down routine kept the brake coil energized while the D.C. Injection brake stopped the motor, then the brake coil dropped out, saving the wear and tear on the brake. But if anyone opened the access door without doing a normal shutdown, or didn't wait for the D.C. Brake to work, the main power dropped out and that released the brake coil, which stopped the blade. So it didn't violate the safety rule of removing all energy, but it did stop the blade. You might consider making that suggestion if you are concerned about it.


I read this whole thing. All Could think of is why don't they slice the bagel all the way through.


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## Southeast Power (Jan 18, 2009)

First thing I thought of was a brake. It could be an option and the specifier just didn't check that box.


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## RePhase277 (Feb 5, 2008)

Someone thought that shutting off all the power during an emergency was more important than stopping it's motion. Is it? I don't know.


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## bill39 (Sep 4, 2009)

It usually boils down to the specifications and sequence of operation. There's probably a memo somewhere.

Reminds me of when they sent a satellite up about 20 years ago. The company building part A did their calculations in inches. Company B did their calculations in metric. Things didn't work out too well.


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## oliquir (Jan 13, 2011)

normally brakes must be fail safe, when you remove power they brake, but shutting down the plc and hmi is the worst thing to do, when i build machines i just cut power to the outputs and i can see what is wrong on the plc/hmi.
some other equipment with moving stuff, the e-stop triggers a reverse move of a conveyor to stop it immediately and on a hydraulic press i trigger a move up sequence. Here the cnesst (osha in us i think) tell us what the machine should do and often i have to modify factory approved machine to make what they want!


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## Sparkee (Sep 22, 2009)

oliquir said:


> normally brakes must be fail safe, when you remove power they brake, but shutting down the plc and hmi is the worst thing to do, when i build machines i just cut power to the outputs and i can see what is wrong on the plc/hmi.
> some other equipment with moving stuff, the e-stop triggers a reverse move of a conveyor to stop it immediately and on a hydraulic press i trigger a move up sequence. Here the cnesst (osha in us i think) tell us what the machine should do and often i have to modify factory approved machine to make what they want!


Yes! That is what I am talking about. That is what PLC manufacturers recommend and you want your HMI powered up so hopefully it tells what door is open, what switch was not made, what drive tripped etc.

The brake is a dynamic brake so it needs regenerated electrical power to work.


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## John Valdes (May 17, 2007)

Sparkee said:


> Yes! That is what I am talking about. That is what PLC manufacturers recommend and you want your HMI powered up so hopefully it tells what door is open, what switch was not made, what drive tripped etc.
> 
> The brake is a dynamic brake so it needs regenerated electrical power to work.


I look at a stop and an E-stop function as two separate actions.
Do you have both a stop and an E-Stop function?

I do agree with you that allowing the machine to coast in E-Stop is as dangerous as allowing the machine to continue to run.
But also understand the "remove all power" option or requirement.

If I were you, I would see if these is a brake designed to fit your motor in question. Or is it more than one motor?
You cannot connect a brake to the motor terminals if the motor is on a drive. But you can wire the brake separately.
You can power OFF the brake, when power is applied to the machine. And then if the E-Stop button or any E-stop contact opens, the brake will engage.

How much inertia are we talking about? It maybe to much for a mechanical brake for the motor.
But they do make brakes that are not attached to the motor that can be connected the same way. Power on, brake disengaged. Power off, brake engaged.


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## JRaef (Mar 23, 2009)

Sparkee said:


> Yes! That is what I am talking about. That is what PLC manufacturers recommend and you want your HMI powered up so hopefully it tells what door is open, what switch was not made, what drive tripped etc.
> 
> The brake is a dynamic brake so it needs regenerated electrical power to work.


Many of us may agree with you, but still, there are many safety regulations that simply say "remove all energy sources", including by the way, air, steam, water pressure etc.

In more modern system, there are sophisticated "Machine Safety Systems" using "safety relays" or "safety PLCs" that will be designed and certified for different levels of "safety integration". As part of the required safety evaluation to be able to certify a machine with these systems in it, this issue of the most safe way to shut something down might have been seen and implemented. These regulations are very strict in most parts of the world outside of North America, but we in the US are being slow to implement them (Canada is a little ahead of us in that regard). OSHA acknowledges them as valid safety systems, but does not out and out require them yet. All of the major control equipment mfrs offer them, but from what I see, not many equipment mfrs selling machines to only the domestic US market use them yet, unless a specific industry segment (like the automotive industry) has their own internal requirements. So if an OEM does not export their machine to other countries that WILL require them, OEMs can satisfy the minimum OSHA requirements by simply removing energy sources. This was on track to change eventually, but I don't expect that in the current political environment of less governmental interference with industry, that it will happen for quite a while now. It will be interesting to see how this plays out now.


