can bathroom extrator fan be fed from shower circuit!

[dandt]

Please dont be too shocked by this question - I have given it some thought..I have recently bought an extractorfan from B and Q to replace one in my new house. I wish I had bought one with a pull chord - could have gone straight into ring main supplied near bathroom. Anyway I ws seduced by the £8 less. I assume most are connected to the lighting circuit in the same way that the bulb is connected. I dont really want it to come on every time the light comes on. What would happen if the flex went into the shower switch which would be more than capable of supplying. The fan demands no earth so I wonder if this would be a concern. If it is possible it would be great. It could come on with the shower pull chord, and would definitely be on when someone was having a shower. many thanks

 

[chivers67]

What protection do you think the cable feeding the fan would have in that instance?

 

[dandt]

sorry you are trying to educate me but I need it spelling out. Do you advise against my intentions. If it went into lighting circuit as it has no earth does your same question stand, or are lighting circuits ok in this respect. Sorry again I mean a cooker circuit can have a 13amp socket spured off (is this ok because of the earth in the extra circuit)

 

[ericmark]

I have wired an extractor fan using current sensing relay where the gases were explosive and it had to shut down the plant if the fan failed but to set up this system to sense when the shower is running would be a bit OTT.
The current transformers and relays etc would require a box to mount them all in and the cost would be around £150 just for parts.
Idea may be good but don't think it would comply with regulations anyway I think they are required when using loo as well as shower I suppose a PIR would be better method.
I note all these fans in new houses and how as soon as people move in they are switched off at isolator and do sometimes wonder at the sense of fitting them in first place but in this nanny state George got it right and you need to look out for the "thought police" since 1984!

 

[rebuke]

You could just get one with a humidistat built in and run it from the lighting circuit. This way, it will only turn on if the humidity builds up, which is only likely to happen whilst you're using the shower.

Note that if in Englands or Wales, this work is notifiable under Part P of the building regulations since it is in a bathroom...

 

[Spark123]

I have wired an extractor fan using current sensing relay where the gases were explosive and it had to shut down the plant if the fan failed but to set up this system to sense when the shower is running would be a bit OTT.

What happens if the fan stalls? The ones I have seen before are monitored by things like paddles in the air flow, pitot tubes and Differential Pressure switches.

 

[Taylortwocities]

Back to Mr dandt

The straight answer is a big NO.

The shower circuit is, well, for the shower. leave it alone.

Just go back to B&Q and replace the fan in your bathroom for a new one of the same type, change the one you have for a pullcord one if you want the on/off option.

Any other course will be:
1. very expensive (much, much more than £8) as you will have to notify the local authority (and pay their fee) that you are doing electrical works in a bathroom

and/or

2. hazardous to you and yours

 

[ericmark]

If fan stalls then overload will trip so no current PLC will then start other fan instead if both fans fail plant is shut down. We did consider flap and we but stalled fan and removed the fan blade and both could be easy sensed by current draw and were not likely to get stuck by the chemicals used.
Although we could program the PLC to check flap dropped if fan was not running if fan stopped during production there was a chance any flap would stick because of type of product.
It also was designed to alternate between to two fans on each start up again to reduce chance of product being deposited on fans and causing failure.
There was of course also manual checks.

 

[holmslaw]

..

 

[ericmark]

I did not want the reader to think the fans were bathroom fans so that's why I talked about the explosive gases.
I did think about just looking up rules and regulations but I could not remember where they are maybe Part L?
But many people are not bothered what the rules say and I considered the idea was to have fan running only when shower was in use.
To connect within shower is clearly not possible and keep the unit sealed and retaining type approval so only method would be current sensing relay which in the main are only able to handle milliamps often standard 4 - 20 ma and so some form of reading and relaying will be required and once we start doing this the price starts to rise.
I hoped the reader would see even if the regulations did not stop this being done logistics would.
We have five optios
Switch on with lights
If no loo included switch on with humidity
Switch on with PIR
Run 24/7
Combine with heat exchanger.
I have never seem PIR's used to do this but have fitted PIR's in loo's mainly to stop people being able to hide in loo's until after shop has closed for some reason fitting camera's is not preferred option!
Again because in the main these are 12/24 volt not as simple as may first seem.
Still not worked out what is wrong with opening window.

