In the normal flow of electrical calculations, you:
- Determine the size and quantity of branch circuits needed to supply the intended loads.
- Determine the size and quantity of feeders needed to supply the branch circuits.
- Size the service to accommodate the feeders, and size the conductors needed to feed the service.
Plus, you're sizing the circuit protection devices at each stage.
You can have as many branch circuits and feeders as you want, but you can have only one service per structure unless one of five circumstances applies [230.2]. These conditions are listed in 230.2(A) through (D) of the 2011 NEC. The list is similar to the one in 225.30(A) through (E) for exceeding the single supply limit when a structure is supplied by a panel in another structure.
However, there are important differences. An obvious one is there's no documented switching procedures [i.e., 225.30(E)]. An alternate supply (e.g., a second utility line) might be a counterpart for this, but it connects to the same service. You don't switch between services. The same holds true for other sources — they connect at your service.
The Special Conditions circumstance [230.2(A)] and Special Occupancies circumstance 230.2(B) are identical to their counterparts in Article 225. But the Capacity Requirements circumstance [230.2(C)] and the Different Characteristics circumstance [230.2(D)] differ from their counterparts in Article 225. We'll examine these in our next issue.