Free space within a box

[9275]

How do you calculate the required free space for conductors not in table 314.16(B)?

 

[George Stolz]

See 314.28, and welcome to the forum.

 

[infinity]

How do you calculate the required free space for conductors not in table 314.16(B)?

Do you mean smaller than #18 or larger than #6? For larger than #6 there's no real free space calculation. The box is calculated according to the raceway size.

 

[Steven M. H.]

conductor sizing

conductor sizing

Table 9

 

[infinity]

Table 9

What does table 9 have to do with conductors not listed in T314.16(B)?

 

[9275]

I have read 314.28 and I guess I'm not understanding.
314.28(A)(2) U pulls is what applies to what I'm trying to calculate can some one give me an example. Please & Thank You to everyone for replying.

 

[George Stolz]

Sure: Say you've got a 1.5" conduit entering the north side of the box, and the conductors leave through a 1.5" raceway on the north side of the box.

1.5" x 6 = 9"

You need a box 9" from north to south and wide enough to fit the pair of conduits from east to west for the box at this location.

 

[augie47]

Sure: Say you've got a 1.5" conduit entering the north side of the box, and the conductors leave through a 1.5" raceway on the north side of the box.

1.5" x 6 = 9"

You need a box 9" from north to south and wide enough to fit the pair of conduits from east to west for the box at this location.

George, would your east-west dimension not have to meet:
"the distance between raceway entries enclosing the same conductor"
section of this rule ? 9" between + 1.5 + 1.5 =12" (plus allowance for locknuts, bushings, etc,)

 

[George Stolz]

Whoops, yes the east - west dimension between the raceways would have to be 9", so a 12" box would be required. Thanks, Gus.

 

[George Stolz]

Wait a sec - if there were a splice, then there would be a pair of conductors, so the math for east-west would be

1.5+1.5 = 3.0"

Also, I screwed up my original answer. There are two raceways. So north - south would be

(1.5" x 6) + 1.5" = 10.5"

So if there are splices, it would have to be a 12" x 4" box, if there are no splices, then it would have to be a 12" x 12" box, provided you can squeeze 9" in between the raceways.

Agreed?

 

[9275]

I'm still not sure if I don't understand or if I'm not asking the right question.
I'm wanting to install four 1 1/4" raceways out of the top of a L 24"x W 4"x D 4" and one 2 1/2" out the center of the backside is this allowed. The 2 1/2" raceway has twelve #2's then be seperated evenly with three #2's in each 1 1/4" raceway.
Thank You all again for replying

 

[Eric R 1973]

Tables 314.16 A and B deal with standard sizes of boxes and commonly used wire sizes I tried to figure out how the volume allowances for 314.16 B were calculated but i had no luck if it were me
i'd post this question on the engineering calculations thread maybe you'll have better luck finding the answer you"re looking for there

 

[jumper]

Here is a good article on pull boxes.

http://ecmweb.com/nec/code-basics/sizing_junction_boxes/

 

[Dennis Alwon]

See if this helps...

 

[augie47]

I'm still not sure if I don't understand or if I'm not asking the right question.
I'm wanting to install four 1 1/4" raceways out of the top of a L 24"x W 4"x D 4" and one 2 1/2" out the center of the backside is this allowed. The 2 1/2" raceway has twelve #2's then be seperated evenly with three #2's in each 1 1/4" raceway.
Thank You all again for replying

One step at a time.
The depth of your box is fine as 314.28 references us back to 312.6(A) in regard to the depth needed for the 2-1/2" with #2s coming in the back (opposite a removable cover)
314.28 also dictates the distance between conduits with the same conductors is
6X the conduit size. In this case it states the larger raceway so your 2-1/2 would have to be 15" from your 1-1/4".
The wall opposite the 1=1/4" would be 6X 1-1/4 = 7-1/2" + (3) x 1-14 but the requirement above would require that anyway.