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Code Quiz

Jan 7, 2005 10:42 AM, By Steven Owen

In a newly designed multi-family dwelling unit (208/120V, 3-phase, 4-wire system) the calculated load on the service grounded “neutral” conductor is calculated to be 475A. What is the demand load, if any, on the grounded “neutral” conductor of this system?

A) 392.5A
B) 200A
C) 475A
D) 406.25A

Answer: A)

Explanation: Article 220 has been reorganized in the 2005 NEC. Sec. 220.61(B)(2) allows a demand factor of 70% to be applied on that portion of the neutral load that exceeds 200A as long as the neutral load doesn’t consist primarily of nonlinear loads, which are harmonic in nature. A reduction isn’t permitted on the first 200A, but the 70% demand factor is allowed for the amount exceeding 200A.

475A – 200A = 275A
275A x 70% = 192.5A
192.5A + 200A = 392.5A

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 necexpert@aol.com.

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