Does a 20amp emergency stop button exist?

[j_arney]

I’ve been asked to provide an emergency stop button for a circuit rated at 20amps. I’ve never installed one before and only really found 10amp buttons at my local wholesaler. I can put a contactor in, no problem but was just interested to see if you can get them?

 

[Spoon]

Welcome to the forum mate.
Who has asked for an "Emergency Stop Button"?
Has it got to be an "Emergence" stop button or just a stop button?
The reason why I ask is if you are fitting an "Emergency Stop Button" to a circuit you have to do a risk assessment to determine what category of Emergency Stop is required. There is a lot more to it than just bunging in a stop button.

 

[j_arney]

Welcome to the forum mate.
Who has asked for an "Emergency Stop Button"?
Has it got to be an "Emergence" stop button or just a stop button?
The reason why I ask is if you are fitting an "Emergency Stop Button" to a circuit you have to do a risk assessment to determine what category of Emergency Stop is required. There is a lot more to it than just bunging in a stop button.

No I think they require just a stop
Button for quick isolation. It’s for a training environment.

 

[Spoon]

So it's for isolating the power to a training area?

 

[mainline]

No I think they require just a stop
Button for quick isolation. It’s for a training environment.

XALK178F | Schneider Electric Harmony XALK Series Twist Release Emergency Stop Push Button, Surface Mount, 40mm Cutout, 2NC, IP66, | RS

uk.rs-online.com

Just noticed you need 20amp, you may need to add a contactor.

 

[James]

XALK178F | Schneider Electric Harmony XALK Series Twist Release Emergency Stop Push Button, Surface Mount, 40mm Cutout, 2NC, IP66, | RS

uk.rs-online.com

Just noticed you need 20amp, you may need to add a contactor.

You are missing the point.
An Emergency Stop, depending on its use and risk assessment of its purpose may need to be far more than just a switch with a red button on the end of it.
Adding a contactor, can make the system less safe than a direct switch as you have no way of knowing if it is going to disengage when needed.
as above, there are different categories of emergency stop systems and it needs to be decided what category of stop system needs to be designed and installed.
If you have little knowledge of industrial control systems and emergency stop systems, you would be well advised to pass up the job for your own good.

 

[James]

Some bedtime reading for you, beware this is just a brief overview and does not cover half of what you need to know to design stop systems for safety.

https://www.controldesign.com/

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4. Standards and options for e-stops

HMI / Safety Components

Standards and options for e-stops​

Safety switches can be used in a number of configurations, meeting different stop category requirements​

By Anna Townshend, managing editor

Jan 28, 2021

Figure 1: E-stop switches are just one of the components of the safety system. (Source: EAO)
A Control Design reader writes: What is the standard method of using circuits for e-stop conditions and their categories? Are there cases in which an e-stop button can be software-based?

ANSWERS​

Safety and risk assessment​

From a machine designer perspective, the safety system that is being designed into the machine and the risk assessment for the machine will determine which components are needed in the safety system. E-stop switches are just one of the components of the safety system. There are many industry standards that need to be followed to accomplish this, below are a few examples:

• DIN ISO 13849-1, Safety of Machinery
• DIN ISO 13850, Safety of machinery—Emergency stop function—Principles for design
• IEC 60947-5-1, Low-voltage switchgear and control gear
• EN 60947-5-5, Control circuit devices.

In my experience, an e-stop has to be a physical switch versus an icon or software-based to meet the above specifications and industry standards (Figure 1).
JOE TORZILLO / vice president sales, HMI components / EAO / www.eao.com

Figure 2: Possibilities exist by utilizing software-based safety, in this case, STO safety subfunction. (Source: Mitsubishi Electric)

