2 wire cable to 3 wire cable on a switch

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  #1  
Old 06-25-14, 01:18 AM
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2 wire cable to 3 wire cable on a switch

Portland, Oregon, USA. House was built in 1945. Wiring in attic is both Romex, and knob-and-tube with 3 wires (black, white, red).

Installing a bath fan in a new location. When trying to feed new wire through the attic to the bathroom wall for a new switch, I drilled a hole through a thick board, a few inches away from the old source wire. I did this with the breaker off. When I was done drilling the hole, I flipped the breaker back on and only the power in my sonís room came back on, not the power to the bath or kitchen lights. (Iím guessing that breaker runs power to my sonís room first, then the bath, then the kitchen. Though I donít know how son's room could have a complete circuit on the same breaker as an incomplete circuit)

So, I assumed I drilled through a cable, or part of a cable so I opened up the drilled area a little more to investigate. The challenge is that everything in this part of the attic is cramped and difficult to reach, to see, fit tools, etc. A recip saw made the decision for me and cut the source cable. No big deal. I spliced it with new #12 cable into a box and it tests fine at 117v. From the bath, I yanked the old source cable and fed the new source cable to replace it.

After hours of running back and forth, testing and troubleshooting, I was out of my mind around 12:30am last night and before yanking the old source cable I unhooked everything at the switch without marking it (I know, sharp as a bag of hammers. I can picture my grandpa having a good laugh at this). This is where I'm stuck, I think because the source wire is black-white-ground whereas the rest of the run is black-white-red (the old K&T cable).

And now, Iím just trying to get the original switch and bath light working again with the new source wire but I canít figure out how the two source wires, switch, and three K&T wires need to be connected. I tried:

1. white source pigtailed to white; black source pigtailed to black and connected to switch, red connected to switch
2. white source pigtailed to white; black source pigtailed to red and connected to switch, black connected to switch

I donít see what other choice there could be unless someone mixed the white with either red or black. I have a multimeter, but Iím mainly familiar with checking voltage. I considered the possibility that I drilled through part of the remaining K&T cable, but I managed to angle a camera inside the wall and saw the cable is intact. Nowhere near where the drill bit popped through. This image shows attempt #2 described above.
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  #2  
Old 06-25-14, 03:35 AM
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Ungrounded cable can not be extended. It sounds like your new source cable extended an ungrounded cable. Since there is no real code compliant way to fix this and you don't understand exactly how it was connected the quickest and simplest is to rewire from the breaker box abandoning what you don't understand. In the days of knob and tube whites were some times switched which might partly explain the white wire. Regardless if I was doing it I would just run new.

Things to consider under current code:
  • The bathroom receptacle must be a 20 anp circuit.
  • Your bath fan can be on that circuit.
  • If your bath fan is on the bath circuit the bedroom can't be.
  • You bath room fan can be on the bedroom circuit instead of the bath circuit but you need to run a second circuit for the bedroom since a the cut circuit can't be extended if ungrounded.
 
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Old 06-25-14, 10:52 AM
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Thanks for the response, Ray2047. I can run a ground wire to the new box in the attic, or run a whole new cable from the breaker box to the switch in the bathroom, but then I'm still stuck in the same spot. Only now I have a grounded source. I plan on doing more work to upgrade the wiring but for now I need lights and a working fan in the bath to clear the humidity. I don't have time right now to pull all the old wiring, of which there is a lot, and reconfigure the whole circuit. Everything I add is going on 20 amp. I do appreciate the code considerations you listed and I will work toward that goal. Is there any other guidance you can offer on the mystery wire?
 
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Old 06-25-14, 08:31 PM
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Never mind. I figured it out. The switch I was using died sometime in the process, and there was a bad leg of old cable. Power is restored.
 
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Old 06-25-14, 08:42 PM
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Thanks for letting us know the outcome
 
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