I want to put an electronic timer on our bathroom fan. These timers apparently only come in a four wire configuration... which I am not familiar with. I have three wires, black white copper, in my wall box. I don't want to use a dial timer. Is there a way to adapt three wires to four? If not, it is a short distance from bathroom to circuit panel, can I add a fourth wire? Is there such a thing as an electronic fan timer that is 3 wire? What is the best way to accomplish this task?

Perhaps it might be easier to understand the meaning of these color codes. In your wall box, the copper wire is ground. The white wire is considered neutral. The black wire is considered hot. The timer should come with a wiring diagram. Many times, this will illustrate the 4-wire to 3-wire connection. Connect ground to ground, neutral to neutral and hot to hot. The extra wire from the timer will most likely go to ground but rely on the manufacturer's instructions on this.

If all you have at your switch location are those wires you mentioned then you do not have a neutral wire. White is most likely the incoming hot and black is the hot back to the fan. The timer you have almost certainly requires a neutral wire so you will have to run new wire to the fan location to bring it to the switch.