# Calculating 750 mcm to a cubic inch allowance

#### CSoliz

##### Member
We have an inspector that wants the wire fill for our 48"x16"x12" gutter. We have 8 750 mcm conductors and 2 500's. I have no idea how to calculate the wire fill for this size of wire. any help would be appreciated.

Thanks

#### augie47

##### Moderator
Staff member
Your gutter is 16 x 12 or 192 sq in. At 20% allowable fill = 38.4 sq in
From Table 5 (pg 677 in '08), 750 kcmil (assuming THHW) has a diameter of 1.1652 sq in, 500 THWN is .7901 sq in
1.1652 x 8 = 9.3216
,7901 x 2 1.5802
Total: 10.9018

If I did the math correctly, you are well within the limit.

#### texie

##### Senior Member
We have an inspector that wants the wire fill for our 48"x16"x12" gutter. We have 8 750 mcm conductors and 2 500's. I have no idea how to calculate the wire fill for this size of wire. any help would be appreciated.

Thanks
Assuming they go straight through and are THHN it would appear you have plenty of room, but I suspect there are some details here like not straight through, splices, bending space, etc that you did not share that would change everything.
750 THHN area =1.0496X8=8.3968
500 THHN area=.70073X2=1.4146
Total area of conductors=9.81
Wireway 16X12=192 CuInX20% allowable=38.4

Must be more to the story.

#### texie

##### Senior Member
Didn't mean to step on/duplicate Augi....you must of posted wile I was calculating.

#### augie47

##### Moderator
Staff member
No problem, I just glad we came up with the "same" answer (taking insulation into account)

#### cowboyjwc

##### Moderator
Staff member
No problem, I just glad we came up with the "same" answer (taking insulation into account)
I did the math in my head and got what Augie and Texie got.:roll:

Are you sure he's looking for wire fill and not for the size of the box (6x or 8x)?

#### texie

##### Senior Member
I did the math in my head and got what Augie and Texie got.:roll:

Are you sure he's looking for wire fill and not for the size of the box (6x or 8x)?
Man, you're good. Do you also have the tables memorized so you don't have to look for just the right table?
Augie had it calculated and posted before I even got to the right page. I must be getting feeble, as I just realized I wrote cubic inch and not square inch. I guess I got a pass as nobody flamed me.
Kidding aside, you may have a point about 6X or 8X as I think there is more to this than we now know.

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#### cowboyjwc

##### Moderator
Staff member
Man, you're good. Do you also have the tables memorized so you don't have to look for just the right table?
Augie had it calculated and posted before I even got to the right page. I must be getting feeble, as I just realized I wrote cubic inch and not square inch. I guess I got a pass as nobody flamed me.
Kidding aside, you may have a point about 6X or 8X as I think there is more to this than we now know.
I have every word in the NEC memorized. I don't have them memorized in the same order that they're in the book, but.....:lol: