Replies

1. 
   Mongo | Feb 09, 2014 05:58pm | #1

   3-way?

   Is it a 3-way switch? With 3-way (or 4-way) there is no real right side up or upside down for the switch.

   How many wires are wired to the switch? What color are the wires? Any other wires in the box that aren't wired to the switch? If so, what colors?

   Have you checked to see if the switch controls an outlet in the room?

2. 
   DanH | Feb 09, 2014 06:08pm | #2

   Your basic "2-way" light

   Your basic "2-way" light switch has two terminals on it.  Juice comes from the breaker panel, into one terminal, out the other panel, to the bulb, back to the panel.

   When the switch is "closed" (turned on) the insides of the switch connect the two terminals to each other, so there's zero volts between them.  When the switch is "open" (turned off) the two terminals are not connected to each other, so any external voltage applied will appear across the terminals.

   Assuming a non-burned-out bulb is installed in the light fixture and all the wires are properly connected, when the switch is open/off the resistance of the bulb will be much lower than the (infinite) resistance of the switch and the (nearly infinite) resistance of the tester, so the tester will glow and the lightbulb won't.

   If the bulb is removed or burned out or there is a fault in the wiring the tester may still glow weakly due to capacitance between the wires feeding the bulb.

   If instead of testing across the switch, you test between one terminal of the switch and the ground wire inside the box you will get a more valid reading.  The terminal connected to the breaker panel should always show "hot" if the breaker is on, and the terminal connected to the lightbulb should show "hot" if the switch is turned on.

1. 
   jyang949 | Feb 11, 2014 01:01pm | #6

   So this doesn't indicate a problem

   The glow is not weak, so I'm assuming that there is no burned-out bulb or disconnect along the circuit.

   I'm getting the impression that mystery switches are not uncommon! Well, I still don't know what the switch connects, but at least I discovered some shoddy connections inside the switch box and took care of those. 

   Janet

2. 
   jyang949 | Feb 11, 2014 01:08pm | #8

   Outlet v. receptacle

   Is an outlet the same as a receptacle? Which term should be used to describe the thing the power cord gets plugged into? 

   Janet

1. 
   calvin | Feb 11, 2014 07:35pm | #9

   Janet

   I'll vote that there's no difference-at least to the common man/woman.  Regional difference perhaps-technical-maybe.

   But there's another possibility for not finding what that switch powers.  I found this not long ago and think I"ve seen it b/4.

   Someone remodeled and decided they didn't want that ceiling fan-perhaps a ceiling fixture.............or sidelights..............whatever.

   So, they capped the wires and covered the box.  Illegal and you can see why, but it is done and was done.  We found the ceiling fixture location (centered two ways in a former dining room) by locating where "we'd" have put a light and using a tick tester (the beeping type) ........sweeping the area around that ceiling.

   Sure enough, it beeped where a fixture was likely put a while back.  Couldn't tell, the patch was good.

3. 
   mikeys | Feb 10, 2014 09:28pm | #3

   I would check if the switch controls an outlet.

1. 
   Condoman | Feb 11, 2014 09:53am | #4

   Or in some cases only 1/2 of an outlet.

4. 
   mikeljon | Feb 11, 2014 11:08am | #5

   also check..

   Second vote for checking the obvious control of an outlet/half an outlet.

   Plus: We recently bought a house and, after working to replace the vast number of burnt out flourescent fixtures (the previous owner was an eco-guy who put in all flourescents in the 80s), there were still a few switches that didn't seem to control anything. Turned out, they were three way switches to control exterior lights. Bulbs were burnt out, and for most of the circuits, one switch was upstairs and another was downstairs. Four sets of lights and eight switches on each side/floor of the house. It took me a while to figure that one out. Of course, the bulbs were two stories up, and a few had rusted into place (if you're going to install these, put them by a window so they can be changed more easily than climbing a ladder!).

1. 
   jyang949 | Feb 11, 2014 01:06pm | #7

   Half-switched outlet

   I considered the possibility that the half-switched outlet was mistakenly replaced with a regular one. That would make it always "on," right?

