old cloth bx to romex confirmation

I thought I had a thread already re some of the attic work I've been attempting. no bx coming out of the sub-panel on the 2nd floor. lots of bx in the attic.
I'm attempting to work backwards from some vintage boxes&bx to romex.
That's going ok.

I got thrown by a switched fixture where the fixture is in the middle of the continuing circuit ('why is the fixture black by itself?'). That bx run is 3-wire (essentially 2 blacks and a white) 1 black for continuing and 1 black back to the switch.

First question: Is there a replacement version of that in romex? (3-wire romex?). I'm thinking, if not, just run two romex and abandon one of the whites. Right or wrong? ok so that's two questions.

other sitch is half-assed. While tracing the circuit run through the cellulose I got back to another fixture which I need to replace. the old fixture was wired into my traced bx which then continued through with a further section of bx. But, also in that box was a another bx and is the end of some other circuit.

I want to -not- pull the bx out but just hang a a traditional 100w fixture with its own pull string (hallway light) on it.

The cloth on the wire ends is not good. I've found absolutely decrepit cloth insulation and quite good cloth. The decrepit stuff is usually in a box -- and especially in a fixture (incandescent heat destroys?).

I'm thinking I'd cut the bx back a foot or two and find better insulation. then junction that with a short run of romex to the fixture.

Second Question: you folks have any pointers on wiring the bx to romex while attempting to preserve whatever ground may be in that bx line?

Thanks!

Almost Funny back story: I was shocked to find that stray bx line was live. I then spent a good hour or two trying to figure out what circuit it -is- on. Never did figure it out.

The only way I can turn that circuit off is to kill the house main at the main
panel in the basement -- No sub-panel breaker controls it.

Its a peculiarity of This Old House. There are two sub-panels below the attic for what used to be two separate apts. When those subs went in someone forgot to bring that circuit in too.

Stranger still -- there's only one bx coming out of the main -- and that's to the boiler. I'm not running 3 flights of stairs for each of about 25 circuits to try and figure that one out. At least not today.

12 3 or 14 3 have a black red and white, that is the new for the old ones with two blacks.
Extra junction boxes should be ok as long as they don't get hiddin in walls.

Your box that won't turn off may have been a common, because they are common and might be live when something else is running.

thanks! was funny, after posting yesterday I went to the hardware store and looked at their romex. Something in my mind flashed on "I've used 12/2 and 14/2, but didn't I see 12/3? maybe that's relevant" ah there it is and there you go gauge/count.

Judging from you description, are you sure you were working with BX and not one of the evolutions of romex?

http://homerenovations.about.com/od/electrical/a/artbxwire.htm

Instead of cutting back, and adding a new Jbox, use shrink tubing to cover the offending wire. Can you confirm that you are working with BX (metal clad) cable or the old "cloth-covered romex"? If you are working with BX, you need to include the metal cladding as part of your ground.

Yup it is cloth with clad (bx). In one of my cut-back sitch's I wrapped the cloth with e-tape (it was in _good_ condition -- but I figured with all the handling and squishing to close the box I didn't want it going friable on me. And! I was successful in grounding the outlet (I reused one of those peculiar grommet things). That was exciting and at the same time distressing: Now I realize I probably screwed things up when I cut a bx in another wall in order to add a box to add a couple of outlets via romex 2 years ago before I really understood BX-- those outlets don't show ground, and the box, not only, might be plastic but is buried in a wall. I know where, just not excited about opening up the wall... Maybe, just maybe I've finally learned the lesson of do it right, now, or do it again and again... I'd wanted to remove that BX run then but was eager to get walls up.