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I'm converting my home to use all Leviton smart dimmers (DH6HD-1BZ) and LED lights. All has gone well so far with neutral being accessible from most switches.

However I've come across an old-school 3-way with load going to the fixture not the switch box, please see the following diagram:

enter image description here

Switch box A looks exactly as is shown in the diagram. Switch box B however is a larger box with other switches where neutral is present.

I know I need neutral in switch box A as well, but I've heard there is some possible trickery where I can bring neutral over to box A from box B.

So my questions are two fold:

  1. Is it possible to bring neutral over to box A from box B, perhaps utilizing one of the travellers? Can I just use ground as the neutral for switch A (I know this is faux pas, but should be possible right?)?
  2. If it's possible to get neutral to box A, I don't entirely grok how the dimmer and it's remote switch should be wired in the first place. The wiring diagram provided with the switch (see below) isn't this type of 3-way configuration so I'm kind of stumped here as well.

Thanks for your time!

enter image description here

(where: 1=line/load, 2=neutral, 3=ground, 4=first traveller, 5=second traveller)

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    Nice job on the question. Can you replace the NM-2 to NB-3 from fixture to switch A? – JACK Nov 14 '20 at 12:37
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    Yes, is replacing the cable from the fixture to switch A an option? – ThreePhaseEel Nov 14 '20 at 15:38
  • It's certainly possible, but much more of a reno than I'd like unfortunately. All the rooms are completely finished – okin33 Nov 15 '20 at 0:19
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    @okin33 Try finding an electrician that's really good with old work. Those guys can do miracles with 6 foot long flexible drill bits and fishing tape. – Harper - Reinstate Monica Nov 15 '20 at 1:58
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No. You cannot poach a neutral from the other switches in Box B. This is a Code violation, potential firestarter, and will trip any AFCI or GFCI breakers in use.

There must be separation between the 3 wires coming into that 3-way and all other wires in the box. Nothing can cross that gap except for safety ground.

Since your circuits apparently do have ground wires, you need to search the market for smart switches which do not require a neutral wire.

Since your 3-way setup is a double "switch loop" (i.e. both 3-ways are on a switch loop with power in the light), then you simply have no option to use a neutral-using smart switch. It cannot be done.

The only possibility is to use a "module" up in the lamp proper, which talks to smart switch(es) in the switch sites. At that point the black & white from lamp to switch could be re-tasked to be always-hot and neutral.

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  • "Nothing can cross that gap except for safety ground." Does this mean the new smart switch in box B cannot pigtail it's neutral screw into the bundle of neutrals already in the box? – okin33 Nov 15 '20 at 0:31
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    @okin That's what I'm saying. A smart switch must get neutral from one of the cables that already has hots connected to it, and there's only one, and it doesn't have neutral. – Harper - Reinstate Monica Nov 15 '20 at 1:56
  • @harper-reinstate-monica That very interesting! Other than not being code, what exactly is the hazard in that case? Just for informational purposes. – okin33 Nov 15 '20 at 3:09
  • @okin33 I know, right? Waze sends you down a neat shortcut and it's all speed bumps. Why speed bumps? There are no children in sight!!! Seriously, with NEC get used to nothing being there without real safety reasons, often several. There are a couple of obvious ones right off the bat. #1 Neutrals don't have fuses. Faith to their partner hots is the only thing that keeps them from overloading. "But it's just a 2 watt smart switch" only everything is working properly. Also someone could grab those wires and extend the circuit later. – Harper - Reinstate Monica Nov 15 '20 at 18:01
  • #2 worker protection. So you tap the neutral off circuit C. Later, Katy needs to rewire circuit C, so Katy correctly shuts off circuit C's breaker and starts taking apart hots and neutrals. BLAMMO! Katy gets nailed by the current flow off that smart switch. Normally when circuits are entangled like that (shared neutral or same yoke) they must be handle-tied so Katy is forced to turn off both. But this is too dodgy to even support in Code. #3 Currents imbalanced in the cable, creating wire vibration/fatigue cracking/hotspots, eddy current heating, and making G/AFCI use impossible. – Harper - Reinstate Monica Nov 15 '20 at 18:07

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