NOTHING in the RV will cause your problem, UNLESS your WHITE Neutral wire at the main breaker panel is loose or not making good contac. Same at the Shore Cord and connection to the shore cord. IF the Neutral wire is loose or not making contac, that will destroy Transfer boxes and other components in the RV. Loose Black or Red wires will not cause a problem except arcing at the loose connection or just no power on that leg. But will not burn out items. When you install or replace a 30 or 50 amp transfer box, you MUST tighten the nuts/screws down tight and then wait about 15 minutes and then go back and retorque the screws/nuts. The copper will give a little after the first tightening. You will be suprised at how much your 2nd tightening allows. Low voltage is also a transfer box killer under load. Doug