Confused by practice exam.

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Sparksy93

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Winchester ky
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Electrical technician
Hello I’m taking some practice exams for my journeyman test i’d like to pass here soon.
I feel aggravated with myself because to me even with the hint on this question it doesn’t make sense why the answer is what it is.
It asks to determine the wire size of a 75 degree aluminum service conductor for a service entrance load calculated at 185 amperes.
I answered 3/0 and it’s says the answer is 4/0.
It claims section 310.15(B)(7)(1) allows 4/0 to be used for a 120volt/240 volt 200 amp family dwelling service. It does not explicitly say that it says the service conductors supplying shall be permitted to have an ampacity not less than 83 percent of the service rating, the service rating is 185, 83 percent of 185 is 153.5, lets even call it 154,
3/0 aluminum at 75 degrees Celsius is rated at 155, which is not less than 83 percent of the “service rating” what am I missing or how can I get it right without the practice test just sort of telling me I’m wrong and that it’s 4/0 just because what I should have assumed it was based on 200 amps instead of what the question said which is 185 amps? Confusion! Any help would be appreciated, thanks.
 
Does the question state that this is a residence? And even so 4/0 is what you would need for a 200 amp service. You don't take 83% of the calculated load. You take 83% of the service size which would be 200 amps. Assuming this is a residence otherwise 83% doesn't come into play
 
Thank you.
I often find these questions mildly convoluted and not straightforward. But I guess that’s why there’s a whole book about it all.

The question says dwelling unit.
 
Dennis Alwon said:
Does the question state that this is a residence? And even so 4/0 is what you would need for a 200 amp service. You don't take 83% of the calculated load. You take 83% of the service size which would be 200 amps. Assuming this is a residence otherwise 83% doesn't come into play
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also what code reference can I look at to explain that I’m looking for the 200 amps, like I’m assuming I’m basing my answer off the over current protection?
 
Table 240.6(A) shows you the standard size overcurrent protective device. You cannot get 185 amp breaker so you must go to 200 amps. Basing the calculation for 200 amps you get 166 amps. Therefore, 4/0 aluminum is necessary.
 
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