Electrical – Combine two independent switches into 3-way

electricalswitchwiring

Currently I have two independently powered switches powering two lights. The dining room is a single pole switch controlling the light. The kitchen used to have two 3-way switches controlling the light prior to removing a wall. After removing the wall, I just capped the old 3 wire in the basement so the remaining 3-way switch is the only control of the light. What I'd like to do is have both existing switches turn on both lights simultaneously but I'm not sure how to (or if I can) accomplish this.

Here's a rough text diagram of the current set up

Dining room:
Feed —– single pole switch —– light

Kitchen:
Feed into light –3wire —3 way switch — 3 wire — terminated in junction

One thing that seems odd to me is that there's a 3 wire from the light to the first (and now only) 3way switch. Let me know if this makes sense.

Thanks Dan enter image description here

The black coming into the hall switch is what provides power here. I think it I tap into the red wire coming off the top of the 3way switch and a neutral, I can pass that power to the dining room light. enter image description here

Best Answer

If you use the hallway circuit to power the three-way circuit, you must run four conductors (plus ground) between the two switch boxes.

new three-way powered from hallway

(If you needed to use the dining room feed you would have to run five conductors.)

With this circuit, you abandon and cap off, or remove completely, the feed cable to the dining room switch. You also abandon and cap off, or remove completely, the useless stub cable to the terminated j-box. I have omitted those cables from my diagram.

I have omitted the fault ground wires from the diagram, but don't omit them from your house.

Using the hallway light j-box as your power source is safer than using the dining room switch j-box. With power coming from the old dining room end, the two-gang (the one with the hallway switch) would have live wires from two separate circuits. A future electrician might not know that he has to flip two circuit breakers to make the box safe to handle.

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