Service Neutral Grounded Conductor Ampacity?

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The writer is definitely using the 70% rule in 220.61 but even if he provided the needed info to apply that section he is still wrong because as it reads: "That portion of the unbalanced load in excess of 200 amperes" He's applying 70% against the entire 200 amp service. It would only apply to the portion above 200 amps. To me it seems like an all around misinterpretation of the code.
 
I would think that is the point of the question. the 70 % reduction is not automatic in applying to all services if the question as stated was applied to a 250 amp service i would apply a 70 % reduction to the 50 amp portion of the service in my answer
 
infinity said:
Why couldn't 1) possibly apply?

(B) Permitted Reductions. A service or feeder supplyingthe following loads shall be permitted to have an additionaldemand factor of 70 percent applied to the amount in220.61(B)(1) or portion of the amount in 220.61(B)(2) determinedby the basic calculation:
(1) A feeder or service supplying household electricranges, wall-mounted ovens, counter-mounted cookingunits, and electric dryers, where the maximum unbalancedload has been determined in accordance withTable 220.55 for ranges and Table 220.54 for dryers
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I never said it couldn't, I just mentioned it wouldn't ordinarily apply to most dwellings or other low capacity single phase applications.

The question is lacking enough detail to be able to answer it correctly.
 
kwired said:
I never said it couldn't, I just mentioned it wouldn't ordinarily apply to most dwellings or other low capacity single phase applications.

The question is lacking enough detail to be able to answer it correctly.
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I agree, I would only have chosen 140 amps because it was one of the answers and was in my thinking exactly what the questions' author had intended.
 
infinity said:
I agree, I would only have chosen 140 amps because it was one of the answers and was in my thinking exactly what the questions' author had intended.
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When given a multiple-choice-answer question, it is always best to select the desired answer... correct or not. :D
 
infinity said:
I agree, I would only have chosen 140 amps because it was one of the answers and was in my thinking exactly what the questions' author had intended.
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But 200A is also one of the answers and is what I think the author intended. So we differ. :)

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GoldDigger said:
But 200A is also one of the answers and is what I think the author intended. So we differ. :)
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But the mere fact that a 200A neutral isn't necessarily the minimum leads me to believe the 'desired' answer is one of the other three. For the desired answer to be 200A, I think there'd be clues in other questions that the author is pretty darn facitious. ;)

Anyone have a premise for choosing 160 or 175? :happyno::happyyes:
 
Smart $ said:
But the mere fact that a 200A neutral isn't necessarily the minimum leads me to believe the 'desired' answer is one of the other three. For the desired answer to be 200A, I think there'd be clues in other questions that the author is pretty darn facitious. ;)

Anyone have a premise for choosing 160 or 175? :happyno::happyyes:
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I guess it comes down to how you interpret the writer's use of "minimum".
It could be either the smallest number that will satisfy any possible 200A service situation (my first impression) or the smallest number that will work for the combination that allows the smallest possible service neutral for 200A service (your reasonable interpretation).
 
Smart $ said:
But the mere fact that a 200A neutral isn't necessarily the minimum leads me to believe the 'desired' answer is one of the other three. For the desired answer to be 200A, I think there'd be clues in other questions that the author is pretty darn facitious. ;)

Anyone have a premise for choosing 160 or 175? :happyno::happyyes:
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The only thing I can come up with is 83% rule for residences which would allow 175 amps conductors.
 
Smart $ said:
You need to know the calculated neutral load under 220.61 to reduce the neutral conductor size to less than the ungrounded conductors.
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Isn't that how the guesting needs to be answered since there is no information given . The size would have to be a min of 200 amp
 
david said:
Isn't that how the guesting needs to be answered since there is no information given . The size would have to be a min of 200 amp
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That just it, 200A isn't necessarily the minimum. It is, however, the safest without knowing the calculated load AND the maximum unbalanced calculated neutral load. But not knowing the latter calc is technically a violation in and of itself if one is trying to determine the minimum service neutral conductor size.
 
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