Sorry, just ONE MORE grounding query. I want to extend a circuit from an old receptacle in a metal box. There two wires, looks like rigid conduit (it has a threaded connector entering the box). I read line voltage between the hot lead and the box. Is this an O.K. ground? I've seen posts saying that older circuits, (BX cable w/out a bonding strip for example), although showing voltage to ground, can't serve as a legitimate grounding conductor). We do want to run electronics (computer) off this circuit extension. If this isn't legitimate, can I run a single green grounding wire to a nearby modern box w/ a ground or does the green wire need to go back to the grounding bus in the service panel?

 

Conduit is a legitimate ground but if you run a new wire it must go to the panel.

 

Run the new green to the panel OR you may connect it anywhere on the grounding electrode system conductor. (The ground wire that goes from your panel to your ground rod outdoors.) You may not attach it to plumbing anywhere other than within 5-feet from the point of entrance to the building of your water main, and only if that main is metallic and in continuous contact with the earth for min. 10-feet underground.

Hope that helps.

Juice