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Removing old switch box by prying it away from the wood stud with an old screwdriver

Adding Bathroom Fan Switch

Dear Mr. Electrician:  How do I add a switch to my existing bathroom light switch to control my bathroom fan separately? Answer:  Depending on how the home was originally wired, it could just be a matter of changing some connections at the existing light switch.  Then you could install a device with two single pole switches on one strap.  NOTE:  Some text links below go to applicable products on Amazon or EBay. METHODS OF ADDING A SEPARATE BATH FAN SWITCH I have had this request a few times and in some cases all I needed to do was open the existing switch up.  I removed the wall plate, unscrewed the screws holding the switch in the switch box, and pulled the switch out away from the wall so I could access the wires.  Sometimes getting the paint off the wall plate screws is the most difficult part. Inside of the wall switch electrical box I separated the black wire that goes to the bathroom fan from the black wire that goes to the light fixture.  Then a combination switch device such as the one below is installed to replace the old single pole switch. In the replacement scenario above, the existing hot wire in the switch box would connect to one of the black screw terminals.  Then the black wire for the fan goes under one of the brass screws.  The other black wire for the light goes under the other brass screw.  The grounding conductor only goes under the green screw. In the photo below you can see the wiring terminals.  Both screws on the left side are the hot connection which is obvious because of the break-off tab between them.  It is possible to have two separate circuits feeding this device just by breaking off that one little tab. ADDING WIRING FOR A NEW BATH FAN SWITCH Because of the original installer's method of wiring, a quick wiring connection change is not always possible.  In that case the next choice would be to install a new separate cable up to the fan or to the light fixture to make it possible to have two separate switches. Depicted below is a job where I replaced the entire bath fan unit and also installed a separate wall switch for the fan.  The existing bathroom exhaust fan was wired from the ceiling light fixture next to it. The replacement of the fan unit was considered a repair and not required to be inspected by a city electrical inspector.  The new wiring and new switch box did have to be inspected, but because it was a small job no rough-in inspection was needed.  I applied for the electrical permit a few weeks earlier before starting the work. The existing switch electrical box was full to capacity with wires so it was necessary to install a two gang old work switch box to be code compliant.  Article 314.16 in the National Electrical Code tells how to calculate the cubic inch capacity required for each wire size. I developed my own method of cutting access...