   So, I broke the tab between screws on the outlet. Now, one of the outlets doesn't work at all<sigh>. Don't know what I did wrong. It was the tab between the brass screws, not the silver-colored ones.

   Janet

1. 
   DanH | Feb 11, 2014 08:08pm | #10

   Well, obviously if there weren't wires on both brass screws then breaking the tab will result in disconnecting one outlet.  And when there are wires on both screws it's usually because the outlets are being "daisy chained" and the second wire is feeding an outlet further downline.

   You'll rarely see the tab broken (intentionally, at least).  When it is it's usually because the outlet is conveniently placed for a table lamp that one might want to control from the wall, and this would be rare in a room with an overhead light.  We have only one such outlet in our house, and it's in the living room, with the switch at the top of the stairs entering the living room.

   (You can fix the goof by simply adding a short piece of wire between the two screws.  Or I've once or twice seen brass strips cut and formed to fit between the screws.)

5. 
   Geoffrey | Feb 15, 2014 09:39pm | #11

   Janet,

   What you have is a single pole switch, which has two side terminals and a ground terminal screw,

   They also are marked "on" and "off" at the base of the toggle. On "Decora" style switches there are no markings for "on" or "off"

   Since you have no power  on the tester when the switch is in the "on" position it means the line coming in is "hot ". and the cicuit is being completed, thus the tester won't read a completed cicuit, but when the switch is "off" the cicuit is open and the tester is completeing the circuit, causing the light to glow on the tester.

   This switch is possiblely  operating an outlet, check nearby outlets by plugging in a lamp that is known to be turned on, then if

   you come across an outlet that the light does not light up, go  throw the switch in question to the "on" position and see if it lights the lamp.

   Also you could check in the attic to see if there's any lighting, or check the outside for a yard light possibly.

   As to the outlet you "broke" don't use any of the "fixes" suggested earlier,  just install a new outlet and save yourself some real potential headaches.

   Hope this is of some help,

   Good luck,

   Geoff

1. 
   jyang949 | Feb 16, 2014 12:42pm | #12

   There is no ground terminal screw--

   —I guess because most of the stuff in the electrical boxes is old (the house was built in 1932). There have been some modifications over the years and, to be honest, I doubt that permits were acquired or inspections done. I want to correct things were not done properly, but little information is available. 

   What, for example, is the meaning of large asterisks penciled in next to two circuit breakers? Something important enough to flag, but not quite important enough to explain? 

   Anyway, this particular mystery switch (there is more than one) is wired like this: 12568501533

   Perhaps there used to be an overhead room light, then the light but not the switch was removed.

   Since I haven't figured out any of the mystery switches  :( , it would probably be a better use of my time to document which circuits control which outlets/fixtures, and tape the list to the circuit-breaker box. More informative than giant asterisks. 

   Janet

1. 
   DanH | Feb 16, 2014 02:39pm | #13

   That is a somewhat bizarre setup.  Do you know which cable power comes in on?

   My best guess is that power comes in on the bottom cable.  Then the top right cable would be switched power to somewhere and the top left cable would supply both switched and unswitched power to somewhere.  Not much of a clue as to what "somewhere" might be, though.  Not particularly consistent with a fan switch set up, eg.

   In terms of figuring out what goes where, be aware that there are various devices for sale for "contactless" wire tracing.  Basically, these inject an RF signal on the wire and then you sense the wire with a hand-held probe.  When I last tried one about 15 years back they were kinda iffy in terms of reliability/effectiveness, but likely that has improved somewhat over the years.

1. 
   jyang949 | Feb 17, 2014 11:52am | #14

   Don't know where the power enters

   I'm not sure what is bizarre about it—too many cables?—but I'm not surprised.

   The closest outlet to the switch looks like this: 12592664703. I've seen wiring diagrams with one and two cables entering the box, but not three. Is this common?

   Janet

1. 
   DanH | Feb 17, 2014 06:25pm | #15

   That's perfectly normal -- power comes in and Ys off in two directions on exit.  All white connected, all blacks connected, nothing unusual.