Under the 2005 NEC, Art. 600.21 (E) requires a 2' x 3' access door and a 2' x 3' passageway with a 12" walkway to all components. A local contractor has questioned why the requirement is this way. I did not want to use the "it's in the code book, so it has to be done" reason (although I did provide the code section and required the installation to meet code), I was hoping to get some insight as to the actual reasons behind the requirement. I have heard in passing that it has to do with confined space requirements for rescue personel, but I have not been able to confirm that. I was hoping that someone on the forum may have some input and I would have a chance to learn something new.