 

[ban-all-sheds]

I hoped the reader would see even if the regulations did not stop this being done logistics would.

Eric - read this exchange:

What protection do you think the cable feeding the fan would have in that instance?

sorry you are trying to educate me but I need it spelling out. Do you advise against my intentions. If it went into lighting circuit as it has no earth does your same question stand, or are lighting circuits ok in this respect. Sorry again I mean a cooker circuit can have a 13amp socket spured off (is this ok because of the earth in the extra circuit)

Did you honestly think dandt would understand a word you said?

We have five optios

There are 2 more options.


1) http://www.diynot.com/forums/viewtopic.php?t=20386


2) Use a timer fan, and trigger it with a flowswitch in the water supply to the shower.
.
.
.

 

[ericmark]

I will agree with method one but that would only switch on fan when shower isolator is on and would switch if off when shower isolator is off no run on.

Note 1 :- Bathroom needs 15 l/s but sanitary accommodation (Think that means loo) needs 6 l/s so where the loo and shower are combined in one room you can't connect to shower alone.

Note 2 :- For a room with no opening window there needs to be a 15 minute over run.

Note 3 :- Intermittent extract can be operated manually and/or automatically by a sensor (e.g. humidity sensor, occupancy/usage sensor, detection of moisture/pollutant release). Humidity controls should not be used for sanitary accommodation as odour is the main pollutant.

It says nothing about using lights!

Note 4 :- It also refers to problems in sucking combustion products into the house and causing draft up stair wells etc.

This is all in Part F of the building regulations.

As to using the flow switch in the shower unit it's self you would need permission from the manufactures or it would invalidate the type approval. Unless of course you are suggesting a second flow switch independent of the one in shower and this of course could include water supply to loo. But the logistics really stop this and as you have pointed out the poster does not seem to follow what we are saying.

So I would go for simple switch to fan most likely a pull switch and used the built in auto run on. I see nothing in Part F that says it must have some sort of auto switch on so why not keep it simple!

As to supply because of cable sizes and ability to physical connect to shower supply and fuse down I would not go for shower supply.
Likely the extractor fan is class II but I would still not want to take from a supply with no earth. So I would be looking and logistics of connecting into ring main.

This would all come under Part P so is only of interest to the DIY man he is not likely to be doing it DIY. With my local council charging £115 to register any Part P likely to be cheaper to call in a registered electrician!

So as to the originator of Post understanding not likely to be an issue as only for interest anyway.

 

[holmslaw]

..

 

[ban-all-sheds]

I will agree with method one but that would only switch on fan when shower isolator is on and would switch if off when shower isolator is off no run on.

Nonsense.

Note 1 :- Bathroom needs 15 l/s but sanitary accommodation (Think that means loo) needs 6 l/s so where the loo and shower are combined in one room you can't connect to shower alone.

You could always switch the shower isolator on. Agreed the flow switch method wouldn't do. Could have a flow switch in the cistern fill wired in parallel though....

Note 2 :- For a room with no opening window there needs to be a 15 minute over run.

Indeed. And either method of triggering the fan works with a timed overrun.

It says nothing about using lights!

What says nothing about using lights?

As to using the flow switch in the shower unit it's self you would need permission from the manufactures or it would invalidate the type approval. Unless of course you are suggesting a second flow switch independent of the one in shower

Use a timer fan, and trigger it with a flowswitch in the water supply to the shower..

?

But the logistics really stop this

Don't see why.

and as you have pointed out the poster does not seem to follow what we are saying.

No, but others might.

Or the OP could say to his electrician "I'd like a flowswitch in the supply to the shower".

So I would go for simple switch to fan most likely a pull switch and used the built in auto run on. I see nothing in Part F that says it must have some sort of auto switch on so why not keep it simple!

Apart from the fact that people might forget to use the fan when needed, which is why linking it into the lights is so popular.

As to supply because of cable sizes and ability to physical connect to shower supply and fuse down I would not go for shower supply.

That's the whole point of the contactor to switch the lighting circuit to supply the fan....

This would all come under Part P

If he's in England or Wales, yes.

 

[dandt]

(I have been off internet for a while)
thanks for the straight forward answer NO..
I think some people missed the point of my question
Ps I still dont understand why its NOT dangerous to run say a plastic radio (with no earth in lead) from the socket which often comes with a cooker socket)
any way
thanks