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I have a pre-existing #6-3 cable (without ground) with metal cladding on a 50-A two-pole circuit that was wired into a range. As shown in the photo, this cable has only black, red, and white conductors, plus a thin bonding wire. existing cable

I am replacing the range, and would like to provide a 4-wire connection, including ground (I'm aware that the 3-wire connection is legal, but the grounded option seems far safer to me).

Can I use the metal cable shield as the ground, even though it won't be nearly as conductive as a separate #6 (or at least #10) ground wire? If so, would I do that simply by making sure that the metal shield and bonding wire are securely attached to the metal box where the receptacle is installed? For easy installation of the 14-50R, I am hoping to use this product, which has a metal back with punchouts.

surface mount 14-50R outlet

If not, what is the simplest way to safely install the range? Can I run a #10 ground from the subpanel along the outside of the existing BX? Or would I need to replace the breaker with a GFCI in order to achieve the appropriate protection?

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  • GFCI <> grounding!
    – FreeMan
    May 5 at 15:19
  • @freeman I have already installed several 240v GFCI’s per customer requests, once in I could not remove them until my state did not adopt that part of the 2020 code (advice from an inspector) he did say he would approve if a ground was pulled. Just FYI depending on the stove or range the ignition circuit may trip the GFCI every time on a dual fuel or ? On all electric but customers not happy with 240v GFCI’s in several cases.
    – Ed Beal
    May 5 at 15:26
  • @FreeMan GFCI isn't the same as grounding, but my understanding is that if a GFCI breaker were used (and the receptacle labelled “GFCI protected / No Equipment ground”), it could offer adequate protection in place of grounding. May 5 at 15:27
  • @EdBeal we are installing an all-electric range. It's good to know that the GFCI might trip frequently in this situation. Do you know what the cause of that might be? For a dedicated circuit with only the range on it, I would have expected it would only trip for a legitimate ground fault. May 5 at 15:34
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    @rhymes_with_dorange NEC 406.4 that allows GFCI protection in place of ground has a note to check with NEC 250.114 for a list of equipment that requires grounding and therefore can't use those receptacles labelled "no equipment ground". A range is on the list. May 6 at 2:54
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Go ahead and install your receptacle, as you have a legal grounding path present

Since that "bonding strip" (bonding wire, really) is present in your cable, you have current-generation armored cable (Type AC), and the combination of armor and bonding strip is your grounding path provided you use an armored-cable fitting (with "redhead" insulating bushing or insulating liner) to attach the cable to your surface-mounted receptacle.

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    +1 Many people don't recognize Type AC cable when they encounter it, here is a good page from AFC (a manufacturer of AC cable) comparing AC and MC cable construction and the termination requirements. afcweb.com/wp-content/uploads/2015/06/mc-ac-installation.pdf May 6 at 3:19
  • @NoSparksPlease that's a great resouce—my cable matches up perfectly with the characteristics of Type AC cable it describes. May 6 at 23:45
  • You mention an "armored-cable fitting". I haven't found the right product using that search term. Is there another name I can use to search for it? I created a question around this (and the particular clamp that came with my receptacle product) here: diy.stackexchange.com/q/223699/83674 May 6 at 23:46
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If it is bx it’s not a valid grounding path under the NEC.

Yes you could run a separate #10 or larger equipment grounding conductor As allowed in table 250.122 this can be done at the panel or even at the grounding rod. But sizes smaller than #6 require protection. 250.130.C allows the new ground to be pulled and requirements to come from the same panel or grounding electrode system.

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  • When you say sizes smaller than #6 require protection, do you mean GFCI protection? May 5 at 15:29
  • Wire smaller than #6 the wire itself requires protection(conduit or a protected space) so sometimes we will run 6 to a box in the crawl space or attic then run the appropriate ground for the branch circuit from that box. Even though it is a ground splices require a box.
    – Ed Beal
    May 5 at 16:03
  • Got it, thanks. The surface-mount outlet I was planning to use only has 2 knockouts, one on the bottom and one on the back. If the BX comes in at the back knockout, does that mean I'll need to run the ground through the bottom one? May 5 at 17:31
  • I'm pretty sure this is modern AC (not old-style BX) due to the presence of the bonding strip/wire May 6 at 2:36
  • @threephaseeel I was not sure I thought that did look like a bonding strip but the op said bx the limit is 60 if 3/4 through 1-1/4” amp NEC 320.108, referring to 250.118. But if BX even if it has the strip as some late versions did before reclassification it would not be code compliant.
    – Ed Beal
    May 6 at 13:22

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