I was talking to someone again Today about this he swears you Do run a ground back from main and DO NOT bond at sub for the simple fact that your GFCI protection will function more accurately .
Thats the best reson so far
The only ground fault protection that will function more accurately is the ground fault protection of equipment and that is already covered by condition three of section 250.32 (B) (2).
(2) Grounded Conductor. Where (1) an equipment grounding conductor is not run with the supply to the building or structure, (2) there are no continuous metallic paths bonded to the grounding system in both buildings or structures involved, and (3) ground-fault protection of equipment has not been installed on the common ac service, the grounded circuit conductor run with the supply to the building or structure shall be connected to the building or structure disconnecting means and to the grounding electrode(s) and shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The size of the grounded conductor shall not be smaller than the larger of
(1) That required by 220.22
(2) That required by 250.122
If ground fault protection of equipment is installed the building disconnecting means and panels must be wired as if they are in the same building as the service supplying them. This is because a bonding connection to the neutral at the second building will cause some current to flow through the earth back to the service and transformer grounding electrodes. This can cause nuisance tripping of the ground fault protection.
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Tom
