Going to start by describing the mess that I found.
Symptom: 220VAC Hot water heater not heating.
Cause Discovered: 1 phase missing in main panel. Upon investigation I discovered that the main feeder to this trailer was a temporary 50 AMP plug style connector. Someone had installed a 100 amp panel and main breaker inside the home. The plug had been been exposed to over-current and one of the prongs as well as half of the receptacle was completely destroyed.
Action Taken: Turned off the main breaker at the pole. 100 amp breaker feeding 1/0 (maybe 2/0) Aluminum conductors in Schedule 40 PVC conduit to the 220 VAC Receptical box.
Weather was getting cold and owner needed to move in within days. Due to limited time we had to rebuild ASAP.
Replaced 100 AMP main breaker inside Mobile home with 50 amp Breaker suitable for the temporary cable that was stamped 50 amps. It has a rubberized outside with molded plug and inside has 4 color coded conductors. It says it is rated for 50 amps and mobile home and RV use etc.
The plug and receptical were destroyed and the box was in bad shape. I could get new receptical but could not get a new cable with molded plug on short notice. I could get a new all weather box with a 40 amp 3 phase GFCI Breaker. I decided to go that way. Originally the temporary 50 amp cable came out of the plug (about 1 foot away from the trailer). Went under the ground (No conduit) for 2 feet under the skirt then up above ground and runs about 6 feet under the trailer. Then up inside the trailer to the main panel inside. Due to time constraints we removed the old box and receptical. Also cut off the molded plug that was destroyed. Conductors and insulation was in good shape so I installed it into the new all weather box with the GFCI (50 Amps). I left it going to the trailer the same way. Direct buried for 1-2 feet until it gets under the skirt. Then above ground and up into the main panel with the new 50 amp main I put in. I tested it at full load and also tested the GFCI. it works excellent even with the branches off. My only concern is that I did not have time to bury a conduit for the 50 amp "temporary" cable. Does it have to have one? The way I read the NEC (08) is yes it does if it is permanent. Also...I read I have to bury it all the way to where it comes up to go into the main panel inside the trailer. Is that correct? I think it is a sprig project either way. Just want to know if I can get away with leaving it the way it is due to being only 50 Amps and already in a cable as opposed to individual conductors.