Outdoor Lampost causing tripped breaker

[user 4883]

A few weeks ago I had a breaker that would trip a few minutes after being reset. This was in a house I was working on. I took amp readings on the circuit and it was no where near 15 amps (around 1-2 amps maybe).
I found the problem to be two outdoor lamp post on a light switch to be the culprit. I changed the breaker to eliminate a weak/bad breaker. Inside the lamp post I found a wirenut had fallen off but, didn't make sense that the breaker did not trip immediately upon reset, indicating a dead short so I checked all connections to make sure they were tight. After replacing the wire nut and checking all connections and verifying the photo-eye wiring, everything seemed to work fine and lasted for 2-1/2 weeks. Today I got a call that the problem has occurred again. However, after all I did to correct the problem, I'm not sure what to check next.
Any ideas where to begin/continue troubleshooting?

 

[JoeD]

Did it rain recently? Could be a bad underground cable that is shorting out.

 

[user 4883]

I replaced the photo-eye and bulb when I did the original repairs. Today I found that the new bulb had burned out. The photo-eye was not new so I suspected that this was the culprit. After reinstalling a new bulb and photo-eye, I discovered I no longer had power to the lamp post. I just took this post off the circuit and the breaker seems to be holding. I found about a 3ft. section of underground wire that was not buried and they ran it up under some concrete into the interior wall of the garage. At this point, I believe your correct that the wire has gone bad (somehow) but, I have to wait for the ground to thaw before I can replace it. Thanks for the tip.