neutral calc question

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I noticed a difference in Tom henry's books and Stallcup's master Electrician study guide on neutral calcs:

On page 11-40 Stallcup
120,000 sq ft office

Step 1

120,000 sq ft x 3.5 va = 420,000 with a check showing it is for neutral sizing

420,000 x 125 % =525,000 va for phase conductor sizing. (for continuous loading)


My dilemma is that in other notable books the neutral is sized based on the VA after multiplying by 125%.

Is the neutral sized based on 100 % va or 125% va even if it is like hallway or office lighting.

I know Tom Henry's calc book shows both the phase and the neutral conductors sized at 125%.

Mike Holt's Elect. Exam Prep. 2002 page 397
shows an office bldg. He used the 125% for the neutral.

I don't know why Stallcup's book does it differently.

Any know why?
Thanks
 

bphgravity

Senior Member
Location
Florida
Re: neutral calc question

The total neutral load of a feeder or service is based on the maximum unbalance of the total load determined by article 220 of the NEC. So, if the total load determined by Article 220 requires 125%of the continuous loads, the neutral must as well.
I am not familiar with Stallcup's calculation book to comment on how the calculations are performed. :)
 
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