I am planning to put an exhaust fan in a second-floor bath with attic access. There is a light switch in place in the bathroom, and I will replace it with a two-gang box, adding a timer for the fan that requires a neutral.

My first instinct would be to steal power for the fan where it comes into the bathroom light switch and run a switch leg up to the fan in the attic. BUT, the house was built in 1952, and I don't see a ground wire in the existing box. In the last couple of years we had an electrician wire new ceiling lights and air-conditioner outlets on the second floor, and all of that power runs through the attic. I expect that this new work has a ground wire, so I'd like to splice into one of these lines to power the fan, and run a switch leg (with the required neutral) down to the two-box in the bathroom.

Does this sound reasonable? Thanks for the help.

TS