New Ensuite - connect extractor fan to light switch?

Extractor Fans with an integral timer or timed switch need a 3 core and earth supply to allow the unit to run on after a light is switched off. It must also be possible to isolate the fan by means of a pull switch inside the bathroom, or a fan isolation (3 pole) switch outside of the bathroom The supply for this can be taken from most existing circuits providing the switched-fused-unit (SFU) is present at the start of the installation and appropriately fused to protect the sub-circuit cabling and accessories. Typically 3A or 5A for a fan installation of this nature is sufficient, but be sure to check the manufacturers specifications for details.

The Right way of installation of a bathroom fan is: If the main feed is at the switch or Ceiling rose. You should take it from there with a three core + earth cable to the Isolator than to the fan.

Wiring an Extractor Fan With an Independent Switch (not turned on by the light switch) As with the option above for connecting to the existing light switch, before you start any wiring, make sure that the power is off to the circuit you are working on!! ... The Minimum cable size for fans yes you can .

Hi… A fan with a built in timer is set to over run by 15 min. The supply needs a permanent live, switched live, neutral and an earth. As it was mentioned you can likely get this from the light in the bathroom but in newer installations you’ll find it all at the switch. So take a 3 core & earth supply from the existing light to a fan isolation switch, then the same type of cable to the fan. Wiring termination should be labelled.