said by Jack_in_VA:Not so everywhere. My electrician installed a ground rod in my new detached garage with a subpanel and the inspector made him remove the ground wire from it and run a 4th wire to the main ground and install a second ground rod tied to the original.
From your description sounds like your electrician only ran 3-wires to the garage and then installed a ground rod and treated it like a service disconnect. That is incorrect, subpanel cannot bond Neutral to Safety ground. That is only allowed at the service disconnect.
In general outbuildings must have its own ground rod
and the Neutral and Ground kept separate. There is an exception for residences that eliminates the ground electrode requirement.
The more ground rods the better, but to be effective they must be connected with heavy gauge wire, 6 AWG or larger and at least as far apart as the rod is long to maximize effectiveness. If they are too close to each other the fields interact and you do not get the full benefit of the ground rod.
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/tom