Safe torque off​

I’m not sure if there’s a standard method of using circuits for e-stop conditions; however, there are a number of ways to configure an e-stop button in a servo drive system. Here is one example: the image in Figure 2 illustrates what’s possible by utilizing software-based safety, in this case, STO safety subfunction.
E-stop buttons can be used in a number of configurations, but in their simplest form, they cut power to drive components when pressed to prevent damage to machine components or to prevent operator injury. In a hardware-based solution, power is cut to drive components via a series of magnetic contactors when the e-stop button is pressed. This serves the purpose of an e-stop by allowing motion to come to an uncontrolled stop, but the downside is that cutting power to the drives requires the drive to fully start up when the e-stop condition is removed.
In a software-based solution, the system configuration uses software-based safety subfunctions, in this case safe torque off (STO). Safe torque off cuts torque producing current to the servo motor when the e-stop button is pressed bringing motion again to an uncontrolled stop. The benefits of using safety sub-functions such as STO is that the magnetic contactors are no longer required, which reduces system costs and the power to the drive is not cut, which reduces start-up time.



We have a full range of safety subfunctions, in addition to STO, offered with safety over network that allow for more advanced safety features. Table 1 includes a full list of the range of offerings, including a brief definition for each.
DAN ZACHACKI / senior product marketing engineer / Mitsubishi Electric Automation / us.mitsubishielectric.com/fa/en/

	Safe torque off (STO)​ Responding to the input signal from external equipment, the STO function shuts off power to the servo motor electronically using the internal circuit (shuts off through secondary-side output). This function corresponds to the Stop category 0 of IEC/EN 60204-1.
	Safe operating stop (SOS)​ This function monitors the position of the servo motor not to deviate from the specified range. Power is still supplied to the servo motor during the SOS function.
	Safe direction (SDI)​ This function monitors whether the servo motor moves in the command direction. If the servo motor moves in a different direction from the command direction, the STO function is executed.
	Safe stop 1 (SS1)​ Responding to the input signal from external equipment, the servo motor starts to decelerate. After the set delay time for the motor stop is passed, the STO function starts. Monitoring the servo motor deceleration based on the motor deceleration rate is also supported. This function corresponds to the Stop category 1 of IEC/EN 60204-1.
	Safe brake control (SBC)​ The SBC signals are outputted for external brake control.
	Safely limited increment (SLI)​ This function monitors the travel distance of the servo motor not to deviate from the specified range. If the travel distance exceeds the range, the STO function is executed.
	Safe stop 2 (SS2)​ Responding to the input signal from external equipment, the servo motor starts to decelerate. After the set delay time for the motor stop is passed, the SOS function starts. Monitoring the servo motor deceleration based on the motor deceleration rate is also supported. This function corresponds to the Stop category 2 of IEC/EN 60204-1.
	Safely limited speed (SLS)​ This function monitors the speed of the servo motor not to exceed the specified speed limit. If the speed exceeds the limit, the motor power is shut off by the STO.
	Safe speed monitor (SSM)​ The SSM signals are outputted when the speed of the servo motor is below the specified speed limit.
	Safely limited torque (SLT)​ This function monitors the torque (or the thrust) of the servo motor not to deviate from the specified range. If the torque (or the thrust) exceeds the range, the STO function is executed.

Table 1: A full range of safety subfunctions, in addition to STO, are offered with safety over network that allow for more advanced safety features. (Source: Mitsubishi Electric)

Emergency stop vs. stop categories​

The idea that the terms “e-stop,” “emergency-stop” and “stop categories” are equivalents is a common misconception. An emergency-stop function, which is normally linked to an emergency-stop pushbutton, or e-stop, in a machine, refers to a safety function that must be initiated by a single human action and is intended to minimize hazards to people, as well as damage to machinery or works in progress. Since this safety function does not prevent people from being exposed, it is considered a complementary protective measure, according to ISO 12100:2010 and ISO 13850:2015.
Stop categories, on the other hand, refer to the way in which a machine will stop. These categories, which are based on IEC 60204-1 and NFPA 79, can be defined as follows:

• Category 0 is a means of stopping the machine through the immediate removal of power to its actuators and is considered an uncontrolled stop. An example of Category 0 is to pull a plug and wait until the machine has completely stopped.
• Category 1 is a controlled stop with power to the machine actuators available to achieve the stop condition. This category allows powered brakes, so the power has to be available until the machine stops. For example, in a machine that uses drives, the stop is generated with a controlled deceleration ramp before disabling the drive’s output to the motor. In this case, the drive works as an actuator to bring the motor into a non-torque state after the deceleration. Once the machine motion has ceased completely, the power will be removed.
• Category 2 is a controlled stop with power left available to the machine actuators. An example of this category is a normal production stop in which the machine is brought to a stop and power is available to start at any point.

