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I have some of the exterior walls of my 1950's house open to insulate and am contemplating taking the opportunity to run a ground wire. The sheathing on the original wiring is mostly in good shape but kind of fragile and at least the outer woven layer crumbles easily. That said the insulation on the individual hot and neutral wires is in good shape. Being an older house the wires are also a heavier gauge copper than the 12 gauge romex I see strung through most modern houses.

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For those reasons, I'd like to run a bare ground next to the existing wire instead of completely new wire, but I was told that that might not be necessary as GFCI breakers added to each circuit might effectively accomplish the same as a ground wire. Is there any truth to this or is now the time, with the walls open, to run the extra wire?

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  • I know with GFCI receptacles without ground wire(like yours), you just need to add label(non equipment ground) to it. I think you do run into problems of not having a ground wire with stuff like surge protectors that do need the ground wire to work/protect right.
    – crip659
    Commented Jun 25, 2023 at 17:49
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    Does that last photo show an all-metal staple? If so - I would be VERY unhappy about that, particularly since the insulation of the cable is starting to fail.
    – MikeB
    Commented Jun 26, 2023 at 8:30
  • Fair point, @MikeB, however that's what was installed in the 50s when this cabling was installed. Don't forget, each wire within the cable is also individually insulated, so while this may be annoying, it's not a critical issue.
    – FreeMan
    Commented Jun 26, 2023 at 17:04
  • Bruh, "The sheathing on the original wiring is mostly in good shape but kind of fragile and at least the outer woven layer crumbles easily." definitely means they are not in good shape. Run new wire since you have the walls open. Consider abiding by both GFCI and CAFCI rules if you're replacing breakers.
    – MonkeyZeus
    Commented Jun 27, 2023 at 17:19

4 Answers 4

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If I were you I'd replace cables that you can access, and when you reach a cable run you can't fully access, retrofit ground to that box. Retrofitting ground is legal per 250.130(C). DON'T go to a water pipe.

Also, consider metal boxes. They're safer and also often cheaper. You can get very inexpensive screw-down cable clamps that go into the round "knockouts" and those clamps are much easier on the wire.

GFCI is a legal substitute, but I think if the AHJ knew you had the walls off they would tell you to do the above. Also, GFCI breakers are costly. I think you're just confused about this wire and thinking it's special wire or something.

You will also regret not having grounds when you go to plug in electronics.

Being an older house the wires are also a heavier gauge copper than the 12 gauge romex I see strung through most modern houses

No, they're not. They weren't particularly wasteful of metal back then. It's postwar, there are metal shortages all over the world because Europe is rebuilding. You might possibly mean that these are 12 gauge, as contrasted with the thinner 14 gauge that you find in any "builder tier" bedroom or living room circuit today.

But that's fine. I install all 12 gauge, I don't even use #14 because the cost of carrying inventory and hauling around the extra spools of wire exceeds the per-foot savings (as little as I use it).

15A circuits require #14 copper.
20A circuits require #12 copper.

Mid 1950s is a tiny bit early for aluminum wire, but that is a thing. It requires -2 larger wire size for the same thing (so #10 for 20A) and that looks larger because it is. There is also "copper-clad aluminum" which looks copper but isn't. Look close at your wires end-on. That old AA-1350 alloy was brittle as heck and tended to break under handling.

So no. 70-year-old insulation doesn't owe you anything.

The sheathing on the original wiring is mostly in good shape but kind of fragile and at least the outer woven layer crumbles easily.

Then it's not in good condition and it cannot be reused. See that bit where you have loose wires with no sheath at all outside a box? And a plastic box whose awkward, molded-in cable "clamp" is not approved for old style wires, and is simply going to destroy what's left of that old sheath.

Unless you plan to just run the bare wires in the walls like in the photo? No.

Any shortcuts you do today will be concessions you'll be taking on the sale price when you sell. Remember you must declare the defect on the seller disclosure and sign it.

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If the only reason you want to keep the existing cables is that you think they are superior to new ones ... they are not, you should replace them. Having the walls open is a great opportunity to bring the wiring 75 years into the future. Also, now you can easily add new outlets in convenient locations and, if desired, exterior outlets if the locations happen to be right.

