switched live from cooker hood

[filo]

Hi,
I have been asked to install a separate extract fan with overrun timer to operate whenever a recirculating kitchen cooker hood is switched on. Has anyone done this? I'm assuming I can 'create' a switched live using some sort of relay on the cooker hood load cable.

Any ideas would be appreciated.

 

[Deleted member 26818]

Take the feed to the extractor fan, from the load side of the cooker hood switch.
You will have to run neutral, earth and permanent live separately, probably from the cooker hood FCU.

 

[filo]

Take the feed to the extractor fan, from the load side of the cooker hood switch.
You will have to run neutral, earth and permanent live separately, probably from the cooker hood FCU.

Hi, thanks but the problem is that cooker hoods only require a permanent live - the switching is done inside the unit. So I need a switched live that is only live when there is current flowing in the supply to the hood.

 

[Deleted member 26818]

How is the cooker hood switched on and off?

 

[Colin Integrale]

Wouldn't it mean somehow tapping into the guts of the hood to get to the load side of the switch?

 

[Colin Integrale]

oops.... missed those last 2 posts..

 

[filo]

I won't be taking the hood apart ('more than my job's worth' as they say)!

 

[Deleted member 26818]

I won't be taking the hood apart ('more than my job's worth' as they say)!

Then you won't be able to do the job.

 

[nickblake]

personally i can see the point of doing it when the extraction is complete shut the cover or press the button , with out altering the cooker hood it will not be possible you need the switch feed from the hood to the motor to be cut so altering the manufacturers design , there is a way of doing it but its very silly and the hood would need to be permernantly on that would be to use a humididty controller so when the steam started the fan would switch on when humididty stop the fan stops but in my eye's that the worst idea ive ever had lol .

 

[filo]

I am convinced there is a way of doing this using a contactor at the consumer unit (which is in the same room).

 

[nickblake]

oh yes there is a way of doing it mate but the warrenty of the main cooker hood will be voide , if you caan get to the motor feed of the fan , use this as your switch feed the pick up the permernant feed from the switch fuse the add a small timer circuit via a contactor something like you get in a bathroom it will work but the problem is that its a bodge it job , you could do it with a ceiling mount PIR problem is with that when you come into the kitchen the fan will switch on , hang on are we talking domestic or commercial here

 

[nickblake]

Sorry been thinking about this one if the extract is just an extract controlled by an external switch it can be done but you would need a fused spur and a switch ,fused spur to protect the fan switch to controll it this way you would pick the permernant live from the incomming of the switch then the switched live from the switch and using a fan timer modual you can controll the other fan or better still use a fan with an overun facility ,so basically when the switch is switched on both fans would operate when the switch is switched off the the one fan will operate till the timer switches off

 

[filo]

It is domestic.

I suppose the fan on the extractor could be left on and the whole thing controlled by a wall mounted switch but it's not entirely satisfactory. Then, as you say, it's fairly straightforward (just the issue of the different circuit ratings)

 

[nickblake]

the biggest problem you have filo is the fact that the main cooker hood has its own controls if it hadnt the what you have been asked to do would be easy, its is difficult there are ways of doing it but its not easy IE pressure switches that work with an increase of air pressure in the duct but these are expensive air flow switches you an do the same again expensive

 

[Dunc]

Could you use a current sensing relay? It may be a touch overcomplicating things but the way i read how they work you could connect the relay in line with the cooker hood (between the FCU and the extractor) then use the output from the relay to connect to the SL of the secondary fan. The whole set up with a bit of tinkering could be made so that when you isolate the hood at the FCU the whole system would be isolated. The only issue i can think of is that the extractor fan will likely operate when the cooker hood lights are switched on but i think it would be unlikely to have the lights on when not wanting extraction of some degree.

Something like this looks like it will fit the criteria plus it means you won't have to hack apart the internal wiring of the cooker hood. I can't guarantee that is the right part to use as i don't do enough PLC type work but it looks like it might be to me from reading through the blurb.