According to IEC 60204-1, an emergency stop must operate as either a Category 0 or Category 1 stop as determined by a risk assessment. Both of these categories require that the emergency stop function override all other operations and functions, so a restart is possible only after a manual reset. Category 2 is not suitable for an emergency stop function because power is still available after the machine stops, and no additional measures are required to restart the machine.

Also read: How to improve the safety of an operating machine beyond just an e-stop button
To provide an example of an emergency-stop function that performs a Category 0 stop, we can consider a safety circuit in which an emergency stop pushbutton (e-stop) is identified as S1, a reset button as S2, a motor as M, and contactors as KM1 and KM2 (Figure 3). All of these devices are connected to a status-monitoring relay, which ensures the switching action and provides contactor monitoring through T31 and T32. When the e-stop is activated, it will cause the contactors to isolate the power from M. The power to M is kept removed until e-stop S1 is released and reset switch S2 is pressed.


Figure 3: An emergency-stop function can perform as a Category 0 stop. (Source: Omron Automation Americas)

This will exemplify a scenario where an emergency stop in a piece of equipment has been pressed and power has been removed completely, preventing the machine from starting. At this point, the machine won’t be permitted to start until the emergency-stop pushbutton is manually released and the reset switch is pressed. After all safety conditions are acknowledged by the safety circuit, then the machine is permitted to restart.
In terms of emergency-stop devices, graphical representations of a button on an HMI or flat panel display are not an option. The standards do not permit flush or membrane-style switches or touchscreen buttons. The specific requirements for an emergency-stop pushbutton to be compliant are as follows:

• It must have a direct opening operation.
• It must be self-latching, meaning that it can only be reset manually.
• It must be colored red and mounted upon a bright yellow background. The yellow background must be a minimum of 3 mm beyond the mounting collar and visible beyond the control actuator, according to ANSI B65.1-2005.
• It must have a mushroom-head shape to make it easy to push.
• It must remain unguarded.
• It must be located at each operator control station and at any other location where an emergency stop would be required.

For additional references on emergency-stop functions and their requirements, please review ISO 13850:2015, Safety of Machinery—Emergency Stop Function—Principles for Design and IEC 60204-1:2005, Safety of machinery—Electrical equipment of machines—Part 1: General requirements.
PAM HORBACOVSKY KLANCEWICZ / product manager—safety / Omron Automation Americas / automation.omron.com/en/us/

NFPA 79 standards​

The best standard method for using an e-stop would be just that, starting with a standard. Using standards such as the latest revision of National Fire Protection Association (NFPA) 79—the 2021 revision was just released—to understand the requirements of an emergency stop and how it should function in your system. NFPA 79 requires the use of a “self-latching” type contact for push-button emergency stops. It is important to also differentiate the categories of an e-stop function versus the categories of safety system design. The stop function has three categories:

• Category 0 is instantaneous removal of power to the machine actuators.
• Category 1 is a delayed removal of power, where a breaking mechanism or a controlled and powered stop is achieved, and then power is removed.
• Category 2 is a controlled stop under power where power is never removed from the machine actuators.

According to NFPA 79, an emergency stop should be stop category 0 or 1. It is important to select the correct stop function for your application. For example, you may think that an instantaneous removal of power would be best for every application, but if you have a large spinning drum or a fast-moving flywheel, removing power immediately could leave them moving and hazardous for a long time. A better solution would be to stop them under power and then to remove power (Category 1). Categories are also used when describing safety system design. Without going into too much detail, essentially design categories B, 1 and 2 are single-channel type designs, and categories 3 and 4 are redundancy designs. For more information on safety categories, reference EN ISO 13849-1 or ANSI B11.19.
There could be applications in which a software e-stop could be used, but it would need to be on a safety visualization package, on a safety network, as part of a fail-safe PLC. I’m not aware of any safety-related visualization software that would allow this type of setup, but with the continued advances in control technology, there may be some available.

