When replacing a nongrounding receptacle with a grounding-type receptacle, you can connect the equipment grounding conductor of a grounding-type receptacle or branch circuit extension to any of six places [250.130(C)]. Those are:
1) Any accessible point on the grounding system as described in Sec. 250.30.
2) Any accessible point on the grounding electrode conductor.
3) The equipment grounding terminal bar within the enclosure where the branch circuit originates.
4) An equipment grounding conductor that’s part of another branch circuit that originates from the same enclosure as this branch circuit.
5) The grounded service conductor within the service equipment enclosure (grounded systems only).
6) The grounding terminal bar within the service equipment enclosure (ungrounded systems only).
Not included in this list is a separately driven ground rod. Why is such a rod not an accepted connection point? Look more closely at what is on the list. Everything listed is part of a system. If you drive a ground rod just for this receptacle, you are connecting to the dirt (high-impedance path to the source); you are not bonding (low impedance connection) that receptacle to the grounding system.
