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I have a pre-existing #6-3 armored cable (without a separate ground conductor), as shown here: existing cable

I am replacing the range this was connected to, and would like to provide a 4-wire connection via a 14-50R by using the steel armor cladding as ground (as discussed in Can I use the metal cladding of a cable as ground for this range installation?).

For easy installation of the receptacle, I am hoping to use this product, which has a metal back with a 1 3/8" punchout. The receptacle product comes with a strain relief clamp, but I'm unsure whether it's appropriate for making a ground connection to armored cable. Is this clamp OK to use? If not, what is the right sort of clamp to use in this situation? I've included some photos of the clamp: clamp clamp on box clamp on cable

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  • Even assuming it is legal in your area to ground via cable armor, you should examine your building and evaluate whether you can get a proper ground wire of correct size to that location. Depending on where you live you may have to cut open a path in drywall so an inspector can examine your work, or if it's particularly expensive to do that way, you may need to hire an electrician to do the work with a concealed work permit. Also in your picture there appears to be a bit of wire you're trying to pinch between the armor and the clamp. What is that for? – K H May 7 at 2:50
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    @KH I'm in California. Since this cable appears to be type AC, I believe it should be OK to use the armor as ground, per NEC 250.118(10). The bit of wire is the AC's bonding strip, which I've folded back over the armor (as I believe is typical practice, but I welcome corrections if that's wrong). – rhymes_with_dorange May 7 at 13:34
  • Hmm IT'S not clear where IT'S coming from. If it's a bonding conductor inside the cable, you would typically attach it to the ground screw in the box the cable terminates in. – K H May 8 at 0:55
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That is not the right clamp

The clamp/fitting you have is a two-screw type clamp designed solely for use with nonmetallic-sheathed cables (NM, UF, and perhaps SEU/SER). Instead, you need an armored-cable fitting that fits a ¾" KO and is of the right size to accept the outside diameter of your cable; there are several styles available, but the one you're most likely to find at a hardware or big-box store looks like the Arlington Industries 8402 depicted below:

Arlington 8402 photo

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  • It looks like the Arlington Industries 8402 is classified on their website in the "NM cable fittings" section. I have easy access to a similar-looking product, which is also labelled as NM. Is this one appropriate? What are the important characteristics that I should look for (and that the clamp I already have is lacking)? – rhymes_with_dorange May 7 at 13:42
  • @rhymes_with_dorange -- that fitting appears similar to an Arlington 4202 or 4203 but it doesn't seem to be listed for use with AC, just NM, for some reason. You might have to shop around a bit to find the correct part – ThreePhaseEel May 8 at 0:15
  • Seems like slim pickings available to a regular consumer. Would McMaster part 8180K33 work? Or is the snap-in connector not OK for grounding purposes? My receptacle comes with 1" knockouts, so I'll need to use reducing washers as well. – rhymes_with_dorange May 8 at 19:33
  • I guess if using reducing washers, the grounding acceptability of the snap-in connector is irrelevant, since I'd need to provide a separate ground path anyhow (reducing washers unacceptable for providing ground continuity). – rhymes_with_dorange May 8 at 19:58
  • @rhymes_with_dorange -- a snap-in connector is fine from a grounding standpoint, although it may not be compatible with a reducing washer since there's no locknut there to "bite" into the washer for good grounding continuity. Generally speaking, though, reducing washers are fine for grounding provided good metal-on-metal contact is made. Also, can you provide us with the OD of your armored cable? That'd help us tremendously when it comes to finding a suitable fitting... – ThreePhaseEel May 8 at 20:40

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