Power past 3-way switch??

I may be stuck, but thought I'd ask for help. Here is the scenario...
Power comes into switch box on 12/2 wire. Connects to 3-way switch. Run 12/3 to first light, then 2 x 12/2 to next light, same thing for three more lights, then 12/3 to 3-way switch. See this link (
http://danswiringpage.com/diagrams/3w3lt_ps.jpg ) for the specifics on how it was wired. This part works fine.
What I want to do is continue the power on through the last switch to feed another light system (switch and two more lights; not 3-way). How can I do this? It seems that I would need to replace the last 12/3 with 2 x 12/2, so I can continue a neutral. But that doesn't seem right to me, or even like it will work.
Does anyone have an idea on how I can do this?
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Just wanted to compliment you on your diagram. Most of the ones I've seen on these groups make things more confusing. This is a thing of beauty. Unfortunately, like Doug said, you need to find a constant feed somewhere else

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I'd love to take credit for the diagram, but it is not mine. Dan's website (http://danswiringpage.com /) was very helpful for me. After making my post last night, I stayed up until I figured out I was stuck at that last switch. Oh well, I'll have a circuit dedicated to five lights! I've already hung wallboard at the first switch, so I can't get a hot wire from that point. I'll branch off a different circuit.
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I realize that the diagram (beautiful, btw) is probably showing standard practice.
BUT: is this setup even to code? It looks to me like the two 12-2 cables are unbalanced. You have nothing but HOT in the one (12-2 shown on top), and nothing but NEUTRAL* in the other (12-2 on bottom). Seems like you are supposed to have both those 12-2's in a conduit, or use a 12-4 instead.
And lastly, one of those whites (the ones in the upper 12-2) should be relabeled as black, or red, since it is serving as a hot.
* OK -- neutral isn't quite the right way to say it. But look at the current when the lights are on. In the upper 12-2, you have a black and white. One will be disconnected (no current), the other will have, say, 3 amps (for 3 mongo lights!), running to the right. The lower 12-2 will have a mixture of amps on the black and white. The first light consumes 1 amp, so the leftmost lower 12-2 will have 2 amps on the black, and 1 amp on the white, both going left. The rightmost lower 12-2 will have 1 amp on the black, and 2 amps on the white, both going left. All of this is a no-no, isn't it?
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There might be a code violation if this design is implemented incorrectly. If all non-metallic cable and boxes are used then there's no problem. If metal boxes are used then the unbalanced cables must go through the same knockout in the box. These details resolve the induction heating issue addressed by the code but would leave a potential source of electromagnetic radiation.
Doug
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Right, I get the point about the non-metallic boxes/cables, running through the same knockouts, etc. Is that all that the NEC requires? I thought that unbalanced runs were just outright not allowed -- that the two current directions had to be either in the same cable package, or run through metallic conduit. I suppose this is so that someone doesn't go introducing some other metalic loop -- say a water pipe, or romex staples (bent funny?), or something else. Or maybe its due to the radiation -- would this screw up hearing aids or pace makers or anything?
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Based on what I know that is all that's required. I'm not a code expert but I did research this issue while rewiring my house. Those are the specific acceptable conditions outlined in the book "Electrical Wiring Residential", 14th edition, which is based on the 2002 NEC. My setup involving 3 switch locations switching half of 2 duplex receptacles passed inspection with unbalanced cables and non-metallic boxes. The inspector blew through so fast I'm not sure he even noted the possibility of this problem, however.
I don't know about the impact of the electromagnetic radiation. There is at least one web page out there claiming health impacts from it but it sounded crackpot to me. I can't locate it now.
Doug
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kevin wrote:

What the US NEC specifically forbids is reversing the polarity of screw socket lamp holders. Carter system three way switching does that and is therefore no longer code compliant if used with screw shell lamp holders.
--
Tom Horne


Well we aren\'t no thin blue heroes and yet we aren\'t no blackguards to.
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Huh? This all has nothing to do with reversing polarity, or socket lamp holders. The issue here is an unbalanced pair of lines forming what amounts to a big current loop. It is essentially a large transformer with only one turn of wire. This is kind of like putting a huge alternating electromagnet up in your ceiling, given the right circumstances. Specifially, I have seen reports here and there that this might screw up certain hearing aids that rely on very small induction coils, (which even small magnetism might plausibly screw up). Sure, this might all be crackpot. Sounds reasonably plausible to me, though, in the less than 5 minutes or so that I have thought about it. Ah well. End of thread, I give up.
-Kevin
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kevin wrote: > Huh? This all has nothing to do with reversing polarity, or socket lamp > holders. The issue here is an unbalanced pair of lines forming what > amounts to a big current loop. It is essentially a large transformer > with only one turn of wire. This is kind of like putting a huge > alternating electromagnet up in your ceiling, given the right > circumstances. Specifially, I have seen reports here and there that > this might screw up certain hearing aids that rely on very small > induction coils, (which even small magnetism might plausibly screw up). > Sure, this might all be crackpot. Sounds reasonably plausible to me, > though, in the less than 5 minutes or so that I have thought about it. > Ah well. End of thread, I give up. > > -Kevin >
If you had broader experience in electrical wiring and specifically trouble shooting old work you would know that a Carter system three way switching circuit reverses the polarity of the connected load in order to use three wires for three way switching and constant power. Given the OPs original question that is very apprapos. The use of that method is now specifically forbidden by the US NEC.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
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Bad me for not reading the entire thread... but this caught my eye.
isn't there NEC code that states you cannot bury junction boxes? (or perhaps it says that boxes with junctions must be accessible)
(of course, you might not be in the USA... so that might not apply)
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be safe.
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You're lacking both a neutral and a source of constant power at that last switch. The hot wire will alternate depending on the state of the first switch. You'd be better off getting what you need from the first switch or some other source.
Doug
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Toddo wrote:

There is no practical way to what you want to do as Doug, the first responder already told you.
But, nothing is truly impossible...
If it was a matter of "absolutely positively" winning a bar bet, I could draw you a circuit which would enable you to use the existing conductors to give you a continuous hot and a neutral at that last switch box and still let you turn the five lights on and off from either present switch location, but it would involve replacing the present switches with momentary contact pushbuttons and installing a "sequencing relay". And, you might run into code limitations as to where you could locate that relay.
The same thing could also be accomplished by using X10 equipment to control the lights from either switch location.
But, best to do it "the right way" and find aomeplace else where you can power up that new line.
Jeff
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Jeffry Wisnia

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As others have mentioned, to do this with your existing 3-way switches, you need one extra conductor from the first 3-way switch all the way to the second 3-way switch (for unswitched hot), and one extra conductor from the last existing light to the second 3-way switch (to extend the neutral).
Note that if you are willing to give up your 3-way switching, so that only the first switch works the existing lights, then your existing cabling is sufficient. Probably not what you want, but an option to be aware of. Or you could use wireless 3-way switches.
Cheers, Wayne
P.S. I bet there's a solution involving a relay that only requires extending the neutral to the second switch box, but I'm not very familiar with relays.
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