Does a 20amp emergency stop button exist?

j_arney · Jul 12, 2022

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 · Jul 13, 2022

mainline said:
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.

mainline said:
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 · Jul 13, 2022

mainline said:
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

[ElectriciansForums.net] Does a 20amp emergency stop button exist?

mainline · Jul 13, 2022

marconi said:
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 · Jul 13, 2022

James said:
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 · Jul 13, 2022

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 · Jul 13, 2022

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 · Jul 13, 2022

j_arney said:
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 · Jul 13, 2022

j_arney said:
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 · Jul 13, 2022

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 · Jul 13, 2022

timhoward said:
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 · Jul 13, 2022

Darkwood said:
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

timhoward said:

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?

Click to expand...

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 · Jul 13, 2022

Do not rely on an MCB for safe isolation

timhoward · Jul 13, 2022

mainline said:
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 · Jul 14, 2022

j_arney said:
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 · Jul 14, 2022

timhoward said:
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.

Does a 20amp emergency stop button exist?

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