AHJ buying off conductors in conduit, at 42% fill?

F

fastline

Senior Member
Location
midwest usa
Occupation
Engineer
Curious of experiences in the field. Have a case where I'd 'like' to pull 7, 500mcm copper conductors (before ground) in a distance of about 25ft with two 90* ells. The conduit is 4" and already in place so I am trying to max it out best I can.

The fill is pushing it, not fun, but also not far to go. I guess examine from both a practical pov as well as AHJ because if AHJ won't accept, nothing else really matters, which backs it down to 400mcm. Because max ampacity is desired, copper is the target.
 
fastline said:
I'd 'like' to pull 7, 500mcm copper conductors (before ground) in a distance of about 25ft with two 90* ells. The conduit is 4"
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According to Table C10 you can only fit 6-500 kcmil THWN-2 in a 4" SCH80 PVC conduit. EGC's count as well. Have you also figured in the derating factor?
 
Yes, derate was considered, numbers are calculated, not from a table, EGC has not been added yet, numbers were run with 7, 500 conductors. Agree on downsize of neutral. Just had this talk and the only thing really needed for 277 is lighting, which is now way more efficient. IE, plenty of reason to downsize neutral.

But to my point, do any of your AHJs do the math and stick you, or do they maybe use the simple table? Obviously the table would screw this deal up.
 
fastline said:
But to my point, do any of your AHJs do the math and stick you, or do they maybe use the simple table? Obviously the table would screw this deal up.
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Not sure I understand the question. The fill limit is 40% which is usually enforced as written.
 
infinity said:
3/1000's%? I think that most inspectors would let that go. You stated 7-500's in a conduit that only allows 6-500's, that is not really close.
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This is prob all I need I guess. you guys just go off the table. 7 puts you only slightly over but whatev. Just talk to the AHJ I guess.
 
fastline said:
The question is....... if it is 40.003%, is that typically a no-go by AHJs you deal with?
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Honestly , I wouldn't expect an AHJ to look at it in the first place, unless it was blatantly off. But I see your occupation is Engineer. Are you going to be the one making up the head and getting this pull through the conduit?
 
1) It may be worth hunting around to different manufacturers to see if you can get compact or compressed stranded copper conductors. This sort of stranding is common in aluminum but rare in copper, and it makes a difference for conduit fill.

2) Make sure you do the calculations yourself with the actual conductor dimensions from the manufacturer. There is quite a bit of variation in the numbers.
 
winnie said:
1) It may be worth hunting around to different manufacturers to see if you can get compact or compressed stranded copper conductors. This sort of stranding is common in aluminum but rare in copper, and it makes a difference for conduit fill.

2) Make sure you do the calculations yourself with the actual conductor dimensions from the manufacturer. There is quite a bit of variation in the numbers.
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Wouldn't you have to change the lugs. Standard lugs won't usually work with compact conductors
 
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