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Old 07-06-2009, 06:46 PM   #1
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strange wiring


Hi,

I'd like to solicit some opinions on what I'm dealing with here. I bought my duplex last year. By the entry ways of both units there are 3 gang single pole switches, one for the exterior porch light, one for the entryway light, and the other?

I've installed new recessed lighting in the living area and would like to use the unused gang so I don't have a dead switch and don't have to cut another hole in the wall.

I've only found two wires exiting the wall header in the attic. One is a 12/3 and the other a 12/2. The 12/2 goes directly to the entry way light. The porch exterior light must have been routed through the walls. The 12/3 wire is the supply. I'm not certain whether it makes another stop or whether it goes straight to the home run to the circuit box.

Here's what's strange. The black wire from the 12/3 is in series across all 3 single pole switches. The two known lights are wired as expected. But the third switch is wired to the red wire from the 12/3, thus when it is thrown, it connects red to black. What the heck is up with this? Both units are wired in this same exact manner.

Between black and ground with the circuit live, I'm getting 120v, but after disconnecting the red wire from the switch, I find that I get 25v between red and ground.

I haven't yet pulled the cover from the breaker box to try and figure out whether the red is actually connected to anything in there. Can anyone hazard a guess what the heck someone was trying to accomplish here? Is the 25v I'm measuring cross talk or something?

My idea, assuming that the red isn't actually connected to anything on the other end was to go up in the attic, and sever the 12/3 feed wire and route it into a jbox, and to splice the black/white/ground wires but to divert the red wire to a new 12/2 that will feed my new lights, leaving the red wire in the source 12/3 wire capped. Does this sound feasible?

Oh, there is also a 12/2 exiting the bottom of the box, which continues into the adjoining room, but I don't think that's relevant.

Thanks!!
Eric

Here's a photo...

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Old 07-06-2009, 06:53 PM   #2
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strange wiring


With the red wire off (or on turn switch off)Check all rec in room Top and bottom.The swich might be for a half-switched outlet

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Old 07-06-2009, 07:17 PM   #3
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With the red wire off (or on turn switch off)Check all rec in room Top and bottom.The swich might be for a half-switched outlet
I wondered about this also. It seems logical because the feed wire disappears into the roof line, presumably into another wall, before going to the service panel. No outlets in the whole room appear switched though. Even stranger, why would it measure 25v?

Last edited by everyman; 07-06-2009 at 07:20 PM.
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Old 07-06-2009, 07:34 PM   #4
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The red wire goes to your unknown device that the switch controls. Where does the other end of the 12/3 wire go? That is where you are going to find what this switch controls. Could it control an attic fan? A receptacle in the eaves for seasonal lighting? a yard light on the eaves?
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Old 07-06-2009, 07:41 PM   #5
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The red wire goes to your unknown device that the switch controls. Where does the other end of the 12/3 wire go? That is where you are going to find what this switch controls. Could it control an attic fan? A receptacle in the eaves for seasonal lighting? a yard light on the eaves?
Honestly I'm not sure. My ceiling pitch is very low and the wire disappears into the roof line and I can't crawl far enough to see where it either terminates or goes down into the exterior wall. I've checked around the house, and there are no exterior fixtures other than the porch light I mentioned and that's already accounted for. Nothing in the attic either. I think my best bet right now is to pull the panel cover and see whether the wire that is attached to the circuit breaker comes from a 12/3. If not then I'm guessing that whatever that red wire was meant to be used for was either deprecated or was never installed.

The 25 volt thing really perplexes me though.
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Old 07-06-2009, 07:55 PM   #6
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The 25 volts is probably phantom voltage. Are you using a digital meter?

Tihs is what it does.

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Old 07-06-2009, 07:57 PM   #7
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The 25 volts is what we call a "phantom voltage", and is due to the high impedance of the digital meter you are using and the close proximity of the measured conductor to live conductors. An electrical potential is being induced across the conductor because it resides within the electric field of another conductor. At the risk of sounding like the nerd I secretly am, an electric field cannot exist inside of a conductor because the free charges will redistribute themselves in an attempt to neutralize. This causes a measurable difference of potential, but will perform no actual work if you were to load it down and attempt to draw some current.

A "Wiggy" solenoid type tester will show whether or not a "real" voltage is present. Anyway, what else goes off when that circuit is turned off? Power is being brought to somewhere, taken to the switch on the black wire, and brought back to switch something. My first guess would be to look at the nearest and furthest receptacles, but it could be anywhere. My money is on one half of one obscure receptacle somewhere. Maybe a place where someone would put a cute lamp in a foryer.
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Old 07-06-2009, 08:17 PM   #8
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The 25 volts is probably phantom voltage. Are you using a digital meter?
Ah okay now I'm making progress. I pulled the two receptacles on the other side of the room. One is connected to a 12/2 (presumably from the service panel) and this is bridged to a 12/3 which jumps to the next socket, which has 12/3 in and out which then goes to the switches. In both of them, black is on the bottom and red on top.

So I'm guessing that some intrepid soul replaced the receptacles at some point, and was careful to wire them up just as they were, but didn't bother to break the union between upper and lower sockets. Sound reasonable?

I think I sort of solved the 25v issue as well. The incoming red wire to the second receptacle is fastened to the upper socket lug (and has 120v) but the outbound red wire to the switch is kind of half ass stuck into the locking hole (with about an inch of exposed wire), and only has 25v. So I guess it's making a crappy high resistance connection, or maybe it melted something inside the receptacle the first time the switch was thrown. What would happen if you fed 120 back in on itself as this person did?

So back to my original question, any reason I can't sever this wire and just utilize the red portion that goes into the switch wall to power my new lights? Since I added 2 new lights, I don't see a need for a switched socket.

Last edited by everyman; 07-06-2009 at 08:26 PM.
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Old 07-06-2009, 08:30 PM   #9
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A "Wiggy" solenoid type tester will show whether or not a "real" voltage is present.
Cool another tool to buy Little suckers aren't cheap, $50. I think that's what I paid for my whole multimeter. So basically these put a load on the line whereas my meter doesn't?
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Old 07-06-2009, 08:32 PM   #10
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I see that all the time, unbroken tabs on what are supposed to be switched receptacles. So, I would disconnect the red wire in those receptacles, to eliminate the parallel red hot wire, then use that freed switch for whatever you desire.
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Old 07-06-2009, 08:38 PM   #11
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Cool another tool to buy Little suckers aren't cheap, $50. I think that's what I paid for my whole multimeter. So basically these put a load on the line whereas my meter doesn't?
Right, it takes some real current to pull the solenoid down in those type of testers. Another home brew method, mentioned by Yoyizit, is to connect a lamp (say 60 W) across the wires in question, and simultaneously measure with your volt meter. If the voltage is real, and is capable of supplying current, it will still be present on the meter. If it is phantom, it will disappear when the lamp is in the circuit and the meter will read 0.

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