Four years ago I had a call for a free standing meter station that had lost one hot leg. The 100A supply came down a pole, underground (about 10') and up to the meter channel. Pulled the wires out and found one of the aluminum conductors was completely separated. The insulation showed no sign of failure (other than some melting right at the break) and the conductor had some oxidation at each open end. Pulled in new URD and all was fine. This spring I got a call that it happened again. So this time the RMC was removed and replaced with PVC. The break occured in the same spot as before. The conduit was inspected for sharp edges or anything that could have caused this failure. Just like the first time the wire showed no sign of damage (nicks, cuts, scrapes). There is very little load on this, it only feeds a 150 watt spot light and a 1/4 HP pump. The original feed lasted 40 years, the second only 4. Any ideas?
The break was in the section underground. The soil is all sand and no strain was found on the wires. The wires had a nice loop in the meter channel and on the pole there was plenty of slack. I'm stumped!