+ Reply to Thread
Results 1 to 7 of 7
  1. #1
    Join Date
    Oct 2008
    Posts
    14

    Default Should I replace old BX wiring - is it unsafe?

    We recently purchased a house built in 1927. The main panel was updated to 200 amp. 75 % of the basement was finished and the master bedroom, main bath were re-done - each of them getting new wiring with Romex.

    However as I am working on the rest of the house I am finding that the rest of the house has the original BX metal sheathing with cloth wrapped wires inside the BX. The condition of the wires seems to be ok but I am wondering if I should bite the bullet and update the rest of the house?

    I know with BX it is important to make sure the metal sheath is grounded properly since that is the ground circuit, but I am uneasy about having an overloaded circuit heat up the cable and cause a fire.

    If I upgrade.... it is possible for most of the new lines to be fished through the paster walls or do they all have to be opened up?

    It is a 3 bedroom house about 1700 square feet, what would be a realistic budget to have this professionally done. (keep in mind that the basement, master bedroom and main bath are already done, so I have about 5 or 6 rooms left.

    Thanks in advanced!

  2. #2
    Join Date
    Jun 2007
    Location
    Shamokin, Pa.
    Posts
    645

    Default Re: Should I replace old BX wiring - is it unsafe?

    The BX cable is grandfathered in the NEC. As are many other wiring issues. I would think all woud be fine.
    But any remodeling would require upgrade to current wiring methods. Romex B, flex cable, EMT, what ever local codes allow.

  3. #3
    Join Date
    May 2008
    Location
    Pacific Northwet
    Posts
    1,360

    Default Re: Should I replace old BX wiring - is it unsafe?

    While you must ensure that the jacket of BX cable is grounded and makes continuity with all of the boxes it's connected to, I don't believe that jacket of BX cable is acceptable as an equipment ground for connected appliances. This means that you aren't supposed to replace two-prong receptacles with "grounded" receptacles (unless it's a GFI). Some BX cable has a strip of metal just inside the jacket; this I *think* is an acceptable ground, if the strip of metal is folded over the end of the jacket and tightly clamped by the box fitting. Modern armored cable contains a separate ground conductor (green insulated) the same gauge as the current-carrying conductors.

    Ernie Fergler is right, existing wiring is "grandfathered" if at the time of installation it was done according to code AND it has not been damaged AND you are not exposing it during remodeling. Once you open up a wall, though, most building inspectors will make you update any accessible wiring.

    My main concern with older cloth-covered wiring is the quality of the insulation. The rubber compounds will degrade over time, especially with heat, and become brittle and crack. Disturbing older wiring can cause the insulation to fail. Where it's impractical to replace it, you can at a minimum use heat-shrink tubing on the conductors within an electrical box to maintain the integrity of the insulation. And remember, it's safer to shrink it with a heat gun than a torch. Where cable is exposed, as in an attic, take measures to ensure that it can't wiggle around or be stepped on.

    Check with your inspector or code book to be sure. I might be wrong.

    P.S. -- with the oler BX armored cable, you have to consider that the effective conductor length of the jacket is around 2 or 3 times the length of the cable. The NEC doesn't consider the contact between one spiral and the next sufficient to be a grounding path. The cross-sectional area of the jacket -- when you unwind the spiral -- is about 1/3 that of 1/2" conduit. The resistance of steel is higher than that of copper. Combine all these factors, and you might find that your "ground" in a 12/2 BX cable is equivalent to a 16 or 18 gauge wire -- insufficient for a proper ground. Note that I'm just making a guess based on circumstantial evidence; I haven't researched this or done the math.

  4. #4
    Join Date
    Oct 2008
    Posts
    14

    Default Re: Should I replace old BX wiring - is it unsafe?

    Thanks for both of your replies, it sounds like I should be replacing it as I am working on the house but not urgent that I remove it all at once if it was properly installed. ( so sooner then later)

    Now that I take a closer look the main box only has 4 or 5 leads coming out of it that are still BX, but unfortunately it then splits several different ways and is powering 5 different rooms. I have to start tracing the line and see if I can use the same paths to run new wires. Since they were never done I am sure the are the difficult ones!

