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Old 12-22-2011, 01:22 AM   #1
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3 way switch -OK to drop down neutral like this to light through switch box via 12/3?


I apologize for my diagram. The circuit is off that powers my computer with Photoshop, so I had to use paint.

I'm wondering if I can wire two three way switches and two lights as shown in the diagram. Although it's my first three way switch experience, I'm pretty sure it will work as diagrammed, but I want to also make sure wiring as shown doesn't violate NEC 2008 code -- or professional/good practice wiring.

Short story is that I'm replacing all the fabric wrapped 14/2 cables in my house that run lights. The hardest run for a new cable is between this set of three way switches and the basement light. Believe it or not, this is the one and only spot in the lighting circuits that already uses plastic romex cable, so if I can re-use the existing plastic romex cable, I don't have to do the tough run.

I wasn't interested in following the original wiring paths, so I ran the two circuits from the panel into the attic. I have a junction box in the attic, corresponding with each switch on the main floor. I'm only dropping down a 12/2 with ground to the switch boxes. Of course, the power source comes to the switch on a white remarked as black, and comes up to the light on the black. The neutral, of course, jumps from the attic junction box's source cable to the neutral on the cable running to the light.

That works great, except for this one light (the one in the basement in this diagram) that needs a neutral that I can't easily drop down a cable from the attic to.

I had to buy a small amount of 12/3 with ground to replace the old cables between the three way switches. I realized that I have enough 12/3 left over to run from the attic junction box to the three way switch that has the outgoing black common.


Assuming this wiring will work in the first place, is it OK to wire it this way?

Is it OK for me to deviate from my standard wring pattern, and drop a neutral down to the top three way switch box that just passes on to the basement light cable? Am I allowed to do this in the first place?

Is it OK to use a 12/3 cable for this purpose -- a neutral going down to branch off to a light, and the black and reds effectively going to the common screws on each of the three way switches?

Do I have the uses of red black and white done correctly, or is there a different way required by code or standard practices? (For example, I know that a white remarked as black wire in a 2 conductor cable to a switch has to act as the source for the switch - not sure if I've violated a rule like this in my diagram.)



FAQ's for my post:
* Michigan is on NEC 2008 still, so I'm not required to have a neutral at switches. I'm not concerned about future capacity for smart switches.
* I left the grounds off my diagram, since those are easy and don't really need to clutter up the diagram. But, all cables I'm using have a ground.
* I know I could have used 14 AWG wires instead of 12.
* I've put this circuit on a 15A breaker, rather than 20A. The original reason why is because the switches are only rated for 15A, and besides, two 15A circuits is overkill for 9 lights. But, since I'm running on a 15A breaker, using the existing 14/2 cable ran between one of the three way switches and the basement light will be OK. I'll mark in the box that the circuit must be 15A both because the switch limitations, and that 14/2 is used at that one spot in the circuit.


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Old 12-22-2011, 01:54 AM   #2
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3 way switch -OK to drop down neutral like this to light through switch box via 12/3?


Looks good to me, but just to make sure: You want the three way switches to control both lights, (upstairs, basement) right? I'm guessing these are lights at the top and bottom of the basement stairs?

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Old 12-22-2011, 01:58 AM   #3
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3 way switch -OK to drop down neutral like this to light through switch box via 12/3?


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Looks good to me, but just to make sure: You want the three way switches to control both lights, (upstairs, basement) right? I'm guessing these are lights at the top and bottom of the basement stairs?
Exactly. Switches are at the top and bottom of basement stairs. One light is in the tiny foyer (4x4ft or 5x5ft) that is the landing platform at the top of the stairs that goes to the back door. The other light is near the bottom of the stairs, but a few feet past where you get to the basement floor. This couple feet difference is what gives us the problem. The ceiling there is what we call a fake drop ceiling. It's tiles that are stapled on, that can't be properly removed and put back. There's floor joists blocking trying to fish between the switch and light. Someday we're going to replace these ceiling tiles with a real drop ceiling, but we don't want to do that yet.

That's how these two lights worked when we got the house, and it illuminates the entire stairway fairly well, since there isn't a light near the middle step.
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Old 12-22-2011, 07:20 AM   #4
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3 way switch -OK to drop down neutral like this to light through switch box via 12/3?


Switch the connections at the common terminal of the first 3-way switch like this...
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3 way switch -OK to drop down neutral like this to light through switch box via 12/3?-mikethreewayswitchdiagr.jpg  
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Old 12-22-2011, 08:11 AM   #5
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3 way switch -OK to drop down neutral like this to light through switch box via 12/3?


If permitted (I think not in Canada), suggest adding a 14 gauge pigtail to an incoming 12 gauge cable with 14 gauge wiring downstream in order to connect to the 15 amp breaker in the panel.

[It is okay to use 15 amp switches for lights on a 20 amp circuit, although 12 gauge wire is still needed beyond the switch. It is okay to have 15 amp receptacles on a 20 amp circuit provided there are at least two receptacles or a duplex receptacle altogether.
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Old 12-22-2011, 08:28 AM   #6
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3 way switch -OK to drop down neutral like this to light through switch box via 12/3?


There is no reason to switch the connections at the commons. It will work just fine as drawn in the original.
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Old 12-22-2011, 09:18 AM   #7
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3 way switch -OK to drop down neutral like this to light through switch box via 12/3?


WHY the #14 to the basement light? Now the whole circuit must be downgraded to 15A.
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Answers based on the 2008 & 2011 NEC.
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Old 12-22-2011, 12:30 PM   #8
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3 way switch -OK to drop down neutral like this to light through switch box via 12/3?


First, thanks everyone! You guys all rock!

SD515 - I'd love to know your reasoning for swapping those two. Even if it's not required by code, somehow your way just looks more appropriate, even though I can't explain why. I'd love to know your thoughts behind this.

AllanJ - Ahh, that makes sense. I'll put that pigtail in before I'm done, so it really stands out to someone in the future.

Speedy Petey - All the cables I'm replacing is the old fabric wrapped romex. There's only one cable in the house used for lighting that's plastic wrapped romex, and it happens to be the 14/2 in the diagram. If it were not that bad to replace it with 12/2, I'd probably do so. However, routing a new cable here would involve ripping open a stapled on fake drop ceiling in the basement. That's a project I know is coming someday, but we'd like to delay doing that for now.
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Old 12-22-2011, 01:09 PM   #9
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3 way switch -OK to drop down neutral like this to light through switch box via 12/3?


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There is no reason to switch the connections at the commons. It will work just fine as drawn in the original.
The strict interpretation is that the remarked white wire has to be the unswitched hot feed.

The more liberal interpretation of the rule that the switched hot to the light fixture may not be white, even when remarked.

The 2011 code requires a neutral in switch boxes also, so new installations having to use a white wire for a hot wire become almost nonexistent.
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Old 12-22-2011, 03:48 PM   #10
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3 way switch -OK to drop down neutral like this to light through switch box via 12/3?


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Speedy Petey - All the cables I'm replacing is the old fabric wrapped romex. There's only one cable in the house used for lighting that's plastic wrapped romex, and it happens to be the 14/2 in the diagram. If it were not that bad to replace it with 12/2, I'd probably do so. However, routing a new cable here would involve ripping open a stapled on fake drop ceiling in the basement. That's a project I know is coming someday, but we'd like to delay doing that for now.
I would have just replaced it with #14. #12 for residential lighting is pointless.

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