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## JRaef (Mar 23, 2009)

sbrn33 said:


> I read this whole thing. All Could think of is why don't they slice the bagel all the way through.


There is an answer to that!

In a high volume bakery making bagels by machine, the slicers are slicing something like 300 bagels per minute, they fly though that thing so fast it looks like a brown blurr. The slicer has two little high speed (10,000 RPM) circular saw blades side by side, separated by a gap that leaves that annoying little area in the middle. If the bagel were to be sliced all the way through, the halves would separate and fall off in the packaging machinery. A certain percentage of them do anyway and it costs them money if they get caught in something and create a back up (I was going to say get jammed, but that might be confusing). There is actually an adjustment of the slice gap that changes with different types of bagels because some will separate easier if sliced as deep as others. Raisin bagels for example, because if there are too many raisins in the gap areas, the bagel doesn't hold together as well.

Now you know...:whistling2:


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## cmdr_suds (Jul 29, 2016)

I suppose it is a matter of semantics. "Removal of all energy sources" in my mind is not the the same as removal of the power sources. A spinning flywheel is still a source of kinetic of energy. 

The problem I feel is that the people in charge with enforcing the rules often either do not understand them completely or simply can not see beyond the letter of the law. Just look at the number of threads on this forum that discuss the mis-interpretation of the NEC by inspectors. I'm not a machine safety expert but I bet there are caveats that
allow exceptions if following a rule creates an even bigger danger.


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## just the cowboy (Sep 4, 2013)

My question is why are they using the E-stop or opening a door?? An E-stop is for emergency only. I think you also have an operation problem. Most machines I worked on an E-stop was rarely hit.


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## telsa (May 22, 2015)

bill39 said:


> It usually boils down to the specifications and sequence of operation. There's probably a memo somewhere.
> 
> Reminds me of when they sent a satellite up about 20 years ago. The company building part A did their calculations in inches. Company B did their calculations in metric. Things didn't work out too well.


STOP.

That's the Mars fiasco.

Remember ?

$250,000,000 straight down the drain -- and many a career to boot.


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## telsa (May 22, 2015)

cmdr_suds said:


> I suppose it is a matter of semantics. "Removal of all energy sources" in my mind is not the the same as removal of the power sources. A spinning flywheel is still a source of kinetic of energy.
> 
> The problem I feel is that the people in charge with enforcing the rules often either do not understand them completely or simply can not see beyond the letter of the law. Just look at the number of threads on this forum that discuss the mis-interpretation of the NEC by inspectors. I'm not a machine safety expert but I bet there are caveats that
> allow exceptions if following a rule creates an even bigger danger.


Exactly.


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## Bird dog (Oct 27, 2015)

My codebook is packed away, but, in Art 430(?) there is some verbiage about not Estopping multi-motor equipment if the automatic shutdown is a greater hazard.


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## gnuuser (Jan 13, 2013)

what you have is an improperly wired control system.
plc system that monitors the entire operation needs to supplied upstream of the contactor it controls.
If this system is shutting everything down including the plc, that was a bit of poor planning! (It happens in industrial more often than not, mostly because of lack of proper documentation)

your e-stop should be the first input and the contactor it controls the first output.
many 3 phase machines run by plc have their own step down or control power transformer.
*that and that only should have a manual disconnect* and should *not* be under the control of the plc.
If the system is wired properly control voltage circuits are the only ones that have power in them when the e-stop is not depressed and if the machine has been shut down properly the contactor for the 3 phase is open.
e-stop depressed disconnects the control voltage loop effectively shutting 3 phase power down, your electric brake system should then stop any motion. electric brakes are supposed to close when the power is removed from them
Ive installed a fair number of brake motors on automated palletizing equipment before i retired

control voltage comes in many flavors! 480, 220,110,48,24,12, and 5 volt.
depending on the solenoid coil voltage.( our automated systems relied on 24 volt control power)
the power it controlled was safely isolated from any personell (much safer) 
safety doors are part of the e-stop system and should never be bypassed for any reason because no mechanical adjustment can be made while a machine is running.


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## gnuuser (Jan 13, 2013)

Bird dog said:


> My codebook is packed away, but, in Art 430(?) there is some verbiage about not Estopping multi-motor equipment if the automatic shutdown is a greater hazard.


you can control an mcc panel running multiple pieces of equipment with plc and inverter drives. this is a soft start situation, start up of the equipment is usually sequential timed as not to cause jam-ups on the line ( as long as you can keep the production twits from tampering with the speeds)
without using plc/slc and inverter drives an e-stop on multiple motor equipment can wreak havok on the equipment and put personell in danger of injury or death due to different speeds the motors may be running at.


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## just the cowboy (Sep 4, 2013)

@gnuuser welcome back. 
the new format throws up old dead thread at bottom so watch old posting dates
Cowboy


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