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Sorry for the silly question. It seems so basic to me. I have dealt with 12v DC car/computer wiring since I was a kid, but have finally purchased a house. Residential wiring is kind of just screwing me up and I feel like I might be overthinking things, so pardon my potentially confusing question.

I have a 3-switch panel next to a closet. Only two of the three switches are being used, leaving the third switch unwired. Each switch is wired to its own fluorescent light fixture in my drop ceiling. I want to add a light fixture (just a single standard 60w light bulb) to this unused switch.

However, I am getting a little confused. I pulled the switch cover plate off and it appears that there are two, sheathed, three-wire feeds coming into the switch box (hope that makes sense, don't know the proper term for the wiring). Each switch is wired to its own wire set.

Grounds are left disconnected (as opposed to the switch itself). Hots go to the hot terminal, and whites go to the neutral terminal on the switch.

I believe the switches are wired like in the following diagram:

light diagram

First, what's the terminology for this sort of wiring? Second, is it possible to add my light fixture to the unused switch by piggy backing off of the hot wire? I was considering this, but I am a little confused. Can this be done? Or does there need to be a connection to a main neutral wire?

With my drop ceiling, it should be pretty simple to rewire the other light fixtures but if I can avoid it, that would be nice. Thanks!

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  • You only think that's neutral because you know you need it, and you're an optimist :) Both wires are hot, one is always hot and the other is hot when the light is on. The reason white wires are used here is because cable makers insist on making the cables with white wires in em! Dec 25 '20 at 6:34
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There are no neutrals here.

That's exceedingly important to understand about a switch loop (extremely common, no longer to current codes, but perfectly fine in older codes, so you will find them in every moderately aged house.)

Given your 12V experience you probably think of colors as being fixed things - this is not quite true in household AC wiring.

The "sheathed, 3-wire feeds" are 2 wire cables (the grounds are not counted in residential cables. So a 14/2 or 12/2 cable has a black, a white and a bare - 3 wires, but it's a /2 cable.) A wire is a single conductor, a cable is multiple wires bundled in an outer sheath.

Modern code would require a /3 cable to the switch location (black, white, red, bare) but you don't have to change the cable to "modern code" unless you are remodeling (changing a switch is not remodeling.) That is "grandfathered" meaning it met code at the time it was installed.

However: adding a cable to an unwired switch IS going to require using a /3 cable from someplace that does have unswitched hot and neutral, or two /2 cables (with white as neutral in both) if the place the power comes from (unswitched hot) is not the place the light (switched hot) will be.

The white wires to the switches are hot. They should be (but rarely are) marked with red or black tape or paint to indicated that they are hot. The black wires from the switches are switched hot.

There is no neutral anywhere in the switch box. Typical arrangement is that power comes to (one of) the lights, and at that light you will find a white wire (that should be, but often is not, remarked red or black) connected to a black wire from the power feed leading to the switch location. The black wire in the same cable will then connect to the black wire from the light, and the white wire from the power feed will connect to the white wire from the light. The cable with the white connected to the feed's black will lead to your switch location.

Thus, power flows from the source, to the switch, back from the switch, through the load, and back to the source.

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  • 1
    Actually switch loops are still in the 2020 code.
    – Ed Beal
    Dec 24 '20 at 17:35
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    Not this way. Neutral has to be provided to a switch location, so you need a /3 for a switch loop now.
    – Ecnerwal
    Dec 24 '20 at 19:31
  • Not in all locations I looked it up not long ago in the 2020 code this and water pipes not allowed for grounding electrodes are things being circulated on this site. If I remember. Correctly the 2020 code still had the exhibit with white wire taped black I will provide code ref on Monday as my code book is on my desk.
    – Ed Beal
    Dec 24 '20 at 19:56
  • Not sure I'm reading "no neutrals here" as intended. Did you mean except for the neutral from the cable at lower left to the light fixture? Dec 28 '20 at 17:55
  • There is no neutral at the switch box, because the neutral from the power feed at the light fixture is not extended to the switch box in a /2 cable switch loop. There's a neutral at the fixture, but the question is are asking about connecting at the switch box where there's an unused switch, but no neutral.
    – Ecnerwal
    Dec 28 '20 at 18:34
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The switch loop is the proper term the white wire that is taped black is the hot and the black is the switched hot. You said 3 wire is that black white ground? Or black red white ground. Electricians call the first 12-2 with ground or 14-2 with ground the wire size is the 12 or 14 , if it has the red then 12-3 with ground all these are normally shortened to 12-2 or 12-3 / 14-2 or 14-3 with Romex or nmb. Cordage (extension cords we state the number of conductors including the ground).

So if you only have black white and ground you can not add another switch. But if it has an unused red then you could.

You can add the light fixture with or without the switch by tapping the existing light and running black white ground to the new location.

If there is a red wire you would jumper the always hot at the switch box to the new switch and connect the red to the other side then at the fixture the red would go to the black going to the new fixture white to the group of whites (not the black white splice that takes power to the switch) and grounds bare copper all together.

Those are the options many times electricians will use 12-3 or 14-3 to a light location so it can be a light/fan combo later with 2 switches but install only the light.

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  • I see. So there is definitely no red. So basically, I just need to find the actual source wires (where the light fixtures are getting power) and run those to the switch instead?
    – ewrjontan
    Dec 25 '20 at 7:44
  • To add a switch on a switch loop the power is normally at the fixture, sometimes in a separate box but that is the normal location.
    – Ed Beal
    Dec 25 '20 at 15:19
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The other answers are very informative and answered your questions well. The only thing I thought was worth adding is some instruction on how to make the switch work the way you want.

Since the only place you have neutral is in the existing light box you need to start there. You can run a /2 cable from the light box to the new ceiling box for your new light. Then you can run a new /3 cable from the new ceiling light box in the wall to the existing switch box and run the third (new) switch on this new switch loop. The white neural wire in this new /3 cable won't connect to anything, will just be capped off, and is required by code in case someone replaces your new switch with a smart switch that needs neutral.

This isn't a lot more work than your original plan of running a cable from the switch to the new ceiling light box. The only other piece required is the cable from the existing ceiling light box to the new ceiling light box but this should be trivial if you have easy access through the drop ceiling.

I have added the diagram below for the wire connections... Although I am guessing you probably understand how it should be wired based on the other answers.

Edit: added pictureWiring Diagram for Additional switch loop

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  • So basically just connect the black and white wires in the existing light fixture, to the black and whites on a new /2 cable. Any reason not to just locate the source cable (which supplies power to my current light fixtures) and rewire it all so that I have neutrals in my switch box?
    – ewrjontan
    Dec 25 '20 at 7:51
  • Check out the added diagram. Should be pretty easy to get what you want, the only tricky part can be fishing the new /3 cable down the wall... but you were going to do that anyways I presume.
    – bigchief
    Dec 25 '20 at 20:06
  • This is exactly what I need. Thanks!
    – ewrjontan
    Dec 26 '20 at 13:33
  • So I examined my actual wiring. Came up with a similar diagram to sort of think this through myself. It is basically the same but instead of using /3 cable it is using /2. Also, I am going from the source to the switch box, then to the light as opposed to your diagram where you go to the light fixture first, then the switch box. Any reason to do one over the other? <img src="i.ibb.co/4N1MT6T/wiring-diagram-final.jpg" width="100" height="100">
    – ewrjontan
    Dec 29 '20 at 5:05
  • Your diagram looks good. I posted mine only because it only requires one additional cable run in the wall to the switch (instead of 2 new cables) and this can be the most difficult part.
    – bigchief
    Dec 29 '20 at 7:45

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