Wiring 3 Way lights where two single ight exist now

[Bill Stock]

Old question,m I'm finally getting around to:

OK, I have two lights, two switches, both lights are on the same fuse. It looks like both junction boxes have other circuits running off them, which I think is the same fuse.

Plan is to run three way wire between the two lights white/red to socket, blacks connected. Then run two way wire to the 1st switch white (black tape) to red (socket) black to black. Then run three way wire bewtween the two 3 way switches (white wire taped).

But I'm not sure if it matters which socket I run the switch to, since they both have other circuits running off them. Can't I just run my other circuits off the black/white in either junction box as it is now? This is where it gets a little confusing.

TIA

[RBM]

Leave all the existing wiring the way it is. Run three wires between the two switches. At one switch location disconnect and tape the existing wires that were on the switch. Disconnect and tape the two wires that were on that switch's light. At the first switch location you can remove the existing single pole switch and now wire both three way switches to control that one light. Last, you need to run a two wire cable from one light to the second

[Terry]

This sounds like a good way to go, but you should be aware that adding wires caused the boxes to overfill. You should also know that adding wires can be tricky in boxes enclosed in sheet rock.

You should be prepared to cut a square section out of the sheet rock covering the switch boxes. You may be able to do the job without cutting the sheet rock, but if you have to use larger boxes this is really not as bad as it sounds.

[Bill Stock]

OK, this is the same as the end run wiring diagrams I've seen. This makes sense, since you're switching the circuit as opposed to the individual lights. The problem is that I don't have access to the wiring and I would have to drill about 10 joists to use your method. I was hoping to use the existing two wire cable between the lights to pull the new 3 wire cable between the lights. So is there some reason I can't use the original method other than it simply won't work?

Thanks.

[Bill Stock]

Thanks Terry, we're also moving one light so I've drilled the new opening and I'm using a retro ceiling mount for now. I'm going to try to use the existing wiring to fish the new wiring (see response to RBM) unless there is some reason I can't use this wiring method. If I can't fish or can't use my planned wiring method, I'll cut out a couple of access holes and get out the REALLY long drill bit. :-)

[Nate Nagel]

1) assuming the original install was to code, the cable will be stapled at each box, and if the run is lengthwise to the joists, at probably a couple locations in between. 2) I don't feel ambitious enough to completely think it through, but keep in mind that you need to maintain zero net current through all cable assemblies (that is, all currents within a cable assembly need to sum to zero, considering "hot" to be positive and "neutral" to be negative.) Or in other words, you can't have a feed coming from one assembly and get your neutral from another. I can't say for sure whether that is what you'd end up with with your plan, but think about it.

nate

[Bill Stock]

Thanks, I've seen lots of three way wiring diagrams done like this, but of course they don't show any other circuits in the box. I don't think there are any (if any) staples on the wire I want to pull. I took pictures when the ceiling was down for renovations. As for being to code, these guys did not pigtail any of the Al to Cu connections and it passed inspection.

I know what you mean about the three way wiring, that's why I was hoping someone could save me the brain work. I'd like it to work AND be safe.

[RLM]

HTH

[Terry]

What you need make sure before you can plan the route is that the existing wiring has to have a hot and a neutral at each box so everything stays hot.

Then, because the you are switching both lights from the switching combo you have to have a red wire connected to the black wire of each light.

So you have to have a black, white, and red between the boxes before you do any switching. The black will be hot all the time (and keep everthing working) The white will supply the light at both boxes (and keep everything existing working). Then the red will be used to switch on and off.

If the electrician installed the cable properly, the existing wire will be stapled to the studs.

Here is a crude drawing of what you are shooting for.

[RBM]

The two wire cable will be stapled at each end, and the holes drilled through 10 joists probably won't be straight and clear enough to use the cable as a pull wire

[Bill Stock]

Thanks Terry,

I'll have something like Option 6 provided by RLM:

Except that I'll have additional circuits feeding out of the black and white in each light box.