2 conductor wires between 3-way switches?


Old 05-03-05, 10:18 AM
Thread Starter
Join Date: May 2005
Location: US
Posts: 179
Question 2 conductor wires between 3-way switches?

This involves a back porch outside light, controlled by two 3-way switches, one inside the back door and the second inside the rear garage door (service entry).

It appears to be 3-way switch - 3-way switch - fixture.

What's unusual is that the wire between the 3-way switches is 2-conductor. There is no 3-conductor wire between the switches.

I cannot find any schematics dealing with this configuration. We began to remodel the garage, but stopped and want to just put this back together so it works; but we can't figure out what to do. There are actually two 2-conductor wires coming from the first 3-way switch. When the first switch is up, the black on both outgoing wires is hot; when the first switch is down, one of the wires still has a hot black, but the other wire has a white hot.

This did work before, as a pair of 3-ways in an "and" configuration. However, we don't know if it was wired correctly, since we just moved in.

Thanks for any help.
Sponsored Links
Old 05-03-05, 10:35 AM
Join Date: Jan 2004
Location: Oregon
Posts: 1,219
This is very likely a non-code compliant installation; this is why you've not found a circuit diagram online. Depending upon the specific configuration, it may simply be non-standard, code compliant with a minor safety issue, or seriously dangerous. Remember that simply because something works it is not necessarily safe.

You will need to do some more investigation.

1) Is this wired with cable (eg Romex, or metal clad 'BX') or with raceway (conduit or other metal channel holding loose wires)?

2) At _each_ relevant junction box (the two switches, the light fixture, and _any_ other junction box holding associated wires), describe the following:
How many cables come or raceways enter the box,
How many wires and of what color come in on each cable or raceway,
How the raceways interconnect,
How the wires in each junction box connect to any devices in each junction box.

Be detailed and specific, giving names to each part to show how they interconnect.

3) When you say that there are two 2 conductor cables coming from the first switch, do they _both_ go to the second junction box? Or does one go to the switch, and the other to something else?

Old 05-03-05, 01:51 PM
Thread Starter
Join Date: May 2005
Location: US
Posts: 179
2-conductor wires/3-way switches: what I can see. Also garage overhead

All the wire is romex 14-2 with ground. Starting at the switch box inside the back door, there are 3 cables inside, along with Switch 1 (3-way). Cable 1 appears to come in from the source, and Cables 2 and 3 go out to the garage.

Cable 1: white and black wires are both pigtailed; black goes to the black on Cable 2 and to the common terminal on switch 1; white goes to the white on Cable 2.

Cable 2: white and black run out into the garage.

Cable 3: white and black both run from travelers on Switch 1 out into the garage.

The box for Switch 2 (3-way) is in the garage. It has a 14-2 with ground running out to the light fixture, where it ends. Coming in is either Cable 2 or 3 (I can't tell which it is because the Cables run through the wall out of sight for a while); in any event, when Switch 1 is toggled up, the black wire on this Cable is hot and white is cold, but when Switch 1 is toggled down, this Cable's white becomes hot and black cold.

The other Cable ends near the box for Switch 2; I'm not sure if it was originally inside the box or not; I think it ran down to a duplex receptacle, maybe after entering the box for Switch 2. In any event, when Switch 1 is toggled up, the black on this Cable is hot, and when Switch 1 is toggled down, this Cable's black is still hot.

Incidentally, the light switch for the garage overhead lights is on this same circuit but I'm pretty sure it's source is separate; toggling Switch 1 has no effect on it. It has a 3-way switch and 3-wire cable running to a light fixture then on to a receptacle for the door opener. I have tried to reconnect this following the usual diagram (red to black on the light, connect blacks and whites and run to the end) but end up with the door opener hot when toggled up and the light fixture hot when toggled down. Not sure what's going on there and wonder if it is related to the porch light issue.
Old 05-03-05, 02:01 PM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
What you have is an incorrect installation.

Whoever wired this used cable 3 for the travelers for the switch. They are using cable 2 for the neutral and an unswitched hot wire.

This is not a serious issue if the boxes are plastic, but if the boxes are metal then a problem does exist.

To be correct, there should be 14-3 between the switches, or 14-4 between the switches and then the always hot and neutral can go to the other loads.
Old 05-03-05, 02:19 PM
Join Date: Jan 2004
Location: Oregon
Posts: 1,219
Okay, you are in pretty good shape. The only thing non-standard about this installation is the use of _two_ 2 wire cables where the normal approach would have been to use a single 4 wire cable. Since this is non-metallic cable, you are pretty much okay. Just treat the system as though you had a single 4 wire cable. It will help (and is required for the white traveller) if you get some different colors of electrical tape, and 'recode' the conductors to their 'proper' colors.

Basically Cable 2 and Cable 3 _together_ form the set of conductors that you need. Cable 2 white is the neutral for the circuit. Cable 2 black is the 'unswitched hot', and is not needed for the switched light, but provides a useful source of power to extend the circuit. Cable 3 black and white are the travellers. I would re-code cable 3 white with red electrical tape, and cable 3 black with blue electrical tape, but those colors are just suggestions. At a minimum, record cable 3 white with black tape to indicate that it is no longer being used as a neutral conductor.

Leave junction box 1 alone.

At junction box 2, connect the white from cable 2 to the white going to the lamp. Cap off the black from cable 2, or use it to feed a receptacle. Connect the white and the black from cable 3 (appropriately recoded) to the traveller terminals on the 3 way switch in junction box 2. Connect the common terminal to the black going to the lamp.

The only thing to watch out for is induction heating at the junction boxes, and then only if they are metal. They way to avoid this is to make sure that both of these cables enter through the _same_ hole, using a cable clamp that is rated for two cables. This isn't a problem at all if the junction boxes are non-metallic. Also, if cables 2 and 3 do not follow the same path, then I would replace them with a single 4 wire (plus ground) cable. There is a general sentiment that all circuit wires travel together in the same path, but as I understand code, this is only really required when the conductors are enclosed in metal armor or raceways, because of the induction problems mentioned above. However putting the conductors on different paths causes current loop issues, with increased circuit impedance and emf production. IMHO two non-metallic cables running side by side meets both the requirements and the sentiment of the code.

Old 05-03-05, 07:32 PM
Thread Starter
Join Date: May 2005
Location: US
Posts: 179
Smile A Thousand Thanks to Winnie and Racraft; and why "and" instead of "or"?

This did the trick; I have the porch light working again. Thank you so much.

I believe this works as an "and" arrangement, by which I mean that if Switch 1 is not toggled up, then Switch 2 cannot turn on the porch light by itself. If I am right about this, I have to wonder why the original electrician would go to this much trouble to create an arrangement less useful than an "or" type of arrangement where you can turn the light on from either switch regardless of how the other was toggled at the time. This puzzles me, and I wonder what your opinion is on this kind of arrangement.

Old 05-04-05, 05:31 AM
Join Date: Jan 2004
Location: Oregon
Posts: 1,219
You certainly have enough wires to make this work as an ordinary 3-way switch arrangement, where either switch is capable of turning the light on or off at any time (what you call the 'or' arrangement).

If this setup is not working in this fashion, then either one of the switches is broken, or one of the switches has a swapped common and traveller connection.

Old 05-04-05, 05:41 AM
Join Date: Nov 2002
Location: SC
Posts: 171
This is compliant as far as I understand, the original elctrician had no 3 conductor cable so he ran 2 2 conductors. It's not uncommon here. It's not much different than running a switch leg.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes