There are so many different units available and I don't want to spend any more than I have to as I am very cheap (translate poor). I see plug and play without isolation. Is anyone running these without any problems to their electrical system....e.g. blown fuses, melted wires, etc. As far as the isolation units are concerened, I see them offered from $30 to over $150. Why the big variable in cost? Thanks for your help.