You should use a 4 wire feeder. H-H-N-G. The ground goes to the ground terminal strip in the panel and from there to one or two ground rods. You cannot run the ground (GEC) separate from the feeder. It all must be in one conduit or cable. You need a #8 green or bare and #3 for the hots and neutral, if they are copper. This ground/bonding wire needs to have the same potential as your service bonding grid.
If you are not under the 2008 code cycle 3 wire feeders are allowed. I would still use a 4 wire feeder regardless.
Ps..Connect the ground in the main panel the same way. To the grounding terminal strip.
If you are not under the 2008 code cycle 3 wire feeders are allowed. I would still use a 4 wire feeder regardless.
Ps..Connect the ground in the main panel the same way. To the grounding terminal strip.