Controlling bathroom extractor fan to existing light switch?

You can connect to the lighting circuit (and this is the preferred way if you are using a run-on fan controlled by a light switch).

You *may* need additional fusing - see the fan data sheet. Some need protection at 3A, some are ok at 6A, and some lighting circuits are protected at 10A.

You will need a 3 pole isolation switch to enable the fan to be fully turned off for servicing / cleaning. This can be either a wall mounted jobby (if placed in zone 2 or outside), or a pull string type. If the isolator is in a separate room from the fan then it ought to be a type that can be locked off (although this requirements is often ignored in practice it seems).

In message , Gareth writes

This may help.

Thanks. The fan needs a 3A fuse and my lighting is 5A so I need fuses.

Thanks for your reply.

Yes, I think that's what I need.

Thanks.