The name of this software package is Feeder 18 and it’s abbreviated as F-18.
The point of connection between the facilities of the serving utility and the premises wiring (Ref.: NEC Article 100 – Definitions).
“Main” is a reserved word in F-18 and represents the ID of the service conductors in a Project.
“Bus” is a suffix added by F-18 to the “Main” or to a feeder, in order to identify the end side (the bus) of the corresponding “Main” or feeder. For example, if a feeder’s ID is A22, its corresponding bus is named by F-18 as A22Bus.
F-18 supports a Project with multiple occupancies. A feeder derived from the MainBus is where the occupancy is set and is referred as a Principal Feeder.
Load Calculation Method
Part III of Article 220 of the NEC is the basis for the Standard method of service / feeder load calculations.
On the other hand, in Part IV, Optional feeder and service load calculations are permitted for the following occupancy types.
Two Dwelling Units
The Optional method is referred in NEC2014, 220.82.
Standard is the default method for all types of occupancies. However, if you select the Optional method, it will be applied only for the occupancies listed above.