New Kitchen extractor wiring install

I have existing kitchen extractor which switches on and off from switch.

I want to install new humidity and timer controlled extractor fan. Existing wiring is Blue, Brown and Green/Yellow at the fan. I know I need a switched live, what is the best way to check wiring, get a switched live and complete install.
(existing wiring disappears into wall, cannot follow this cable, where it leads to?)
Thank you.

Presumably the timer is so that the fan will stay running for a pre-determined length of time after you have switched the light off. If this is the case, it sounds unusual that it has humidistat control aswell as the fan would normally be switched on when the light is on.
If it is the case that you have a fan with both controls then I would expect it to be connected in the same way as a conventional timer fan (I have never met a fan with both controls!). This being that it requires 3 wires to run properly (4 including the CPC or Earth wire coloured green and yellow - for the moment I shall ignore this wire.
You will need 3 wires, a permanent live feed, a neutral and a switched live from the light or the light switch or anywhere in between. The wires you describe will become the permanent live feed and neutral (brown live, neutral blue). This would be when the existing switch is in the on position. The switch can either be replaced for a blank plate and the wires connected together in the switch box or just leave the switch on all the time.
You will need to connect the third switched live from the light to the fan.
Just take the wire directly from the light fitting and connect to the switched live terminal (the brown connection to the lampholder).

It is also a requirement to have an isolator (3 pole) somewhere accessible and close to the fan position (but not IN the bathroom if that is the location) to isolate ALL 3 wires to the fan.
You must also have the earth wire present in all switches and at the fan even though you will more than likely find there is no earth connection to the fan itself. If this is the case, just sleeve the wire with green and yellow sleeving and coil uo the wire in the connection box of the fan, ensuring it will not come into contact with any other wires or connections.

Please note, you should also have an RCD protecting the wiring to the fan to comply with current regs although this isn't essential for the operation of the fan.

Hope this helps!

This is very helpful.
Replacing the kitchen extractor fan with a timer/humidity model has become a mini-project in itself, as this would entail, removing laminate flooring and wooden flooring in bathroom to get at the lamp holder, in order to run one switched live cable from the lamp holder to the fan.

Is there a possibility of installing a pull cord extractor fan, which has timer/humidity controls using the existing wiring (live, neutral and earth).

Last week I replaced the bathroom extractor fan, with a timer/humidity model, however the existing wiring (3-core) was already (live, switched live and neutral).

If there is no other way, am quite prepared to go back into the bathroom (which incidentally I have completely re-decorated). Will have to show humility to OH.

Is the fan to be ceiling or wall mounted?

Does the existing fan supply come from a switched fused spur from the sockets? Or from the lighting circuit?

If it is fed from a double pole switch eg a switched fused spur or similar, you could fit a 16 amp double pole pull switch on the ceiling adj the fan.

The existing supply cable could go to the pull switch, then run a 3 core and earth cable to the fan.

At the pull switch connect supply live and brown of 3+e cable to LIVE IN.
Connect black (sleeved brown) of 3+e to LIVE OUT.
Connect supply neutral and grey (sleeved blue) of 3+e to NEUTRAL OUT.

Connect earths (sleeved green/yellow) to the earth block.
Leave NEUTRAL IN empty.

At new fan
brown is perm live
black sleeved brown is switched live
grey sleeved blue is neutral.

There are various other ways of doing this, if the supply cable is too short a joint can be formed in the fan if there is room.

The wall mounted switch, if double pole, will provide complete isolation to all three conductors at the fan.

You will have perm live and neutral at the fan for humidistat and overun, the pull cord will act as overide, and will overun for a short time when this is switched off.

This is all assuming your fan is to be ceiling mounted, where a built-in pull cord would be useless.

The separate ceiling switch suggested could be substituted for another wall mounted one of course.

I fit unswitched spurs >> an airtech remote pullcord + humidi >> fan.

I dont like the idea of having a timer fan in the kitchen because its not always necessary to use the light, and also you dont always need the fan on.

the extractor is 6" wall mounted, and I cannot tell whether the supply is from lighting circuit or from sockets. Suffer terribly from condensation, hence timer overun and humidity fan install.
I need to lift floorboards in bathroom and check supply and proceed from there.

Have managed to partially lift floorboards in bathroom (above kitchen). The supply to current kitchen extractor fan is from cable from MCB (3 core) and has own switch on/off.
Nearby is ceiling light for kitchen which has it's own on/off switch and the cable is separate and emanates from MCB, .
My question is "where can I get a switched live supply from somewhere to proposed new humidity/timer over-run extractor fan."

Can I run a single cable from the ceiling light (live) to extractor fan and call this switched live, and would switching the ceiling light on/of affect the supply to proposed extractor fan.
Thankyou.

is the existing fan switch actually on the fan? or somewhere else?

The existing fan has a switch by the door entrance of kitchen. The ceiling light has a switch adjacent to this.

Correction to earlier post, the cable to the existing extractor fan is black/red/unsleeved copper wire.

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