A 120/208V, three-phase service has a total connected

load of 1,450A:

600A of these are phase-to-phase loads

300A are balanced 120V fluorescent lighting

550A are other 120V loads

The neutral calculated load for this service is _____.

The answer is

30. (c) 745A, [220.61]

Total feeder load is 1,450A

Phase-to-phase loads 600A at 0%: 0A

Discharge lighting 300A at 100%: 300A x 1.00 = 300A

First 200A of the 550A at 100%: 200A x 1.00 = 200A

Remainder of the 550A at 70%: 350A x 0.70 = 245A

Total Neutral Calculated Load 745A

Where does the 0 %, 100 % and 70 % calculations come from, I read the suggested 220.61 article but do not see how this applies?