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I've been investigating a light switch that seemingly doesn't control anything, and discovered that there is continuity between the line and load wires going to the switch. When the circuit is powered, I can measure ~120 volts from line to ground as well as load to ground when the switch is off. I've verified that the switch is fine by disconnecting it from the wires and checking that there is no continuity between the terminals when the switch is off.

I've marked up these photos for clarity to explain the wiring: switch wiring

  • Wires A, B, and C were all connected with a wire nut.
    • A goes into the wall (up towards the ceiling if it matters)
    • B goes to an outlet close to the light switch (verified by checking continuity between the switch box and receptacle box)
    • C is a tail going to the switch
  • Wire L is (presumably) the line wire coming from the panel
  • G is ground
  • N is two neutral wires connected with a wire nut shoved way in the back of the box.
    • One of these wires is connected to the same outlet as wire B (checked continuity to the receptacle box)
    • The other goes into the wall

With the circuit unpowered (breaker open), I can detect continuity between wire L (line) and wire A (load going into wall) while A is not connected to anything else (as shown in the photo). I can't see any obvious reason why there would be continuity between these wires. Isn't this effectively just bypassing the switch and closing the circuit all the time? Does this indicate a short between the line and load wires somewhere inside the wall?

My assumption is that the outlet connected to the wires in this box was supposed to be switched, but because of the continuity the outlet is always powered. Is there anything else I can do to investigate why this continuity exists/fix the issue?

It's also worth mentioning that the outlet I mentioned above was originally covered with a blank wall plate, I had no idea the outlet was there until I unscrewed the blank plate on a hunch. Was this meant to indicate anything, or did the builder just run out of receptacle wall plates?

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  • there's probably a dual purpose outlet somewhere with too many tabs.
    – Jasen
    Commented Feb 23, 2023 at 10:37
  • I am finding this confusing. is their continuity between load and line or between load and ground (when the breaker is off). And how are you measuring the continuity - voltage or beeper? I would suggest measuring AC volts first and if the value is not over 20 then try AC and DC resistance. The load is probably connected to what you are calling ground. That is the light may be connected to A and G. Commented Feb 23, 2023 at 10:50
  • "Switch seemingly doesn't control anything" yet there's a feed from this switch to an outlet. Did you try plugging a light/radio/something into the outlet and flipping the switch to see if that makes the something turn on/off? Did you try both outlets? Often one of the two is switched so you can turn on plugged in lights - it's one of two ways of meeting a code requirement.
    – FreeMan
    Commented Feb 23, 2023 at 13:30
  • @RohitGupta there is continuity between load and line. I measured voltage on the switch terminals between line/ground and load/ground when the circuit was hot, then disconnected wires from the terminals and measured continuity when the circuit was cold (breaker open). Commented Feb 23, 2023 at 18:43
  • @FreeMan Yes, I tested both outlets in the connected receptacle. Both outlets are always hot regardless of the switch position (which makes sense now that I know there is continuity between line and load). Commented Feb 23, 2023 at 18:44

1 Answer 1

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The red wire from the switch is most likely LOAD to a switched outlet.

C is the LINE getting power from the panel, when tied to A & B. (A most likely from the panel.)

This makes all the black wires hot with the breaker on.

My bet is one black, ( possibly the one you say goes to an outlet) does indeed go to an outlet that still has the bridge intact. That red wire also goes to that outlet and was supposed to make 1/2 of the outlet switched. That is why you read continuity and the switch does nothing. (both wires at the switch are hot with the breaker on.)

"I've been investigating a light switch that seemingly doesn't control anything"

Check that outlet that was covered. ( It never should have been.) This indicates electrical ignorance and thus the likely hood of an outlet being the issue. There is some outlet in the room that was to be powered by the switch. Someone replaced the outlet and didn't remove the bridge. Possibly because they thought the outlet was faulty because only 1/2 worked, not realizing it was switched.

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  • The outlet connected to wire B does indeed have the bridge intact, however the red wire (R) doesn't go to that receptacle, it follows A into the wall up towards the ceiling. The outlet in question only has three wires connected (ground, neutral, load), if it was originally a half hot outlet wouldn't it need a fourth wire (as shown here do-it-yourself-help.com/images/…)? Commented Feb 23, 2023 at 18:50
  • probably a different outlet then.
    – Jasen
    Commented Feb 23, 2023 at 19:36
  • I don't think it's a different outlet as I've tested every individual outlet in the entire home. The fact that there is a wire running from the switch box to the receptacle makes me think it was intended to be a switched outlet that has some wiring issues. Commented Feb 23, 2023 at 21:50
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    The individual wires in a cable can't (shouldn't) go different directions! All the wires in the cable must go to the next junction box together. That's a Code requirement. Are these individual wires with writing on the wires, that are not in conduit? Maybe someone did something stupid. Commented Feb 23, 2023 at 22:34
  • @Harper-ReinstateMonica sorry maybe I wasn't clear, wire A and the red wire are in the same cable and exit the box in the same direction. Wire B is in a separate cable which goes to the outlet. Commented Feb 24, 2023 at 21:46

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