Sizing conductors for branch panel board

[Inspector411]

The scenario is as follows:

1. 250at/af 75C main breaker w/ 250kcmil 75C 3phase/4wire cu feeder serving MCC to 250at/225af 75C breaker
2. Tap for lighting panel on load side of 250at/225af breaker
3. Panel board 240/120 100amp 1phase/ 3wire w/100amp 75C main breaker
4. Total LP load 2954 VA
5. Line current 13A/ea phase

Questions:

1. What codes apply for sizing conductors for a branch LP?
2. How would one determine the proper sizing of feeder conductors for this LP?
3. Are there any special considerations for the terminal connectors at the breakers?

 

[don_resqcapt19]

The tap rules in 240.21(B) apply.

 

[augie47]

difficult post for me to decipher but I'll give it a try.
Sounds like you have a 100 amp M/B panel tapped off a 225 amp breaker.
The minimum wire size to the 100 amp panel be controlled by the tap rules in Art 240.21 since this is a tap and the 100 amp breaker protecting them at the load end.
Barring any conditions such as ambient or conduit fill, a #3 Cu would be your minimum size
because of the 100 amp breaker. The length of those conductors will be limited by the applicable tap rule, most likely 25 ft.
The breaker lugs would need to be rated for the size of and number of conductors.