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In my house, I fortunately have a well-labeled circuit breaker. There are a few rooms that could be better named, but it's fine.

As such, it's very easy to identify almost every switch and what it does and what breaker switch it's attached to.

Except for one light switch at the entry way of my house.

I turned it on and stuck a voltage tester next to it. I went through every single breaker switch, even the ones for other floors, and the voltage tester continued beeping. I skipped the doubles (washer, dryer, and HVAC), because I assume a light switch wouldn't be connected with a major appliance.

I've also tried plugging a light into various outlets and turning the wall switch off and on, but I don't see any change in the light.

The voltage tester only stopped beeping once I turned off power to the entire house. So as far as I can tell, this switch seems to do nothing.

  1. Is there another method I can use to trace what this switch connects to?
  2. What should I do with this switch?

Update: I have finally figured out where this mystery switch goes to: an outside outlet. I never even noticed it until y'all pointed it out so thank you! I still don't know which breaker it goes to, which is annoying but I've got at least half the mystery solved

Update 2: I have found it! Once I realized it went outside and was GFCI, I guessed that the cable was connected to the Basement GFCI circuit and that did it. Personally I would have labeled it "basement + outside gfci" or wired it to the first floor outlets or put it on a separate breaker but it's fine. I'm not bitter at all

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    perhaps it operates an outdoor plug for christmas lights ... look for power outlets outside, up high – jsotola Oct 18 at 2:11
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    Have you considered the age of the house? Example: My 60 year old house was originally built as off-base military barracks with 3 front doors. I still have 2 front doors but the middle door had been framed over but a powered switch was left behind with no fixture to power. Consider the location of the switch. – G Warner Oct 18 at 13:23
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    Next step should be to test the 30A (double) switches. With electrical work, especially older work that you inherited from an unknown source, never assume. – TylerH Oct 18 at 21:37
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    So that's why my living room lights keep flickering on and off... – FreeMan Oct 19 at 14:39
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    I've discovered it goes to an outside close-to-the-ground outlet that I never noticed before. Would it be safe for me to wire this up so it's permanently on? I've done this before with inside outlets but I don't know if outside outlets require switches. – Merlin -they-them- Oct 19 at 15:02
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Divide and conquer.

You turned off the main breaker and the switch went dead. So you know it is going through that panel.

  • Leave the main breaker on and turn off everything else.

If it is still on at this point, then you have something really strange going on - time for a professional. But assuming that does turn power to the switch off:

  • Turn on the breakers one at a time until the switch comes back on.

This will take a while, so you can also try:

  • Turn HALF the breakers on and see if the switch comes back on.

If it does, then turn half off and see if it is on or off. Lather, rinse, repeat. If you have 32 breakers, the first test gets you to 16, the second to 8, the third to 4, the fourth to 2, and on the fifth test you have your answer.

As far as what the switch does, is there any chance you have some outside lights that don't work properly? Also look for any receptacles or covered junction boxes (which might previously have had a light on the switch) outside.

Update: Now that you have determined the switch controls a receptacle, there is an easy way to find the breaker if you don't have a helper (i.e., if you have to run between breaker panel and switch/receptacle to test):

  • Plug a radio into the switched receptacle.
  • Turn on the radio loud enough to hear it from the breaker panel. Might be best to do this during the daytime :-)
  • Turn off breakers one at a time until the music stops.

For anyone wondering why "turn off one at a time until the music stops" instead of "turn on one at a time until the music starts", this gets to the "old vs. new equipment" issue. An older radio has a simple power switch. Turn it on and unplug it and plug it back in and it is guaranteed to be "on". Many newer radios (like TVs, computers, etc.) have a power switch that does not really turn everything off. A small circuit stays on to power a clock, status lights, etc. For normal usage that's just fine. But the default behavior (sometimes configurable, sometimes not) for these devices is typically "on external power restore go to 'off' state", which wouldn't be very helpful here.

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    I have traced switch wiring to outside walls with covers on the junction boxes and the wires capped inside connected to nothing.They were put in for future use for lights or whatever.+1 – JACK Oct 18 at 2:24
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    NB - for anyone curious/interested, the deterministic method suggested here is called a 'binary search' and mathematically is the quickest way to determine an unknown value inside of a fixed, known range. – TylerH Oct 18 at 21:39
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    This is a solid idea. I'll definitely try this, even though, ugh, it's so annoying. I wish all switches and outlets were labeled and houses came with circuit diagrams – Merlin -they-them- Oct 18 at 22:30
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    Forgot to add, as for outside lights, I know which switches those are but I will look for possible junction boxes or receptacles. – Merlin -they-them- Oct 18 at 22:32
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    This is the right approach if you're working alone. However, if you have a helper you turn everything off, put them at the panel while you're watching your voltage tester and you have them turn breakers on one at a time until you say STOP. – Loren Pechtel Oct 19 at 1:44
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One problem with using a non-contact voltage detector is that it can be befuddled by adjacent circuits. To really determine if the switch is powered or not you need to remove the switch cover and attach a wired voltmeter to what you perceive is the "hot" wire in the box.

And, unfortunately, this is not even 100% reliable if the voltmeter is an electronic "high input impedance" unit. When faced with this possibility I dig out my 50-year-old Heathkit meter.

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    Most readers, especially those who might benefit from this question, will certainly not have half-century-old "old faithful" equipment, for what it's worth. – TylerH Oct 18 at 21:40
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    I did remove the cover and pointed the voltage tester directly at the top wire and it only beeped when the switch was on. Plus the other nearby switches were definitely off since I know which breaker switch works for those – Merlin -they-them- Oct 18 at 22:19
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    Yeah, modern gear is too good. More than once I've been tempted to get another set of leads for my meter and wire something like a 50k Ohm resistor across them. It would go a long way towards getting rid of phantom voltages that sometimes show up. – Loren Pechtel Oct 19 at 1:47
  • @LorenPechtel Higher end gear will have a Low-Z (that's the Fluke name, anyways) input mode for that reason. I don't know if any of the cheaper brands have gotten around to imitating that yet. – mbrig Oct 19 at 18:15
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    Ah, yes!! I remember their motto from my college days: If it works it's a Fluke! – Hot Licks Oct 19 at 23:16
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You can buy a tone wire tracer (sorry I don't know the name in English) in several electrical stores or online, their use is fairly simple, first remove all electrical power, then you attach the generator on one side and with the tip tool start moving around the wall to follow the path that gives you the loudest sound, with that you can follow the cable all around your house and trace it to the end

https://www.youtube.com/watch?v=UAEq-yvjryQ

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If you're turning off breakers one at a time and it's still registering a signal then there's possibly two circuits going through that switch box, there is a live wire behind the wall which is neighboring that switch box, or the switch's wiring is simply getting cross-talk from a neighboring wire somewhere before or after the switch.

You should turn off all breakers and turn them on one at a time. Once a breaker registers a signal then make note of it and turn it back off. Then continue turning on the rest of the breakers one at a time.

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