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I have a switch on the wall that doesn't seem to do anything. I decided to investigate by pulling the switch out and to my surprise, it was a 3-way switch with only two connections (black and white but no red wire). An even bigger surprise was that the white wire always measured live on my outlet tester regardless of the position of the switch. I figured that either the switch had failed short or the white wire was connected to live for some reason. I disconnected the switch and the white wire still tested live. I did a continuity check between the black and white wire (with the breaker off) and found that there was indeed a direct connection.

All of this explains why the switch didn't do anything. What I can't explain is why this junction box was wired like this in the first place. I've changed just about every other switch/outlet/light fixture in the house and this is the only instance I've seen of dubious electrical wiring. I'm chalking it up to an electrician's error and planning on capping the two live wires and putting an unconnected dummy switch into the wall. Does anybody have a better idea on what might be going on here or what I should do about it?

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  • You need 3 wires between two 3 way switches.
    – Tony Stewart EE75
    Commented Dec 9, 2018 at 14:42
  • 3
    You don't need to put a "dummy" switch there -- just get a blank cover plate for the box.
    – Dave Tweed
    Commented Dec 9, 2018 at 14:45
  • Can you post photos of the insides of the boxes involved?
    – ThreePhaseEel
    Commented Dec 9, 2018 at 16:07
  • Wires to 3-ways are often not black, white and red. Also it is very common for novice electricians (esp. With some EE experience) to decide that "the last guy" made a mistake. It's practically a trope. And that is not true and actually this is their inexperience talking. Since you changed most of the receptacles and switches so far, most likely you biffed something up at the other end of this circuit.
    – Harper - Reinstate Monica
    Commented Dec 9, 2018 at 16:15

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Its a split/switched receptacle

And you forgot to break the tab off.

At the other end of this cable, one of the wires (most correctly the white) is spliced in with the hot wire(s) going to one socket of the outlet. The other wire goes to the hot terminal of the other socket. This causes this one socket to be switched-hot with the switch, while the other socket is always hot.

This is done to support a floor lamp; it meets the technical requirements to have a light in the room that Code requires, without the expense of cabling an additional outlet (point of use) at the ceiling.

When you did not break off the tab on that receptacle, you caused both sides (black and white) to be shorted, annulling the function of the switch.

Hunt it down. The giveaway will be a white wire where one is not expected (pigtailed with blacks, or on a brass screw).

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