I had the same issue with my AS. I discovered that the shore power cable was completely shot. It was dry rotted and had small cracks throughout the entire length. The power cable on my trailer goes through a hole drilled in the floor and skin. I enlarged the hole and installed a nylon strain relief at that point to prevent any future rubbing. Additionally, I discovered that the breaker box wiring was in bad shape as well and replaced the wiring between the breakers. This problem is completely gone.
A quick and easy way to see what is going on with your cord is to check for continuity between the different legs on your plug. Set your VOM to read ohms and set it at the a low setting. Mine has a 20 ohm setting. Touch one lead to the trailer skin and one to the ground stud on your plug. It should read 0 or very close to that.
Next touch your meter lead to each power stud and the trailer. You should not read anything. It should show as an open circuit. If you read any resistance you definitely have a short somewhere in your electrical system.
Louis & Sergio
Four Corners Unit