There is a ceiling fan up and a set of four recessed lights. The lights are controlled from a dimmer/switch in the wall and they work fine. Next to the switch for the light there is room to install the control for the fan (has knob for light and one for motor). That's the state of things as of now.
I'm trying to install the control for the fan and got it working but have some questions.
In the wall outlet I see two live wires and it seems there is only one common. The two live wires are on two different 15 amp circuits. Currently one live wire is used to power the switch for the recessed lights. The common is then used for return path.
For the ceiling fan switch should I use the other live wire and share the common or should I share the live wire and just cap off the second live wire on the other circuit.
The wiring should be about 15 years old. Why would there be a live wire without common?