Mike Holt part 3 electrical calculations question 30


I need assistance with how to find the answer 2014 Master electrician simulated exam question 30 which reads
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?


It is a combination of Code and Knowledge of Electrical Circuitry.

First, Phase to Phase loads have No Neutral, so zero Current. 0%
Next, ED Lighting is a Non -Linear Load and therefore no reduction per Art 220.61 C(2) 100%
Last, the "other loads" are given a partial Neutral Reduction for anything over 200A, per Art 220.61 B(2) which is the 70%.