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my 3-way switch is wired this way, because i am unlucky:

3-way with no neutral in one switch

so i have neutral in the line box, no neutral in the load box. i want to use a leviton smart switch that requires neutral in both boxes. if i were crafty enough, could i pigtail a new line off the neutral line in the fixture to run down to the load box? i am super green at this, so forgive me for asking a stupid question. there's also some information out there saying i can use one of the travelers as neutral, which i'll try first... i'm just playing 'worst case scenario'.

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    You are not unlucky this was the common way to wire a 3 way switch until recent code changes very few homes have neutrals at all the switches. – Ed Beal Apr 7 '20 at 13:23
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    Wow, never thought I'd see that. A web drawing that is correct. – Harper - Reinstate Monica Apr 7 '20 at 20:25
  • What model of Leviton smartswitch do you want to use? – ThreePhaseEel Apr 7 '20 at 22:24
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    @ThreePhaseEel it's a leviton decora digital w/ wifi. this model: leviton.com/en/products/dw6hd-1bz – david Apr 8 '20 at 3:29
  • How hard would it be to replace the wiring from the line-side switch to the light(s)? – ThreePhaseEel Apr 8 '20 at 22:54
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Your problem isn't what you think it is

Getting neutral down to the load-side switch for the remote (DD00R-DL) used with your dimmer (Leviton DW6HD-1BZ) is easy enough; the white wire in the existing cable can simply be un-redesignated (if it was taped in the first place), then moved over to the neutral junction in the light fixture box.

However, this isn't what's stopping you from installing your dimmer. Your problem is that the DD00R-DL remote needs line-hot, a signal wire, and a neutral; however, the incoming hot is only available at the line-side switch box in your setup. So, you'll have to re-run one of the cables with /4 instead of /3 (or an ENT with THHNs in it) if you want to use this dimmer, or use different hardware that can work with the remote being on the load-side of the setup instead of the line-side.

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  • gotcha. yes, this makes sense. i don't think i'm really in a position to run all that cable. current plan is to make the 3-way a single-pole, install the dimmer where all the right wires live and abandon the second switch. it's not really that handy, anyway. any problems you can foresee with that fix? – david Apr 10 '20 at 5:38
  • @david only problem could be if Code requires multi-location control. what space/room does this light serve? – ThreePhaseEel Apr 10 '20 at 13:57
  • it's a bachelor, and it's ridiculous. the switches are maybe 8 feet apart on adjoining walls. if you picture the walls like an L, one switch is at the tip of the short end, and the other switch is just mid-way down the long end. the LIGHT, however is 15 feet from both. so the travelers run from the line box at the short end of the L, ALL THE WAY TO THE LIGHT, then BACK to the load box. so a 30 foot cable run between two switches 8 feet apart. that's why it's maddening to have to deal with this 3-way business, just so i don't have a dead switch above the bed. – david Apr 11 '20 at 1:45
  • @david -- it's a what, again? (autocomplete seems to have gotten your tongue :/) – ThreePhaseEel Apr 11 '20 at 1:57
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It appears pretty clear to me that you can't run the neutral separate from the existing cable, it would be prohibited by NEC 300.3(B) that requires all conductors of a circuit to be contained in the same cable raceway, cable or cord.

We don't know the configuration required for the specific smart switch you are using, at least one model I have used only required one "traveler" between switches, so I was able un-reidentify the white for use as a neutral.

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  • That was my initial thought about not being able to run a separate neutral too. You can run grounds but not neutrals. there are smart switches that don't need a neutral.+ – JACK Apr 7 '20 at 14:33
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If your circuit is wired per the drawing, then the answer is yes you can. The key is the neutral must be the same neutral as the line side circuit.

The second part of your question is a little trickier. If you are going to use mechanical three way switches you cannot eliminate one of the carriers since it is necessary to complete the switching sequence. If you use a smart switch which uses electronics for control then you can, but you will have to rearrange the circuitry to get a neutral and a line side circuit to the second box.

There is no standard on electronic controls so we cannot tell you exactly how to connect them up until we know exactly what you are buying. If you are super green you may want to seek some local help before making a final purchase.

Good luck

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You cannot run a separate, loose neutral wire.

Absolutely not. The neutral must be in the same cable or conduit as the other wires. So for instance you cannot use 2 cables and just combine em.

It would work if you replaced the /3 in the wall with /4, or if you ran conduit between the two 3-ways.

However, that won't be a problem with smart switches.

You select a pair of smart switches able to use powerline or wireless signaling. Then you re-task all the wires as follows:

  • Black = always-hot (connects everywhere but the lamp)
  • White = neutral (connects everywhere)
  • Red = switched-hot from one of the switches to the lamp. Note the other red segment is unnecessary and should be capped.

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