NEC Ch.9 Table C.11 Error?

[RookiEE]

Hi all,

I was doing some calculations to get familiar with Ch.9 of NEC regarding conduit fill and found the following, if someone can help confirm that I did it right.

Q: 4#3 RHW and 1#8 RHW GND in PVC Sch 40, find the minimum size of PVC Sch 40.

Per Table C.11, 4#3 RHW can fit in 1-1/4''C PVC Sch 40. The problem is when you use Table 1, 4, & 5 to find the cross-section area of 1-1/4''C PVC Sch 40 for 40% fill is 0.581. But when you add up the cross-section area of the 4#3 RHW cables (Ignore the #8 ground wire and use the RHW without *) = 4 x 0.1521 = 0.6084 which is bigger than 0.581 (the cross-section area of 1-1/4''C PVC Sch 40). Does that mean Table C.11 is wrong on 4#3 RHW cables can fit in 1-1/4''C PVC Sch 40 conduit?

Thanks

 

[infinity]

4 x 0.1521 = 0.6084 which is bigger than 0.581 (the cross-section area of 1-1/4''C PVC Sch 40).

Is the bold correct?

 

[RookiEE]

Yeah, you use the approximate area of Table 5, no need to calculate the cross-section using the diameter.

 

[infinity]

Yeah, you use the approximate area of Table 5, no need to calculate the cross-section using the diameter.

Are you using RHW* without covering? That is .1134 cu inches for #3.

 

[RookiEE]

No, I’m using the one without *, with covering.

 

[infinity]

So from Table C11 RHW with covering says 4-#3 conductors in a 1¼". I agree with you that number is incorrect based on the 0.581. These tables have been known to have inaccuracies and they are not part of the enforceable code.

 

[RookiEE]

Got it, just want to make sure I’m not missing anything, thanks.