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?