[mikehinton]

I'm obviously not communicating what I'm doing properly.

Right now, the breaker is connected to the sub panel, AND the supply lines that feed the individual buildings. In front of each building is a PVC junction box underground. Connected to the main supply lines at each point is 12/2 direct burial Romex (in PVC conduit) that goes into a metal junction box in each building. From that metal box, additional 12/2 Romex goes to the various outlets and light switches.

At this point, I'm testing to see if any of the "branches" from the metal junction box has a short circuit in it that would trip the breaker. I disconnected one of those last night, but the problem remained. I plan to disconnect each additional "branch" one at a time to see if the problem gets resolved.

If disconnecting each "branch" does not solve the problem, then the only remaining possibility is that the short is in the main supply wires.

One of my initial questions was whether or not there was a way to test for a short circuit in one of the branches without disconnecting them one at a time. It seems that there isn't, but no one had addressed that directly.

Hope that clears up the present situation.