NEC 220.82 - OPTIONAL FEEDER & SERVICE LOAD CALCULATION

Hi
1. What is the meaning of "208Y/120 Volt of 3 wire service or feeder conductors"?
2. Can I apply the optional method to calculate the residential service with 2 sets of 4 wire conductors?
 
Thanks & which is the correct method to calculate the residential service with 120/208V 3 phase, 4 wires?
If I have for example 3 panels single phase in the house.

Method "A": First, Calculate Panel X, Y & Z currents applying the optional method. The each current result are: I(X), I(Y), I(Z)
The Phase A current is the sum of I(X)+I(Z)
The Phase B current is the sum of I(X)+I(Y)
The Phase C current is the sum of I(Y)+I(Z)
The neutral is calculated applying the neutral formula for wye system
or
Method "B": Calculate the sum of total connected load (VA) in Panel A + Panel B + Panel C (including 100% of air conditioning)/360V
 
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