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My master bedroom has a single light switch for the overhead fixture; however, it was built in the 50's and has end-line "power at the light" wiring like so:

Power at the light wiring

Image borrowed from this question, but I don't have the option of #2 as suggested there, since this is a bedroom light and not a utility light. Another reason I'm asking, is I'd like to keep my work code-compliant.

EDIT: Yes, I plan on replacing the switch with a smart switch (ZWave, which I can't seem to find in a non-decora style that doesn't require a neutral, and this particular switch has a switch plate that is a decorative one inherited from family so it has strong sentimental value and thus replacing with a decora style switch isn't an option for us).

Is it code-compliant to just re-fish 14/3 down into the wall in place of the old wire, and use the traveler to bring neutral into the box (and make damn sure the white wire is black-tagged, because I'm pretty sure the existing wire isn't), or should I rewire the whole thing as power-through, bringing 14/2 wire from the breaker down into the switch with the neutral, and having another run of 14/2 taking both hot and neutral back up to the fixture? Or is there another (code-compliant!) option I'm not seeing?

As tagged, this is USA, so NEC/NFPA70 applies.

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  • 14/3 wires are black, white and red. 14/3 has many, many uses and so do those 3 wires. One of those uses, 3-way switches, involves two travelers. There is no "1 traveler" in home wiring normally. The 2 travelers can be any of the 3 colors, depending on how the circuit is wired and Code requirements relating to use of the neutral wire. Oct 24, 2022 at 23:59
  • If you fish 14/3, use the white wire for neutral, the other two for the switch loop and don't tag anything. Also while you're doing all this, assuming you're cutting open the wall to fish the wire, if the switch box is metal you should replace it with plastic to give Z-Wave a better chance at working reliably.
    – jay613
    Oct 25, 2022 at 19:33
  • 1950s? You probably have metal-clad cable without a ground wire. Your new cable will be NM, hopefully your ceiling box will have a knockout where you can put an NM clamp, and somewhere to connect its ground wire. Check it out before buying parts.
    – jay613
    Oct 25, 2022 at 19:34
  • @jay613 nah it's braided fabric insulation. In hoping to not open the drywall if I can help it.
    – Doktor J
    Oct 25, 2022 at 22:20
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    @jay613 in the attic crawlspace; in my experiences with this house's wiring thus far, vertical runs seem to not be stapled, and even horizontal runs aren't as secured as they should be (I intend to fix this in the process; NFPA70 has exceptions on securing wire in inaccessible fished runs in residential homes). Once I'm sure the old vertical isn't secured, I'm going to just attach the 14/3 to it from above and pull it down through the existing hole. I will probably replace the box too because the old one's a tiny POS.
    – Doktor J
    Oct 25, 2022 at 23:04

3 Answers 3

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First make sure the breaker is 15A. If it is 20A you must use 12/3 cable.

The most elegant way to do this is to use the /3 cable as you plan. The wires will be assigned as follows:

  • White = actual neutral (mandatory per NEC)
  • Black = always-hot from the panel (often also onward to other points of use)
  • Red = switched-hot from switch to light.

No travelers will be involved.

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With 14/3 the white stays as neutral. Use the black and red on the switch(if non smart).

So 14/3 from light to switch with neutral(white) having a wire nut at the switch( in case someone puts a smart switch in).

You do not mention of having the weird idea of adding a smart switch. If so you wiring is code compliant now.

Only if you were adding a new light circuit/device would you need to use 14/3 for new code compliant.

Maybe explain why you want or need to rewire or replace the wire that is there now. It is in code and does not need to be changed just because the code as changed for smart switches.

Edit for edited question. Both options are doable, depending on which is easier for you. 14/2 from panel to switch will require you to wire nut/cap off the power cable at the light. Should find the next junction of that wire and wire nut it also.

14/3 from the light might be easier to do, but drywall repair probably required after. Both will give neutral at the switch.

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  • I wondered that too. Why replace the wire unless a smart switch is desired.
    – JACK
    Oct 24, 2022 at 23:57
  • Yes, sorry – I do intend to replace the switch with a smart switch (ZWave, can't find any no-neutral versions that are in the normal toggle style... see edit on question for more details)
    – Doktor J
    Oct 25, 2022 at 0:05
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Based on your diagram and wanting to keep the existing switch plate, consider using a Z-wave controlled relay instead of a smart switch. There are no additional wires to run and you keep the existing light switch. I can't comment on code compliance.

You can install the relay where the three legs of the circuit come together. Live and neutral are already available to power the relay. The relay switches current to the light fixture. The relay should have a switch input, so it can be controlled by the existing light switch.

Z-wave dimmers are also available at additional cost.

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  • Good idea .. but .. What are the chances there's room in the 1950s ceiling box for a relay?
    – jay613
    Oct 25, 2022 at 19:38
  • Would appreciate input from others on whether putting such a relay in the box would be code-compliant. It seems ambiguous, but if there's nothing explicitly prohibiting it then I might consider this.
    – Doktor J
    Oct 26, 2022 at 16:45

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