E-Stop requirement 1

[Histor]

Hi,
Please help me on understanding the requirement of field motor E-Stop/ Motor Control station.
it is a process plant and Our process Engineers are telling that there is no requirement for Estop or MCS at the field for all the motors. they intend to stop all the motors at the MCC side is what they are telling. Is there any standard that states we must use the field estop or MCS?
They say that they already considered ESD which shuts down the system. But my concern is to shut down the Specific motor during unforeseen situation using field estop.
The concept they are discussing is very unusual. Please help how to correct them with proper reasons?

 

[RedSnake]

I am not sure there are any specific requirements other then that there must be a emergency stop, not exactly where it should be and that a risk analyzes should be done.
And I am sure when doing that it will show that there must be emergency stop buttons in the vicinity of the equipment where you can see it and stop it as you say if and when something happens.
If it is in anyway possible to get into the equipment without making it powerless, manual maneuvering with a open fencing, or if the security on the fencing is not high enough you will need emergency stop buttons there too.
As you say it is a unusual concept not having any in close proximity, but it hard to say without a complete picture of the function and layout of the whole plant.

Don't know what MCC and EDS stands for by the way?

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[BrianPetersen]

At least in my area ... it is not "motor" dependent. It is "operator station" dependent. There has to be a stop control that an operator can use, near any start control. There should be a stop control available wherever an operator could foreseeably need one. (Yes, that's vague. Be reasonable.) It doesn't matter if there is one motor or 50 motors, that isn't a factor.

There may be code requirements for having local disconnect switches for motors more than a certain distance from the main disconnect...but that isn't an e-stop, and an e-stop would not satisfy the requirement.

 

[jraef]

Assuming you are in the US because of using the term “MCS”, there are no enforceable codes requiring an emergency stop button. It is considered a best practice in most cases, which may be why you were trained to have them installed, but is not mandated. In some cases, such as where there are dire process consequences of a disordered shutdown, it may be better to NOT have a local E-Stop or MCS. Case in point might be a chemical process that, if interrupted, might result in an uncontrolled reaction and possible explosion or fire. So if your process engineers are telling you they don’t want anything other than the ESD shutting things down, you should a side by their decision.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[Jaycen]

I'm not 100% sure what you're asking in terms of a "field motor E-stop". Are you saying you're concerned about something having to do with the field created by the motor windings?

I've done industrial controls for 20+ years. When I first started, we would open up motor contactors and let things "free wheel" during an E-stop condition, including heavy, fast-moving, servo-controlled axes. As digital servo control got better, we started using their internal E-stop functions (Indramat/Rexroth calls it "best possible method of deceleration".) Are you talking about something like that?

I also recall a customer who had a lot of 2-post mechanical presses. In an E-stop condition, they wanted to make sure the flywheel was at a complete stop before the Operator could open any guards. They found some devices to mount on the shaft of the flywheel that would generate an electric current that kept the gates locked closed until the flywheel came to nearly a complete stop before the current would drop out a field and unlock the gates.

Obstacles cannot crush me; every obstacle yields to Stern Resolve.

 

[TugboatEng]

Field E-stop most likely refers to the location of the motor. Example, the MCC is in the control room and the motor is far away. Should there be a means to stop the motor locally at the motor?

Personally, I would evaluate each installation. A motor close coupled to a pump poses little risk to adjacent personnel and may not need a local e-stop.

A motor running a winch with exposed moving parts which could entangle personnel must have a local e-stop switch

Also consider the additional functions each e-stop needs to provide. In the winch example, due to the long coast down of the motor it may not be sufficient to only de-energize the motor. You may want to also set a brake to stop the machine quickly.

 

[che12345]

Dear Hi, .. Histor (Electrical)(OP)21 Dec 22 01:46
" #1. ....Please help me on understanding the requirement of field motor E-Stop/ Motor Control station....it is a process plant and Our process Engineers are telling that there is no requirement for Estop or MCS at the field for all the motors".

1.1. I am unable to locate any standard in the IEC and NEC that state E-stop SHELL be installed for each motor either at the Motor Control Center (MCC) or Motor Control Station (MCS).
1.2. The intention of E-stop (different from normal start/stop) is to effect an immediate disconnection of ALL ungrounded power conductors. To stop the rotation/robotic, conveyer motion etc.
1.3. Attention: As an E-stop operation may cause damage to the equipment or process proper shut-down, it is operated upon only when there is a potential danger to life or damage to the equipment.

