It is up to the installer to decide if they want to run a EGC or not between separate buildings and structures.
If the distance is long and you can be sure of no continuous metallic paths between the buildings or structures using the grounded conductor as the grounding means can save a lot of matrial. Less conductors perhaps a smaller raceway etc.
You also end up with a larger conductor for the fault path.
A 200 amp copper service with a EGC will have a 6 AWG for half of the fault current path, use the grounded conductor as the grounding means and the fault path will probably have at least a 2/0 copper all the way as the fault current path.
Bob