    Just an FYI someone at some point changed the outlets to 3 prong outlets.
    Last edited by Neun93; 12-15-2008 at 08:34 PM.

  5. #5
    Join Date
    May 2008
    Location
    Pacific Northwet
    Posts
    1,360

    Default Re: Should I replace old BX wiring - is it unsafe?

    Way back when, it was common to have just a few circuits, each providing power to several rooms. The typical service was 60A or less. When the only appliances were fans, irons, and a vacuum cleaner, and the only light in the room was a single 25W bulb, having lots of outlets on many circuits would have seemed wasteful. When electricity came to my grandparents' home on the Dakota prairie, they only saw fit to put a single outlet upstairs, and my grandmother had to fight for even that! But with the modern home having several small appliances in every room as well as computers, big screen TVs, home theater systems, and microwaves, having one or more circuits per room is not unthinkable. Many new homes over 2000 square feet have two large breaker panels totaling 400 amps!

    I say if the walls are open, take the opportunity to upgrade the wiring. Put in more than you think you need; it will be cheaper to do it now than later.

  6. #6
    Join Date
    Jun 2007
    Location
    Shamokin, Pa.
    Posts
    645

    Default Re: Should I replace old BX wiring - is it unsafe?

    Quote Originally Posted by Fencepost View Post
    While you must ensure that the jacket of BX cable is grounded and makes continuity with all of the boxes it's connected to, I don't believe that jacket of BX cable is acceptable as an equipment ground for connected appliances. This means that you aren't supposed to replace two-prong receptacles with "grounded" receptacles (unless it's a GFI). Some BX cable has a strip of metal just inside the jacket; this I *think* is an acceptable ground, if the strip of metal is folded over the end of the jacket and tightly clamped by the box fitting. Modern armored cable contains a separate ground conductor (green insulated) the same gauge as the current-carrying conductors.

    Ernie Fergler is right, existing wiring is "grandfathered" if at the time of installation it was done according to code AND it has not been damaged AND you are not exposing it during remodeling. Once you open up a wall, though, most building inspectors will make you update any accessible wiring.

    My main concern with older cloth-covered wiring is the quality of the insulation. The rubber compounds will degrade over time, especially with heat, and become brittle and crack. Disturbing older wiring can cause the insulation to fail. Where it's impractical to replace it, you can at a minimum use heat-shrink tubing on the conductors within an electrical box to maintain the integrity of the insulation. And remember, it's safer to shrink it with a heat gun than a torch. Where cable is exposed, as in an attic, take measures to ensure that it can't wiggle around or be stepped on.

    Check with your inspector or code book to be sure. I might be wrong.

    P.S. -- with the oler BX armored cable, you have to consider that the effective conductor length of the jacket is around 2 or 3 times the length of the cable. The NEC doesn't consider the contact between one spiral and the next sufficient to be a grounding path. The cross-sectional area of the jacket -- when you unwind the spiral -- is about 1/3 that of 1/2" conduit. The resistance of steel is higher than that of copper. Combine all these factors, and you might find that your "ground" in a 12/2 BX cable is equivalent to a 16 or 18 gauge wire -- insufficient for a proper ground. Note that I'm just making a guess based on circumstantial evidence; I haven't researched this or done the math.
    I would agree with your post, Fencepost. At one time, no longer allowed early Romex had a very small diameter ground wire as well. No longer allowed to be used in new work, as we both know, but still grandfathered just the same.

  7. #7
    Join Date
    Aug 2008
    Location
    British Columbia, CANADA
    Posts
    46

    Default Re: Should I replace old BX wiring - is it unsafe?

    Neun:

    I don't know if you are still following this thread that you started. I have the same problem that you do....older wiring buried in plaster walls and very difficult to replace.

    I replaced as much as I could and brought the accessible circuits up to standard. Where I could not easily get at the older wiring, I put the entire branch circuit on an Arc-Fault Circuit Interrupter (AFCI) instead of a standard breaker. At least that way, if arcing occurs in the circuit, then we have a greater chance of interrupting the power before a fire occurs. You can also split up some of the older circuits that have multiple branches....at least the electrical loads are reduced on the circuits that have older wiring.

    Hope this helps.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •