Fitting a bathroom fan...again.

[amfisted]

I've purchased a bathroom extractor fan. Its a humidistat model, and I've attached an image of manufacturer's wiring guidance: top left picture, bottom diagram (model DX100HTA).

I can see that the live and neutral will be connected via a double pole isolation switch to the fan itself, but my question relates to connection T.

In layman's terms, how would that on/ off switch be wired?

I do intend of course to have a spark check the wiring before I use the fan.

Edit..its not come out as clear as I'd hoped it would, so if it proves to be unreadable I'll try something else.

Thanks.

Untitled

• amfisted
• 15 Oct 2014
• 1

 

[ban-all-sheds]

It would be wired as shown in the top left picture, bottom diagram.

Why do you think it would be done differently?

 

[ericmark]

The question is how do you intend to control the fan? The diagram shows simple on/off switch but often we want to use the light switch to control. When using the light switch then we normally use a triple pole isolator after the light switch rather than a double pole before the light switch.

The building regulations stipulate where there is natural lighting and no opening window then you must be able to switch on the fan without switching on the light. If the window opens then no need for a fan.

Also again building regulations talks about open flues and the problems with fans drawing in CO due to a depression in the house. Same of course applies to using a vented tumble drier.

From using special isolators to double pole light switches there are many methods used so step one say what you want to happen.

Including does your bathroom have a toilet in it.

 

[AndyPRK]

frequently people do not bother to fit the fused double pole isolator.

but use a 3 pole fan isolator.

 

[ericmark]

frequently people do not bother to fit the fused double pole isolator.

but use a 3 pole fan isolator.

That would depend on where the supply comes from. With a lighting supply in the main it's no more than 6A because ceiling roses are only rated 6A so relying on the main 6A MCB rather than use a 3A fuse as you say is common.

But if from the ring final then relying on the 32A MCB is clearly a no no.

I drew this

many years ago to show fan wiring but in this case there is a humidistat and without getting out the approved document think Part J I can't remember if it's permitted to use just the humidistat or if it's required to have an override switch? I am sure if a window which does not open and a toilet is also in the bathroom it would need an over ride switch.

I remember BAS giving the wiring for use with both light and over ride switch but it starts to get complex. So I was hoping the poster would come back and say what they wanted the fan to do.

Oh red wire would be T connection.

Reading the full instructions it would seem the switch connected to T is an over ride and the fan would work without this connection once the humidity reached the set amount.

Since there is an over run built in a self return switch may be good enough to start the fan off then it will stop when either timed out or dry enough.

 

[AndyPRK]

Even on a humidistat model its useful to connect the T terminal up, for getting rid of smells and early stages of a shower, and some manual control

 

[amfisted]

Thanks for the replies.

To clarify, this would not be a light-controlled appliance because there's plenty of natural light in this bathroom, and I wouldn't want to have to burn a bulb unnecessarily in order to activate the fan. I've gone for a humidistat due to recent problems with condensation in the rest of the property, which I think may be mitigated to some extent if we leave the bathroom door open, as well as controlling condensation in the bathroom itself.

There is a toilet in the bathroom, a sink and a bath with electric shower. The fan would be positioned on a wall above the toilet, well out reach of anyone standing in the bath, about six feet above the floor and opposite the door.

Incidentally, I didn't "think it would be done differently" than as shown in the diagram. I asked the question in order to clarify that diagram.

 

[ban-all-sheds]

As Andy says it's useful to still have a switch if you want it to run even when the room is not humid - just get one with a neon so you know it's on. Or if the fan also has a timed function one with a momentary action.

BUT - it won't solve your problem of house-wide condensation. It will be nowhere near powerful enough to ventilate the entire house, and humidistat bathroom fans only trigger when it starts to get steamy, not at "normal" levels of humidity.

Have you done anything to cause ventilation problems? Or to put more water into the air?

 

[amfisted]

The only thing I can think of (and I've not heard of this before) is that the drying out of a few square yards of recently applied emulsion paint has temporarily upped our condensation levels. Otherwise no; we've moved to a bungalow with cavity walls and reasonably modern double glazing, and both kids having now left home we've also reduced the household population to just myself and the wife.

Clearly and as also advised by others on a different part of the forum, lifestyle can have a dramatic influence on levels of humidity and thanks to that advice I'm now approaching this issue from a more informed position. Hopefully.

 

[flameport]

The other option for a switch is one of these:
http://www.tlc-direct.co.uk/Products/MK3190.html
which works as pull to start, fan then runs for as long as the timer is set for, and it can't be left on accidentally.

Supplied with red cord but you could easily change that for a white one.

 

[JohnW2]

The other option for a switch is one of these: http://www.tlc-direct.co.uk/Products/MK3190.html which works as pull to start, fan then runs for as long as the timer is set for, and it can't be left on accidentally.

Indeed - but you woz beaten ...

.... Or if the fan also has a timed function one with a momentary action.

Kind Regards, John

 

[ban-all-sheds]

The only thing I can think of (and I've not heard of this before) is that the drying out of a few square yards of recently applied emulsion paint has temporarily upped our condensation levels.

I'm sure we've all had the situation where you paint the walls of a room and in the morning the windows are streaming with water, but it's a short lived thing, wouldn't cause condensation problems for long enough to be a problem needing solving, unless you like to paint your walls every weekend.

The trend to more air-tight houses is one of the major culprits. Old draughty ones were well ventilated. People who would like to breathe, cook, wash clothes etc put water into the air, and you have to get it out of the house.

Yes, a bathroom fan is needed to stop vapour from there getting into the house, ditto a cooker hood, especially if you cook with gas, but ultimately good whole-house ventilation is a necessity.

 

[amfisted]

Yes, I've been given similar advice on another part of this forum.

Thing to do is to wait until the next spell of cold weather and see how bad the condensation issue is, then take the necessary steps to address it long term, alongside use of my dehumidifier in the short term if necessary. There's more painting to come, but not until I've rested from the stress of trying to word my questions on this forum to best advantage.

The issue of bathroom ventilation is now in hand thanks to the excellent advice from you guys.

 

[amfisted]

Well, sort of "in hand". I'm still not 100 per cent clear about the wiring.

The diagram above shows the cable splitting from the live feed to the fan and routing via a switch to the T connection on the fan itself. Does this mean that the switch would have a live feed only?

All the switches I've ever come across in the past had, at the very least, a neutral and live. Fairly confused about that bit, to be honest.

I did ask an electrician to quote me for the job but he never got back to me, so I'm determined to sort it myself; although as stated above I won't use it until a spark (if I can get one to turn up) has checked my work.

Apologies if I'm asking for answers already supplied. Just want to be absolutely sure about the wiring.

 

[AndyPRK]

yes the switch would have a live feed only


Light switches only have a live feed and switched output (T)