contactors and emergency stop buttons.

[netblindpaul]

Joe,
The problem is I actually am still hands on, I am also apprenticeship served with a gold jib card, 16th, 17th, 2391-01&-02, 2377, HNC, BSc(Hons.) in engineering, MEng & I also hold a NEBOSH General Cert. I am IEng TechIOSH, & MIET, amongst others qualifications.
I currently run my own engineering co. & I am also the only spark.
I am also the PDH & QS for the NICEIC AC (with DI) recognition for the company, the remainder of the employees hold other roles in the organisation.
I regularly design and install systems of varying kinds from domestic wiring through commercial, industrial, to control systems.
I have in the past designed complete machine control systems, undertaken design and applications engineering on machinery control systems with conventional relay logic, PLC, CNC, and other electronic controls, I was at the time employed with one of the largest global players in the industrial control & automation sphere.

I fully understand the principles and the function of an emergency switching system as you are describing. This is covered in PUWER98 & there in you are guided to BS EN 60204-1.

If you are installing to the clients spec, then you're in trouble because unless there have been some typo's then the client spec you have posted is wrong and dangerous.

To control the system with a reasonable degree of integrity I do not believe that a single contactor will be acceptable in the manner described.

If the client has provided a spec then hopefully you're OK as they are the designer but it is still not acceptable to energise/de-energise a contactor via a single e-stop.

It needs to be wired largely "the same" as a DOL starter control circuit.
However, you should check the requirements.
It would not be convention to have a single e-stop, these would normally be evenly spaced around the work area to provide adequate access in the event that they are required in an emergency.
These e-stop buttons must comply with the EN standards.
Does the client require this for control of operation, i.e. does the stop need to be key released?
You will require at least one start button, this must be momentary in operation and green in colour.
Any more than 1 button and they must be wired in parallel.
You should provide a control supply CPD really unless you can go for a single enclosure with the contactor in & the start/e-stop on the door. Only OK if you have a single e-stop.

Do you want me to go on?

Gonna get a drink, for 5, let me know?


Paul

 

[joe_berks]

its a red pushbutton in a yellow enclosure. i'm energising the circuits next week so i'll let you know how i get on. FMEA means nothing to me

 

[netblindpaul]

That sounds like an EN compliant e-stop as long as it is latching, it should give you the funciton you require however, it will have to be wired NO rather than NC as you have specified an NC contactor not an NO one.
To use this on its own to control a contactor would not be acceptable under statutory legislation.
There is a good functional description of what you are trying to achieve in BS 4163 which is a code of practice.
The system once installed and commissioned must meet PUWER98 legislation.
Please refer to HSE ACoP L22, this will give you an idea of the safety requirements for machine control systems which is where this is going, it is part way away from 7671.
You would be well advised to suggest to your client that the single button may not be compliant.
How will the no-volt release on the contactor operate?
This could even be in contavention of 7671.
It is doubtful that a single e-stop would meet the H&S requirements that the designer had in mind.
I strongly suspect that they don't really understand the requirements.

You should if you are undertaking design of electrical installations at least have a grasp of FMEA you may do but without realising it.
FMEA is a very common design term, it stands for Failure Mode and Effects Analysis.
It means you consider the possible failure modes of system and the effects these have on the remainder of the system etc.

Paul

 

[Davey101]

Paul, can you explain to me why you need to have a start button to re-energise a contactor, rather than just releasing the stop button(s)?
Is it just the fact that the em buttons are controling 'machinery', rather than, say, a ring main?
I'm not talking about motor control, or any other machinery control, just a bog standard em stop/contactor circuit (which seems to be what the op is trying to achieve)?
Also, why not just use 2 contactors with common feeds from the control circuit?
If the stop circuit is just to stop the machine's working, why is there a need for D.P switching?
Who says you need two stop buttons, apart from the obvious, such as size of room/number of staff etc?

Not arguing with you at all mate, just genuinely interested to learn.

BTW, nobody seems to have picked up the fact that the o.p is planning on taking a neutral to/from the stop buttons.e.