 

[mainline]

You are missing the point.
An Emergency Stop, depending on its use and risk assessment of its purpose may need to be far more than just a switch with a red button on the end of it.
Adding a contactor, can make the system less safe than a direct switch as you have no way of knowing if it is going to disengage when needed.
as above, there are different categories of emergency stop systems and it needs to be decided what category of stop system needs to be designed and installed.
If you have little knowledge of industrial control systems and emergency stop systems, you would be well advised to pass up the job for your own good.

I'm not missing the point
I'm aware of different types of emergency stop systems

But he said:
j_arney said:
No, I think they require just a stop
Button for quick isolation. It’s for a training environment.

 

[j_arney]

So it's for isolating the power to a training area?

Yes

You are missing the point.
An Emergency Stop, depending on its use and risk assessment of its purpose may need to be far more than just a switch with a red button on the end of it.
Adding a contactor, can make the system less safe than a direct switch as you have no way of knowing if it is going to disengage when needed.
as above, there are different categories of emergency stop systems and it needs to be decided what category of stop system needs to be designed and installed.
If you have little knowledge of industrial control systems and emergency stop systems, you would be well advised to pass up the job for your own good.

 

[James]

I'm not missing the point
I'm aware of different types of emergency stop systems

But he said:
j_arney said:
No, I think they require just a stop
Button for quick isolation. It’s for a training environment.

Sorry, but you are.
A training environment may well bring in added risks that are not there in the normal working environment.

I.e. In the work environment, if you are to be working on electrical systems you should have a good grasp of safe isolation and testing procedures.

In training, mistakes happen and the idea of an emergency stop is a good one.
however, if the training risk assessment relies on the fact that an instructor can kill the power if a danger appears and therefore reduces or removes that danger.
IT MUST HAVE A REALLY GOOD CHANCE OF WORKING CORRECTLEY!!

we do not know what the risk assessment is or how serious it may be if the emergency stop button fails to function when required so we should not be advising on how to do it.

 

[j_arney]

Appreciate all the info, but I just wanted to know if you could get a 20amp stop button. Do you know the answer to that?

 

[mainline]

Sorry, but you are.
A training environment may well bring in added risks that are not there in the normal working environment.

I.e. In the work environment, if you are to be working on electrical systems you should have a good grasp of safe isolation and testing procedures.

In training, mistakes happen and the idea of an emergency stop is a good one.
however, if the training risk assessment relies on the fact that an instructor can kill the power if a danger appears and therefore reduces or removes that danger.
IT MUST HAVE A REALLY GOOD CHANCE OF WORKING CORRECTLEY!!

we do not know what the risk assessment is or how serious it may be if the emergency stop button fails to function when required so we should not be advising on how to do it.

What the OP asked for was :
I’ve been asked to provide an emergency stop button for a circuit rated at 20amps. I’ve never installed one before and only really found 10amp buttons at my local wholesaler. I can put a contactor in, no problem but was just interested to see if you can get them?


He asked for a 20 amp stop switch, that's it.

 

[mainline]

Appreciate all the info, but I just wanted to know if you could get a 20amp stop button. Do you know the answer to that?

Yes you can get a bench saw switch, I'm sure there are others though

Big Horn 18806 Large Table Saw Push Button Switch with Emergency Stop Cover : Amazon.co.uk: DIY & Tools

Free delivery and returns on all eligible orders. Shop Big Horn 18806 Large Table Saw Push Button Switch with Emergency Stop Cover.

www.amazon.co.uk

 

[mainline]

Sorry, but you are.
A training environment may well bring in added risks that are not there in the normal working environment.

I.e. In the work environment, if you are to be working on electrical systems you should have a good grasp of safe isolation and testing procedures.

