A customer recently called me and reported that the 50A breaker for their hot tub was tripping. Usually, this means that the ground-fault breaker in the disconnect located next to the hot tub had picked up some leakage in the heating element, and as such, would not stay closed. But to my surprise, it was the feeder breaker in the house panel that was tripping out. I disconnected everything in the outside disconnect box, and tried to restore power again. The breaker stayed on for about 5 seconds, then POP!! My first instinct said that there was a problem in the underground wiring from the panel out to the tub. Upon inspection, it appeared that it was run in 1-inch PVC conduit, buried from the house to the tub. I disconnected all conductors from both ends, and attempted to pull them out, to replace them. I could only muster about a foot of wire out of the conduit before it would get "stuck" and unable to pull any further. At this point I noticed the equipment grounding conductor was a 10 AWG THHN green wire at the panel end, but it was an 8 AWG THHN black wire, with green tape applied at the tub end. I figured there was an underground splice box somewhere along the conduit run. When I questioned the homeowner, they indicated that the hot tub had been replaced a year ago, and subsequently relocated to its present position. This just about confirmed my suspicions, but I needed to do a little more looking.
Out with the shovel, I attempted to locate the conduit and the offending underground splice by digging in several locations, but no splice box was apparent. In desperation, I finally cut the conduit in 2 different places and tried to extract the existing conductors. With some effort, the wires came out of the conduit, and lo and behold, there was this lump among the wires. It seems that someone had used a "uf heat shrink splice kit" on the original wires and inserted the whole mess back into the conduit before extending the run to the new hot tub location. There was no splice box to be found. Of course, there was some water in that conduit, and the heat shrink did not keep out the moisture due to there being 4 conductors inserted on each side of the splice block, with no outer sheath. You could smell the connection was burnt after we removed it.
I repaired the cut sections of conduit, and pulled in new conductors to the disconnect box. Once energized, the hot tub began operating normally. The entire run was only 75 feet, I can't for the life of me understand why someone would go to the trouble of splicing those wires like that, when installing new ones would have been a simpler procedure. It takes all types, I suppose.