Cheers, Dave.

BTW, I am presuming that the sterilisers at present only have a rotary on/off switch, rather than a starter.

 

[netblindpaul]

The requirement under PUWER98 is that a separate deliberate act is required to re-energise a system after the initiation of a stop or emergency stop command.

Please refer to HSE ACoP L22.

Think of a DOL motor starter would you find it acceptable for say a saw to restart on the release of the e-stop button? Or would you expect to have to depress the start button first?

Think of the failure modes for a moment, the OP’s specifier appears to have given them a cursory thought. He has asked for an “overall” e-stop. Presumably this would be in case there is a failure in the control system of the machine such that the stop system did not function, or the machine started unexpectedly, thus A.N. Other could de-energise the machines remotely without having to approach the local isolator, which by definition is local to the machine!

However, is a single e-stop adequate, this boils down to the old chestnut of risk assessment. As you said based on room size accessibility etc.

However, what is unacceptable under PUWER98 & BS EN 60204-1 is the re-energising of a control circuit via the release of a stop control.
The nearest analogy is the central switching systems specified by BS4163.
Here in the link is drawn to PUWER98 and the guidance there in which takes you to 60204, even though these systems are fixed wiring in buildings, 7671 does not cover these types of control, thus bows out to statutory legislation, i.e. EAWR89, & PUWER98 which takes you to 60204.

You should not allow a contactor to be re-energised by the release of a stop button under any circumstances, I have frightened a few people with this scenario!

A bog standard em-stop/contactor circuit would be controlling machinery!
Why would you fit a contactor to control a ring main as a ring main is a standard arrangement of circuit from 7671?
This does not require an e-stop, if it does, then other legislation/guidance has come into play & you thus must therefore comply with that. Ergo my previous comments.

DP switching requirements should be checked, IIRC & it is now late & my copy of 4163 is not to hand, this requires all live conductors to be switched.
You must remember that in the event of an incident then the most appropriate guidance to the system will be selected and expert witnesses may well draw analogies to 4163 as it is the most similar to this situation.

Missed the comment wrt the neutral. No reason at all for the N to be taken anywhere except A2 on the contactor!

O/L protection should be looked at for the control circuit as the control devices will not be able to take the full 32A load of the power CPD. Also the controls are controlling supplies from 4 CPD’s.


I would utilise 2 or 3 contactors at least, however, first would be an FMEA, RA & PUWER98 assessment of the install and draft a design & functional spec from that.
You also need to understand that once you start fitting e-stops then you are suggesting that the equipment is safety related, thus it becomes a safety related part of a control system. As I have already stated, you would need to assess the SIL required, remembering that much of the standards in this area are in a state of flux at the moment.

There comes another whole raft of legislation and guidance, testing proof, acceptability trials etc. when you start with safety related parts of control systems En 954 being one standard, but please see last paragraph.

BTW I still think the original design is flawed and unable to function correctly, safely or even at all based on the info given, which is one of the limitations of such forums.

There is more to this circuit than 7671 which was the point of my advice to the OP.

I have probably said too much already, at this point I probably need to add my legal disclaimer FWIW.

This post is NOT a rigorous technical paper, is simplified and does not cover every conceivable condition, or variable. It is also not written in strictly correct technical terminology. I have worded the post to hopefully explain the situation with regard to the previous posts and the typical situations that may be seen.
I cannot give formal professional advice on this forum as my professional indemnity insurance will not allow this, and due to the remote nature of the information and advice, any communications cannot be construed as such professional advice.
The above comments are advice given as seen in good faith, as I personally understand the legislation based on my qualifications in engineering & H&S, along with the information which I have been provided at the time they were made.
They are made in good faith based on the situation as understood.
Please remember I do not have the full facts relating to the situation, nor am I able to obtain these easily, thus my advice has to be taken in the context which it is given. It cannot be taken as a substitute for the advice given by a professional consultant who is in possession of all of the relevant information.
In this situation my advice and comments cannot be taken as formal professional advice or consultancy.

