What is an acceptable way to ground receptacles branched off of an old 2-wire electrical circuit?

Question

I have a house built in the '50s, and some of the runs are done with what appear to be original 12/2 cloth-sheathed wire without a grounding conductor (just hot and neutral). I'm looking to install some new outlets on this circuit, and want to branch off an existing splice with modern 12/2 NM wire with a grounding conductor.

Is it acceptable to run a grounding conductor from my new splice to the nearest other splice that has a grounding conductor on a separate circuit? If so, are there any considerations for the wire that is needed, i.e. insulated or bare? If running a bare solid copper grounding conductor from box to box, does it need to be stapled?

Here is the part of the NEC which I think is applicable, especially 250.130(C)(1)

250.130 (C) Nongrounding Receptacle Replacement or Branch Circuit Extensions.

The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following:

(1) Any accessible point on the grounding electrode system as described in 250.50

(2) Any accessible point on the grounding electrode conductor

(3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates

(4) An equipment grounding conductor that is part of another branch circuit that originates from the enclosure where the branch circuit for the receptacle or branch circuit originates

(5) For grounded systems, the grounded service conductor within the service equipment enclosure

(6) For ungrounded systems, the grounding terminal bar within the service equipment enclosure

See this diagram for reference as to what I'm trying to do. Box 1 is a junction in the circuit I'm branching off of (it used to power an old doorbell transformer that has since been removed), and Box 2 is a junction on a separate circuit (same amperage).

Im in Denver which follows the 2020 NEC. Thanks in advance.

Answer 1

As long as the donor is large enough, you're fine

Your proposal works under NEC 250.130(C) as long as the donor circuit's grounding wire (EGC) is as large or larger than the required grounding conductor size for the recipient. (In other words: larger circuits can donate to smaller ones, but smaller circuits can't donate to larger ones, at least when dealing with cable wiring methods.) You can use an insulated (green) or bare wire provided it is large enough and protected from physical damage by way of being run inside building cavities. However, the Code isn't clear about how such a wire is to be run, though; I'd simply support it in the same fashion as a NM cable.

Answer 2

Your plan is perfectly fine - basically retrofit ground via any reasonable route (bare or green wire, totally new or connecting to an existing grounded location).

But there is another alternative, which can actually be better in some ways:

GFCI

A GFCI (Ground Fault Circuit Interrupter) is required in certain locations - kitchen (with some very specific exceptions), bathroom, garage, laundry, outdoor - primarily where water is a realistic concern, because water, electricity and humans don't work together nicely.

A GFCI works by watching for an imbalance between hot and neutral. The implication is that nay current not going between hot and neutral is going to ground (either ground wire or physical ground) and may be doing so through a person. A GFCI stops incredibly quickly - faster than a regular circuit breaker (except under very high current situations) - in order to save lives and prevent serious injuries. A nice side-effect is that if there would have been current going through a ground wire, had the circuit been properly grounded, a GFCI would trip. Effectively, the GFCI actually replaces the primary use for a ground wire. There is a secondary use for a ground wire, which is to handle additional current such as static, surges, etc. The result is that GFCI protection provides substantially the same, and in some cases much better, life protection than a ground wire, though not the same level of protection for sensitive equipment.

If you install GFCI in lieu of ground wires (I haven't done this myself - in every place in my house where I thought I would need to do that I found that I had an available ground wire that was simply not used by the original 2-wire receptacles), you are supposed to label it to indicate that there is no additional ground wire, as a warning for those who may really want a true ground for sensitive equipment. In addition, as always with GFCI (but rarely done in practice), any receptacles chained off the Load terminals (old 2-wire or new 3-wire) should be labeled to indicate they are GFCI protected.

Depending on the layout of your house, accessibility of ground wires, etc., installing GFCI may be much easier than retrofitting ground. On the other hand, GFCI can have nuisance trips, so beware, particularly if you connect critical equipment such as refrigerators where an unknown nuisance trip can be very expensive.

I think most people are reluctant to add additional protection where it is not required. Adding GFCI in lieu of ground clearly makes sense for any places where GFCI is required on new installations. For other places (bedrooms, living room, etc.) the "right" answer is not always so clear. You can also do both - retrofit ground and add GFCI.

One more key point: Adding GFCI can be done with the common "GFCI/receptacle replaces plain receptacle" but can also be done in the breaker panel. That depends, of course, on the type of panel that you currently have. GFCI/receptacle tends to be cheaper, GFCI/breaker may be better if you have a circuit that splits to multiple areas of the house. But if you are considering GFCI/breaker, AFCI (which is required for new installations in most places where GFCI is not required) is worth looking at as well.

Oops! I didn't realize (until Harper noted it) that "I'm looking to install some new outlets". GFCI in lieu of ground is only valid to upgrade existing receptacles. If you install new receptacles, they need to meet current code - which means they need to have a proper ground. That ground could take a strange route, but GFCI by itself will not satisfy that requirement.