(I absolutely welcome suggestions for improved title – there's two facets to this question)
I have a 1960s home with a few three prong receptacles and many two prong receptacles. I read some online guides and they suggested that as long as I can verify ground on the box, I can screw one of those handy green pigtails into the box and attach that to the receptacle.
After taking a good look inside some of the boxes I see that there is in fact: a) a ground wire inside the bundle, and b) it's twisted with its counterpart ground wire leaving the box, and c) it's screwed into the box.
So, the box is grounded, though I don't have a third wire to ground the receptacle.
It seems to me that the most craftsmanlike way to do this would be to remove those ground wires from the box, untwist them and retwist with a third wire, screw them into the box again and run that third grounded wire to the receptacle.
However, I'll need to get the parts (whatever bit that is that screws wires to the box), wire and tools to do it that way. I have a perfectly good alternative, which is to screw a green grounding pigtail into a waiting hole on the box, knowing the box is grounded.
- Am I missing something unsafe here? The box is in the loop as grounding conductor, but that's a pretty common setup anyway.
- Will my inspector/the NEC get annoyed at me for this? I can't find anything specifically relating to multiple ground wires from the same circuit in an outlet.