pull box size calculations

[james_mcquade]

we are in the process of getting our contractors license and everyone is studying to take the test.

a question that puzzles me involves pull box sizes.

the pull box has the following:
top side - no items
left side (1) 3" (1) 2 1/2" and (1) 2" conduits
bottom side (3) 2" conduits
right side (1) 3" and (1) 2 1/2" conduit.

here are the questions
1. what is the minimum horizontal size for the junction box.
2. what is the minimum vertical size of the junction box.
3. what is the minimum distance for the 2" conduits next to each other on the bottom for a u pull.

my answers
#1 minimum horizontal size is 8*2 + 2 + 2 = 20"
#2 minimum vertical size 6*3 + 2.5 + 2 = 22.5
#3 u pull distance 6*2 = 12"

answers based on 2002 article 314.28 (a)(2) angle or u pulls.

the answer book states the following answers:
#1 24" result of multiplying 8*3
#2 16" result of multiplying 6*2 + 2 + 2
#3 12" result of multiplying 6*2

would someone please explain the answer if i am wrong.

thanks in advance.
james

 

[charlie b]

Re: pull box size calculations

The question is badly worded, in that it does not make clear which runs are straight and which have angle or u-pulls. The third part talks about a u-pull, and the ?book answer? seems to use that fact in its solution of the second part. The question does not talk about the horizontal runs at all. Specifically, it does not account for having three conduits on one side and two on the other. I will assume that the horizontal runs are straight pulls and that the vertical run is a u-pull, since it is clear that that is what the "book answer" has assumed.

For the horizontal run, the largest conduit on either the right-hand side or the left-hand side is 3 inches. You use 314.28(A)(1) (it?s a straight pull, not a u-pull). The ?book answer? is correct, since you multiply the largest conduit size (3 inches) times 8, and get 24.

For the vertical run, you use 314.28(A)(2) (it?s a u-pull). Here again, the ?book answer? is correct, since you multiply the largest conduit size (2 inches) times 6, then add each of the other conduits (a 2 inch and another 2 inch) and get 16.

For the separation between the two bottom conduits, you use the sentence that follows the Exception under 314.28(A)(2). Once again, the ?book answer? is correct, since you multiply the largest conduit size (2 inches) times 6, and get 12.

 

[james_mcquade]

Re: pull box size calculations

charlie b,

thanks for the reply.
looking at my post, i typed the question correctly, but didn't type in my answers correctly. thats what you get when you don't proof read your work

i cannot insert pictures like others on the forum, but will try to detail my problem.


--------------------------
| |
3 in. | | 3 in.
| |
2.5 in. | |
| | 2.5 in.
2 in. | |
| |
---------------------------
2" 2" 2"

thanks again,
james