Paul

 

[davelerave]

i mistakenly thought you said 3 machines

as already said -all live conductors(if required) would need 8-poles for 4-machines


the design may include 'redundancy' if required

afraid i don't know any UK rules ,hoping to learn though

- anyhow you're prob well capable of the installation work but let someone else do the all-important 'design'

 

[joe_berks]

thanks davelerave so what you are saying is to isolate the neutrals aswell as the lives. i will suggest it to the design engineer

 

[Davey101]

Think of a DOL motor starter would you find it acceptable for say a saw to restart on the release of the e-stop button? No, I would not.Or would you expect to have to depress the start button first? Yes, absolutley.

Think of the failure modes for a moment, the OP’s specifier appears to have given them a cursory thought. He has asked for an “overall” e-stop. Presumably this would be in case there is a failure in the control system of the machine such that the stop system did not function, or the machine started unexpectedly, thus A.N. Other could de-energise the machines remotely without having to approach the local isolator, which by definition is local to the machine! I presume that the sterilisers do not have any control circuit, or e.m stop's, which is why the OP has been asked to provide them.

However, is a single e-stop adequate, this boils down to the old chestnut of risk assessment. As you said based on room size accessibility etc.
Agreed.
However, what is unacceptable under PUWER98 & BS EN 60204-1 is the re-energising of a control circuit via the release of a stop control.
The nearest analogy is the central switching systems specified by BS4163.
Here in the link is drawn to PUWER98 and the guidance there in which takes you to 60204, even though these systems are fixed wiring in buildings, 7671 does not cover these types of control, thus bows out to statutory legislation, i.e. EAWR89, & PUWER98 which takes you to 60204.
I have no knowledge of PUWER, I presume a lot of sparks haven't?
You should not allow a contactor to be re-energised by the release of a stop button under any circumstances, I have frightened a few people with this scenario!
Can you circumvate this reg with the use of lockoff stop buttons?
A bog standard em-stop/contactor circuit would be controlling machinery!
Why would you fit a contactor to control a ring main as a ring main is a standard arrangement of circuit from 7671? Have seen plenty of ring mains/radials controlled by contactors and e.m. stops, 'gasguards' and other such devices are regulary used in conjunction with stop buttons in schools, laboratory's etc.
This does not require an e-stop, if it does, then other legislation/guidance has come into play & you thus must therefore comply with that. Ergo my previous comments.

DP switching requirements should be checked, IIRC & it is now late & my copy of 4163 is not to hand, this requires all live conductors to be switched.
You must remember that in the event of an incident then the most appropriate guidance to the system will be selected and expert witnesses may well draw analogies to 4163 as it is the most similar to this situation.
Unsure of DP switching requirements.
Missed the comment wrt the neutral. No reason at all for the N to be taken anywhere except A2 on the contactor!

O/L protection should be looked at for the control circuit as the control devices will not be able to take the full 32A load of the power CPD. Also the controls are controlling supplies from 4 CPD’s.
Agreed, anyone wiring a control circuit without appropriate O/L protection shouldnt be wiring anything!

BTW I still think the original design is flawed and unable to function correctly, safely or even at all based on the info given, which is one of the limitations of such forums.
I presumed that there was at least one typo.
There is more to this circuit than 7671 which was the point of my advice to the OP.
Paul

Like I said, genuinely interested to learn, I think this is something which could benefit a lot of forum members.

 

[netblindpaul]

My responses in green, I'm rubbish with this forum software it took me half an hour to get my msg with Davey's modifications into a post!!!
Please excuse any typo's /spelling its been a bad day!

Originally Posted by netblindpaul

Think of a DOL motor starter would you find it acceptable for say a saw to restart on the release of the e-stop button? No, I would not.Or would you expect to have to depress the start button first? Yes, absolutley.

Think of the failure modes for a moment, the OP’s specifier appears to have given them a cursory thought. He has asked for an “overall” e-stop. Presumably this would be in case there is a failure in the control system of the machine such that the stop system did not function, or the machine started unexpectedly, thus A.N. Other could de-energise the machines remotely without having to approach the local isolator, which by definition is local to the machine! I presume that the sterilisers do not have any control circuit, or e.m stop's, which is why the OP has been asked to provide them.

