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Effectiveness of 1920's armored cable ground

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    Effectiveness of 1920's armored cable ground

    I have a situation where a customer wants to replace some of the original two-prong receptacles in a house from the 20's. I understand the options available in Article 406.4 (D) and although AC does satisfy the requirements for an equipment grounding conductor in and of itself, I am concerned that it would be better to simply replace with two-prong devices rather than to install grounded devices and rely on the integrity (continuity, effective impedance, etc.) of the original AC wiring method. The cables are connected to the boxes with a snap-in connector (no lock-nut) and I just don't think I want to count on these to provide a very good bond (I don't even know if they were intended to provide an effective grounding means when they were designed or installed). If i were to install grounded devices, I couldn't even use a grounding pigtail because there are no tapped holes in the boxes to attach it. I would have to use a clip or self-grounding devices. I just don't like it and don't feel good about it. I will ask the Dearborn, MI electrical department, but I wanted your opinions first.

    #2
    If the house does not have a service change to a standard breaker panel, that would be my obvious first suggestion, suggest a service change and put the old BX they want to keep on GFI breakers.

    If the panel is there, GFI breakers is the obvious direction to move in. Small subpanel for the GFI breaker seems a waste of time relatively.

    The 3" x 2" switch receptacle boxes will be too small for the wire count to do any modifications. You may be limited to a wire count of two #14 ga plus ground. So if you want to stay grandfathered, you may be able to only replace what's there with same.

    The BX may be grandfathered for equipment grounding IDK, it's possible, but the loads will be sensitive electronic equipment along with vacuums and table saws.. If you want to spend the customer's money wisely, I can see changing what's there for devices with same device, move the circuits up to GFI breaker supplied, and running new grounded direct lines for the present heavy loads and leaving the old wiring for small light convenience type loads.
    Lasciate ogne speranza, voi ch'intrate

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      #3
      Originally posted by richwaskowitz View Post
      I am concerned that it would be better to simply replace with two-prong devices.......
      Two prong recpts or gfci is my opinion.

      There was a lenghty thread on this topic not long ago if you want some other opinions.
      If Billy Idol is on your playlist go reevaluate your life.

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        #4
        Thanks for the feedback. Sounds like neither of you like the idea of depending on the existing AC for a reliable EGC either (I don't). Is that what I am hearing?

        I am only talking about the general purpose outlets in bedrooms, living room and the ONE in the dining room. All kitchen, laundry, bathroom and basement receptacles are to be updated with new circuits.

        Comment


          #5
          Originally posted by richwaskowitz View Post
          Thanks for the feedback. Sounds like neither of you like the idea of depending on the existing AC for a reliable EGC either (I don't). Is that what I am hearing?

          I am only talking about the general purpose outlets in bedrooms, living room and the ONE in the dining room. All kitchen, laundry, bathroom and basement receptacles are to be updated with new circuits.
          Depending on the sheath of old BX for EGC is asking for a fire if a ground fault ever develops which does not trip the OCPD. Tales of red glowing BX can be found in some other threads.

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            #6
            If the BX or AC cable has a thin steel strip inside the armor and the connector is listed for grounding then the BX is suitable for use as an equipment grounding conductor.
            They say I shot a man named Gray and took his wife to Italy
            She inherited a million bucks and when she died it came to me
            I can't help it if I'm lucky

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              #7
              Originally posted by Dennis Alwon View Post
              If the BX or AC cable has a thin steel strip inside the armor and the connector is listed for grounding then the BX is suitable for use as an equipment grounding conductor.
              and it hasnt been hacked apart in previous renovations.

              tmk, MI has temporarily abandoned all nec req's for afci breakers. I've replaced 2 prong with the same, or gfci. I dont think they make tr 2-prong, but sometimes its about making it better, not right.
              Electricians do it until it Hertz!

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                #8
                There is no way I would ever trust old BX armor (without a bonding strip) as an EGC. I frequently observe corrosion at box clamp when I take apart or have to work on old BX systems, and deteriorated cable armor as well. Most of that old BX in my area was installed in the 1930's and has long since outlived its useful life.

