contactors and emergency stop buttons.

[joe_berks]

bit of advice plz guys... im working in a hospital decontamination room. there will be four big sterilising machines to clean endoscopy instruments.
they are single phase, on 32amp rotary isolators. (each on their own 32amp rcbos)
have to put in a push button emergency stop, that knocks a 32amp 4 pole NC contactor (230v coil)
any advice on how it would be wired?
im thinking put the live from each 32 amp supply into each pole terminal on the front of the contactor, then use a live and neutral from the push button into a1 and a2 on the contactor, will this then make the contactor "open" and turn off all the machines?
the push button has got two buttons inside it , one red one green. no wiring details. can anyone explain how to wire it up? is one side NC and one NO?

 

[bugsy]

Stop button with normally closed contacts feeding contactor coil, load circuits wired through contactor

 

[Sintra]

bit of advice plz guys... im working in a hospital decontamination room. there will be four big sterilising machines to clean endoscopy instruments.
they are single phase, on 32amp rotary isolators. (each on their own 32amp rcbos)
have to put in a push button emergency stop, that knocks a 32amp 4 pole NC contactor (230v coil)
any advice on how it would be wired?
im thinking put the live from each 32 amp supply into each pole terminal on the front of the contactor, then use a live and neutral from the push button into a1 and a2 on the contactor, will this then make the contactor "open" and turn off all the machines?
the push button has got two buttons inside it , one red one green. no wiring details. can anyone explain how to wire it up? is one side NC and one NO?

Yes what you are saying is correct but you may have to fuse down from your 32A for your stop circuit or run in seperate 6A radial for stop circuit.

Yes generally Em stop buttons have NC & NO contact just a matter of belling out switch.

 

[davelerave]

prob a N/O contactor so the stop de-energizes the contactor,you may need a key-stop or remote start to prevent it being re-energized( if neccessary)

just use 3-poles on the contactor and don't feed a neutral through it

 

[netblindpaul]

Firstly this is a hospital environment, thus you have to comply with what remains of the relevant parts of the NHS engineering standards.
Next, this has also to comply with PUWER98. See HSE ACOP L22 for guidance.
You also need you clients requirements.
If I understand the OP correctly.
It may be necessary to isolate all live conductors, thus you will need 8 poles, or 2 off 4 pole contactors, in which case it may be better to use another contactor to control these.
Next, you need to understand why this is being done, what is the SIL required for the control system.
You need to remember you are now moving away from the realms of BS7671 as such control systems are covered by statutory legislation and ACoP's along with other BS & EN / ISO standards.

An EM stop button may or may not have NO/NC contacts, EM stops are conventionally NC contacts only.
They are often colour coded. Green NO, red NC.
What control voltage is specified?
Remember the characteristics of the load when selecting a contactor to ensure it is suitably rated.
If the hospital electrical engineer has specified a 4 pole NC contactor then he needs sacking as he is totally incompetent.
You cannot switch 3 lives and a single neutral through one contactor when supplied from 4 separate RCBO’s.
You would be instigating a shared neutral situation.
Also an NC contactor will fail to danger!
That is if the coil fails open circuit, most common failure mode for a contactor coil if not the only one really then the emergency stop will no longer function, thus the primary failure mode for the system will be a dangerous one, thus you will fail in your FMEA analysis at the first hurdle under CDM & all other statutory legislation.

If releasing the EM stop reapplies power then this will NOT comply with statutory legislation.
You MUST have a momentary switch to re-energise the supply for compliance.
Remember non compliance with statutory legislation is a criminal offence.
Non compliance with BS7671 is a slap on the wrist.

That is when something goes wrong.

Sorry but it goes against the grain to say this as I am a bit of a have a go merchant myself, but, you need to get the requirements and understand the systems and the consequences here, if you are unsure then please get some professional advice from a competent control systems design engineer who understands the safety requirements in this scenario, because your post as I understand it means you could be looking at a goodly spell behind bars IF something goes wrong & if I were the expert witness I’d hang you out to dry.
Sorry

Paul

 

[Notsosmart]

Joe,

How are the sterilisers started? If they are using one contactor that suggests a common start pushbutton. If this is the case than the stop button will go before the start button in the circuit.

If you want me to draw a simple circuit diagram for you PM me and I will get one to you.

 

[netblindpaul]

Notsosmart,
That cannot be the case as the machinery would then not comply with PUWER98.

 

[Notsosmart]

Good point.

 

[joe_berks]

i think the contactor is suitable, as its 32A, but then again i know what you mean as there are four lots of 32A's coming in through the four pole connections.
whoever said about running a 6A supply to the pushbutton yes you are right . it does say that on the schematic.
well i think youve helped me understand how it is wired . just the issue about wether its a suitable contactor now.
if someone could send me a diagram how to 2nd fix pushbutton that would be great though

 

[joe_berks]

there wont be a borrowed neutral, i will just bypass the contactor with the neutrals

 

[joe_berks]

well paul i think your being a bit overboard, no-ones going to jail mate. i just asking for advice and by the sounds of it i had it pretty much right anyway just wanted confirmation. im only 23 but im qualified so im fully justified in carrying out this work. its not as complex as you think. just cos your in a hospital, does'nt mean that much difference i still follow 7671 and that pretty much covers every thing i do.
i am a have a go merchant but i always do it the right way. you wont learn anything if you dont try it

 

[netblindpaul]

Joe,
Sorry my lad, but 7671 may well NOT apply to certain parts of the wiring of this system.
You need to understand the SIL for this system to comply with statutory legislation.
This in turn will lead you to the correct FMEA outcome.
That is unless you are simply wiring to a client spec.
However, I still stand by my comment that if the client has specified a 4 pole NC contactor they should be sacked.
You are only switching the phase conductors and by passing with the N.
I trust that you are ensuring separation of the N conductors to ensure suitable division of circuits.
IF you are installing safety circuits which this would be classed as.
It would be an emergency switching system, which is covered by PUWER98, if you don't have competence in designing control systems to comply with this statutory legislation then you should bow out.
Paul

Sorry my man, but having re-read your OP, your OP does NOT add up, your functional description of the circuit and the components is not compatible.
You really need to investigate this spec and make certain of the requirements.

 

[mogga]

Puwer theres a forum there

 

[joe_berks]

yeah im doing it to a client's spec. bow out? how ridiculous. the responsibility lies with the designer at the end of the day. i'm just wiring a push button for a few oversized washing machines... lets not make a mountain out of a mole hill.
it doesnt say any where to seperate both poles, and you wouldnt isolate using the stop button, you would use the rotary isolator if you needed to work on the machine. its just to stop the machine running.
bow out! whatever next. i can tell your not a practical sparks, youd be no good to us coming out with all that crap. i would tell you to get your tools and bow out yourself.
especially in a recession are you unwell?
of course yeah i would seperate the neutrals, im not exactly gonna put them all together am i?
just cos i asked a question im not a numpty

 

[joe_berks]

can i ask, paul, what do you suggest?

 

[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