Article 250.32(A) of the National Electrical Code, tells us that we need a grounding electrode at a detached garage. It also says that it has to be "installed in accordance with Part III of Article 250.".
National Electrical Code 2014
Chapter 2 Wiring and Protection
Article 250 Grounding and Bonding
250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).
(A) Grounding Electrode. Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or (C). Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed.
Then the first part of Part III of Article 250 says, "All grounding electrodes... ...that are present at each building or structure served shall be bonded together to form the grounding electrode system.".
III. Grounding Electrode System and Grounding Electrode Conductor
250.50 Grounding Electrode System. All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used.
Does that mean that the electrode(s) at the garage, has to be connected back to the electrode(s) at the main structure?