I like green! The sterilisers must have their own control cct to comply with the machinery directive CE PUWER98 etc.


However, is a single e-stop adequate, this boils down to the old chestnut of risk assessment. As you said based on room size accessibility etc.
Agreed.
However, what is unacceptable under PUWER98 & BS EN 60204-1 is the re-energising of a control circuit via the release of a stop control.
The nearest analogy is the central switching systems specified by BS4163.
Here in the link is drawn to PUWER98 and the guidance there in which takes you to 60204, even though these systems are fixed wiring in buildings, 7671 does not cover these types of control, thus bows out to statutory legislation, i.e. EAWR89, & PUWER98 which takes you to 60204.
I have no knowledge of PUWER, I presume a lot of sparks haven't?
You should not allow a contactor to be re-energised by the release of a stop button under any circumstances, I have frightened a few people with this scenario!
Can you circumvate this reg with the use of lockoff stop buttons?
No you can not if would not comply with PUWER98.

A bog standard em-stop/contactor circuit would be controlling machinery!
Why would you fit a contactor to control a ring main as a ring main is a standard arrangement of circuit from 7671? Have seen plenty of ring mains/radials controlled by contactors and e.m. stops, 'gasguards' and other such devices are regulary used in conjunction with stop buttons in schools, laboratory's etc.

So have I & they don't comply with 4163 or PUWER98 or EAWR89. More often than not they have been designed and installed by damn good installation sparks who don't understand control systems because it is not their area of expertise. you can't treat a contactor control circuit in this sort of application like a glorified light switch!
An e-stop button is not designed to make current flow it is only designed to break it.
It is not the fault of the install sparks it is just tha tthey have probaly never experienced it or been taught it correctly.
This sceanrio is the one I describe, there are other requiremetns in place than 7671 at play.
These installations MUST have a start & a stop button at the very minimum otherwise they DO NOT COMPLY.
If they have a momentary start button along with one or more e-stops which function in the same general manner as a DOL motor starter, or a lighting contactor circuit with push button on & push button off control then they may well comply.
However, just e-stops which when released re-energise the contactor then they DO NO COMPLY.


This does not require an e-stop, if it does, then other legislation/guidance has come into play & you thus must therefore comply with that. Ergo my previous comments.

DP switching requirements should be checked, IIRC & it is now late & my copy of 4163 is not to hand, this requires all live conductors to be switched.
You must remember that in the event of an incident then the most appropriate guidance to the system will be selected and expert witnesses may well draw analogies to 4163 as it is the most similar to this situation.
Unsure of DP switching requirements.
I can't remeber the exact requirements either, I would have to look it up & I have a few other things on tonight.

Missed the comment wrt the neutral. No reason at all for the N to be taken anywhere except A2 on the contactor!

O/L protection should be looked at for the control circuit as the control devices will not be able to take the full 32A load of the power CPD. Also the controls are controlling supplies from 4 CPD’s.
Agreed, anyone wiring a control circuit without appropriate O/L protection shouldnt be wiring anything!

BTW I still think the original design is flawed and unable to function correctly, safely or even at all based on the info given, which is one of the limitations of such forums.
I presumed that there was at least one typo.
There is more to this circuit than 7671 which was the point of my advice to the OP.
Paul

Like I said, genuinely interested to learn, I think this is something which could benefit a lot of forum members.

Hope my comments make sense.

It is NOT allowable to use an e-stop button like a light switch to switch on and off a contactor to control machinery. it will not comply with STATUTORY legislation.

You can even get this from the BRB, & that is not statutory.

Paul.

