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-   -   old wire, backfed switch question (http://www.diychatroom.com/f18/old-wire-backfed-switch-question-23090/)

Jack A. Trades 07-02-2008 03:38 PM

old wire, backfed switch question
 
I have a fan and a light that are both operated by the same switch.
Okay, bear with me here and try to visualize this.

This circuit is a combo of old knob and tube and new wire.
The old wire (which is the home run) hot connects to a new 2 wire hot which goes directly to the switch. The new 2 wire neutral goes from the switch to a j-box in the attic where it is used as a hot for the fan and the light. Nice work by the previous owner on backfeeding the switch, right?
The old wire neutral is tied to the fan's neutral and the light's neutral in the j-box.

I want to add a switch next to the existing switch to control the light independently of the fan.

I'm thinking I will remove the hot from the j-box to the light and run a new switch leg from the light to my new switch.
I can use the hot to the existing switch as the hot for my new switch- the switches are going to be in the same box.
I will leave the neutrals alone.

I'm wondering if this will be an acceptable solution.
I don't like that if I run a new switch leg (14/2) and leave the neutrals as they are, then I will end up with an extra unused wire in the switch box and in the light canopy.

I'm guessing I need a little advice, and I hope all that makes sense.

jimmy21 07-03-2008 12:41 AM

i couldn't really follow you. Maybe you could draw a wiring diagram? What i gather from you..... The knob and tube homerun goes to your switch? And then a 12-2 romex goes to the fan (through a jbox first) but they switched the nuetral instead of the hot? (Where is the fan getting power from)

im a little confused But don't worry about having an extra wire, it happens. I would run 14 as your old stuff is probably 12. You don't want to start mixing and matching wire sizes on a circuit

Jack A. Trades 07-03-2008 06:26 AM

I knew that would be confusing. I think the next paragraph may clear it up a bit.

The old knob and tube wire goes from the panel to the attic.
A new wire 12/2 goes from the knob and tube hot to the hot side of the switch , and the neutral leg of that new 12/2 goes from the switch up to the junction box where it is used as a hot to feed both the fans and the light.

Now I want to add a new switch to switch the light separately from the fan.
So I was going to disconnect the hot for the light at the jbox and run a new switch leg to my new switch.

The neutral from the knob and tube goes straight to the jbox where it is tied to the fan and light neutrals. I was going to leave this alone.

wirenut1110 07-03-2008 06:31 AM

Sounds good to me.

HouseHelper 07-03-2008 08:00 AM

The white wire running to/from the switch is NOT a neutral. It is part of a switch leg. Properly wired, it should be the constant hot to the switch, and the black should be the switch hot to the fixture.

Best way to do what you want is to replace the 12/2 with 12/3. Use the white as the constant hot to the switches and the red and black as the switched hots to the light and fan.

Jack A. Trades 07-03-2008 11:51 AM

"the neutral leg of that new 12/2 goes from the switch up to the junction box where it is used as a hot to feed both the fans and the light."

Dude, I know the neutral is used as a hot. :thumbsup:

I like your suggestion of the 3-wire better than my idea, but I already wired it up. :hammer:

jimmy21 07-03-2008 12:05 PM

ya, but he's saying its not a nuetral. Its simply the white wire of a 12-2 piece of wire. There is a big big difference.


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