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I have a knob-and-tube circuit in the ceiling of a basement of a 1941 house that was powering two lights and an outlet. Power comes in via a flexible armored cable and then the hot/neutral separate into the traditional air gapped layout. See photo below:

Metal Conduit

  1. Does anyone recognize the type of conduit, or the connector at the end?

  2. I thought knob-and-tube needed an air gap between the hot/neutral for safety, is the conduit safe with both conductors next to each other? Would this have been available and a standard practice when originally installed?

  3. Any concern with abandoning this entire circuit by cutting and capping the hot/neutral inside a junction box?

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    I suspect that is what is called BX wiring. I know the the hard way that if there is a short in a outlet box, the outer metal can become energized and carry load back to the panel. A breaker will not trip. There is a pretty good write up on the bx wire issue here:kuhlmanelectricalservices.com/…
    – jeffatrackaid
    Commented Jan 26, 2023 at 21:42
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    The biggest issue with abandoning the K&T wiring is reducing the fire hazard! (That's a Good Thing™, in case that wasn't clear.) If you're disconnecting both ends, you can cut the cable and push it out of the junction box - no need to specifically cap it inside. You may want to make additional cuts through the K&T at various places to ensure it's obvious that this is no longer in use and to prevent future use of it (not everyone knows or cares about code).
    – FreeMan
    Commented Jan 27, 2023 at 14:25
  • I'm a bit surprised to see k&t wiring in a 1945 structure. 1945 renovation of an older structure would be less surprising. (My place is ca 1889, but presumably was rewired several times since then.)
    – keshlam
    Commented Jan 27, 2023 at 15:40

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This wouldn't have been done when the K&T was originally installed. My guess is that there were renovations done elsewhere in the house that required the K&T to be replaced or a panel upgrade. Normally the K&T can't be terminated in a new panel so the greenfield flexible condiut and new wire were added to a junction box and then connected to the K&T you see there. If the basement wasn't renovated, the K&T could remain. That connector looks like a type of weatherhead fitting. There's no problem abandoning the circuit but you'll loose the lights. Upgrading it would be better and adding a ground.

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    I'm planning to pull power from a different circuit in the next room that is grounded romex. I'll wire new ceiling lights and outlets from that and abandon/remove the old stuff.
    – tbridge
    Commented Jan 26, 2023 at 21:53
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The corrugated metal conduit could be one of a number of wiring types: flexible metal conduit, armored cable, metal-clad cable, etc. The fitting shown was (and is) used where transition is made between conduit wiring and any type of open wiring, such as knob-and-tube (K&T). Such transitions were (and are) not at all uncommon in older homes, for instance anywhere the wiring had to emerge from concealed areas to connect with equipment such as furnaces or water heaters. There is no requirement for conducter spacing with K&T wiring where the wires are in boxes, enclosures, conduit, or where wrapped in the non-metallic flexible sheathing called "loom" widely used in K&T wiring. The insulation used on K&T conducters is perfectly adequate for such use.

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