Two buildings: Home and Detached Garage (circa '04 US). Service comes in through a Meter on the Garage to a PVC conduit into the Main box in the home (Single phase 240V with Neutral). In the main box Neutral and GND are bonded and bare ground wire coil heads out somewhere towards the front of the house, presumably to a ground rod.
There is an additional PVC conduit from the main panel back to the garage with 2 Hot, Neutral, and Ground that is used as two 120V runs (opposite phase), one for lights one for outlets and no sub-panel.
I'm planning on putting a 240V outlet in the garage and increasing the conductor side for 50A service. I will replace the two 120V breakers in the main panel with a 240V breaker and pull new wire (6ga x3 and 10ga Gnd) to a new sub-panel. From the sub-panel I'll wire back in the lights/outlets and the new service. Ground and Neutral will not be bonded and I know I need at least one grounding rod on this panel.
So finally I get to my question: There is an existing grounding rod that is being used by the Meter and apparently nothing else. Can I just add a new ground rod clamp to use with the sub-panel? Any code I'm violating?
Best Answer
You must tie to the existing grounding rod...
Since there's a rod present there already, you must tie your new subpanel's grounding electrode conductor to it, as per NEC 250.50 and the reference to Part III of Article 250 in NEC 250.30(A).
...and may be required to drive a second
If your existing rod is judged not to meet the 25ohm standard in NEC 250.53(A)(2), or if the AHJ wishes it, you may need to drive a second grounding rod 6-8' away (or more, if you wish) from the first.
You can either tie to the existing grounding electrode conductor with a 6AWG copper wire and an appropriate tap connector, or simply run the new rod's grounding electrode conductor back to the grounding bar on the subpanel, though.