Can I run extractor off shower switch?

In short no, it is not permitted under BS7671:2008 (17th edition wiring regulations) to take a spur off of the 10mm shower circuit to feed the fan. As all electrical work in the bathroom comes under part P of the building regulations, so if you are planning to do the work yourself you need to pre-notify your intention to your local building control and get part P consent (you'll need to pay their fee) and on completion get them into inspect and test the work. If its absolutely necessary for the fan to only switch on and run when the shower switch is on, then the safest way to achieve this this and that is fully compliant with BS7671 is to use a contactor rated at 50amps with a 230v coil. The contactor imput and output terminals can be wired using the 10mm cable and a separate 230v feed wired in 1.0mm or 1.5mm can be run to control the contactor coil, this control circuit can then also run onto the fan and so that the fan and shower will operate together but the 10mm supply to the shower is completely isolated from the fan/control circuit. I think you would be best advised to get a part P registered electrician in to do this job if you want it to be fully compliant with BS7671:2008. Remember if you do DIY electrical work and fail to nitify it under part P of the building regulations you can be fined up to £5000, plus £50 for every day thereafter until the work is certified and/or put right.

Yes you can run a fan from a shower pull switch as long as the circuit to the fan is fused down. A Part P certificate will be needed so you will need to get this work done by a qualified Part P registered Electrician.

Hi Firstly don't be tempted to wire your fan into the shower circuit. The set up you want can be done but first of all call a part p registered electrician for some advice on the best options for your bathroom. Matthew