"Small' does not have a def within the UCC (5:23 et al) but...
The 'book' 5:23-2.15 (Construction Permits-Applications)
5:23-2-15 (f)(1) (iii) and ((vii) (1)
All that says that a Lic EC (or Plumber) can prepare plans for a Class III structure; and all other Comm require a seal by PE/EE or Architect
I cannot tell you the exact def of Class III without the right book.
Some areas require a signed/sealed plan for ALL comm; others base that requirement on the proposed scope of the intended work.
The 'best' I can tell you is I'll get the exact Class III definitions on Wed 12/26/2008
PS: Please remember the UCC is a 'Law' book, basically the Administrative Laws/Rules and adopted trade specific codes with amendments to suite the State.
Let me know if you want the Class III definition.