Q: Can cardboard boxes be stored in an electrical room that is over 50 square feet, fully sprinklered, and has only dry transformers under 112 1/2 kVA?
A: Yes, only if the room qualifies as a hazardous room under sections 18.3.2.1 or 19.3.2.1 of the 2000 edition of the Life Safety Code, depending if the room is considered new construction or existing conditions. With the exception of NFPA 1 (2012 edition) NFPA codes and standards do not prevent storage in electrical rooms as long as it does not obstruct access to the electrical equipment. Since NFPA 1 is NOT a referenced standard by the Life Safety Code, the restrictions found in that standard does not apply. You must maintain at least 36 inches clearance in front of all electrical panels, and at least 30 inches clearance to the side of electrical panels. Now, other authorities having jurisdiction may have their own rules and interpretation, so I would suggest you check with your accreditation organization, state and local authorities to see if they have any issues with that.