 

[davelerave]

thanks davelerave so what you are saying is to isolate the neutrals aswell as the lives. i will suggest it to the design engineer

afraid i can only help with general advise as i don't work in UK(may be moving over which is why i'm here)

but the basics for emergency stopping would be similar anywhere

ie: stop de-energizes contactor/s + releasing doesn't re-energize

stops located where needed

system 'designed' to relevant standard

if it was required to switch neutral prob separate poles because

- for single phase the neutral current is the sum of the phase currents
and for 3 phase there's a risk of unbalanced star connected load if you used 1 neutral pole

 

[joe_berks]

thanks a lot for all your posts. tbh i had never heard of puwer98 i know thats probably well bad considering i work in hospitals! not that it makes any difference, but the em stop button is a twist to release, so it wont just re-energise, but i'm guessing to comply it must completely isolate the circuits.?
im going to defo bring it up with with the design engineer, cos i have had a few issues with him, for instance he said wire the general power (32A ring) in 4mm L&N with 2.5mm cpc. i always thought cpc must be same size as line conductors, unless the cpc is incorporated in a multicore cable (ie T&E) in 7671 it does say this i think in chapter54. also , we ran in a 95mm 4 core swa and he said to use 35mm earth , and use the steel wire armour to achieve Ze. i thought the earth should be at least half the size of line conductors. he also suggested wiring the sterilisation machines in 16mm at first! its only a 32amp isolator! was only when i brought it up and said you could use 6mm he agreed! bit dubious about him.

 

[davelerave]

don't work in the UK but for 4sq rings wired in pvc singles we use 4sq cpc

out of interest are you talking about steel trunking/conduit and singles

 

[netblindpaul]

joe,

PUWER98 applies to all work equipment in all work places whether in use by the employed or self employed. From a screwdriver to a nuclear reactor, the same as EAWR89 applies to all electrical equipment in workplaces from a say 1.5V button cell up to a 400kV installation.
Nothing is exempt, it is just that the hazards & risks and thus the mitigations are different.

It may be useful you get yourself on the HSE website and have a look at a few of the publications that are on free download there to ensure that you are compliant with statutory legislation.
A twist to release e-stop is a normal e-stop.
It is still not allowed to energise a supply with this type of device. (Full stop)

If you are employed, then the onus is on your employer and you should turn to them for advice, your supervisor, manager, QS, PDH etc. but, this does not remove your personal responsibility even as an employee.

HSE have a test case on their site where a spark in charge of an apprentice was not sufficiently diligent and the apprentice was injured, suffered an electric shock, I can't remember the outcome to the apprentice, but it did involve hospitalisation. The spark was prosecuted and fined personally due to the negligence of his actions. The spark was an employee, not a director, manager, QS or anything or any role with supervisory responsibility above that of his own work & that of the apprentice.

IF you are self employed, or running your own ltd. co. then you really need to do a bit of self study to ensure that you do not inadvertently do something that gets you into the dock, because expert witnesses will hang you out to dry. You would also be subjected to more severe punishment than an employee.

Remember "ignorance of the law is no defence", sorry, also with H&S legislation the statute is overturned, from "innocent till proven guilty" to “it is down to the defendant to prove their innocence”.

Bad I know, but that is how it is.

So you could end up in jail and just saying I did not know may only get your sentence reduced if the judge is lenient and believes you.

Also, not having a fundamental understanding of the design and function of the circuits that you are designing and installing, would not go down well in court.

p.s.
Nearly did the IEE expert witness training a few years ago but it clashed with some other stuff, so dropped it.

Paul

 

[joe_berks]

to give u a bit of an insight into my setup... im working for a building firm on a self employed basis. there is a qs but he has very little to do with things, he just basically puts his name down on the cert, he trusts all my work etc. so i am the only spark. there is a design engineer who has been out to site twice, and he is the one who obviously came up with the install , done the drawings etc. the only drawing i have relating to the pushbutton circuit etc is one showing a 4 pole contactor 32A, withe the four line conductors for the isis machines (sterilisation machines) going through the fore pole connections , and a seperate 6A circuit feeding the pushbutton, which in turn feeds the contactor coil.

 

[joe_berks]

yeah davelerave i put steel trunking with 20mm steel galv conduit.