314.28 box sizing

Status
Not open for further replies.
K

Ken Forest

Member
Location
Knoxville
Occupation
electrician
I never had any problem with an inspection regarding box sizing, but I always wonder how it works...
I am bringing 3" (x2) conduits, using angle pull (x6), the min width must be, 3"x6 plus 3", 21". so I get a box 24"x24"X12". I thought it would be big enough.
this inspector wants some calculation, then, I think it through, the conduits coming in from outside the wall into the back of the box. Not from side. Does that mean, the depth being 12", the box is not deep enough? has to be min. 21" deep? it looks stupid to mount the box sideway on the wall... any thoughts?
 
If the box has a removable cover opposite the conduit entries see 314.28(A)(2) Exception which will refer you to 312.6
 
so now, I went back to the job site, there would be 10 of the TC-ER XHHW-2 (500kcmil with 4/0 ground) bundles comes in and out of the box in addition to the parallel sets of 500kcmil with 4/0 ground already there. there would also be 5 of 12 port Polaris taps that are 75.0541 in2 in volume. to make taps of all 12 conductors. The box I have installed now is 30"x30"X12". the electrician said the box may be too small.
I was looking into some calculation I can use to add all the volumes of the conductors and the five Polaris taps to convince the electrician and an inspector that the box is good to go... I only found 312.8 (A) but that is for switch and overcurrrent protection, using 75% of the box space.
what can be the right way to figure this out? Thoughts?
 
Ken Forest said:
so now, I went back to the job site, there would be 10 of the TC-ER XHHW-2 (500kcmil with 4/0 ground) bundles comes in and out of the box in addition to the parallel sets of 500kcmil with 4/0 ground already there. there would also be 5 of 12 port Polaris taps that are 75.0541 in2 in volume. to make taps of all 12 conductors. The box I have installed now is 30"x30"X12". the electrician said the box may be too small.
I was looking into some calculation I can use to add all the volumes of the conductors and the five Polaris taps to convince the electrician and an inspector that the box is good to go... I only found 312.8 (A) but that is for switch and overcurrrent protection, using 75% of the box space.
what can be the right way to figure this out? Thoughts?
Click to expand...
There are no conductor volume calculations for box sizes where the conductors are 4 AWG and larger expect those used with small dimension boxes as provided for in 314.28(A)(3). It is all based on conduit size and the rules in 314.28(A)
 
Status
Not open for further replies.
Top