Overcurrent Protection and Adjustment factors(table310.15(B)(2)a)

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squaredan

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Hi,
This is my first post on this forum andI hope I am in the right section for this question.. I have been studying for my master and I came across a question in the Mike Holt Exam Prep Book and I am not understanding why would not use Table 310.15B2a for Adjustment in this question.. The Question is
" What size overcurrent protection device is required fro a 45A continuous load? the circuit is in a raceway with 14 current carrying conductors. (a) 45A (b) 50A (c) 60A (d) 70A "
The answer in the book is 60A

I understand we take 125% (210.20) of a continuous load 45A x 1.25= 56.25A and 240.4B lets us go to the next higher size 60A but then why wouldnt we take the Adjustment factor of table 310.15B2a of 14 current carrying conductors? I have been trying to find a code rule but not finding..Maybe it is wrong in the answer key??? Hope someone can help me on this one.. Thanks

Dan
 
infinity

infinity

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jumper said:
The question asks what size OCPD/breaker/fuse is required, not what size conductor will be needed after derating. The 14 conductors in a raceway is not relevant.
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I agree. The 14 CCC's is just there to confuse you. It will change the conductor size but not the required OCPD size. Keep in mind when reading test questions that some of the information provided is irrelevant as Jumper stated.
 
charlie b

charlie b

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I agree with Derek and Rob, but would like to add one other comment.
squaredan said:
. . . 240.4B lets us go to the next higher size 60A
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True, but not relevant. This question is not about using a higher rated OCPD to protect a conductor, and being allowed to go to the next standard size. The relevant code article is not in 240, but rather is 210.20(A). This article talks about the load and the breaker. The breaker cannot be smaller than 125% of the continuous load plus 100% of the non-continuous (which this test question doesn't have). So in your example the breaker cannot be smaller than 56.25. Article 240.4(B) ALLOWS you use a higher rated breaker, but does not REQUIRE you to do so. Here, you are forbidden to go smaller than 56.25, and so 60 is your minimum choice.

By the way, I have a quibble with the way the question is worded. You could use a 70A breaker if you wish, or even a 500A, as long as you choose the proper conductor sizes.

Welcome to the forum.
 
jumper

jumper

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charlie b said:
I agree with Derek and Rob, but would like to add one other comment. True, but not relevant. This question is not about using a higher rated OCPD to protect a conductor, and being allowed to go to the next standard size. The relevant code article is not in 240, but rather is 210.20(A). This article talks about the load and the breaker. The breaker cannot be smaller than 125% of the continuous load plus 100% of the non-continuous (which this test question doesn't have). So in your example the breaker cannot be smaller than 56.25. Article 240.4(B) ALLOWS you use a higher rated breaker, but does not REQUIRE you to do so. Here, you are forbidden to go smaller than 56.25, and so 60 is your minimum choice.

By the way, I have a quibble with the way the question is worded. You could use a 70A breaker if you wish, or even a 500A, as long as you choose the proper conductor sizes.

Welcome to the forum.
Click to expand...

I write this post with great respect and fondest regards Charlie, but I had to chuckle at "quibble". No one I know, besides my wife - a librarian and Shakesperean scholar - use such words.
 
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