The load on the service grounded "neutral" conductor in a newly designed commercial office building (208/120V 3-phase, 4-wire system) is 475A. The loads being served are nonlinear. The ungrounded service entrance conductors were sized based a calculated load of 775A that took into account numerous 3-phase loads, such as air conditioning and heating, that have no neutral load. What is the demand load, if any, on the grounded "neutral" conductor of this system?
A) 775A, neutral has to be the same size as phase conductors
B) 392.5A, 70% demand on portion exceeding 200A
C) 475A, no reduction permitted when serving nonlinear loads
D) 406.25A, 75% demand on portion exceeding 200A
Answer: C)
Explanation: Art. 220 has been reorganized in the 2005 NEC. Sec. 220.61(C) doesn't allow a demand of 70% or any other value to be applied to any portion of the neutral load. The grounded “neutral” conductor shall be based on the 475A calculation.
Owen is the owner and president of National Code Seminars and the holder of master electrician certifications in 46 states. He can be reached at [email protected].
