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I'm looking at adding a three-way switch to a room. I'll probably drop the hot and neutral into Box #1, but 12/2/2 (hot, 2x travelers and a neutral) is fairly esoteric cable (nobody locally sells it by the foot) and it's pricey.

I got to thinking about it some, and was wondering if I need a neutral in Box #2 at all if Box #1 is covered. If not, I can easily buy 12/3 and just call it good.

  • I think you need the neutral. But why do you need the hot after box 1? Shouldn't it be panel->hot/neutral->box 1->travelers(2)/neutral->box 2->switched hot/neutral->light ? – manassehkatz Mar 25 at 21:59
  • All switch boxes now require neutral (they didn’t use to). Another solution nowadays tho is don’t run the circuit as a 3-way, use a smart switch and smart switch remote. – Tyson Mar 25 at 22:21
  • Yeah really, why is anyone using steam switches in this day and age. – Harper Mar 25 at 22:31
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No, you do not need to extend the neutral to all locations in a multiway setup

NEC 404.2(C) governs the provisioning of neutral at switch boxes (irrelevant parts snipped, emphasis mine):

(C) Switches Controlling Lighting Loads. The grounded circuit conductor for the controlled lighting circuit shall be installed at the location where switches control lighting loads that are supplied by a grounded general-purpose branch circuit serving bathrooms, hallways, stairways, or rooms suitable for human habitation or occupancy as defined in the applicable building code. Where multiple switch locations control the same lighting load such that the entire floor area of the room or space is visible from the single or combined switch locations, the grounded circuit conductor shall only be required at one location.

The emphasized sentence applies to basically all multi-way setups you will run into in a house: it would be very strange indeed if you could not see what you are doing with the light from at least one controlling switch location.

Furthermore, the way multiway smart switches work only requires more conductors than fit in a /3 cable at the location of the "master" switch; a /3 is sufficient to connect the remotes to the master in all systems I have seen.

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