Max wire fill in a conduit

[tbischoff9]

I had a test question which said "[FONT=LatoWeb, Helvetica Neue, Helvetica, Arial, sans-serif]How many # 750 THHN Copper conductors fit in a 5” PVC Sch 80 conduit?"[/FONT]
[FONT=LatoWeb, Helvetica Neue, Helvetica, Arial, sans-serif]If I were to use Annex C10 it says that I could fit 7 750kcmil THHN conductors in a 5" PVC Schedule 80[/FONT]
[FONT=LatoWeb, Helvetica Neue, Helvetica, Arial, sans-serif]If I were to use Chapter 9 of the code it says that a 750 kcmil fills 677.2 mm^2 (1.0496 in^2) per conductor and that a 5" PVC Schedule 80 conduit has a max fill for more than 2 wires of 4607 mm^2 (7.142 in^2)[/FONT]
[FONT=LatoWeb, Helvetica Neue, Helvetica, Arial, sans-serif]According to the math I can fit 6.8 wires in the conduit which would mean that I would have to go down to 6 wires in that 5" PVC conduit
Why is there a discrepancy between the math that is calculated in Chapter 9 Tables 4 and 5 and Annex C10?
Both 6 and 7 were possible answers on the multiple choice test, which of the two answers would be the most correct and why?[/FONT]

 

[augie47]

Welcome !
If you look at Note 7 at the beginning of Chapter 9, Table 1 you will see when your calculations are equal to or greater than 0.8 you can go to the next number of conductors.

 

[Dennis Alwon]

Gus nailed it. That Note to the tables always catches people.

 

[MAC702]

I picked 7 because I'll always try to get one more in there....

 

[Besoeker3]

Nah, I'm not puting Max in a conduit..............

 

[augie47]

OOH!, my aching back
(7) 750 cu would be 17 lbs per foot
"I think we are gonna need a bigger forktruck!"

 

[electrofelon]

750 CU, and 5 " PVC.....there's some stuff most of us don't see every day....

 

[jmellc]

The most correct answer is not to mess with 750 at all. 600 is the biggest wire I ever pulled & it had me sore for a month.

 

[kwired]

Nah, I'm not puting Max in a conduit..............

Keep in mind Max fill for two or more conductors per NEC is only 40% of cross sectional area, so there is still room for conductors if you go a little over 40% and is not the same thing as trying to use more than 100% of the available space.

 

[Dennis Alwon]

Keep in mind Max fill for two or more conductors per NEC is only 40% of cross sectional area, so there is still room for conductors if you go a little over 40% and is not the same thing as trying to use more than 100% of the available space.

I think Bes meant his dog Max.

 

[LarryFine]

. . . is not the same thing as trying to use more than 100% of the available space.

Next, you're gonna tell us that the ID of a conduit may not exceed the OD.

 

[kwired]

Next, you're gonna tell us that the ID of a conduit may not exceed the OD.

It can't, but next you are going to give an exception