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As noted previously, my stove is currently on a grandfathered hot-hot-neutral circuit. I really should replace that with one that includes safety ground.

Currently (sorry) this is fed by an NMC cable presumably installed around 1965, which I am betting simply doesn't have a ground wire. (I need to open the box and check that. There seem to be no helpful markings on this cable; it has a white jacket if that helps at all.)

Assuming it doesn't... I presume I can not run a separate ground wire alongside it, and would have to replace this cable. The good(?) part would be that it'd push me to make sure the run, and breaker, are actually adequate for this stove. They probably are, since I was replacing an also-1960s stove with a higher-efficiency induction/convection type, but I really should confirm that.

TL:DR: is there any way to just add a ground to existing NMC in the US, or is that afterthought only possible when pulling the new wire thru real metallic conduit? It's just a ground, he says hopefully...

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  • From what I read on here, ground is the only wire that you can run separately. So you should be lucky if you do need ground. You might be lucky also with a 65 cable, more than an earlier age cable. Think I had stopped putting stuff(not plugs) into outlets by 65.
    – crip659
    Jun 21, 2023 at 19:11

1 Answer 1

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It depends on your wire.

  • If it is NM "/3 no ground", it will be black-white-red. If the cable is in good shape, retrofit a #10 ground and Bob's your uncle.

  • If it is NM "/2+ground" it was illegal the day it was installed. Leave it in place and run a new /3+ground cable. Why leave it in place? You might get separates later, and one probably doesn't need neutral.

  • If it is type SE, 2 hots wrapped in a bare mesh neutral, then take care to insulate the neutral from metal box etc. and retrofit a #10 ground same as above.

Surprise! My new range does not require neutral.

Well, that's a whole different kettle of fish, then. But not completely surprising. Really, the only thing in a range that really needed 120V was the oven light, because in the 20th century everyone had a house full of 750-2000 hour 120V incandescent bulbs, thus handy spares, and they work fine in ovens. This very stupid thing is the only reason we continue to kill children by using the 3rd wire not for ground.

So what if your new thing doesn't need neutral?

  • If it is NM "/3 no ground" you can obliterate all accessible insulation on the white wire, and this reclassifies it a ground.
  • If it is NM "/2+ground" that was illeg-- oh wait. That's fine! You're all set.
  • If it is SE type with mesh neutral, you can declare the neutral to now be a ground, and use it for that. Make sure to move it in your subpanel from the neutral bar to the ground bar.

Wait. Retrofit ground, you say?

Yes. They "legalized it" as of NEC 2014. Well, it had been largely so already; NEC 2014 just threw it open to every circuit instead of only certain ones. See NEC 250.130(C).

You can run a #10 ground wire (due to the oven being 25-60A) to any of the following places:

  • Any junction box with #10 or larger ground back to the panel
  • Any junction box with non-flex metal conduit back to the panel
  • The panel, obviously
  • Anywhere along the Grounding Electrode Conductor (that bare copper wire running to ground rods or water pipe). Never cut this! Use a split-bolt to clamp onto it.
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  • It made me so happy when my new cooktop didn't require a neutral. I had room in the conduit for it, but no reason to run the wire if I'm just going to cap it off in the J-box and hard wire the two hots and a ground from the device. It's nice to see sanity finally arriving for this one little area.
    – KMJ
    Jun 21, 2023 at 20:32
  • Nice to know about NM "/3 no ground". I now know not to answer you can never use white for for ground, if enough insulation is removed.
    – crip659
    Jun 21, 2023 at 20:37
  • If you answered your question "why leave in place?", I missed it...?
    – keshlam
    Jun 21, 2023 at 21:46
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    @keshlam thanks, fixed. Jun 21, 2023 at 21:54

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