I have a standardly wired Manrose Timer Remove Transformer with isolation switch powering a extractor fan in zone 1 of our shower.
It sort of works ok, although I do not think it's wired properly - and by this I mean it's safe, but the delay is it coming on, not it running for x minutes and then turning off, so we have to use the isolation switch to turn it off.
Anyway, what I want is to fit a smart switch (inline powered, remote controlled switch, 240V 10A) to turn the fan on using a remote control.
Yes it can be done, but they can be rather expensive, I am not sure of the wattage of the fan but likely over the 5 watt which seems the minimum that a smart light switch will control, but they are designed for lights and not sure if the back EMF from a fan would damage the switch.
So likely you would need a switch using a neutral, the problem then is physical size and mounting.
The rules are if you have an opening window in the bathroom you don't need a fan, so you can do what you like, if no window then the fan can come on with light, and if non opening window the normal method is a PIR to turn on the fan.
Over the years I have found the fan is often turned off as it simply does not work, the humidity control does not really work as there is nothing to draw the damp air into the sensor, so it is slow starting, by which time sensor gets saturated and takes ages to dry again, so fan runs for hours.
What I found is the shower can cause the chimney effect if in a restricted area open top and bottom, the moisture laden air fills the room. But either remove the cubical as with a wet room or seal at the bottom, and the water simple goes down the drain, adding a fan makes it worse not better.
My first house with a shower it was in the bath, so clearly a hole at bottom as door only went down to bath top, so the moisture filled the whole room, and we got problems with mould, next house was a wet room, no shower curtain or cubical, and the moisture stayed local to shower head, and quickly dried after use, fan fitted but never used. And this house it is a purpose built shower, and the glass doors seal at the bottom, so no circulation of the moisture and again shower dries fast. Curtains are useless as they don't seal at bottom.
Depending on location of fan it can actually make it worse rather than better, as it can draw the moisture into the room.
However building regulations require a fan if windows don't open, and even if they do, if some one can see into bathroom when open then the LABC inspector still says fan must be fitted. And the run on time is down in the regulations.
It seems there is nothing to say the fan must be automatic, so the simple method is a pneumatic time switch, you push switch and fan runs for 15 minutes, so simple.
As to a smart switch, you need a method to switch on without using the phone, I use Energenie not the best, but it does allow you to can remote controls as well as the phone or direct on the switch or socket, but it would need an IFTTT program to get the 15 minute run on, can't really see it working. Also needs a hub so works out quite expensive, in our case we have removed two light switches because they started doing their own thing, switching off without being told to switch off, at least by us, we think possible the Nest Mini which some times does seem like a mischievous boy.
Switching on central heating or air conditioning works fine, and three of the five light switches also work fine, even monitor my battery charger, but two light switches seemed to have a life of their own, and not only switched off on their own, but would not switch on again unless I turned off all the power to the lights.
So 4 TRV heads, three double sockets, three light switches, one four output extension lead, one energy monitor, and one combined energy monitor and remote switch latter used to turn on the AC. All work A1, but the last two light switches have a life of their own. But one of those switches was first used in the last house, and worked A1, so with smart switches you have to accept they may not work as intended.
The Nest Mini is great to listen to music, and ask how to spell words, or listen to radio, and ask random questions, but as to controlling lights or heating, don't trust it. It makes mistakes, today had to turn off phone to stop it playing music after google Nest Mini turned it on.
We would ask it to turn off music, and it would turn off lights, but ask it to turn them on, and it says don't know how to do that yet. So be careful what you use with Smart switches.
I would suggest if you have either a google assistant or an Echo you look at getting a "sonoff" unit. These have a relay so can turn a fan on or off no problem, and you could put it in the loft in line with your fan as is, then when all set up you can "ask" for the fan to be turned on. (Downside you have to ask to turn the fan off) But you can also use a smart phone.
Unfortunately I think this requires a 100-240V input and outputs the same. Therefore it can't be placed between the transformer and the fan as the transformer outputs 12V, unless I am wrong?
So I am left with putting it before the transformer, which has a Live, Live Switch and Neutral input. I just can't work out how to power the switch and then send the "switch" signal to the transformer.
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