Yes or no?

[hardworkingstiff]

On page 753 (2008 codebook) table C.10(A) says I can install 6 4/0 THWN conductors in a 2.5" conduit (schedule 40 PVC).

On page 678, table 5 says a 4/0 THWN conductor has an approximate sq. in. area of .3237. Multiply that by 6 and you get 1.942.

On page 675, schedule 40 PVC has a 40% area of 1.878.

Since 1.942 is larger than 1.878, may I install 6 4/0 THWN conductors in the 2.5" PVC per table C.10(A) even though the math says no?

Am I missing something?

For those that need to know, the 2.5" conduit is existing and we need to maximize the size of our conductors. Installing a larger conduit is not allowed (at this time).

 

[augie47]

It's early here, so sleep may effect my understanding, but, you're missing "A", I believe.
Table C10(A) is for compact conductors
Table 5A, Pg 680, is for compact conductrs.

 

[Dennis Alwon]

On page 753 (2008 codebook) table C.10(A) says I can install 6 4/0 THWN conductors in a 2.5" conduit (schedule 40 PVC).

On page 678, table 5 says a 4/0 THWN conductor has an approximate sq. in. area of .3237. Multiply that by 6 and you get 1.942.

On page 675, schedule 40 PVC has a 40% area of 1.878.

Since 1.942 is larger than 1.878, may I install 6 4/0 THWN conductors in the 2.5" PVC per table C.10(A) even though the math says no?

Am I missing something?

For those that need to know, the 2.5" conduit is existing and we need to maximize the size of our conductors. Installing a larger conduit is not allowed (at this time).

You may not do this legally...:smile:

 

[hardworkingstiff]

It's early here, so sleep may effect my understanding, but, you're missing "A", I believe.
Table C10(A) is for compact conductors
Table 5A, Pg 680, is for compact conductrs.

You are correct, but I just checked table C.11 and the problem remains the same. This table also says I can install 6 4/0 conductors in the 2.5" conduit.

 

[hardworkingstiff]

You may not do this legally...:smile:

Table C.11 (page 755) says I can. :smile:

 

[Dennis Alwon]

You are correct, but I just checked table C.11 and the problem remains the same. This table also says I can install 6 4/0 conductors in the 2.5" conduit.

What is Type "A" Pvc conduit. That is in the heading of c 11

 

[hardworkingstiff]

What is Type "A" Pvc conduit. That is in the heading of c 11

Dang, my lack of attention to detail is showng. Thanks Augie and Dennis.

Let's try table C.10, and the problem is unchanged.

 

[augie47]

I believe Type A is a PVC product designed to be used only encased in concrete, and has a different wall thicknes from "EB", Sch40

 

[steve66]

Table C.10 seems to say you can do it. But your AHJ might have issue with the first line of the annex:

"Annex A is not part of the requirements....."

So if the Code section says you can't, and the annex says you can, I would tend to give more weight to the code section.

And of course, if you have a long run, or has a lot of bends, you will probably never get them pulled in no matter what the code says.

Steve

 

[Cow]

I was taught to only use the conduit fill tables as a rule of thumb, for exact fill, you need to calculate manually. Those tables have more than one error in them too, better to be safe and double check.

 

[don_resqcapt19]

See Note 7 to Table 1 in Chapter 9.

 

[hardworkingstiff]

See Note 7 to Table 1 in Chapter 9.

Thanks Don, you 'da man'. :grin:

 

[C3PO]

See Note 7 to Table 1 in Chapter 9.

So 1.878(area avialible to fill) / .3237(area of 4/0 THWN) = 5.80167
Round 5.80167 up to 6

Is that what note 7 means?

 

[LarryFine]

Round 5.80167 up to 6

Is that what note 7 means?

That's exactly what it means.

 

[ceb58]

Mike Holt's free calculator says 3" Go with it