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I have an outlet in the age that appeared to be from 1960s. I decided to replace it with a GFCI receptacle after getting charging issues with EV. After opening the outlet up, it appears that the metal box has no grounding screw and the existing grounding wires are wrapped behind the mounting screws (the box has two mounting bracket, one on the top and one on the bottom and each bracket has some space to the back of the box - see the picture). So my question is, how can I be code compliant with the installations of GFCI?

  1. Connect a pigtail wire to the mounting screw then wire nut both grounding wires and the two pigtail wires?
  2. Install GFCI with no device grounding and put a label on it.
  3. Drill a hole for 10-32 and add a grounding screw - this is what I am least capable of doing.
  4. Any other solutions?

Having never dealt with an older house, appreciate your advice and help!

mounting screw on the box

Charles Chen
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    Look again, **very** carefully. There is almost always a 10-32 hole hiding somewhere, possibly behind your cables. It's the smallest hole in the box, and usually pre-threaded. On a vintage box it won't be in a raised hump as most modern boxes are. – Ecnerwal Sep 11 '21 at 15:36
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    Option 1 would not be legal, 250.148 specifies "used for no other purpose", Option 2, the sections that allow ungrounded GFCi receptacles specify no grounding conductor present. A Grounding clip (Raco 975) might be another option, but it would likely not fit in that style of box with a GFCI receptacle. You might find it easier to use a GFCI Breaker with that type of box anyway. – NoSparksPlease Sep 11 '21 at 16:05
  • Are you plugging your car into a simple 120V, 20A outlet for charging? Seems to me that you'd do a lot better for your charging if you had higher amperage, if not also voltage to charge with. – FreeMan Sep 11 '21 at 16:30
  • If "age" is supposed to be "garage" you can [edit] to correct. I'm guessing that, but not to the point that I'll make an edit I don't **know** is correct. Also, what "charging issues", specifically, did your car/charger report? – Ecnerwal Sep 11 '21 at 16:31
  • Thanks all for chiming in! I did not find a 10-32 hole since the back of the box is flush that I don't see obvious hump other than the two brackets with mounting screws. But I'll check again. The house is only powered with 150A, so adding delicated 50A service is not an option for now. I am happy with 120V, 15A outlet for charging since my commute is short. But that outlet has cracks and caused problem with my Model 3: 4 flashes and adaptor plug warm, hence the decision to replace it. – Charles Chen Sep 11 '21 at 16:34
  • You should NOT expect a "hump" on that vintage of box, just the hole. No grounding screw hole is not unheard of, but it's rare in practice. – Ecnerwal Sep 11 '21 at 18:35
  • Update - tried again last weekend, and found the screw hole hiding behind the splinted sheath from load wires. Problem solved. Your comment "look again, very carefully" is right to the point :) – Charles Chen Sep 22 '21 at 01:00

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I'd use a self-drilling grounding screw

If there truly is no 10-32 tapped hole in the box, then I'd remove the grounding wires from the box mounting screws, nut them to a pair of 12AWG bare pigtails, and land one pigtail on the GFCI's grounding screw and the other on a self-drilling grounding screw (Garvin GSST or equivalent, note that it must be 10-32 UNF to meet NEC 250.6, coarse pitch screws are not acceptable) screwed into the box, then proceed with the GFCI install as normal.

ThreePhaseEel
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  • Similarly, you could drill the correct sized hole in the box (for tapping #10-32), then drive a standard grounding screw in with a powered drill. Most grounding screws in big box stores are kind of self tapping (tapered threads). – blarg Sep 11 '21 at 16:52