" #2. ....they intend to stop all the motors at the MCC side is what they are telling. Is there any standard that states we must use the field estop or MCS?"
2.1. In the case where the (E-stop) is [installed on the starter door] in the MCC; which are usually distance away and are NOT within sight of the operator. Therefore, it does NOT comply with NEC.
2.2. When E-stop is deemed essential/needed, it SHELL be installed at the MCS , within sight of the operator. See 2.1.
Che Kuan Yau (Singapore)

 

[Padlock01]

Histor, (Electrical)(OP)
I suggest you ignore the process engineers they won't be the ones who are locked up if there is a fatality.
As an electrical engineer / reasonable person I would Install an E-Stop adjacent to the motors. In RSA its Mandatory.

 

[jraef]

I suggest you ignore the process engineers they won't be the ones who are locked up if there is a fatality.

Again, the Process Engineers may know something about the process that an EE is not privy to and an E-Stop that circumvents an orderly shutdown may cause worse consequences than what the person hitting the E-Stop is trying to solve. In a refinery, ignoring the Process Engineers is often cause for dismissal…


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[RedSnake]

Well since Histor is in Singapore and I don't know what kind of rules they have.
Here in EU there is almost no way to get away with not having, in most cases multiple emergency stop buttons.
It doesn't make any difference what kind of machine it is or what the motor is connected to pump, fan, belt, crane and so on.
An emergency power shutdown isn't necessarily free wheeling it can be done with electrical brake, apply brake and then cut of the power.
As Jaycen says power means all kinds of power not only electrical but hydraulic, pneumatic, kinetic.
If a machine can't take a emergency stop power shutoff without risk of causing greater damage it needs to be reconstructed and dimensioned in another way.
Apply greater brakes or more then one etc.

A motor close coupled to a pump poses little risk to adjacent personnel.

Maybe the motor doesn't but the hydraulic pressure do. ;-)

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[BrianPetersen]

I can think of one example that I had involvement with, in which an e-stop in the traditional sense would lead to a greater hazard than not having one: An industrial bakery oven. Carefully shaped blobs of cookie dough go into the oven on a conveyor at one end and come out the other end as baked cookies headed for the packaging line.

If you e-stop that conveyor (in a traditional sense of an E-stop), and you don't get it going again within a very limited time (I don't recall what that time was, I'm going to say order-of-magnitude 1 minute), the oven catches fire.

Yes, the oven has automatic fire protection on it, but (A) this requires the fire protection to be actively energised (which is against emergency-stop principles of de-energisation) and (B) you really don't want that happening unless you really, really need to, because it leads to a big mess and a very lengthy recovery procedure.

If I remember right, the conveyor did have an e-stop to satisfy "thou shalt" in the equipment standards, but it was oriented and labelled in a way that really, really discouraged anyone pressing it unless they really had to.

 

[TugboatEng]

We have a hydraulic winch that is the same story. The emergency button opens a free spool valve attached to the motor. Closing the valve with the drum turning will break the winch as 40,000 lbs of wire has quite a bit of inertia. You commit to losing your tow wire and whatever is attached to it when you push that button. Terrible design.

 

[RedSnake]

We had a bakery burning down because of a oven fire not long ago, not sure what the cause was though.

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

 

[che12345]

Dear Hi, .. Histor (Electrical)(OP)21 Dec 22 01:46
@ Ms RedSnake (Electrical)22 Dec 22 19:11
"... Well since Histor is in Singapore and I don't know what kind of rules they have...."
General information on the EE Standards, use of SI unit and utility LV supply voltage and frequency....in Singapore.
1. I am in Singapore. Singapore being a member of IEC, we do not only have the obligation but also to comply with strongly encourage adoption of the IEC standard in full ; when we do not have our own standard. Practically ALL our (electrical engineering standards) are [identical to the IEC standards], without any "national appendix".
2. In EE we have the MKS system and use SI units.
3. LV power source from the utility is 1-phase 230Vac, 3-phase 400Vac , 50Hz.
4. The NEC, ANSI, NEMA, CS, UL , (imperial unit of measurement)..... etc. which are "national" NOT "international"; play a much lower role here compare to the IEC.
Che Kuan Yau (Singapore)

 

[jraef]

E-Stop for a single motor is what was asked about.

They say that they already considered ESD which shuts down the system.

ESD (Emergency Shut Down in this context, not Electro Static Discharge) is apparently already in place. ESD systems in Process Control take into account all of the potential energy systems and the overall effects of shutting them down outside of a specific sequence. So an ESD system in a processing environment is the functional equivalent of an E-Stop, but does so in an orderly manner taking those consequences seriously. Hence, the OP should not be second guessing that decision. Ask? Sure, but then accept the response.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden