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I have two lights currently controlled by two switches (on the same wall plate), which I wanted to combine into a single switch. However, the wiring on the inside isn't what I was expecting, and wanted to check to make sure I understand what's going on.

The wires look like this:

Unexpected wiring

The wire labeled "north" is for the light receptical on the north side of the room, and south for south. However, what I wasn't expecting was for the white wire on the south side to be hot. Is this simply a case of the wires being mistakenly reversed, or is this something that was likely intentional? If the later, what's going on, and which wires would I need to combine in order to use one single pole switch instead of the previous two?

Edit:

Here is the original switch, labeled with how the wires were before I removed the switch

Original switch

  • How were these wires connected to the two switches? – A. I. Breveleri Apr 30 '17 at 21:49
  • If the wires weren't reversed, they might be coming from a three-way switch. The two wires act like buses that the switch at each end selects. Power would be fed to the switch at the other end, and the position of that switch selects which of the two wires is hot. The switch at this end controls on and off by selecting one of the two wires and the output goes to the light. You need a source for the neutral connection at this end (by tying into another line). – fixer1234 Apr 30 '17 at 21:50
  • I can't conjure a scenario where these could be 3-way switch loops. Typically with those, only the incoming power cable is 2-wire. Also, OP didn't mention 3-way switches. – isherwood Apr 30 '17 at 21:56
  • They aren't a 3 way switch, unless perhaps that was the original intent, but never followed through on – Jedediah Apr 30 '17 at 21:57
  • 3-way switches would require /3 cable. OP said two switches. – Harper Apr 30 '17 at 21:59
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Getting switch loop wires mixed up isn't any big deal. They are both hot, just one is always hot and one is switched hot. Since they are both hots, the whites should be marked with tape at both ends.

It appears both switches are on the far end of switch loops, and may even be derived from different circuits, possibly on different poles (notice how the installer broke off the common tab on the old duplex switch). So the easiest way to control them with one switch handle is a double-pole switch. Fortunately these do exist in household form factors, such as this Leviton CAB2-20W, which is rated for 277V so it's good for opposite poles (240V). AB goes on one pole, CD on the other.

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There have been different conventions for switch loops over the years, depending on local codes and installer preference:

  1. Send the black to the switch, since it's an extension of the hot from the light/outlet that's being switched. The white coming back is then marked with black tape in the light/outlet box to indicate that it's really a hot.

  2. Send the white to the switch so that the black coming back to the light/outlet box is obviously a hot. Mark the white with black tape at the switch box.

Many times the tape indicators are forgone out of laziness or ignorance. Looks like you have one of each scenario, and they may be marked at the other end.

Regarding your stated goal, it's not clear from the information at hand whether this is safely feasible. You need to return power to each switch, but it's not legal to do so outside the original cable. You'll need to investigate further and add details to your post about the entirely of both circuits.

  • So in that case, would I cap C, pigtail B and D, then attach A to the bottom of the new switch, and the B/D pigtail to the top? – Jedediah Apr 30 '17 at 22:49
  • Answer updated. – isherwood Apr 30 '17 at 23:14
  • Added a picture of the original switch with how it was wired. Other than that, that's all the additional information I could add. With that additional image, if it's still not clear what to do, I'll just put it back how it was and not worry about it – Jedediah Apr 30 '17 at 23:29
  • The bottom line is that you can't combine two circuits willy-nilly. If you can't say more about the circuitry, I suggest that you don't continue. – isherwood Apr 30 '17 at 23:40

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