Can I run a new ground wire from junction box in attic down the wall to replace 2 prong outlet

Question

I have an older home where some of the house has updated electrical and some doesn't.

In a few rooms I still have several of the 2 prong outlets with no ground wire in the box and I want to replace them with 3 prong tamper proof outlets with proper grounding.

If I had an easy way to run a new line from the panel I would not be wasting your time, but I live in a split level home and several of these rooms have their lines fed from below, in-between floors, so I don't have any way to run a new line easily.

I know I can add GFCI outlets for some human protection but I want to do better.

I need to know if it is safe and/or legal to run a ground wire from a junction box in my attic (there are several) down the wall to use as ground when I replace the 2 prong with a 3 prong. The junction box likely leads back to a different circuit but it is all originating from the same panel (I only have 1)

Answer 1

This is fine, provided you're under a new enough Code

The 2014 NEC added a new point 4 in 250.130(C):

(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

that, along with 250.134(B) exception 1:

Exception No. 1: As provided in 250.130(C), the equipment grounding conductor shall be permitted to be run separately from the circuit conductors.

lets you do precisely what you are describing (running a separate ground wire to an existing point on the equipment grounding system originating from the same panel).

The minimum wire needed for this is a 14AWG bare or green (THHN) wire, but I would use a Bare Armored Ground cable instead (to make it clear to future remodelers that this isn't something they can just cut through willy-nilly). You will also need the Bare Armored Ground cable if it's exposed to physical damage to comply with the protection requirements of 250.120(C).