I have a switch that's part of a three switch panel, and it doesn't seem to do anything. The other two switches go to a ceiling light in the same room, and a ceiling light in an adjacent room. I've checked most, if not all of the plugs in this and adjacent rooms by plugging a lamp in and flipping the switch, to no avail.

After additionally searching the attic, I've discovered two cables obviously connected to the switch panel. These seem to go to the two lights that are affected by the other two switches. There's a third cable leading from an exterior motion light to an area between the 3 panel switches and the nearby breaker panel. I can't tell which it might be connected to. The motion light doesn't seem to activate in either position of the switch, but I've known those things to be finicky.

How can I determine what the switch is meant to do?

  • Is there a ceiling fan or light in the ceiling? – Tyson Nov 13 '17 at 23:33
  • Updated question to clarify, but yes, there's a light in this and another room that are controlled by the other two switches. – THiebert Nov 13 '17 at 23:41
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    I suspect it's set up for separate controls for a ceiling fan and light. – Tyson Nov 13 '17 at 23:43
  • The room it's in isn't practical for a cieling fan. It's a utility/laundry room. – THiebert Nov 13 '17 at 23:45
  • Have you verified the switch is connected? Is the switch close to an attic access hole? Other than the other comments the only thing I can think of would be an exhaust fan since it is a utility room. Maybe for the room or attic. – Ed Beal Nov 14 '17 at 0:04

Like someone said on the comments, sometimes a house is wired so that there are two lines going to a fan/ceiling enclosure: one for controlling the fan, and the other for controlling the fan's light (tho some fans' wiring don't allow for this type of setup). So one switch could be just going to a ceiling enclosure (where there might be just a light) and it's not connected to anything.

Edit: just saw your comment that's unlikely for a fan. Another possibility it's that it controls one of the power outlets.. you could test this by plugging a small light/hairdryer/w.e. and switch the light to see if it turns on/off the appliance you connected.

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    When you do this be sure to separately test both the top and bottom outlet in each receptacle - it may control just half of one receptacle. – Mark Nov 14 '17 at 2:13
  • Could be for an extractor fan in the laundry room. – mmathis Nov 14 '17 at 16:32

Check your outside lights. It may control one or more of those.

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  • I have checked against it working on exterior lights and receptacles as well. – THiebert Nov 14 '17 at 0:41
  • Correction. It appears there's a motion light that I hadn't previously noticed. It may be connected to that, but I'm having difficulty verifying. – THiebert Nov 14 '17 at 1:49

Does it have an "On" and "Off" legend on the moving part of the switch?

No on/off marking

It is a 3-way switch sharing control with another point. You don't realize this and have always been controlling it from the other point, thinking that was the only switch.

Unfortunately, this is hard to find becuase throwing the switch will only "flip" the on/off status of the device. You'd have to throw it, walk the house, throw it, walk the house, etc. while looking for something that has changed.

If the controlled thing also has motion sensors, this could be messy.

As a rule, you don't want to sever power to motion sensors, because it wipes out their memory of the terrain, and of day/night luminance levels for the light sensor. The latter in particular takes at least 24 hours to recalibrate. Default values often work, but in dark or well-lit areas, sensors take a few 24hr cycles to learn what "normal" is.

On/off marking

This is likely the only switch controlling that device.

  1. Turn the switch "OFF" and tape it in that position.
  2. Live your life.
  3. Eventually you will find something that does not work.
  4. Try the switch. Eureka!
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