I am renovating my bathroom. I am bringing in new circuits for all the electrical, and replacing the boxes.

I will have no problem capping off/removing the live (black) knob and tube wires in boxes.

However, I won't be able to cut the neutral/white wires back to boxes easily (they drop down from distribution boxes that are inaccessible in the 4" "crawlspace" between the ceiling joists and the roof rafters. Thank you, 1938).

Since they aren't carrying any power/voltage, is it OK to just cut them and leave them in place? Possibly adding a note so that the next guy knows what's happening? It's not ideal, but I have no other idea how to cut them back to a box without ripping out a lot of original plaster.

  • +1 for leaving a note. I wish the previous people had done that on wires they left under floorboards.
    – ChrisF
    Commented Oct 19, 2010 at 18:09
  • 1
    Do you have a whole new set of boxes, so you'd have one set with modern wiring and another set from the original? Or would the new boxes be in the same places as the originals, with the neutral wires terminating in them?
    – Niall C.
    Commented Oct 19, 2010 at 18:44
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    @ChisF: The note would say "Not sure what to do with these wires, so I'll just leave them for the next guy".
    – Tester101
    Commented Oct 20, 2010 at 13:51

2 Answers 2


I think it's very common to leave disconnected knob-and-tube wiring in the walls. Leaving a note sounds like generally a greate idea, but I didn't understand where you intended to put the note.

I think the most important thing is to label the circuits going out from your distribution panel so it's clear which circuits still have knob-and-tube wiring. If you know where the active knob-and-tube wiring is (physically), that would be great to document, too. It will come in handy if you ever consider blown-in insulation.

  • 3
    I would put the note in the distribution box, maybe even written on the inside of the door. Maybe on the back of the outlet and switch covers in the relevant rooms as well.
    – KeithB
    Commented Oct 19, 2010 at 19:08
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    Also might be a good idea if your leaving the wires to terminate the hot and neutral together, this way if anybody in the future tries to energize the lines it will trip the breaker.
    – Tester101
    Commented Oct 20, 2010 at 13:54

In Canada, you can leave old knob-and-tube wires in the walls, but you must treat them as though they are "live". You can cut them back to the nearest knob, with a couple of inches to spare, then double back the wire and tape it well to the wire on the other side of the knob. That will satisfy the inspector. If there won't be an inspection, then at least fold over the end of the wire and tape it.

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