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
Hopefully this can explain:
Common<->black of incoming powerTraveler1<->black of outgoing 12/2 wireTraveler2<->white of outgoing 12/2 wire
Traveler1<->white of incoming 12/2 wire from Switch 1Traveler2<->black of incoming 12/2 wire from Switch 1Common<->black 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
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
Please help if you understand this interesting wiring scenario. Thanks.
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"
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
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.
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.
Article 300-3 (b) might:
Conductors of the same circuit. All conductors of the same circuit and, where
grounded conductor and all equipment grounding conductords shall be contained
same raceway, auxillary gutter, cable tray, trench, cable, or cord....
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.
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.
I'm pretty sure an AHJ would allow it either, but the wording is vague
(I don't have the actual text with me at the moment).
There are a few other issues, too, but all agree it's not good
A true California 3 way would put the bulb between two neutrals or
Were there changes since the 2002 code regarding this? If not, then
300.20B covers metal raceways OR metal enclosures in scenarios such as
this. The metal enclosures part is what applies here.
I'm not an electrician but I did rewire my house with an inspection
including a circuit with an imbalance like this in the past year. The 2002
code applied. The circuit involves 3 location switch control of half of 2
receptacles with the other half of the receptacles always hot. The room
has 3 entrances. A book I have that interprets the code (Electrical Wiring
Residential by Ray C. Mullin) has several pages devoted to this topic. My
understanding is that this is a well respected textbook for electricians.
The author's interpretation is that the code is concerned with induction
heating and that is avoided by using all non-metallic wiring and boxes or
non-metallic wiring and passing divergent conductors through the same entry
point in a metallic box.
4 wire romex is out there but hard to come by and overpriced for what it
is. I couldn't get a reasonable quantity for my purpose.
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.
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).
(Description of emf problems that can be caused by described wiring)
(Same 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).
(A 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.)
I agree with you on everything else you said, and you may have noted I
was in the ranks of those who told the OP to straighten out and do it right.
The worst example of this sort of thing I've personally experienced was
when some clod who was too lazy or cheap to go out and get a piece of
the correct size conduit used what he had and ran three three lengths of
1/2" conduit about 30 feet long between a breaker panel and a disconnect
switch and then put the three conductors for a 75 amp three phase
circuit through them, one conductor in each.
He called me in to explain why he was getting arcs and sparks where the
conduit fittings attached to the panel housing and the switch box every
time he tried to start the machine it powered.
Because of voltages induced in the conduit, which is why the code is
specific about all conductors of a circuit having to be in ONE conduit
Each of the three conductors acted like the primary winding of a
transformer, and each piece of conduit acted like a secondary winding.
The ends of the conduits were connected together by the boxes, and some
of the mechanical connections there weren't tightened as well as they
shold have been. So sparks and a bit of smoke happened at those joints
because of the current flowing in them from those shorted out
"transformer secondaries" when 75 amps of current flowed through the
Even if those mechanical joints had beed socked down so they had low
resistance, the conduits would probably have gotten pretty hot just from
induced current flowing through them.
If all conductors were in ONE conduit, the magnetic fields from the
three wires would have canceled out nearly completely, leaving a
negligible remaining field to induce a voltage in the conduit.
Same principle applies for two conductors in a single phase circuit.
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
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
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
So what is the deal with colors, esp white & green?
I think green (or green with yellow chaser) is. Not sure about
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.
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