In training, mistakes happen and the idea of an emergency stop is a good one.
however, if the training risk assessment relies on the fact that an instructor can kill the power if a danger appears and therefore reduces or removes that danger.
IT MUST HAVE A REALLY GOOD CHANCE OF WORKING CORRECTLEY!!

we do not know what the risk assessment is or how serious it may be if the emergency stop button fails to function when required so we should not be advising on how to do it.

j_arney said:
Appreciate all the info, but I just wanted to know if you could get a 20amp stop button. Do you know the answer to that?

 

[j_arney]

Yes you can get a bench saw switch, I'm sure there are others though

Big Horn 18806 Large Table Saw Push Button Switch with Emergency Stop Cover : Amazon.co.uk: DIY & Tools

Free delivery and returns on all eligible orders. Shop Big Horn 18806 Large Table Saw Push Button Switch with Emergency Stop Cover.

www.amazon.co.uk

Thanks for your help. I think the contactor route will be better!

 

[James]

Yes you can get an emergency stop button that is rated at 20A,
however by fitting it you run the risk of being in court for corporate manslaughter or a number of other nasty legal challenges to your freedom.

in my opinion, after re reading what i have posted, i think the advice is sound.
you are of course free to take it on board and use it or ignore it.

 

[mainline]

Yes you can get an emergency stop button that is rated at 20A,
however by fitting it you run the risk of being in court for corporate manslaughter or a number of other nasty legal challenges to your freedom.

in my opinion, after re reading what i have posted, i think the advice is sound.
you are of course free to take it on board and use it or ignore it.

You are being ridiculous, you have no idea what he's switching it, maybe a spa pump for instance.

He simply asked if they did a 20 amp stop switch, and you accused me of missing the point, when in fact it was you who missed the actual question.

 

[James]

You are being ridiculous, you have no idea what he's switching it, maybe a spa pump for instance.

He simply asked if they did a 20 amp stop switch, and you accused me of missing the point, when in fact it was you who missed the actual question.

Fair point, however I have never seen a training environment where the "training is wire up this spar pump"

like I said, if the risk assessment deems it suitable then go ahead but i think it is a vital step that both you and the op are missing.
OP, has anybody done a risk assessment and if so, what stop category are you trying to design. also, is a single point of failure likely to bring a risk of significant harm to anybody?

I am done with this for tonight and my final thoughts are Simpley that on the face of it neither @mainline or @j_arney have the information and knowledge required to design a suitable safety system for this project.

 

[mainline]

Fair point, however I have never seen a training environment where the "training is wire up this spar pump"

like I said, if the risk assessment deems it suitable then go ahead but i think it is a vital step that both you and the op are missing.
OP, has anybody done a risk assessment and if so, what stop category are you trying to design. also, is a single point of failure likely to bring a risk of significant harm to anybody?

I am done with this for tonight and my final thoughts are Simpley that on the face of it neither @mainline or @j_arney have the information and knowledge required to design a suitable safety system for this project.

You have no idea what the project is ... and you deem it that neither me or the op have the knowledge required ???

Are you for real or is it that you can't stand the fact that you were wrong.

I also take umbrage at you saying I lack the knowledge when you have no idea what my background is.

 

[westward10]

You have no idea what the project is ... and you deem it that neither me or the op have the knowledge required ???

Are you for real or is it that you can't stand the fact that you were wrong.

I also take umbrage at you saying I lack the knowledge when you have no idea what my background is.

As opposed to arguing the right and wrongs, what is your background.

 

[mainline]

As opposed to arguing the right and wrongs, what is your background.

I worked in electronics and programming for over 40 yrs before semi retirement and now work to suit mostly repairing various radio test equipment from all over the world, for 3 days a week i look after 21 cottages on a holiday complex mostly electrical.

Things like this but now more as a hobby

 

[James]

I worked in electronics and programming for over 40 yrs before semi retirement and now work to suit mostly repairing various radio test equipment from all over the world, for 3 days a week i look after 21 cottages on a holiday complex mostly electrical.

Things like this but now more as a hobby

Love the workshop.
I still stand by everything I have said though.
if you don’t have the info you can’t make the call for correct advice.

