3-Way (Electrical Wiring) Confusion

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  #1  
Old 05-02-05, 01:39 PM
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3-Way (Electrical Wiring) Confusion

The stairs to my basement have a single light which is controlled by one 2-way switch at the top of the stairs and I want to replace this switch with two 3-way switches (one at the top and one at the bottom of the stairs). The light is mounted half way down the stairs on an octagonal junction box and when I open up this JB I have: One 14/3 cable with white, red and black conductors (lets called it cable A), one 14/2 with white and black (lets called it cable B) and another one 14/2 with white and black (lets called it C). Cable A is the power, cable B is going to the switch and cable C is feeding a wall plug in the living room which is always hot (with power). The copper ground cable is omitted here for clarity. I know how to wire 3-way switches but there is something on this JB wiring I don’t understand. The white of cable A is connected to the silver screw of the light fixture and then is connected to the white of cable C. The red of cable A is connected to the brass screw of the light fixture and then is connected to the black of cable B. The black of cable A is connected to the black of cable C plus to the white of cable B and that is the part I don’t understand. It is normal to have the black feeding power to the plug in the living room but why the white from the switch is also connected there and how would you go to wire the 3-way switches? Thank you all.
 
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  #2  
Old 05-02-05, 01:52 PM
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You have misidentified the cables. It is illogical that power is coming in on a 14/3. Cable C is the power feed. Cable A goes to the living room receptacle, and cable B goes to the switch. To confirm, look in the living room receptacle box and see if there is a red wire there. If you experiment, I believe that you'll find out that one half of that living room duplex receptacle may be controlled by the same switch. Report back on these.

Cable B is a switch loop. Code requires that the white of a switch loop be used to supply power to the switch, and the black bring switched power back.

All you need to do to accomplish your goal is to run a new 14/3 from the exising switch to the location of your new switch. Can you do that?
 
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Old 05-02-05, 02:02 PM
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It's theoretically possible that power comes in on the 14-3, but doubtful. I agree with John's assessment. But to be sure, investigate and find out where the 14-3 goes to.
 
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Old 05-02-05, 03:45 PM
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I verified and there is no red wire in the LR receptacle and both parts of the receptacle are unswitched. Yes I can run 14/3 from the existing switch to the new location. My 1st thought was also that the LR receptacle will be switched since the white from cable B is connected to the black of cable C but this is not the case. So what I did, I used the red from cable A as the power source and wired my 3-ways but had no power at the light but had power at the receptacle. Then I used the black from cable A as my power source and it works; light works from the 3-way’s and the receptacle in the LR has power. So for now I have capped the red from cable A and left it inside the junction box. I am still wondering why the white from cable B was connected to the blacks from cables A and C. Tomorrow I will verify if cable C is the power source and I will let you know. Thank you all.
 
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Old 05-02-05, 04:25 PM
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If you can run wire from the existing switch to where you want the new switch, then it makes no difference what the wiring is at the light. You should just run your new wire and leave the light wiring alone.
 
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Old 05-03-05, 01:38 PM
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To add a new switch and make this a three way setup you need to run a 14/3 cable from the existing switch to the new switch. It makes no difference what the wires are in the fixture. You can't do it from there anyway.
 
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Old 05-03-05, 02:57 PM
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As I suspected, cable C is not the power source. So I left it as I explained before with the red capped inside the JB and all work fine. Thank you all
 
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