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(Very) uncommon 3-way light circuit?

#1
08-28-14, 08:18 PM
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(Very) uncommon 3-way light circuit?

The attached diagram shows the circuit I found in the bathroom of my finished basement. I had to pull out both lights and switches because I could not figure out how this was working until I could map all the wires.

Like I said, it works, but it seems very unusual to wire a 3-way circuit this way. It's basically a circuit where both switches have power (same circuit), and the hots (black) and neutrals (white) coming into each switch are tied to that switch's traveler leads. The common leads (red) are used to transfer current to two lights wired directly to each other.

When both switches are on then both common leads (red) are connected to hot (black) and the circuit back to the breaker is broken. When both switches are off then both common leads (red) are connected to neutral (white) and the circuit back to the breaker is still broken. Only when one switch is on and one switch is off is the circuit completed back to the breaker.

The ground wire between the lights is connected to one of the fixtures but is left dangling in the second fixture. The ground wire from the power source is not connected to either light switch. and there is no common ground between the light fixtures and the switches.

So the question is: Is this circuit fine and I should leave it alone? Or is this circuit dangerous and I should rewire it correctly?

Attached Images

Last edited by electroneer84; 08-28-14 at 08:28 PM. Reason: Added ground wires to attachment
#2
08-28-14, 08:35 PM
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Welcome to the forums.

When we discuss wiring and diagrams..... the grounds are left out. We all know the grounds need to be connected so we leave them out of the discussion and diagrams. You can leave them in where you have them.

What is S ?

However.... you have not drawn that circuit correctly. You've created a dead short that couldn't work. There are MANY ways to wire a three way circuit. None are uncommon.

Actually.... the way you've drawn it.... it will work in theory but how does the cabling work ?
You can't just have two reds going to the lights.... or is this in conduit ?

#3
08-28-14, 08:54 PM
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I had originally left the grounds out, but I edited the post to include them only because I was concerned about them NOT being wired up and I wanted to make it clear that there were NO ground lines currently running between the lights and switches.

"S" just stands for source (i.e. some line running from a breaker). It's a symbol used in electronic circuit schematics. I don't know the correct symbol for a house circuit.

I assure you I have drawn the circuit exactly as it is wired in my house. Also, it works in practice and not just in theory, and with no shorts in any of the four states of the switches.

As for the red lines, there are literally just two single red lines running independently to the lights. No wire bundles, no conduits.

#4
08-28-14, 09:16 PM
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There are just two red wires running in the wall to the lights ?
Then there is no ground at the lights either so a ground between them means nothing.
That is not correct. There needs to be a cable making the connection.

Your circuit does work but I've never seen a neutral switched like that. I'm not even sure if switching the neutrals like that is acceptable by code.

#5
08-28-14, 10:35 PM
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Ya just the two red wires that connect the switches to the lights. Looking at the diagram, current will either be flowing clockwise or counter-clockwise depending on which switch is on and which is off.

I have no idea why someone would wire it this way even if it does work. It looks like all the wiring was done before the drywall was put up (e.g. there are nicely drilled holes through the 2x4's for the red wires).

I've never seen one wired that way either, but I was hoping someone could confirm whether or not it's acceptable by code.

#6
08-29-14, 03:23 AM
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I've never seen one wired that way either, but I was hoping someone could confirm whether or not it's acceptable by code.
It is not

So the question is: Is this circuit fine and I should leave it alone?
It is not fine and should be replaced.

Or is this circuit dangerous and I should rewire it correctly?
this circuit is dangerous and you should rewire it correctly
right now you can have a hot at the lights with the lamps not lit.

you should look around for other wiring with the single red wires

#7
08-29-14, 03:38 AM
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The source only services the common on one switch. The load is attached to the common of the other switch. It seems you are feeding both switches from the source. Runners just go from the other two screws on the switches in no particular order. The neutral goes all the way back to the source.

#8
08-29-14, 05:20 AM
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I assure you I have drawn the circuit exactly as it is wired in my house
If your diagram is correct, and the whites are connected to travelers, How are you getting a neutral to the lights?? I don't see it on the diagram.

And out of curiosity, why would a bathroom need 3-way's, it has two doors??

#9
08-29-14, 05:25 AM
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Maybe a variation on a Carter 3-way but too early to wrap my mind around it. If Carter it works but hasn't been legal since K&T. Maybe wired by a very old electrician.

#10
08-29-14, 07:10 AM
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If your diagram is correct, and the whites are connected to travelers, How are you getting a neutral to the lights?? I don't see it on the diagram. - Handyone
When one of the switches is on and the other is off, one red line will be hot and the other will be neutral. Potential flips based on which switch is on on and which is off.

And out of curiosity, why would a bathroom need 3-way's, it has two doors?? - Handyone
And yes the bathroom has two doors. The basement was finished with a master bedroom design, with one door leading to the bedroom and the other door leading to a hallway.

you should look around for other wiring with the single red wires - johnsc
I've touched most of the wiring in my house at one point or another and have not come across anything like this until I started remodeling the last couple of rooms in the finished basement. Looks like I'll be ripping out more drywall than I originally thought, unless I can easily pull new line through the walls by taping it to the existing red lines when I pull them out.

Maybe a variation on a Carter 3-way but too early to wrap my mind around it. If Carter it works but hasn't been legal since K&T. Maybe wired by a very old electrician. - ray2047
Thanks for finding a name for this circuit. I attached a diagram I found online for a Carter 3-way and it's identical to the circuit in my house except mine has two lights.

http://en.wikipedia.org/wiki/Multiwa...#Carter_system

Attached Images

Last edited by electroneer84; 08-29-14 at 07:28 AM.
#11
08-29-14, 07:47 AM
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this circuit is dangerous and you should rewire it correctly
right now you can have a hot at the lights with the lamps not lit. - johnsc
Is there a way I can reconfigure the existing wiring to have the switching happen only on the hot line and have the light shells always neutral? I plan to eventually replace the wiring once I get around to remodeling that room, but for I now I would at least like to eliminate the shock potential of having hots on the light shells.

#12
08-29-14, 08:19 AM
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Having individual unsheathed conductors means there is no way to make it code compliant without new cable..

#13
08-29-14, 09:15 AM
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Here's how I plan to rewire this for modern 3-way switching. I'm basically replacing the single red lines with 14/3 cable and capping off the power in one of the switch boxes. I'll also have to run a new 14/2 line between the light boxes for the travelers between the switches. Does anyone see any issues with this?

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#14
08-29-14, 01:34 PM
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I find the easiest way to wire 3 ways is power in to S1. From S1 to S2 with xx-3 cable. From S2 to L1 with xx-2 cable. Power in and power out are the black of the xx-2 cable. Travelers are the black and red of the xx-3 cables. Whites splice through.

#15
08-29-14, 02:21 PM
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I find the easiest way to wire 3 ways is power in to S1. From S1 to S2 with xx-3 cable. From S2 to L1 with xx-2 cable. Power in and power out are the black of the xx-2 cable. Travelers are the black and red of the xx-3 cables. Whites splice through.
Ok good, I think that's how I have the diagram in my previous comment wired up.

I'm just connecting the switches with xx-3 in a round-about-way through the light boxes because I'm hoping I can pull the new xx-3 cable through the ceiling and down the walls in the bathroom as I remove the existing red wires from the old "Carter" install.

I'm hoping that saves me some time, but I may have to end up ripping out some of the wall and ceiling and just run new cable directly between all the boxes. And, of course, there's always the capped-off power lines in the second switch box...