 

[Spoon]

You have no idea what the project is

That is correct mate. All we know is it's a place where someone has decided they want a way to isolate the power for trainees.
Why do they want this? What are the dangers that they have requested this? What level of injury could happen?
The project may just need a key switch that can isolate the power, or it may need a push button that is monitored and wired to a safety device. Only a risk assessment will answer this.

 

[Darkwood]

You are being ridiculous, you have no idea what he's switching it, maybe a spa pump for instance.

He simply asked if they did a 20 amp stop switch, and you accused me of missing the point, when in fact it was you who missed the actual question.

With all respect to the conversation, your premise of ridiculous is not founded by any of the posts, we simply do not have the info to make such accusations, if this is for course work then we don't permit direct answers only nudging but is this is real then we indeed need to question the context of his circumstances because this falls in a category that information is crucial to responses.

 

[telectrix]

a point that has been missed so far, unless i've missed it, is that a stop button is wired into the control circuit, so no way will it ever see a 20A load current.

 

[Spoon]

a point that has been missed so far, unless i've missed it, is that a stop button is wired into the control circuit, so no way will it ever see a 20A load current.

I think the OP's intensions were to use the stop button as an isolator and wire directly into the power circuit.

 

[Intoelectrics]

a point that has been missed so far, unless i've missed it, is that a stop button is wired into the control circuit, so no way will it ever see a 20A load current.

This is why the op was asked what the stop button was for and advised that its not as simple as just wiring in a "stop button". would have been just easier to search on google for the 20amp switch, than ask on this forum, if there is no intent on taking advice or explaining what the job is.

 

[mainline]

This is why the op was asked what the stop button was for and advised that its not as simple as just wiring in a "stop button". would have been just easier to search on google for the 20amp switch, than ask on this forum, if there is no intent on taking advice or explaining what the job is.

That's what the op did, he said he basically just wanted to know if a 20 amp stop switch existed, as he couldn't find one.

I get the questions being asked concerning a risk assessment, but the op a number of times said that he just wanted to know if one existed and wasn't interested in anything else.

I'm sure if he is learning in a training environment, then the trainer will put him right.

If the op returns, then maybe he can explain the scenario.

 

[Intoelectrics]

That's what the op did, he said he basically just wanted to know if a 20 amp stop switch existed, as he couldn't find one.

I get the questions being asked concerning a risk assessment, but the op a number of times said that he just wanted to know if one existed and wasn't interested in anything else.

I'm sure if he is learning in a training environment, then the trainer will put him right.

If the op returns, then maybe he can explain the scenario.

Yeah, but is an unusual request so quite rightly raised interest in what it was required for.

 

[Electro-tech]

I would use an electrical contractor, not a contactor. leave the liability to someone who knows.

 

[Spoon]

That's what the op did, he said he basically just wanted to know if a 20 amp stop switch existed, as he couldn't find one.

We understand this. But there is more to it than that.

Lets say we go with his first post.... We give him a stop button that can do 20A...
He then sticks it in his circuit and then someone comes along and says "According to table 537.4 you cant use that stop button as an isolator". He replies "But I was told I could... on a forum"

Things are rarely straight forward in our work.

I get the questions being asked concerning a risk assessment, but the op a number of times said that he just wanted to know if one existed and wasn't interested in anything else.

Again, see above.

 

[marconi]

I worked in electronics and programming for over 40 yrs before semi retirement and now work to suit mostly repairing various radio test equipment from all over the world, for 3 days a week i look after 21 cottages on a holiday complex mostly electrical.

Things like this but now more as a hobby

Dear mainline,

I gather Gibsons jigsaw company are looking for a suitable picture to continue their ‘workshop‘ category of puzzles.

Thank you for the great photos of your lab bench. It clearly is a place where work is indeed done.

Regards

Marconi

 

[mainline]

Dear mainline,

I gather Gibsons jigsaw company are looking for a suitable picture to continue their ‘workshop‘ category of puzzles.

Thank you for the great photos of your lab bench. It clearly is a place where work is indeed done.