If you have access to the cabling from this room down into an unfinished basement and all the way to the breaker panel, you absolutely should replace them. If the cable disappears into walls that you are not breaking open, it's not so simple, but you should try to find ways to do it.

To answer your question: If you have the ability to properly add ground wires, you can do it either way. From a safety perspective they are both good.

There are some subtle differences.

  • A real ground will pop a breaker immediately if there is a hot-to-chassis fault in equipment. A GFCI will wait for a human to touch the chassis and complete the circuit to earth!
  • A GFCI will protect humans from hot-to-human faults NOT involving a chassis, notably ones through water. A real ground will not do that unless/until the current through the human is enough to pop the breaker at its current limit.
  • Where water is a high risk, even with a copper ground wire you can (or must) add GFCI outlets.
  • A real ground is required by some equipment for non-safety reasons such as noise reduction (audio equipment) and surge suppression (electronics).

So ... replace the cables and add GFCI outlets where required for wet conditions.

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It is true that you can hook up GFCI without a ground and get protection because the GFCI measures an inbalance in the current between hot and neutral. The problem is that any equipment plugged into that outlet won't be grounded. So you'd need to run a ground wire.

Depending on how many walls are exposed, you should consider, and it may be required, replacing the cloth wire with NM cable. I'd be curious to know your measuring method to determine that #12 copper in cloth wire is larger than #12 copper in NM cable. The insulation in the old cables might be thicker but the newer types of insulation are superior to the old types. You already mentioned that the outer layers crumble easily. The ends of the old wire in junction boxes are always a problem to work with. This is the time to do it.

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  • Subjective comparison was my only measure. I've added some runs on an existing circuit on other walls and the white (#12 ?) romex I used has slightly narrow stripped wires, than the stripped wires you see in the photos. I assumed they were #10.
    – Conner M.
    Commented Jun 25, 2023 at 18:57
  • If you were using new romex and it had a white sheath, that was most likely 14AWG. New 12AWG is yellow. Decades ago they were both white.
    – jamesbtate
    Commented Jun 26, 2023 at 17:26
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GFCI breakers added to each circuit might effectively accomplish the same as a ground wire.

I'm just going to focus on this part of the question because I feel it's important to point out this is completely false. They accomplish two different safety features, but they work even better when used together.

JACK's answer addresses this well:

It is true that you can hook up GFCI without a ground and get protection because the GFCI measures an inbalance in the current between hot and neutral. The problem is that any equipment plugged into that outlet won't be grounded.

But to expand on this:

Say you plug in a typical electric fan, one that has a metal case.

The purpose of a ground wire is to ensure that the case (and any other metal parts that aren't supposed to have electricity flowing through them) is grounded. That means that if any fault occurs that lets a hot wire touch the case (or other grounded parts) - which is definitely not supposed to happen - the electricity conducts to ground.

Without a GFCI, if the fault current is high enough it should trip the breaker, shutting off the circuit and preventing you from getting a shock off of it - but this will only happen if the current is high enough, so if there's enough resistance in the fault circuit then it might not trip and you could still get a shock. But with a GFCI, you only need a tiny current for it to trip - usually a few milliamps, rather than tens of amps for a breaker - so combining both a ground wire and a GFCI is always the best option.

If you have a GFCI but no ground wire, and this fault occurs, then the case will become live (hot) but the breaker won't care, and the fan will appear to operate as normal. If you touch it, and you're isolated from anything else, you probably wouldn't notice - but if your body made a circuit between the live case and ground somewhere else, the GFCI would most likely break the circuit then, but that may or may not be after you feel the shock. With neither GFCI nor ground, that shock would go on as long as you held on to it - so a GFCI on its own that breaks the circuit after a fraction of a second is definitely better than that, but again, combining both a ground wire and a GFCI is always the best option.

(I'm writing from the UK, but I do believe all the above is equally correct for US electrical systems - though our voltage is higher so we have more harm to suffer if something does go wrong!)

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  • @Rohit Gupta Thanks for your edit, but these weren't typos, so I rolled it back. "inbalance" was part of a quote from another user, so I don't think it should be corrected here. "Conducting to ground" is a common phrase in electrical engineering - "conducting to the ground" might sound more grammatically correct but we never say that in this context IME.
    – Keiji
    Commented Jun 26, 2023 at 12:39

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