closed circuit coil on 3 phase contactor needs to have time delayed off switch

[sparki steve]

I have wired up a couple of remote switches for a three phase fan in a paint room, two switches by the door, one inside the room one outside, this so fan can be controlled when entering and leaving the room, i have wired these as a closed loop hold on circuit with momentary switches, my problem is that they also require the fan to run on for 15-30 mins, to clear the air at the end of jobs, I just cannot find the right type of relay/timer because it is a hold on contact, once the timer button is pressed i need it to maintain the contact for the period of time required, break the contact then once the coil has dropped out ,make the contact again, so the hold on loop is ready for the next operation, i thought i had cracked it, by feeding the coil from the common of a n/o , n/c timer switch, so the feed is looped through the n/o , n/c . then when the timer changes from one to the other the contact would be broken, works on paper but in practice it is to quick and the coil remains energized,.
I have tried RS , but cannot find what i want. Any help would be much appreciated.

 

[snowhead]

How is the fan switched off without the timer?

 

[sparki steve]

ok , at the moment i have momentary on switch ( push to make )and momentary off switch, ( push to break ) these are manually operated, i then have another momentary on switch which will operate the timer circuit when it is installed,

 

[Knobhead]

What sort of paint is it? Some are highly flammable so the starter and P/B’s should be outside the storeroom.
I will do a drawing for you when you answer the question.

 

[sparki steve]

They have an existing spray booth within the room, this has been operational for a couple of years, the reason for the controls by the doors is that they were having problems with the negative air pressure, so every time they opened the door ( which was difficult in itself with the fan on ), all the crap from outside would fly in , ( up to now the controls were adjacent to the fan ) none of the electrical items, switches or light fittings are explosive resistant type, so i dont believe this to be an issue. I should tell you that the coil is 400volt type , with one side permanently connected to incoming phase, I have extended the other side of this to control the contactor , although this is obviously on a different phase
i am therefor only running 230 volts through control equipment,

 

[Knobhead]

Your on your own kid, I'm having nothing to do with it.

 

[sparki steve]

Thanks anyway mate, at least you had a think about it.

 

[cliffed]

jus a quickie of 2 play golf, can u put the stop ctrl thru a time delay off contact,via a c/o contact,this will then alow norm operation ,then when the time delay is needed,maybe via a push button,this brings in the timed contact.cheerio

 

[sparki steve]

Hope the golf was good,

... the time delay is the problem, everything else is wired and working, I need a timer which will open after a set period then close again, allowing the closed contact circuit to drop out, ready for the next time it is energised. I have tried a couple of changeover relays to do this but they do not open long enough for the circuit to be broken.

 

[RogertheBodger]

Still struggling Steve? have a look at these, you should find something there that is suitable.
Remember that these operate on 230V and from the sound of your post No.5 you do in fact have 400V running through your control equipment.

http://www.farnell.com/datasheets/70903.pdf

 

[Darkwood]

Im with tony on this one known of 2 explosions and 1 death resulting from spray paint rooms... you start by getting a COSHH on the paint or any other products used in the room to establish whether to walk away or tell the customer it needs a complete new system (expensive to say the least).

Ive got a very dark feeling about this job... intrinsically safe gear and/or remote operation, as goes your problem their are plenty of solutions from small plc program to having the start stop signal a timer relay that controls contactor coil, the stop signal would be the timer signal to time out. You can also get plc relays that can be programmed or set up to act or time to your needs.

Ill re-iterate my feelings though, because you have started this job you are wholely responsible for the existing regardless to its compliance or not before you got there, hope you can appreciate the hole you may be digging as its clear from reading you are not sure about the materials been used etc and the risks they pose.

 

[silva.foxx]

...they also require the fan to run on for 15-30 mins, to clear the air at the end of jobs...

What if a situation arises when the fan needs to be stopped immediately?

Are these fans in paint booths desired to run-on in fire alarm situations?

Please excuse my naivety.

 

[Darkwood]

What if a situation arises when the fan needs to be stopped immediately?

Are these fans in paint booths desired to run-on in fire alarm situations?

Please excuse my naivety.

Its not usually employed in the codes of practice but common sense would denote that explosive gasses should be expelled with a fire alarm incident hence they should carry on running or be linked to fire alarm, i will stand corrected but believe its an oversight in fire safety at present.

 

[sparki steve]

Mmmmm, i did think long and hard about this one, alas not long enough or hard enough, as i am taking the control wiring from one phase to operate the 400v coil, using momentary switches, you are correct, at the moment of contact at the point of energising the coil , there would be 400 v at these switches/contacts. I have taken a neutral with the control circuit to allow for an indicator lamp and to operate timer, this is what i was referring to as 230v control circuit.........honest.

 

[sparki steve]

This is a good point,.... if i can just get the timer circuit up and running , i should be able to link in the fire alarm to allow a run on in the event of a fire. I shall bring this to their attention.
If i send them a communique explaining that i feel all electrical items should be intrinsically safe etc. within this area , will the responsibility pass back to them ??.
I,m off to look at plc relays.

 

[Darkwood]

The responsibility cant be put on their lap as you are the designer and installer of your work and where you cross the line in altering someone elses work then you take on the responsibilty that the previous is in compliance, what should have happened here was a risk assesment as well as an inspection of existing, that way you would have informed the customer that the existing dosn't comply and poses a potential explosion risk (if thats your findings), then you would have quoted for the necessary works to be carried out.
Having already started the works you have become responsible and the only way out if it is deemed to be an environment where explosive vapours and gases would exist is to remove any work you have done and cut your loses, if you know your customer well it may be just the case that you have a chat explaining your concerns and why you cant do the alterations they requested but either way it may make you look unproffesional, lacking competence etc in the fact you didnt bring the issue up at the beginning.

I would suggest you get a COSHH report on all products used within the paint booth, and if its the case they do pose risks of explosion then i wouldn't be touching any of the install as it exists.... the risks and liability is too high, also the very fact it seems you were originally unaware of these concerns would indicate you are not knowledgable regarding requirements and safety measures associated with these types of room which go beyong your green Reg's book.

 

[Richard Burns]

Agree with the above posts about the use of unprotected electrical contacts in an explosive atmosphere, not something I would like to attempt even though i know somewhat about the use of tools in potentially flammable areas I do not know enough about electrical installations in this situation.

From an electrical wiring point of view I think the below work around would operate as you hoped. The left hand side is what you have at the moment the right hand side is replacing the 400V contactor with a 230V contactor, inserting a double pole momentary switch, hold on relay and a timer relay set for an (off) pulse a time after energising.
Just a thought and probably too much hassle to wire.
Can switch off if required with the off switch at any time but the on switch would not maintain on if pressed whilst the timer was operational.

 

[Knobhead]

Steve, are you intending to continue with this project? By now I hope you realise you’ve stepped in to a minefield.

Unless all equipment is outside the booth it must be Ex class. 230V control is not acceptable or practical for the control if you want a run on timer. As regards fire this is a two edged sword, depending where the fire is, running the fan could make matters worse.

 

[netblindpaul]

You cannot use 400V control for more than a specified number of devices and comply with PUWER98.
Sorry but if you don't know the number of devices, and what is classed as a device, and what is allowed in the environment, then I can't help.
As has been said this is a minefield.

Tony,
Sorry to drag up old discussions, but "now" can you see what I was on about?
No offence.