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| Subject - House Wired With BX; Grounded Recepts | |
| JimmyDee |
I have been asked a question about what to do in replacing receptacles in a house wired with BX. Can a grounded recept be used? If so does it have to be bonded to the box? It seems to me that the casing on BX is not a good ground. (old style, not the new kind with the ground wire in it. I want to not only give a NEC acceptable answer but also one that is 100% safe. Jim |
| SteveMc | Jimmy, if this actually AC cable that you have, then per 320.108, it can be safely used for equipment grounding. See also 320.120 to determine the type cable you have. |
| JimmyDee | quote: I think this is the newer stuff. The older BX that is in this house didn't have the internal bonding strip in it.  Jim |
| JimmyDee | quote: My next question is, does the older style BX (AC) without the additional internal bonding conductor, meet the requirnment for 320.108? I have my doubts. Jim |
| Electricmanscott | I would have no problem using that old stuff as a ground. There are probably millions of homes with this setup. I always thought that was one of the puposes of the armor. That old stuff needs no internal bonding strip. It is very well made as anyone who has worked with it will know. Install a bonding jumper to the box and you will be fine. |
| journeyman491us | ...Ummm Guys HOLD YOUR HORSES!!! ...First let me say this about first generation BX as I have some experience with it. If it does not have the internal metal strip you should not be quick to rely on the armor as a ground. It is a judgement call. Have you ever seen a high resistance short in BX??? It can glow like a toaster element!!!! If the BX does not contain that metal strip (sometimes reffered to as the "drain") it is not a good grounding path. If the BX is located in a damp area (such as a moist basement) it can be more dangerous than knob and tube wiring! Old BX without the bond strip can rust in between the wraps and turn into a heater element in short circuit conditions!!! I have seen service calls where this has happened (quite rare but possible) many factors involved...so educate yourself!!!! |
| JimmyDee | I have not seen this happen but my original electrical instructor said it was a common occurrence in the area that he worked. He stated that they stretched out a 30' piece of bx coil which would give you a piece of steel ribbon about 95' long. They shorted out the end of it feeding with #14 wire and a 15 amp fuse and it would not blow the fuse. 29' would blow the fuse. What was happening is people would install a 20 or a 30 amp fuse and if they had the hot touching ground, just like journeyman491us said, you have a hot toaster element. That happened after the coil corroded with whatever and no longer was a continuous shield but a 3.14 times as long steel coil ribbon. Lots of fires as a result. Jim |
| lctrc789 | If it does not have a metal bonding strip in it I would be very leary of using it for a ground alone. I know that there are probably a lot of older homes that rely on this I have seen 2 cases in 24 years that the ground became a heating element in both cases the house caught fire. If you do use the B/X or A/C as a ground you should still bond the box and the recpt. together to answer your question. |
| stedder | Have you ever seen the burn marks (you can tell the difference between them and dust) where AC has been tight against the joists and over heated, whether a bonding problem or a 30 amp fuse (or slug)on undersized wire? If only the customer could see it that decided it was too much of a hassle to stop overloading and just overfuse. As for safety, the best thing to do would be install a GFCI in the circuits and wait for the nuisance trips. |
| Energreen | What I'm getting out of this is that old bx is a greater hazard than I thought! Not only can't it be used as an equipment ground for the box and receptacle, but when it gets so old the conductor insulation starts crumbling.... well if it shorts to the termination connector the metal armor can heat like a toaster and start burning lumber! Can any inspectors out there tell me if I can run a single solid #14 ground conductor from the outlet box to the ground buss? (Instead of replacing the cable.) I know the code allowed this at some point. But where do we stand now? Thank you, EG |
| lctrc789 | yes you could run a 14 wire for ground to the bus or the nearest water pipe if you use the proper grounding device for the wire to ground to. |