Three way switches with 12/2 wire?

[corbettandkerri]

My older house is wired differently than any of the books or online schematics I've seen and need some help and feedback. They have wired two three-way switches and an outlet using only 12/2 wire. How you ask?

Hopefully this can explain: Switch 1 Commonblack of incoming power Traveler1black of outgoing 12/2 wire Traveler2white of outgoing 12/2 wire

Switch 2 Traveler1white of incoming 12/2 wire from Switch 1 Traveler2black of incoming 12/2 wire from Switch 1 Commonblack of outgoing 12/2 wire to outlet

Additional wiring in Switch 2 box White of incoming 12/2 wire (second power source)White of outgoing

12/2 wire to outlet Black of incoming 12/2 wire (second power source)two-way switch on an unrelated light

Outlet Typical hot/neutral 12/2 wiring

What I want to do is add a light that is also three-way switched using these switches. I want to keep the outlet as is and wire the light between Switch 1 and Switch 2. The outlet is not accessible to pulling additional wires.

Please help if you understand this interesting wiring scenario. Thanks.

[Joseph Meehan]

I understand enough to know the kind of language someone working on them

10 years from now is likely to use, it they can speak at all.

[SQLit]

Ideally you could come off of one of the light locations and run a new cable to the location of the light. Or you could add a cable from switch 2 to the new light location. Is your box big enough to add another cable. into it?

By the way in residential the only thing that is odd is that they used 12.

Any other solution is not as "clean"

[kevin]

You are in for some trouble, since your existing wiring is completely against code, and a bad situation to boot.

Just think for a second about how this circuit looks. The current's path starts at a circuit breaker (on a black wire) goes to a switch 1, goes to switch 2, goes to the outlet, goes into the appliance, (and now on the white wire) back out of the appliance, back to the outlet, back to switch 2, but now takes a turn and heads down a different path to possibly a handful of other boxes and junctions, who knows where else, then eventually back to the neutral in the breaker panel.

Essentially you have a big 1-wind electro-magnet here. Besides breaking code, I can think of dozens of consequences, e.g.:

You are broadcasting emf interference all over the place, probably interfering with radios, televisions, and other wireless devices. (And I have heard stories of such circuits interfering with hearing aids and all sorts of other sensitive electronics and things with antennaes, even over to your neighbors houses).

You can get inductive heating in several of those junction boxes, posing a fire hazard.

Heaven forbid someone reverse the hot/neutral in some other place in your house that happens to share one of those power sources. You would either get two same hots at your outlet, or 240V. You don't even mention if the two power sources are on the same circuit breaker or not.

If someone puts a GFCI somewhere on one of those two now-joined circuites, it would either trip constantly (b/c of too little current on the neutral in the one case), or it would not protect you in the way it is supposed to (b/c of too much current on the neutral).

In other words, besides the potential for future changes to make this much worse than it already is (and who knows, maybe it already is much worse -- you don't know unless you have traced through the WHOLE circuit on both sides, everywhere it goes), you have some active problems like inductive heating and radio interference.

Lucky for you, this is pretty easy to fix. Just ditch the one power source, and add a 12-3 cable where it belongs.

-Kevin

[Jeff Wisnia]

Everything you've described so far "works" circuit wise, but probably not code wise.

But you didn't mention what's with the white of the incoming power at Switch 1. Does it just dead end there or does something else connect to it?

And, what does the return (hopefully white) from that unrelated light controlled by the second switch in the "Switch 2 box" connect to? Hopefully it comes back to that box and connects to the white of the "second power source". If it doesn't, you may have even more of a mess than you've described already.

But, what do you mean when saying you want to wire the added light "between Switch 1 and Switch 2"? That question could be taken a few different ways.

Anyway, I agree with what the others have already said. What you've described is a ghastly abortion and shouldn't be left that way to trap someone in the future.

I couldn't help noticing you never once mentioned anything about ground conductors. Is the place so old that those aren't used?

Since you felt you needed to ask here, I hope you'll follow the majority advice you'll undoubtedly be receiving. A little knowledge can be a dangerous thing.

Jeff

[SQLit]

Ok Kevin get out your code book and post the back up to your statement, give sections and page numbers.

I have never found a color code in the NEC, especially when it is residential. ( ok there is one reference to a color code but it does not apply to this situation)

I await your code sections.

[Jeff Wisnia]

Really? At 60 Hz? I hardly think so. Way too low in frequency to cause any radio or televison interference. The degaussing coils in TV sets put out a hell of a lot stronger magnetic fields than 10 or 15 amperes flowing in a single turn loop will, and I've never heard tell that they bothered any adjacent devices.

Maybe, just maybe, a hearing aid held a couple of inches away from a monoconductor carring a few amps of 60 HZ might pick up a litle hum, but that's about it Kevin.

If you furnish some valid cites I'll be pleased to learn something new and back down.

Jeff

[Kevin Ricks]

From box 2 connect the black of the new light cable to the black wire on the switch common. Connect the new white wire with the neutrals in box 2. The only thing I would worry about is if the 2 hots of box 1 and 2 are both on the same breaker. They should be. You may need to change out box 2 to a deeper box.

You could run your new light cable from box 1 if you want to reconfigure box

2 so that the outlet is full time hot.