Regards

Marconi

View attachment 99430

Thanks for the kind words

A place where work used to happen.

 

[j_arney]

Fair point, however I have never seen a training environment where the "training is wire up this spar pump"

like I said, if the risk assessment deems it suitable then go ahead but i think it is a vital step that both you and the op are missing.
OP, has anybody done a risk assessment and if so, what stop category are you trying to design. also, is a single point of failure likely to bring a risk of significant harm to anybody?

I am done with this for tonight and my final thoughts are Simpley that on the face of it neither @mainline or @j_arney have the information and knowledge required to design a suitable safety system for this project.

 

[j_arney]

Hey
Im back and done the job. In the end I had a 6amp circuit feeding the stop button then the coil and 20 amp circuit supplying a socket via a rotary isolator and contactor.
So you had a stop button and rotary isolator switching the socket on and off. I was asked to do this for a colleague at one of our sites and have no idea what he intends to do with this system. He’s designed it, he’s an engineer and I haven’t asked any questions. I can totally understand the repercussions from making mistakes in certain working environments and appreciate all the feedback. I’m on this forum to hopefully learn a bit, but sometimes there’s no need for some of the negative/ condescending replies.

 

[Darkwood]

If this is paid work and invoiced you better have a paper trail of proof to who designed it and takes responsibility otherwise it still falls at your feet, imagine is someone is injured or worse, do you expect them to put their hands up to possible dangerous installation practices or point the finger at you showing your invoice.

If you are invoicing it it would be an idea to make it part of the invoice declaring no responsibility for design or safety making it clear it was requested, this would not remove you from and possible legal action because unless you have a full paper trail to this the responsibility lies on you to assess any requests meet standards applicable, so tread carefully.

 

[timhoward]

Hey
Im back and done the job. In the end I had a 6amp circuit feeding the stop button then the coil and 20 amp circuit supplying a socket via a rotary isolator and contactor.

This is intended as a constructive comment. Where possible I would have fused down the 20 amp circuit for the coil. Then one MCB safely isolates the lot. It sounds as though you'd have to turn off two MCB's for everything at the contactor to be safely isolated?

 

[James]

Hey
Im back and done the job. In the end I had a 6amp circuit feeding the stop button then the coil and 20 amp circuit supplying a socket via a rotary isolator and contactor.
So you had a stop button and rotary isolator switching the socket on and off. I was asked to do this for a colleague at one of our sites and have no idea what he intends to do with this system. He’s designed it, he’s an engineer and I haven’t asked any questions. I can totally understand the repercussions from making mistakes in certain working environments and appreciate all the feedback. I’m on this forum to hopefully learn a bit, but sometimes there’s no need for some of the negative/ condescending replies.

I hope you have not seen my comments as either negative or condescending.
I have tried to remain professional throughout.

I presume you have used the 3 signature form to certify it.
He is responsible for design and has signed that part.
you have signed the parts for installation and for testing.

from your comment of “I have no idea what he Intends to do with the system” I can understand that you were unable to give more information so we could advise on how best to proceed.

if you were not responsible for designing the system in the first place I wonder why you asked for advice on how to get a 20A stop button when the design clearly didn’t require one.

just be absolutely certain that the certificate passes the design responsibility back to the person who gave you the design.

 

[timhoward]

I also think we need to give this guy a break. It was well worth pointing out that providing this kind of arrangement carries responsibilities, but he was given the spec, it wasn't his idea, and he's a new member.

 

[mainline]

Then one MCB safely isolates the lot. It sounds as though you'd have to turn off two MCB's for everything at the contactor to be safely isolated?

A Mcb does not provide safe isolation, especially on a TT earthing system

After all, we wouldn't want the OP thinking that It's OK to do so he could end up killing someone

I can see that James actually agreed with your post

 

[j_arney]

If this is paid work and invoiced you better have a paper trail of proof to who designed it and takes responsibility otherwise it still falls at your feet, imagine is someone is injured or worse, do you expect them to put their hands up to possible dangerous installation practices or point the finger at you showing your invoice.

