I think my question might be similar to Controlling two fixtures on same circuit independently but I don't need anything as fancy.
Summary: I'm remodeling a bathroom. Presently it has one switch which controls a single light. I want to add a vent/fan.
Is there an easy way to wire a second switch off of the same circuit and have one switch control the fan while the other controls the old light?
The walls will be exposed so it should be relatively easy to run additional wiring.
Best Answer
No problem at all.
Power at the switch
If the power feeds into the switch box, you'll simply pigtail the ungrounded "hot" conductor to feed each switch. Then you'll run 14/3 or 12/3 nonmetallic sheathed cable (Type NM); whichever is appropriate, between the switch box and the ceiling outlet. Then connect the white (grounded "neutral") from the feed, to the white (grounded "neutral") to the ceiling box. Connect all the bare/green grounding conductors, and don't forget to ground each switch and the box if it's metal. Connect the black wire from the cable that runs to the ceiling, to one switch, and the red to the other switch.
When you wire up the fan/light. Connect all the grounded "neutral" conductors together. Connect all the bare/green grounding conductors together, and don't forget to attach a lead to the box if it's metal. Then connect one ungrounded conductor to the light, and the other to the fan.
Power at the light
The old way
If the power is at the light, things are slightly more complected. But it's still quite easy. Again you'll need 14/3 or 12/3 cable between the switch and ceiling. You'll still connect all the green/bare conductors together at each place, not forgetting to connect all devices and metal boxes. In the ceiling, connect the white (grounded "neutral") to the white wire from the light and fan. Put a piece of black tape around the white wire from the cable between the boxes, and attach the wire to the ungrounded conductor of the fan or light. Connect the red (ungrounded "hot") conductor from the cable between the boxes, to the ungrounded conductor of the light of fan.
In the switch box, connect the red wire to one of the terminals on one of the switches. Put a black piece of tape on the white wire, and attach it to the other switch. Splice the black wire, and attach a lead to each of the switches.
The new way
If your area has adopted National Electrical Code 2011, you'll be required to have a grounded "neutral" conductor at the switch box. To accomplish this, you'll have to run a 14/4 or 12/4 NM cable between the boxes. Then in the ceiling box, you'll connect all the grounds as before. Connect the white (grounded "neutral") conductor from the light, fan, feeder, and cable between the boxes together. Connect the red wire from the cable between the boxes, to the ungrounded "hot" conductor of the fan or light. Connect the blue wire from the cable between the boxes, to the ungrounded "hot" conductor of the light or fan. Connect the black (ungrounded "hot") conductor from the feeder, to the black wire in the cable between the boxes.
In the switch box, cap the white wire (unless one or both of the switches requires a grounded "neutral" connection). Connect the blue wire to one switch, and the red to the other. Splice the black wire, and connect a lead to each switch.