Question re wiring for SELV extractor and LV mirror demister

[Rupie12]

Hi

I am trying to get my head around my bathroom wiring as there are a few different ways of configuring it, and I want to make sure it is right and future proof before putting the ceiling back up. I would love some input from someone with a lot of bathroom experience.

Extractor:

My electrician is planning to run the LV fan off the lighting circuit, but have it on a separate switch alongside the 2 light switches outside the bathroom door. Obvs there will also be a fan isolator switch at high level outside the bathroom. My electrician is proposing to position the fan transformer under the bath at the end without the taps. This seems a little unconventional, but I don’t have a loft space so if it went above the ceiling, it wouldnt be accessible. Does anyone have any better ideas about where the transformer should go?

Demister:

My electrician hasn’t installed one before but proposes running this off the lighting circuit and having it switch on with one of the two bathroom lights. This made sense to me, but I am now wondering whether it is wise as my daughter spends a long time in front of the mirror. I don’t really want another switch in the row outside the bathroom door as that would make it 4 gang (2 lights, extractor + heat pad) which seems confusing to me. Does anyone have any clever suggestions?

Other demister questions are...where would you normally position the transformer? and...as it is low voltage, does that mean it doesn’t need to be fused or isolated? (Am thinking that things that heat up usually are).

Sorry for the long and boring post. Hoping someone here can come up with a nice simple to solution!

 

[EFLImpudence]

Does anyone have any better ideas about where the transformer should go?

Back in the shop. Use a 240V fan.

Demister:
My electrician hasn’t installed one before but proposes running this off the lighting circuit and having it switch on with one of the two bathroom lights. This made sense to me, but I am now wondering whether it is wise as my daughter spends a long time in front of the mirror. I don’t really want another switch in the row outside the bathroom door as that would make it 4 gang (2 lights, extractor + heat pad) which seems confusing to me. Does anyone have any clever suggestions?

It's up to you and how/when you want it to work.

Other demister questions are...where would you normally position the transformer? and...as it is low voltage, does that mean it doesn’t need to be fused or isolated? (Am thinking that things that heat up usually are).

I wouldn't think there is a 'normal'.

It's your house. It's up to you.

I'm sorry if you think this is not very helpful but you are the one who has to live with your choices.

 

[Rupie12]

Thanks for your reply.

The fan will be at the shower end of the bath in zone 1. Is 240v ok in that position? The size of the room, and position of the windows means I have no choice re location of bath, shower and fan unfortunately.

 

[ericmark]

One it is unusual to have a transformer with a low voltage fan, most are 230 volt, you can get extra low voltage fans, often with a extra low voltage lamp in the centre, I fitted one in the bathroom here, it is still there, as it was too big to remove without removing ceiling, so now only three lights and a fan which to be frank is hardly ever used.

If the fan is within a zone which requires extra low voltage then OK, other wise keep it simple and use 230 volt. The same applies to lights.

As to fan operation it should be ideally able to be switched on without the lights, the old building regulations required it if there were non opening windows. But it seems to have been now dropped I assume as energy saving bulbs use that little power?

The problem is where a fan is required by law, it is also required to run on, and although you can use double pole switches and have it so it can either be worked with lights or independently, normally people select one or the other, not both.

The debate is will the fan ever be used if not with the lights, or reverse will anyone switch on the lights during the day just to run the fan, and of course is the fan required?

I lived in a house with hot air central heating, and we suffered from very dry air, even this house has loads of vents, and has never had a problem with mould growth in the wet room, yet our other house it is a continuous battle to keep black mould from growing. It is so much dependent on how well sealed the house is, squirting expanding foam in the air bricks may stop drafts, but it also makes house damp.

And with any extractor there has to be a way for air to replace it, and it depends how dry the replacement air is.

However you are paying for the work, so unless breaking a law, you have it as you want it, powering a fan from lights is OK, however you need to be able to isolate it should it fail, and it would need to be a RCD protected supply, adding a RCD to lights needs a risk assessment, should the RCD trip can you see enough to avoid danger? I have windows above each door to light the landing so also if bathroom light fails there is light from rest of house, i.e. the emergency light above the stairs.

 

[EFLImpudence]

The fan will be at the shower end of the bath in zone 1. Is 240v ok in that position?

Yes, if IPX4 or better.

 

[EFLImpudence]

The problem is where a fan is required by law, it is also required to run on

I don't think the law comes into it.

That is all the law says.

 

[JohnW2]

I don't think the law comes into it.

Indeed not - and nor is there any way that the law can force house occupants to actually make use the "provided adequate means of installation", particularly when it takes the form of an openable window. Even if what was 'provided' were a lights-connected fan, it would probably not get used during daylight hours if there were adequate daylight in the room - and, even when the room was dark, those who, for example, didn't like the noise of the fan might take a candle into the room with them

Kind Regards, John

 

[flameport]

Does anyone have any clever suggestions?

If your daughter spends too long in front of the mirror, don't bother with the demister or extractor at all - she'll spend far less time in front of it then.