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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

Merlin -they-them-
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    perhaps it operates an outdoor plug for christmas lights ... look for power outlets outside, up high – jsotola Oct 18 '20 at 02:11
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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. –  Oct 18 '20 at 13:23
  • Quite possible that your neighbours pay the electricity for that light. Is there actually a light anywhere controlled by that switch? – gnasher729 Oct 18 '20 at 18:43
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    @gnasher729 no it's not, OP confirmed that the switch loses power when the main breaker in the same house is turned off. – Z4-tier Oct 18 '20 at 18:46
  • Could it be for a ceiling fan? – JGH Oct 18 '20 at 20:27
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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 '20 at 21:37
  • No ceiling fans, and I know which switches work for the outside lights, but I had not considered an outside plug so I'll look for that. As for house age, it was renovated 8 years ago so and the switch is part of a 4-gang at the entrance, so I feel like it should go to something. But that's good to know a switch can just go to nothing – Merlin -they-them- Oct 18 '20 at 22:27
  • 4 gang at the front sounds like a light switch - or a switch for an outlet that the owner had a floor light on maybe? Doesn't help identify it of course, but that's where I'd be guessing. And - if the electrical was *really* done poorly, any chance it's actually on two breakers somehow?? – Joe Oct 19 '20 at 05:39
  • Could it be for a doorbell? – Andrew Morton Oct 19 '20 at 08:42
  • You're using a non contact tester? If so, I would also suggest switching to a regular tester that requires you to touch the contacts, like a volt meter. The non contact testers can be quite "generous". – PhilippNagel Oct 19 '20 at 13:25
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    So _that's_ why my living room lights keep flickering on and off... – FreeMan Oct 19 '20 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 '20 at 15:02
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    @Merlin-they-them- No, the previous owner probably installed the switch so they could control outdoor lights, an engine block heater, etc. Outdoor outlets can absolutely be on all the time. Make sure the circuit or the outlet, at least, are GFCI protected and that the outlet box is outdoor rated - this is required. You can remove the switch and connect the outlet directly with a wire-nut. The outlet box cannot be buried in the wall, though, so you'll need to install a blank cover over the box. – J... Oct 19 '20 at 15:25
  • Thanks! Good to know it's safe for them to be on always. It is gfci and covered so I'm good there. I still wish I knew which breaker it went to but I'm just glad to finally know what it does – Merlin -they-them- Oct 19 '20 at 17:48
  • Thank you for mentioning it had to be GFCI. That helped me figure out if was on the basement GFCI circuit. At some point, I'll move all outside lights/outlets to a separate circuit but at least I know what goes to what now – Merlin -they-them- Oct 19 '20 at 17:56
  • @TylerH just to emphasize your point about never assuming, I know a house (not mine) that has a power strip with the plug cut off wired into half of the electric stove 240v receptacle, to provide countertop 120v power for a coffee pot. Its absolutely horrifying, and also has been that way for 20 years. – nexus_2006 Oct 19 '20 at 18:15

4 Answers4

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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.

manassehkatz-Moving 2 Codidact
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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 '20 at 02:24
  • @JACK If you ever decide to put it to use, make sure that it is on a breaker of the appropriate rating for the wiring and your intended use. – sdenham Oct 18 '20 at 13:59
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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 '20 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 '20 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 '20 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 '20 at 01:44
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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.

Hot Licks
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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 '20 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 '20 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 '20 at 01:47
  • @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 '20 at 18:15
  • @mbrig It would be quite a Fluke if you could afford their gear for home use! – Loren Pechtel Oct 19 '20 at 22:45
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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 '20 at 23:16
  • @LorenPechtel heh, well, its quite a lot compared to a cheap multimeter, but ~210usd for a 117 is only the cost of a couple AFCI breakers. Could be worth it if you're doing a decent bit of work in the house. – mbrig Oct 21 '20 at 03:59
  • @mbrig A bit more checking shows the lower units don't have the Low-Z mode. – Loren Pechtel Oct 21 '20 at 21:52
  • @LorenPechtel I think the Fluke 114 is the cheapest one that has it. ~$150 USD. Not cheap but I know I've spent more on things that are less useful... – mbrig Oct 22 '20 at 02:30
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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

Chico3001
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0

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.

MonkeyZeus
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