3-way switch possible to wire another switch from constant hot

Discussion in 'Electrical Forum discussion & Blog' started by mcat, Dec 10, 2020.

  1. mcat

    mcat New Member

    Joined:
    Nov 19, 2017
    Location:
    New Hampshire
    I've run into a snag with a rewiring project in my kitchen. The original wiring is old black almost asphalt like coated 2 wire wrapped in heavy amounts of brown paper that when stripped is just plastic/rubber coated white/black wires without ground. I'm replacing all of it with new romex with a ground.

    The issue is that in one particular part of the home there is no feasible way to pull new romex down to the wall switch so the wiring has been reversed in the order it comes into the boxes. I'll do my best to explain below.

    Currently there is a ceiling box that has a constant hot feed running into it that is tied into another 3 wire feed ( red/black/white) and that wire feeding down the power to an adjacent wall switch from the ceiling which is using one of the black wires (wire nutted ) as a constant hot for another light switch in the same box running to another room. So one single pole switch and a 3-way switch in one box. From that wall switch another 3 way wire is running to an adjacent wall switch on the opposite side of the room.

    Since I can't run the wires to the initial wall switch with the single pole and 3-way switch from the ceiling I went in the opposite direction but at the cost of not having a constant hot wire in the initial wall box for the single pole switch so I'm not able to add a constant hot to the other switch for the other room, or so I think?

    I'm wondering if there is any way I can wire nut one of the black wires from the 3 way switch that used to have a constant hot in it and pull to the other single pole switch in the outlet that does not have a constant hot feed to it?

    Alternatively I have two other options and I'd like opinions on this since I can't make up my mind which way to go.

    There is another old asphalt coated romex wire that goes from the switch panel with the single pole / 3-way switch that I could re-connect to a outlet box I have already re-wired with new romex/ground and feed the single pole that way? There would be a ground in the other box, but the feed itself would just be the old two wire ( this somehow bugs me still ). OR, I could just run another 3-way wire that would have a constant hot to the first box from the ceiling, down an adjacent wall, under the basement and back up again ( since there's no way to go from the top down due to the design of the house/roof etc ). I already ran one 3-way wire from this spot so doing another wouldn't be terrible, just have to re-drill/fish etc.

    So thanks if you made it this far and I welcome anyones opinion or suggestion.



    As another alternative to this ( and I don't like it, but I'd be curious to hear others thoughts on this ) there is an old 2 wire ( it's in the wall and can't be easily removed ) without ground feed that I can usewith the single pole and 3-way switch and ground everything from the other romex that is there and still be ok, but I wanted to check this first before doing that.
     
  2. wwhitney

    wwhitney Well-Known Member

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    Location:
    Berkeley, CA
    Tried to follow your narrative but couldn't quite picture everything. This calls for a diagram. Also, a picture explaining "no feasible way to pull new romex down to the wall switch".

    Cheers, Wayne
     
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  4. mcat

    mcat New Member

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    Nov 19, 2017
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    I knew this was coming :) I tried to find diagram making software but I did not have much luck. I whole heartedly agree a diagram would be nice. I'm gonna try to put a quick one together to bring some sense to this so everyone else isn't scratching their head thinking we've all gone made in the north ( though that may be true ).
    [​IMG]
    https://ibb.co/FnCpRMw
    [​IMG]
     
  5. wwhitney

    wwhitney Well-Known Member

    Joined:
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    Location:
    Berkeley, CA
    OK, I think I follow. The diagram shows the current situation, you have constant hot and neutral in the "adjacent kitchen wall switch" and you ran 3 conductor NM to the "kitchen wall switch", consisting of two travelers and one return.

    So the first question is where is the neutral that the load controlled by single pole switch in "kitchen wall switch" uses?

    Seems the thing to do is add another 2 conductor NM parallel to the 3 conductor NM labeled "Run under basement". That would provide your neutral and constant hot for your single pole switch. Basically like you would do if the single pole and the 3-way in that box were in separate boxes.

    Cheers, Wayne
     
  6. mcat

    mcat New Member

    Joined:
    Nov 19, 2017
    Location:
    New Hampshire
    Thanks Wayne,
    The neutral controlled by the single pole switch in the "kitchen wall switch" was tied into the "run under basement" 3-way line. I've opted to just go with the 2 conductor and run parallel and that will sort this mess out. Thanks for the advice and suggestions!
     
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
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    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    In a switch leg, the white wire is often not a neutral! It is the switched line. Technically, it should be marked red to indicate it is switched hot at each end. That step is often omitted.

    Today's code wants a neutral at the switch.

    Wherever you're tapping off the hot lead, the neutral for that circuit must also be paired up with it to the new fixture. When the hot is run from the ceiling, you may not have a neutral at the switch box (but, again, today it is required).
     
  8. wwhitney

    wwhitney Well-Known Member

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    Location:
    Berkeley, CA
    As Jim pointed out, that "run under basement" 3 conductor cable has no neutral. You need 2 conductors for the travelers, and 1 conductor for the return hot to the light, so you don't have a conductor for a neutral.

