Home>Discussions>ELECTRICAL & LIGHTING>Adding 3-way switch - Figuring out current configuration
4 posts / 0 new
Last post
Adding 3-way switch - Figuring out current configuration

I’ve added a diagram to hopefully illustrate what I’m trying to describe.

I’m wanting to add a 3 way switch to an existing ceiling light switch and I’m having trouble just understanding the current configuration. I currently have a wall switch that controls the ceiling light on the porch. The switch is near the kitchen door and I want to add a 2nd switch that is closer to the exterior door. I should mention that my house is about 80 years old and is mostly re-wired but still has some knob and tube left.  The existing wall switch is only connected to 2 knob and tube wires that come up from the basement– one to the power terminal and one to the neutral. Since there are only 2 wires, I assumed the power must be coming to the light first, then to the switch. But there is a breaker box on the porch wall (no breakers – just used to house the junction boxes). It has 2 junction boxes in it with at least 4 or 5 wires coming in. I found that when I disconnected the 2 knob and tube wires on the right (see diagram), it kills power to the ceiling light (and several others in the house) but the switch still has power so I don’t see how power could come to the light and then to the switch.

I’m completely confused. Can anyone help me sort this out?


Re: Adding 3-way switch - Figuring out current configuration

You don't give the wiring in the J-box so I can only guess at this point. You have hot and netral going into the box from the braker. The hot is connected to one wire going to who knows where, it is also connected to the wire going to the switch. The other wire from the switch is connected to the hot going to the light. The other conductor from the light is connected to the house netral along with one conductor from the cable going to who knows were. K&T wiring is not two conductor it is two single conductors. It sound like you are discribbing old two conductor cables.



Re: Adding 3-way switch - Figuring out current configuration

I attached a pic of the junction boxes and also a pic to show how I'm thinking I need to wire the 3-way.  So then if I understand what you're saying, the switch may not have 1 hot and 1 neutral?  It may have 1 hot coming in from power and 1 hot going to the light?  So then if I want to add a 3 way switch, here's what I'm thinking I need to do:  

1. run 12-3 from the old switch to the new switch.  2. New 3-way switch would be wired normally, with black to the common terminal, white and red to the brass terminals, and ground to the ground terminal.  3. Replace the old switch with a new 3-way with the white and red to the brass terminals, ground to the ground, then the hot wire coming into the old switch would be tied together with the black wire from the 12-3.   4. then the hot wire going to the light would go to the common terminal on the new switch.  Any chance that's right?  

Re: Adding 3-way switch - Figuring out current configuration

Update:  what I described above worked.  I removed the old switch and wired in my little pigtailed setup and it worked fine.  I meant to say 14-3 instead of 12-3 above.  Also, I understand that in this situation, the ground wire is not doing any good because there is no ground coming into the original switch but I'm thinking I'll wire it anyway because someday I might have an electrician replace all the knob and tube and that way it will be available to tie into the new ground wire.  

Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.