I had a contractor install a Fantech PB 360-2 bathroom fan in my
master bathroom. It is currently connected to an on/off wall switch. I
purchased a Decora 20 Amp wall timer. FD 60EM. The wall timer has four
wires coming out of it. They are green, blue, black and white. When I
removed the wall plate and switch, I discovered only three wires,
white, black and bare copper. When I read the directions that came with the
timer, it shows an application where the switch is inline, with a hot
wire going into it, and a switched wire coming out. It would appear
that the hot wire must have been run to my fan in the attic, and then a
switched wire must come from that fan down to the wall switch. How do I
hook this timer up? Do I need a different timer? I'm usually pretty
good at figuring these things out, but electrical wiring is not my
forte. any advice would be appreciated. Wiring diagrams are readily
available on the web for both the switch and the fan system. Thank you in
advance for any assistance you can provide.

 

The romex in the wall carries 115 VAC on the black wire. The white is common - used to carry current when any circuit is completed. The bare wire is the protective ground.

Your timer should have had a wiring diagram included with it. You should be able to follow it to hook things up. Be sure to open the circuit breaker before touching the wiring.

If you have a meter, you may be able to work out the timer. I would guess that two are for the timer motor, and will always have a constant resistance, no matter is the timer is on or off. The other two will read shorted when the timer is on, and open when off.

In theory, then, either wire for the timer motor connects to the white wire. The other and one of the wires to the internal switch hook to the black wire. The bare wire attaches to the timer case (should be a green screw for that purpose). The remaining wire hooks to the black wire that goes to the fan. The fan also should have a white wire that goes to the white supply, and a ground wire.