I would like to add a ground to an ungrounded outlet so that I can use a surge protector with some electronics. How do you add a separate ground back to panel on 2 wire ungrounded outlet?

The copper wire in the picture below runs across the joists in my basement from the water supply entry back to the electrical panel (It is definitely wired into the panel, no cuts along the path). This ground wire is about 10Ft from the outlet I want to ground. Can I use a split nut like the one pictured below to clamp a bare 12AWG ground wire to the existing ground?

copper wire stapled to joists

grounding split nut

  • What was the year of when the wiring was installed?
    – wallyk
    Mar 3, 2018 at 17:09
  • You don't have to use bare copper wire. You can use green insulated.
    – wallyk
    Mar 3, 2018 at 17:13
  • The only thing I can tell is the panel appears to be from the 90's. Can THHN ground be stapled to a joist and routed through holes in joists? Or does it always have to be in conduit or raceway? Mar 3, 2018 at 17:35
  • 1
    Somebody once asked me about an inline splice like that, and I was cold to it initially, but it made a lot more sense when they said "split bolt". Is that cable part of your grounding electrode system for the same panel the circuit is out of? Whether you can use THHN grounds outside conduit is another question. Why don't you ask it? (I've got enough rep lol). Mar 3, 2018 at 18:34
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    @Harper -- the answer to your question's 250.120(C) by the way Mar 3, 2018 at 21:27

1 Answer 1


Go for it

For a retrofit equipment grounding conductor, your case falls under NEC 250.130(C) point 2:

(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

So, your plan with the split bolt is good. You can use green THHN without a conduit for this provided it's protected from mechanical damage and routed within the building structure, by the way, as per 250.120(C):

(C) Equipment Grounding Conductors Smaller Than 6 AWG. Where not routed with circuit conductors as permitted in 250.130(C) and 250.134(B) Exception No.2, equipment grounding conductors smaller than 6 AWG shall be protected from physical damage by an identified raceway or cable armor unless installed within hollow spaces of the framing members of buildings or structures and where not subject to physical damage.

If you do need to make an exposed run, though, a bare armored ground cable is going to be cheaper and easier to handle than having to run conduit just for a ground wire.


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