Light switch upgrade

[Cochese]

I'm not an electrician, but I know I can do this. Just need a little bit of help.

Have a switch that right now controls a set of lights and a fan in a bathroom. Somewhere along this circuit is also an outlet.

In the box, it's wired as follows:
Three lines of three wires each, black white and ground. All ground wires are tied together and led to the ground on the switch. All the white wires are terminated together. Two black lines are tied together to the top pole of the switch, and the lone black wire is tied to the bottom pole.

What I would like to do is control the fan separately from the light, as I don't always need it on when lit. The new switch is a double switch in a single plank body. Two poles on each side plus the ground. Instructions are provided but I haven't quite figured it out yet. Any help is appreciated.

[mpc]

Okay, my guess is:

One of the two black wires tied to the same screw is the "hot" input wire from your circuit breaker/fuse box. The other black wire on that screw continues on to the always-hot outlet. (by the way, this may not be per code - using a single screw terminal to connect two wires) The 3rd black wire, on the other terminal of the switch, goes to the lights & fan. This is the switched "hot" wire for those two devices.

The whites are the "neutral" which is really the return wire for everything. So that's why they're tied together - since the outlet, fan, and light are fed from one circuit breaker/fuse, there should be one return neutral as well back to the fusebox. And of course the grounds are tied together.

The first problem for your situation is the outlet. You want it "hot" all the time, right - not tied to the switches? That's why your existing setup has the two black wires connected at one screw: the "hot" input from the fusebox and a "hot" output to the outlet. Depending on code, you may have to use a wire nut to "T" the input black wire into 1) a pigtail that goes to the switch and 2) to the black output wire going to the outlet.

The other black wire (on the other end of the switch - the switched "output" hot wire) then continues to both the fan and the lights... the second (and tougher) problem. So to make them operate independently you'll have to run another 3-wire cable from the new switch to one of them. Odds are the existing wiring goes from the switch to the closer of the lights or fan... then from there continues to the other device. I'd bet it goes to the lights first, then to the fan if the fan was added after the house was built. Either way, whatever wire "continues from the first device to the second" needs to be disconnected and replaced by a new 3-wire cable from the new switch to the device. And do NOT leave the old wire ends "tucked in the wall." Code generally requires the wire to either be totally removed or for the ends to be capped in an electrical box that has a blank cover on it - visible/accessible in the room, not hidden in the walls. I'm not sure if leaving the ends disconnected in a pre-existing box (i.e. in the light switch box and the fan/light fixture box) is allowable or not.

Also, is the outlet a "ground fault interrupter" (GFI) outlet? Most code these days requires a GFI for bathroom outlets. It can be used as a "starting point" for other bathroom outlets though; everything "after" the GFI is then protected by the GFI. And it's allowable in most codes to use the GFI as a "T" to implement this outlet chain since most GFI units have multiple terminals. (otherwise there wouldn't be any physical and/or legal method to make the GFI the first in a chain of outlets) Is there room to add a GFI in the electrical box with the switches - or to replace the box with a bigger one? Bring the fusebox "input" wires to the GFI, then go from it to the outlet and to the switches.

...my best understanding anyway; I'm not an electrician either.

mpc

[vaking]

I will make a different guess. Single black wire on the bottom pole is the hot line from power source. 2 black wires on the top screw are going to fan and light. Outlet is nowhere in this picture - there is no reason to run wires to the outlet thru the switch at all.
If this is the case - your rewiring is very simple. Single black wire that delivers power goes to the common screw on the dual-switch. One black from top screw goes to one of the new swicthes, another to the second switch in the new dual-switch assembly. I suggest to first check with the meter with the current switc h in the off position - which side is hot? If mu guess is correct - the screw with single black wire will show hot against the neutral or the ground.
If you find that the screw with 2 black wires is always hot against the ground - then guess by MPC is better than mine. It means hot wire from switch continues uninterrupted to the outlet.

[Cochese]

Thanks for the replies. At this point, this little project is getting put on hold until I can do some investigation in the attic as to how the fan branches off.

[crokett]

The only way you are going to know is test this. Shut the breaker off. Pull the switch out and disconnect it. Separate the two black wires that were attached to one of the switch screws. Turn the breaker back on. Carefully use a multi-meter or light tester to figure out if the incoming hot is the single black wire or the one of the pair of blacks is the incoming hot. You want to test these back to the white wires. My guess is one of the two black pairs is the incoming hot and the other single black goes up to the fan/light. If it does, you can't switch the fan and light separately unless you pull a second set of wires up to the light/fan box.

[Rand]

I think mpc has probably got it right.

You should be able to take the cover off the fan and get access to the wiring. It should be under a sheet metal cover held on by a screw. No need to go into the attic until it's time to pull wire.

[BigguyZ]

Crocket has it right.

The important questions are: is the power to the light/fan on a single hot wire from the switch to the fan/light, and is the outlet before or after the switch in the circuit.

Really, the latter question is key.

If the outlet is before the switch, then likely the two wires on the same terminal for the switch are separate lines for the fan and for the light. In that case, you can add a double switch to have each line switched. But if the outlet is after the switch, then likely the lines coming to the same terminal are the incoming hot, and the hot feed to the outlet.

Test as Crocket noted, but if you don't have an older voltage tester, be wary of the new ones that can do low voltage as well as standard voltage. I've found them to be WAY too sensitive, and will go off if you're even close to the wire- which is counter productive if you're trying to test 3 wires in close proximity...

Another thought- the two wires to the same terminal- are they going out of the top of the box or the bottom? Not a absolute, but generally a good indicator as to where the lines are going to. If they're both going up, it's most likely to the fan for both. But test it all the same.