If you are invoicing it it would be an idea to make it part of the invoice declaring no responsibility for design or safety making it clear it was requested, this would not remove you from and possible legal action because unless you have a full paper trail to this the responsibility lies on you to assess any requests meet standards applicable, so tread carefully I

This is intended as a constructive comment. Where possible I would have fused down the 20 amp circuit for the coil. Then one MCB safely isolates the lot. It sounds as though you'd have to turn off two MCB's for everything at the contactor to be safely isolated?

i did consider that option, I don’t regularly install contactors and seen it done that way a few times before. Will take on board though

 

[mainline]

Do not rely on an MCB for safe isolation

 

[timhoward]

A Mcb does not provide safe isolation, especially on a TT earthing system

After all, we wouldn't want the OP thinking that It's OK to do so he could end up killing someone

I think you know my point was really about multiple sources of supply.

( I'll take your point that an MCB isn't always suitable for isolation. It isn't as simple as saying it never is though - after all if that were the case it wouldn't appear in table 537.4 with a "Yes". )

And to be clear, I wasn't meaning to refer to "safe isolation" in the sense of the procedure to ensure it is safe to commence working. I said "safely isolated", maybe unwise words but I meant there are two things to turn off not one, a trap for the unwary and reg 537.1.2 could be worth considering.

 

[Mike Johnson]

I’ve been asked to provide an emergency stop button for a circuit rated at 20amps. I’ve never installed one before and only really found 10amp buttons at my local wholesaler. I can put a contactor in, no problem but was just interested to see if you can get them?

Have a look for a NVR switch (No Volt Release) they are on most woodworking machines that can cary high loads, this one is rated at 18amp: Axminster Workshop KJD17B NVR Switch 230V 1ph - https://www.axminstertools.com/kedu-kjd17b-nvr-switch-230v-1ph-102532?queryID=caac039e86bf11f04a93756c659eea3e

 

[mainline]

I think you know my point was really about multiple sources of supply.

( I'll take your point that an MCB isn't always suitable for isolation. It isn't as simple as saying it never is though - after all if that were the case it wouldn't appear in table 537.4 with a "Yes". )

And to be clear, I wasn't meaning to refer to "safe isolation" in the sense of the procedure to ensure it is safe to commence working. I said "safely isolated", maybe unwise words but I meant there are two things to turn off not one, a trap for the unwary and reg 537.1.2 could be worth considering.

Yes I get the " I wasn't meaning safe isolation when I said safely isolated

Most of this thread has been about risk assessment and a rant at me about not knowing what sort of circuit it's being used for etc etc.

But it seems to be OK for someone else to then give misinformation and say that a mcb is fine for isolation when it clearly isn't without knowing the circuit.

537.4 it clearly states for TN not TT even then using a mcb for safe isolation isn't really safe as the circuit could have a borrowed neutral for instance.

 

[mainline]

Have a look for a NVR switch (No Volt Release) they are on most woodworking machines that can cary high loads, this one is rated at 18amp: Axminster Workshop KJD17B NVR Switch 230V 1ph - https://www.axminstertools.com/kedu-kjd17b-nvr-switch-230v-1ph-102532?queryID=caac039e86bf11f04a93756c659eea3e

Woodworking switch pointed out at the beginning of the thread

 

[Mike Johnson]

Can't find any reference to an NVR at the beginning of the thread, can you post a link?

 

[mainline]

Can't find any reference to an NVR at the beginning of the thread, can you post a link?

Its not nvr but looked the same at first glance #13

 

[Mike Johnson]

An NVR has an additional level of protection, and that link is to a unit that is not available, so not much use to the OP.

 

[mainline]

An NVR has an additional level of protection, and that link is to a unit that is not available, so not much use to the OP.

It was in relation to does a 20 amp stop switch exist.

If you want to be picky the op has completed the job, so you're a bit late also yours isn't rated at 20 amp anyway so not what he asked for.

We don't know what the circuit was intended for, so a NVR may not have been suitable anyway as it may have been wanted for a fan cooling system for instance and would have needed to come back on after a loss of power.