Non-timer shower fan wiring query

[gksb1]

Hi,
I should start by saying I'm a plumber and normally go out of my way to avoid anything to do with wiring, however my electrician is on holiday all week and I have promised to have all chasing and cables run ready for him to connect when he returns. I realise I should've asked him for a wiring diagram and he probably assumed I knew what to do, but it turns out I don't hence here I am!

The project is my own bathroom which has taken me nearly 6 months (near completion) since I only get the odd free day to work on it here and there, therefore any advice which prevents it dragging on would be very much appreciated. Really what I need is a step by step description of which cables to run from what and to what?

I'm fitting an in-line ceiling extractor fan in the loft space above the shower (which doesn't have a timer.)

The wall outside the bathroom door is block work in which I already have a chase from skirting to ceiling (for underfloor heat mat cables to stat, then 2.5mm T&E which runs up to and through loft space and back down to consumer unit in kitchen). The chase is large enough for additional cables I just need to know how many more boxes to cut in and where etc.

As I would rather not have a pull cord inside the bathroom is it possible to use a fan isolator switch outside?
Do I need an additional fused spur? Does this need mains power?
Also do I need a fused spur before the u/f heating stat?
Which size cable to I need for each step?

Any help very much appreciated, many thanks.

 

[flameport]

Extractors are normally powered from the lighting circuit. If you wanted it from the same one as the UFH, a fused spur would be required.

For a on/off switch on the wall, the simplest option will be to put a single 1 gang box in the wall, with a length of 1mm twin & earth cable from there to the fan position.
Power for the fan can be taken from the lighting circuit in the loft space, with the isolator next to the fan in the loft.

 

[PrenticeBoyofDerry]

Generally you would install a bathroom ex fan on the lighting circuit, whether it is then connected to a fused connection unit would depend on what the MI states. If you search through WIKI, there should be enough information in there for you to complete your tasks. As you are chasing cables into walls and energising bathroom equipment then RCD protection is required. It is not unusual to have the fan isolator external of the bathroom. Cable sizing would be generally between 1.00mm and 1.5mm for this type of load. I personally would install 3 core and earth, so you then have the provision for a timer if ever required.

//www.diynot.com/wiki/Electrics:speclcn
//www.diynot.com/wiki/Electrics:Installation-Techniques

 

[endecotp]

You don't mention the bathroom lighting. Is that new?

I.e. would you like to put the switch for the fan on the same box as the light switch? Is that where your chasing goes?

 

[ericmark]

OK with me it was a wet room so all switches were outside and lights were recesses. The problem comes up again and again to keep the switches away from possible water being outside is likely the best way. Human nature we dry hands before leaving bathroom so switches outside are likely used with dry hands.

However children I am sure have not changed and switching off the power shower, lights or any other item when no one can see who did it has always amused children so I can see why people want the switches inside.

As to fans the first question is if the fan is required by building regulations or just an extra your fitting? Building regulations all hinge around windows, with no window you can work fan with lights, with a fixed window fan must have independent method of switching on, with opening window fan not required. Also of course heating systems with what is called an open flue (this means fire draws air from inside the flue is not really open) then measures are required to ensure no depression is caused which can draw fumes into the room. Often a heat recovery unit is required to satisfy this requirement.

Having said that the rules are often broken and often fans are connected to light switches and little or no thought is spent on working out where the replacement air comes from. The run on time I think 15 minutes does seem rather long and it could be done with a pneumatic switch or a timer. With the former the time is from when pressed not from when leaving room so likely not 15 minutes anyway.

As stated using three core and earth does allow change latter.

As to under floor heating the one I fitted was a flop. It just took too long to reheat the floor after a shower remember it was a wet room. The heating mat has to be earthed which limits brands that can be used or an earthed mat has to go over the heaters, also it needs a pocket for the thermostat and in my case the bend was too sharp and when the sensor failed it could not be removed. The underfloor heating often has two sensors one for the floor temperature and one for the room. With my experience the extractor shifted too much air for the underfloor heating to keep the room warm. However entrance was from a cool hall if the area where air comes from is warm then maybe it would work. But maximum temperature to be able to walk on the floor means the differential between floor and air temperature is too low for it to keep room warm. Some other form of heating is required. In my case the towel rail was swapped for the largest we could fit which was enough to keep room warm.

All electrics in bathroom need RCD protection in my case a new consumer unit was fitted, but this may alter how wired. Often lights were not RCD protected so it could be better to have a RCD FCU running lights and fan and heating in the room. It does need some design. There is no real one size fits all.