Its in the Florida Building Code -
section 105.3.1.2.
The statute itself is somehwere in "61G15" chapter,
section 471.003. Click the link below and look mid-way down, this is the Florida statute, to access it click below:
http://www.myfloridahouse.gov/FileStores/Web/Statutes/FS07/CH0471/Section_0471.003.HTM
Please note that just because it says it in the statute, the AHJ can still require an engineer to seal the drawings if the municipality requires it. If you want to fight, you probably wont win, you would have to call the city/county attorney to argue it.
We used to get a lot of electrical contractors trying to design their own stuff, no problem with it I suppose if you ask me, as long as it is right. Good Luck