bathroom vent fan and new switch

I just finished a new install bathroom vent fan (2-story house, 1st floor ceiling). I fished the new electrical wire (3-wire) through the ceiling and down the wall to the existing light switch. The light switch has a ground, white, black. I pulled out the light fixture and the box is FULL of wires. It looks like the white wire to the light switch is pigtailed with several black wires. I just had plumbing replaced and the back side of the wall is open for access. I want to move the junction (right term?) box away and to the clostest stud and have only the electrical wires for the fixture in a new box. Now, I know this was wordy, but I am guessing I need to run another 3-wire to the switch for a power source since I do not have a neutral. Right? I bought a duplex switch so I can run the fan and light separately.

 

You have read this pretty well. The switch is wired with a switch loop, i.e., no neutral.

Here are your two main options:

(A) 12/2 from light to fan, plus 12/2 from fan to switch.
(B) 12/3 from light to switch, plus 12/2 from switch to fan.

Which one do you want?

I would feel more confident of my next answer if you would be more precise about the box FULL of wires. Exactly how many cables, how many wires of each color, and full connection information. I.e., tell me enough so I can draw the picture.

 

Okay. One power source wire goes in. Three out: one to a GFI; one to the light switch, and the other goes on (and I assume to a light in the hallway, etc.- not sure). In the light fixture box:
3 black +1 white pigtailed.
3 whites pigtailed
1 black (by itself for fixture)

Also, my house was built in '54, and the wires are cloth coated, (except for the GFI).

 

Okay, the wiring at the light is perfectly clear now. No problem there.

The new information opens up more options.

(A) 12/2 from light to fan, plus 12/2 from fan to switch.
(B) 12/3 from light to switch (replacing the existing 12/2), plus 12/2 from switch to fan.
(C) A second 12/2 from the light to the switch (leaving the existing 12/2 there), plus 12/2 from the switch to the fan.
(D) 12/2 from GFCI to the switch, plus 12/2 from the switch to the fan.
(E) 12/2 fromthe GFCI to the fan, plus 12/2 from the fan to the switch.

Please pick one of the options: (A), (B), (C), (D) or (E).

 

I'll guess that you are going to pick option (A). If you choose another option, let me know.

The new 12/2 from light to fan is "F".
The new 12/2 from fan to switch is "S".

First, break off the tab on the side of the duplex switch that connects the two screws on that side. You do not want it there.

At the light:
(1) Fb to the three blacks and one white.
(2) Fw to the three whites.

At the fan:
(1) Fb to Sw.
(2) Sb to fan black.
(3) Fw to fan white.

At the new duplex switch.
(1) Two wires that are connected to the old switch to the two screws on the bottom half of the duplex switch.
(2) Sb and Sw to the two screws on the top half of the duplex switch.

Connect all grounds everywhere.

 

B or C are options.
A would be across two ceiling joists, and D and E are more difficult an A. That leaves B and Option C...

Either B or C will require the same effort. (I forgot to tell you it is a wall light fixture over the sink- the sheetrock was cut in the adjoining room behind the sink- I can look into the bathroom ceiling to the first joist). I can drill a hole through that ceiling joist and run either the 12/3 or 12/2 to the switch.

I already have a 12/2 from fan to switch in place.
Which option will make wiring the switch easier?

 

Oops. I guess I took too long to get my reply back! I did not choose option A and I am guessing it is because you did not know where the light fixture was located.

I look forward to your response to my last posting regarding Options B and C.

 

Okay, let's do (B). It causes less box crowding than (C).

12/3 from light to switch (replacing the existing 12/2) is "S".
12/2 from switch to fan is "F".

First, remove the 12/2 from the light to the existing switch, and remove the existing switch.

In this case, we're going to leave that tab in place between the two screws on your duplex switch.

At the light:
(1) Connect the light's black wire to Sr.
(2) Connect Sb to the three blacks (you already removed the white from this wire nut).
(3) Connect Sw to the three white wires and to the light's white wire.

At the duplex switch:
(1) Connect Sb to the side of the switch that has the tab connecting the two screws (either one of the two screws).
(2) Connect Sw to Fw.
(3) Connect Sr to the bottom screw non-tab side of the duplex switch.
(4) Connect Fb to the top screw on the non-tab side of the duplex switch.

At the fan:
(1) Connect Fb to the fan's black wire.
(2) Connect Fw to the fan's white wire.

Connect all grounds everywhere.

 

Thank you. I will let you know how it went when I am finished.

 

Everything went quite well with the diagram you gave me. Replacing the 12/2 with the 12/3 from light to switch worked great. I ended up with very minimal sheetrock repair inside the bathroom itself with only the 4"x2" L-cutout at the wall/ceiling above the switch. I notched out a vertical groove through the top framing (as shown in one of my wiring books) and it shows a "nail plate" to protect/secure the wire before repairing the sheetrock. Is this a hardware store item?

 

You should find nail plates just about anywhere. They are required when the wiring will be to close to the sheetrock.