Simple Question on Annex C:

[new_ee]

Tables on maximum number of conductors in conduit. For example in table C1 it says the max number of #4 THHN in 1" conduit is 4. Does that mean you cannot also have at smaller EGC conductor in the conduit? I know if I do it the calculation way (adding up the areas of all the conductors) it says that I should be able to fit 4-#4 THHN and an #8 EGC in a 1" conduit. Is annex C enforcable code?

The reason I ask is I had a plans reviewer quote it and said that my conductors (on my plans) would not fit based on table C1 in annex C. And it was a similar situation (all conductor sizes have been changed to protect the innocent).

 

[charlie b]

No annex is enforceable. But the rule about 40% fill is enforceable. If you can show that the cross-sectional areas of all conductors add up to less than 40% of the internal area of the conduit, then you meet the code requirement.

The only hitch is that the Inspector might want to see a formal calculation bearing the signature and seal of a licensed Professional Engineer, before he accepts the proposed installation. That said, the Inspector cannot say, "Annex C limits you to four wires, and that is all you can install."

One more point, and it's one I have no experience in applying. You might be able to prove that your installation is under 40% fill. But that does not mean that the installer will have an easy time pulling those conductors through that conduit. Sometimes it is better (meaning cheaper) to go up one conduit size, in that the reduced installation costs offset the increased material costs.

 

[jtester]

Tables on maximum number of conductors in conduit. For example in table C1 it says the max number of #4 THHN in 1" conduit is 4. Does that mean you cannot also have at smaller EGC conductor in the conduit? I know if I do it the calculation way (adding up the areas of all the conductors) it says that I should be able to fit 4-#4 THHN and an #8 EGC in a 1" conduit. Is annex C enforcable code?

The reason I ask is I had a plans reviewer quote it and said that my conductors (on my plans) would not fit based on table C1 in annex C. And it was a similar situation (all conductor sizes have been changed to protect the innocent).

A better way to look at Annex C is that you can't put in 5 #4 conductors. It is possible, likely that there is a bit of room left over after the 4 conductors are installed, but not enough for another #4.

Your calculations are correct.

Jim T

 

[charlie b]

A better way to look at Annex C is that you can't put in 5 #4 conductors. It is possible, likely that there is a bit of room left over after the 4 conductors are installed, but not enough for another #4.

I agree. That is the right way to interpret that Annex.

 

[new_ee]

I would have no problem if the plans review quoted the 40% fill. I just didn't understand why he quoted the annex C table.

 

[dnem]

I would have no problem if the plans review quoted the 40% fill. I just didn't understand why he quoted the annex C table.

You still shouldn't have problem. . Annex C is only saying that you can't put another #4 in there, just like these other guys have been saying. . It's not saying anything else.

Annex C is only usable when:
1) installing conductors that all have the same size or
2) mixing sizes but staying with the number limit of the largest conductor

In other situations you have to do the math in the chapter 9 tables

 

[qcroanoke]

"One more point, and it's one I have no experience in applying. You might be able to prove that your installation is under 40% fill. But that does not mean that the installer will have an easy time pulling those conductors through that conduit. Sometimes it is better (meaning cheaper) to go up one conduit size, in that the reduced installation costs offset the increased material costs."

Can I get an AMEN!!!
Just because the code says it will fit doesn't mean it will be easy.

 

[dcspector]

Good point. Before becoming an Inspector I was an EC. Example. Yes, one is mathematically allowed to pull 35 # 12's THHN in 1" "thin wall" (EMT)...... but why would you want to?

 

[don_resqcapt19]

Charlie,

The only hitch is that the Inspector might want to see a formal calculation bearing the signature and seal of a licensed Professional Engineer, before he accepts the proposed installation.

I can see were the inspector may want to see the calculation, however I see no reason that this calculation would have to be done by a PE. All of the information required to make the calculation is found in the Chapter 9 Tables.
Don

 

[Rockyd]

Thanks Don,

I was thinking along the same way. Journeyman are supposed to test into their position with the AHJ (normally a state certificate), and apply code in common installations, or per print. If it's beyond scope, that is exactly what engineers are for. No one knows it all, but each position in the industry, comes with a certain amount of expectations.

 

[celtic]

I would have no problem if the plans review quoted the 40% fill. I just didn't understand why he quoted the annex C table.

Because it was easy ~ aka, involved no math or actions on his part other than cracking a book open.

 

[dnem]

The only hitch is that the Inspector might want to see a formal calculation bearing the signature and seal of a licensed Professional Engineer, before he accepts the proposed installation

Charlie,
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I can see were the inspector may want to see the calculation, however I see no reason that this calculation would have to be done by a PE. All of the information required to make the calculation is found in the Chapter 9 Tables.
Don

I agree. . The calculation doesn?t need to be done by a person with certification because the inspector is certified (hopefully) and he should be able to check their math and tell them if they did it right or wrong.

Thanks Don,

I was thinking along the same way. Journeyman are supposed to test into their position with the AHJ (normally a state certificate), and apply code in common installations, or per print. If it's beyond scope, that is exactly what engineers are for.

Even in the states where journeymen have no certification, the contractor would have a license that he passed the requirements for. . The fact that the contractor has his license shows him to be viewed as competent by the state to apply the code, apply the instructions on the plans, and apply the manufacturers instructions.

What the inspector might want is the Engineers OK to deviate from his plans. . He's responsible for designing the job and the inspector is responsible to enforce those plans. . If the pipe size or wire numbers differ from the approved plans, the Engineer would need to agree with the change.

David

 

[LarryFine]

The section that the inspector so dilligently quotes cleary states:

Annex C
Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size
This annex is not a part of the requirements of this NFPA document but is included for informational purposes only.

Now, add to that the following notes to Ch. 9 Tables:

Notes to Tables
(1) See Annex C for the maximum number of conductors and fixture wires, all of the same size (total crosssectional area including insulation) permitted in trade sizes of the applicable conduit or tubing.
(6) For combinations of conductors of different sizes, use Table 5 and Table 5A for dimensions of conductors and Table 4 for the applicable conduit or tubing dimensions.

Annex C is included to make it easier for us to select conduit size based on known conductor count. When mixing conductor sizes, we are steered to Tables 4, 5, and 5A.

 

[Rockyd]

I agree with what Larry is saying, but some things fall out of the ordinary.

If it's beyond scope, that is exactly what engineers are for.

Such as a VFD operating at 480 will operate somewhere north of 650 V on the norm, at times. So do I install medium voltage cable? RFI time for me, or the wave of an engineer's hand to "solve" my problem. Normally approaching unknowns, I ask, 1 is it conceivable and workable, 2 is it safe, and finally, 3 is it legal?

Somedays I feel like a genious, and somedays -we'll not go there...

Sometimes I get saved on the print footnotes and a trip to references, or posts here in the forum, before I have to ask.