Posting here because I'm guessing there might be a few electricians on here.
Yesterday, I helped a friend rewire his bathroom. Job was pretty straightforward, except when I went to splice into an existing run of BX (from the early 40's) in the attic, I found the insulation was incredibly brittle, and had apparently melted, fused to the cloth and paper, and literally crumbled in my hands when I attempted to pull off the armor to make the splice.
My initial theory was that this wire had experienced a significant overload, looking at what appeared to be evidence of a small fire in the wall in the distant past (downstream, but on the same circuit, with the original wiring having been replaced with Romex in that area). Obviously, once I saw the condition of the insulation, my original plan of reusing the original BX was out the window and we cut a couple holes in the adjacent wall to replace that BX entirely with new Romex. How this ran was breaker box -> receptacle in bedroom -> up into attic, then to wall light in bathroom. It was the last run that was badly disintegrating when we messed with it.
Oddly, the BX from the wall receptacle to the breaker box was in fine shape, and we left it, as the breaker panel will be replaced soon anyway so I told him to just ask the electricians to replace that run then.
Now my current theory is that this degradation of the insulation was simply caused by the heat of the attic (this was near the side of the house, so the roof was maybe a foot above this run of BX at the point where I was trying to splice it) which is OK ish. I know that when Romex was first introduced the insulation was rated at 60C and today (and for the past few decades) it's been rated at 90C, so I am comfortable that what we did will last for many decades to come. I have no idea if there even was any such rating back in 1940-whatever when this house was built. However, this prompts the question, does this mean then that we should be planning on replacing pretty much any run of BX in the attic if it is in any way touched? It seems like that's the prudent plan to operate on. The good news is that I have been advising him and it sounds like the electricians he's called for the panel replacement are savvy as well and we are all in agreement that we will be using AFCI breakers nearly universally (and the dedicated circuits that would be exceptions are likely all going to be pulled using new cable anyway) so there's some protection there until we can get the job all done.
Yesterday, I helped a friend rewire his bathroom. Job was pretty straightforward, except when I went to splice into an existing run of BX (from the early 40's) in the attic, I found the insulation was incredibly brittle, and had apparently melted, fused to the cloth and paper, and literally crumbled in my hands when I attempted to pull off the armor to make the splice.
My initial theory was that this wire had experienced a significant overload, looking at what appeared to be evidence of a small fire in the wall in the distant past (downstream, but on the same circuit, with the original wiring having been replaced with Romex in that area). Obviously, once I saw the condition of the insulation, my original plan of reusing the original BX was out the window and we cut a couple holes in the adjacent wall to replace that BX entirely with new Romex. How this ran was breaker box -> receptacle in bedroom -> up into attic, then to wall light in bathroom. It was the last run that was badly disintegrating when we messed with it.
Oddly, the BX from the wall receptacle to the breaker box was in fine shape, and we left it, as the breaker panel will be replaced soon anyway so I told him to just ask the electricians to replace that run then.
Now my current theory is that this degradation of the insulation was simply caused by the heat of the attic (this was near the side of the house, so the roof was maybe a foot above this run of BX at the point where I was trying to splice it) which is OK ish. I know that when Romex was first introduced the insulation was rated at 60C and today (and for the past few decades) it's been rated at 90C, so I am comfortable that what we did will last for many decades to come. I have no idea if there even was any such rating back in 1940-whatever when this house was built. However, this prompts the question, does this mean then that we should be planning on replacing pretty much any run of BX in the attic if it is in any way touched? It seems like that's the prudent plan to operate on. The good news is that I have been advising him and it sounds like the electricians he's called for the panel replacement are savvy as well and we are all in agreement that we will be using AFCI breakers nearly universally (and the dedicated circuits that would be exceptions are likely all going to be pulled using new cable anyway) so there's some protection there until we can get the job all done.
