NEC 220.82 - OPTIONAL FEEDER & SERVICE LOAD CALCULATION

[electrical_engineer]

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?

 

[Dennis Alwon]

208Y/120v is just 2 legs from a 3 phase 208 system

 

[Dennis Alwon]

You can use 220.82 for the individual units, assuming they are not 3Ø, but not for the 3Ø service

 

[electrical_engineer]

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

 

[Dennis Alwon]

Look at Annex D in the back of the NEC Example D5(a) may help