Kevin

[Rick]

Article 300-3 (b) might:

Conductors of the same circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductords shall be contained within the same raceway, auxillary gutter, cable tray, trench, cable, or cord....

[Doug]

"Rick" wrote in news:cI_zf.3412$ [e-mail]:

You left out "unless otherwise permitted in accordance with (1) through (4)". One of those exceptions is for non-metallic cable. Since the OP says "12/2" it sounds like the exception would apply in this case. The exception does reference another section requiring such cables to use the same opening in metallic boxes.

Doug

[buffalobill]

[Rick]

You are correct-I didn't read 300-3-b-3....

[kevin]

You may be right. My "probably interfering with radios, ..." was perhaps too strong. I think that my point stands however. This kind of multi-path circuit is specifically forbidden, and is a bad idea for many reasons, including the reasons I cite: emf, inductive heating, potential for mistakes down the road including messing up GFCIs. Another one that I did not think of, but noticed upon searching, is the potential for increased impedence of the circuit (related to the inductive heating, I beleive), and impedence of the ground path (depending on how the grounds were run).

I don't claim expertise in this area, but there seems to be fairly strong agreement out there that the wiring described is bad. Here are some relevant citations, easily found via Google (I can't back these cites up, you will have to evaluate them yourself).

(EMF)(Description of emf problems that can be caused by described wiring)

site, describing the 300 section of the code which forbids this wiring -- and no, SQLit, it has nothing to do with "color", it has to do with conductors of the same circuit passing through different raceways, different metallic conduits, different metal holes in boxes, etc., which are all extremely likely given the wide physical separation of the hot and neutral circuits as described).

fairly convincing report on the generation of emf from poor wiring identical and similar to that described by OP, with code citations for you SQLit, along with description of other effects of this poor wiring including inductive heating.)

[corbettandkerri]

Thank you for the feedback and suggestions. The "second power source" in box 2 is on a different circuit breaker in the same breaker box. I had to flip two breakers to make sure all wires in box 2 were dead. I imagine the other three-way switches in the house are wired this same way. ;-( I guess I should fix them all. Did they not have codes 35 years ago?

After I fix the "second power source" problem by replacing the 12/2 with a 12/3 cable between the two switches I plan on pulling an additional 12/2 cable to box 2 and pigtail it with the switched outlet's cable and pull it up to my new light.

[Keith Williams]

When the guy in the next office comes to work in the degausing coil in his monitor makes my monitors go all jumpy. There is a hell of a magnetic field there, but only for a second or so. ;-)

[BobK207]

ok guys, help me out here............

I learned my electrical skills working with industrial / commericial electricians on a couple of long term residential upgrades / rewires, by reading the NEC & various texts that interpret the NEC in to real English.

I was under the impression (& have always done work this way) that green & white were "restricted colors";

white only for solid neutral & green for ground; all other colors ok for hots & swiitch legs

I have seen lots of installations (only in residential) where 12/2 NM with ground was used for bathroom & bedroom switch legs;

that is where the white conductor in the NM cable was attach to one of the switch poles & it was also wired nutted to a hot (black) in the ceiling box!

Very confusing & a pain in the ass to reowrk when someone discconects all the connections & fails to label them & says "I can't get it to work now"

So what is the deal with colors, esp white & green?

cheers Bob

[Keith Williams]

Whoa! I'm just an engineer! ;-)

I think green (or green with yellow chaser) is. Not sure about white.

12/2NM should have black, white, and bare conductors. The switched leg should be black.

Ugly, but I think it's legal. The "white" should have a hunk of tape on it or "painted" black with a marker.

It can also lead to "I can't get him to breathe now".

You won't see too much green anymore in home wiring. Grounds are usually bare. White *should* be reserved for the "grounded conductor" (neutral). Black or red *should* be used for the hots or switched hots. ...but I don't do wiring for a living. When I do it, I make sure it's more than right.

[Kevin Ricks]

You can use the white as a switch leg if it is marked with black tape or something. That is the only way to do it if your hot feed is at the light box. (Well you could run 2 cables or a 12/3 but then you have unused wires which is just as, if not more, confusing later on). I always do my switch leg connections so that I end up with a black (switched) and white (neutral) coming out of the light box. If you have power at the switch box then you don't have the problem.

From what I have experienced it seems like most people don't bother to mark the white switch legs properly, even on relitivly new construction. I have seen a bit of scribble with a ball point pen or 'sharpie' which 9 times out of 10 gets painted over by the painters. Kevin

[Bud--]

The hot and neutral are from different circuits. In addition to being a code violation as wired the neutral can be overloaded if the 2 breakers aren't on different phases. Your solution is the right one.

bud--

[Bud--]

I disagree. 300.3B3 refers to 300.20B which covers different wiring IMHO. Inconcievable the code would permit wiring from 2 divergent paths as in the situation described. It used to be a California 3-way, which requires 4 wires, could be wired with 2 2-wire Romexes run together. It can't anymore because of changes to 300.3B unless you can find 4 wire Romex.

While a light bulb in the open loop as described by Kevin is unlikely to produce interference problems, a high current could. It does not take much 60Hz magnetic field to affect a computer monitor. One of the reasons to run circuit wires together is magnetic field cancellation.

bud--