    Cheers, Wayne
     
  9. mcat

    mcat New Member

    Joined:
    Nov 19, 2017
    Location:
    New Hampshire
    I've put together the current electrical as it is in the house, without the new romex pulled. There is a neutral wire at the ceiling light that is brought down to the first switch box that has a single pole switch and a 3-way switch but not the second. I don't see how I could get a neutral wire in that other switchbox or why I would need it as there wouldn't be anything to connect it to? I must be missing something here.

    Original wiring in the house as it currently stands shown below.
    DIAGRAM #1

    [​IMG]


    After thinking a bit on the suggestions made here, would converting this over to this setup in the diagram below, be the better move out of the two? The diagram below is what I think would solve the lack of a neutral in the adjacent wall switch box at the expense of an additional romex wire in the ceiling box but it should not be too much of an issue I would think but again I'm open to suggestions.

    DIAGRAM #2

    [​IMG]
     
    Last edited: Dec 11, 2020
  10. wwhitney

    wwhitney Well-Known Member

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    Mar 17, 2019
    Location:
    Berkeley, CA
    Setting aside your previous posts, and just looking at your last two diagrams, either one would work. [And nice diagrams, much clearer than your narrative or your earlier diagram.]

    The first seems simpler, and it avoids the possible future error of tying all neutrals together in the ceiling box, which would create parallel neutral paths and is prohibited. The rule on providing a neutral at a switch box applies to only one of a pair of 3-ways (possibly only in the case the two 3-ways are in sight of each other, I'd have to check).

    Cheers, Wayne
     
  11. mcat

    mcat New Member

    Joined:
    Nov 19, 2017
    Location:
    New Hampshire
    The first is certainly simpler but means I won't have a neutral in the other switch box, as I am understanding that's more for newer smart switches and the like, still if I could accomplish this I would like to.

    Regarding the parallel neutral paths on the second diagram I made, it's all on one circuit still or perhaps I'm not understanding something here? Is it the fact that the second neutral wire for the light is inside the same box where the supply neutral is? I can't just connect all the neutrals together either in this instance and be safe/good?

    What if I was to do the following below instead ( see diagram below where line for the light switch neutral ties into the supply), where in the ceiling box I connect all the neutrals together, my gut is telling me that this is a no no as it's simply going in a circle back to the supply again?

    DIAGRAM #3

    [​IMG]

    Or as another alternative, to have a neutral in the last switch, can I simply cap it off ( see diagram below) and not extend it back to the ceiling box or is that not good either?

    DIAGRAM #4

    [​IMG]

    Analysis paralysis has me at this point :)
     
    Last edited: Dec 11, 2020
  12. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    With 3 way switching from two locations, typically it is enough to have a neutral at one location, where the smart switch goes, and the other location is a regular switch or a companion 3-way that doesn't need a neutral.

    In the #2 grey background diagram, the way you've drawn the white wires in the ceiling junction box is correct. If you did connect all 5 white wires together, you'd have parallel paths, basically a loop of white wire, so there's two different routes on the white wires from the ceiling box to the box with two switches. That's prohibited for conductors smaller than 1/0. Also, any current on that neutral from the load controlled by single pole switch would divide along the two routes, and there would be excess emf within the white wire loop (if the two different cables don't take identical routes).

    I'll look are your diagrams 3 and 4 shortly.

    Cheers, Wayne
     
  13. wwhitney

    wwhitney Well-Known Member

    Joined:
    Mar 17, 2019
    Location:
    Berkeley, CA
    OK, diagram 3 is obviously what you don't want to do for the reasons described.

    Diagram 4 is allowed if the boxes are non-metallic, but it's not a good idea unless the conductors drawn in parallel on the diagram are physically in proximity (e.g touching each other). By that I mean the 2-wire NM feeding the double switch box is next to the 2 wire-NM return, the box with the single pole switch, and the 3-wire from that box to the double switch box. Because it creates a loop for the ungrounded conductor, and again any region within that loop would be subject to excess emf.

    Just go with Diagram 1 (grey background). If you really want a neutral in the single switch box (which is not needed), the correct way to do it is to run 4 conductor between the two switches, rather than 3 conductor. You can get actual 4 conductor NM cable, or you can just use 2 runs of 2 conductor, being careful to run them touching the whole way, and if the boxes are metal, bringing both 2 conductor cables into the same opening at each box. The only downside is having the extra EGC in each box to deal with.

    Cheers, Wayne
     
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  14. mcat

    mcat New Member

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    Nov 19, 2017
    Location:
    New Hampshire
    Thank you for the time you took to look over my diagrams. I was doing more research and re-educating myself on NEC codes and the neutral in a single switch box from your information which helped clarify things better. I also learned about parallel neutrals which I did not consider in the past as all my previous retro-fits have been very straightforward.

    The original boxes are were metal that I have converted to plastic due to the lack of available CU IN capacity and no ground screw however going with diagram 1 is certainly the way to go over diagram 4 and certainly not diagram 3. As you've pointed out that if a smart switch was to be used, it can be installed in the box that has the neutral.

    Again thank you and now I'm off to finish the last piece of this kitchen puzzle! Thank you again Wayne!
     
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