I have a long Ethernet run (about 280 ft/85 m) that goes through a conduit between two buildings. On each end, I have an APC Ethernet surge protector that is grounded to the main ground for each building. While I had some trouble getting it to work at first, once I stumbled across Zyxel's very fine 24-port switches, it has worked really, really well.
Then, a storm hit and the link quit working. As far as I can tell the switches were fine and I've tried replacing both APC surge protectors. It appeared the cable in the conduit -- which has a water leak in it -- was damaged. However, I tried new, better insulated cable and it didn't work (either through the conduit or running on the ground). On the other hand, I had three spare 100ft (30m) pre-terminated cables that I coupled together and that worked just fine running across the ground. I can't imagine why three unshielded cables patched together would work while nicely terminated, shielded direct burial grade Cat5e cable would not.
There is one difference I just observed after putting everything away for the evening: I've been using the TIA 568A wire pattern to the RJ45 connectors and the pre-terminated cable used the TIA 568B pattern.
Could that make the difference in signal loss? Can you think of anything else that would cause 3 patched together cables to work but one solid run not to work?