enter image description hereI have an unused junction box on the ceiling that I would like to install a light fixture (1 white and 1 black wire). When I open the lid, the junction box has 1 white wire with no ends (just running from one end of the junction to the other end of the junction), and a yellow wire that also runs from one end to another, but there's one open end. Do I need to cut the white wire in the middle and connect my light fixture's white wire together? And the black to the open end yellow? enter image description hereenter image description here

  • OP - I may be misinterpreting your picture, but I see a single port on the left side with two yellows and two whites exiting that port. On the right side I see two ports. The upper port appears to have the white wire that loops and continue to the left side. The bottom port appears to have at least a white wire that runs straight to the left side. Can you confirm that you really only one white and one yellow coming and exiting that junction box. You did state that the yellow ran through but has a cut end, which is impossible. Nov 18, 2021 at 2:56
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    Add a picture of the wires exiting the right side of the box. How many wires are in the port on the left side? Nov 18, 2021 at 3:01
  • The grey wire is another neutral wire - the colors for neutral, when run in conduit are White and Grey. It, most likely, is paired with the yellow wire that exits the box through the left-hand conduit in the last pic. Note that this other yellow wire has some slack, but not very much. It looks like your electrician did everyone a favor by providing just a bit of slack (maybe at every junction box) which will make it easier in the future if you ever need just a bit more wire at a box.
    – FreeMan
    Nov 18, 2021 at 15:34

3 Answers 3


Yellow is a hot wire color, same as black.

In conduit wiring methods, white is always neutral.

Given that they left you a single yellow wire that ends here, that is clearly the switched hot to the lamp.

Given that one of the neutrals passing through this box was given a generous loop, that is clearly the correct neutral to be used with the solo hot. (It matters). Cut it at the halfway point and pigtail to your lamp. It needs to go through, because it’s also returning current for other stuff.

  • I agree with this. But what doesn't make sense to me is why they put in a neutral loop instead of a single wire. Any connection to ongoing could have been done at the source, along with ongoing hot. Seems like a waste of wire. Nov 18, 2021 at 0:34
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    @mana yes, that is odd, I suspect it might be a new-fangled switch loop. (Conduit removes the need to actually run the neutral, just need to reserve space in the pipe. Regardless, We must assume the other neutral is a different circuit. Nov 18, 2021 at 3:21
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    "Conduit removes the need to actually run the neutral, just need to reserve space in the pipe" say what now. That's a bootleg. Did you mean ground, if so what's that about "reserve space in the pipe"?
    – Mazura
    Nov 18, 2021 at 12:10
  • @mazura I think he means pull the neutral at a later time if needed. Nov 18, 2021 at 16:47
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    @mazura wires are easy to add to conduit without damaging wall surfaces. Someone upgrading to a smart switch is expected to pull the neutral at that time. The builder’s obligation is to leave room for the wire in pipes (conduit fill and 310.15 B3a derate ) and boxes (cubic inches). Nov 18, 2021 at 17:47

You are probably correct: cut the white wire and connect both halves to your fixtures white wire, and connect the yellow wire to the fixtures black wire. That yellow wire is probably connected to a switch somewhere, which will control your fixture.

  • More than "probably" right...
    – FreeMan
    Nov 18, 2021 at 0:18
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    Added are the pic taking from the right and one from the left. If I read all the comments correctly, I should cut the white in the middle and have both ends connect to the white of the light, and connect the open yellow to the black of the light fixture. Sounds about right? Also, I just saw the grayish wire with the new picture. Is that a ground wire?
    – Damian Ng
    Nov 18, 2021 at 14:48
  • The original comments were based on One White with loop and one Yellow and the one picture that DID NOT show all the wires. As clearly shown in the new pictures, you have more wires coming in and passing through this book. Give views time to analyze the wiring. Look for answers and posting dated after your new picture posting. Nov 18, 2021 at 22:03

Thanks everyone for all the responses. I cut the white wire and connected the the two halves with the white of the light fixture, and connected the open-end yellow wire to the black of the fixture. It worked! I can turn it on/off using the existing light switch. Thanks!!!

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