                Comment


                  #9
                  Originally posted by GoldDigger View Post
                  Depending on the sheath of old BX for EGC is asking for a fire if a ground fault ever develops which does not trip the OCPD. Tales of red glowing BX can be found in some other threads.
                  Never saw it glow, but I've seen the spiral burn marks it left behind in rafters that remained after the fire was put out.

                  GFCI them.
                  Tom
                  TBLO

                  Comment


                    #10
                    Originally posted by richwaskowitz View Post
                    . . . AC does satisfy the requirements for an equipment grounding conductor in and of itself, I am concerned that it would be better to simply replace with two-prong devices rather than to install grounded devices and rely on the integrity (continuity, effective impedance, etc.) of the original AC wiring method. The cables are connected to the boxes with a snap-in connector (no lock-nut) and I just don't think I want to count on these to provide a very good bond (I don't even know if they were intended to provide an effective grounding means when they were designed or installed). If i were to install grounded devices, I couldn't even use a grounding pigtail because there are no tapped holes in the boxes to attach it. I would have to use a clip or self-grounding devices. I just don't like it and don't feel good about it. I will ask the Dearborn, MI electrical department, but I wanted your opinions first.
                    The Code minimum is that since the 1913 NEC, all armored cable installed (to Code) has been Type AC. Today's list of acceptable Equipment Grounding Conductors includes the "armor of Type AC cable," 250.118(8). I agree with your statement that I bolded above.

                    I have lived and worked in a Metro of 3 million souls all my career. Historically, local ordinances required all power and light wiring in new construction be encased in metal for work that was done from the Thirties into the Seventies. As a result there is a huge amount of housing stock in this Metro of 3 million that is wired with "BX". I can anecdotally offer that Minneapolis - St. Paul is NOT consumed by BX armor ground fault fires.

                    In fact, IMO, 406.4(D)(1) guides one to use the existing EGC of Type AC cable armor to provide for grounding-type receptacles.
                    Another Al in Minnesota

                    Comment


                      #11
                      Originally posted by richwaskowitz View Post
                      . . . there are no tapped holes in the boxes to attach it. . .
                      Greenlee markets a great all-in-one drill and tap that works well for this:

                      Another Al in Minnesota

                      Comment


                        #12
                        Originally posted by al hildenbrand View Post
                        In fact, IMO, 406.4(D)(1) guides one to use the existing EGC of Type AC cable armor to provide for grounding-type receptacles.
                        In fact?

                        Is that not a point of contention with many of us?

                        Comment


                          #13
                          Originally posted by iwire View Post
                          In fact?
                          In my opinion.
                          Another Al in Minnesota

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                            #14
                            because the bx has a snap in connector ill assume that its been messed with. does it in fact have the skinny AL ground in the cable? check at the panel. if so, great. if the cable is that old with the rubber/cloth insulation, don't be surprised if it gets a short after handling or bending it. in phoenix the heat just disintegrates the insulation. call backs, liability ect. could be whoever messed with it cut the ground at the conn...
                            I never do side work but one neighbor got me to help the old lady across the street when her indoor Edison fused panel mounted outside caught fire in a monsoon. EVERY damn bx (oven, swap cooler, gl's etc) disintegrated right in front of me! that was a long, long day. and made 80$ :/ I told ol lou, don't solicit work for me from retired public school teachers on a crappy pension!

                            Comment


                              #15
                              Originally posted by richwaskowitz View Post
                              Thanks for the feedback. Sounds like neither of you like the idea of depending on the existing AC for a reliable EGC either (I don't). Is that what I am hearing?

                              I am only talking about the general purpose outlets in bedrooms, living room and the ONE in the dining room. All kitchen, laundry, bathroom and basement receptacles are to be updated with new circuits.
                              i've seen a couple old installs around here that had a bond wire hitting all the boxes, not just kitchen and bath.
                              *if* there is a bare bond wire connecting the boxes, you may have a leg to stand on, but using the bx sheath
                              as an EGC isn't gonna get a lot of rave reviews here.

                              service change with GFCI on the old circuits sounds like your best bet.
                              i've put GFCI devices in to replace individual devices, with no daisy chaining,
                              but old, small boxes don't work well for that.

                              note: good luck with bending that old wire around with a service change.....
                              better you, than me......
                              ~New signature under construction.~
                              ~~~~Please excuse the mess.~~~~

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