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My house has two switches in a 3-way circuit that controls two light fixtures. The lights are physically located in between the two switches.

Diagram

Here's a diagram of all the wires I see inside the two switch boxes and the two light fixture boxes:

This layout mirrors the physical layout of the four boxes.

  • Wavy symbol: a "bundle" of wires coming into the box
  • Small tan circle: plastic connector joining wires together
  • Rectangle: light switch
  • Bright yellow circle: light fixture

Switch 1:

A single bundle of wire containing black, white, red, and ground. The ground is tied to the switch next to it (which is on a different breaker).

Light 1

There are 3 bundles of wire coming into here:

  • A: Black, white, ground
  • B: Black, white, red, ground
  • C: Black, white, ground

Things that are tied together:

  • All of the ground wires
  • All of the white wires
  • Two black wires
  • A red wire and the other black wire

Light 2

A single bundle with black, white, and ground

Switch 2

Two bundles of wire come into the box:

  • Black (not connected to anything), white (connected to switch via red wire), and ground
  • Black, white, and ground

The grounds are tied together.

More info

Unlike everything else in my house, these don't have the twisted-together neutral wires inside the box (sort of like this picture: https://i.stack.imgur.com/k5RZu.jpg)

Additionally, although this circuit is on the bottom floor, the same breaker also cuts power to lights on the second and third floors (towards the rear of the house, which is also where Switch 1 is located). Not sure if that is relevant.

The black wires inside the switch boxes are definitely hot on both ends (when disconnected from the switches).

The red wire is not hot at switch 2. My non-contact voltage detector could not give me a consistent reading on the red wire at switch 1.

My Question

Any thoughts on how this might be wired? I ultimately need to know which wires at the switch boxes are:

  • Line (connected to breaker box)
  • Load (connected to fixture)
  • Neutral (if they exist)
  • Traveler(s)

Any other details or hints about this wiring would also be appreciated.

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10
  • Did you use a non-contact voltage meter? These are notorious for showing ghost voltages and anomalous indications. Even a contact voltage meter can be too sensitive when measuring live home wiring. I think the only reliable way to test for voltage is to place a light load, such as a 25w lamp, on the wire.
    – A. I. Breveleri
    Mar 28, 2017 at 21:26
  • You should also open up the light fixture boxes and test which wires are continuous with the switch 1 and switch 2 wires. At least try to find out where the power comes into this circuit.
    – A. I. Breveleri
    Mar 28, 2017 at 21:29
  • What are the black and white wires in the cable with the red wire in the first box doing?
    – ThreePhaseEel
    Mar 28, 2017 at 22:11
  • @A.I.Breveleri I have updated my question with a diagram showing all the wires and visible connections.
    – Colin O'Dell
    Mar 28, 2017 at 23:22
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    I can't help but comment on how strange this looks from a remodeler's perspective. It is obvious that this wasn't all original work by looking at the various types of boxes, wiring techniques, and wire nuts themselves. While it's not illegal to use different boxes, a real electrician rarely if ever does this. It also appears the black new construction ceiling box isn't mounted to anything, or it was mounted so poorly that it is standing 1/2" proud of the surface. I am saying this only because it has DIY written all over it, and DIY wiring can be impossible to decipher.
    – Benjamin Lane
    Mar 29, 2017 at 20:53

1 Answer 1

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Figured out the wiring!

enter image description here

Huge thanks to @A.I.Breveleri and @Shalvenay for guiding me through this - I couldn't have done it without their help.

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  • 4
    Later readers note: We also concluded that there is another junction box in a currently unknown location. Those color breaks in the above diagram must be inside that box.
    – A. I. Breveleri
    Mar 29, 2017 at 4:36
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    those whites being switched should be marked with a turn of electrical tape to signal they can contain a switched live.
    – ratchet freak
    Mar 29, 2017 at 8:39

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