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12/2 UF wire in 1/2" PVC

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Btbamfan4

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I have never seen a clear answer on this subject. According to the NEC, my calculations were .1104. I used the eleptical cross sectional formula. The NEC clearly States that, when checking pipe fill, a cable wire is to be considered "one conductor for calculating percentage conduit fill". That means you can use "53%" of the pipe. 1/2" schedule 40 at 53% is .1510. So why does every thread I read say its impermissible?
 
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infinity

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Btbamfan4 said:
I have never seen a clear answer on this subject. According to the NEC, my calculations were .1104. I used the eleptical cross sectional formula. The NEC clearly States that, when checking pipe fill, a cable wire is to be considered "one conductor for calculating percentage conduit fill". That means you can use "53%" of the pipe. 1/2" schedule 40 at 53% is .1510. So why does every thread I read say its impermissible?
Click to expand...

If your numbers are correct it is permissible.
 
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GoldDigger

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Btbamfan4 said:
I have never seen a clear answer on this subject. According to the NEC, my calculations were .1104. I used the eleptical cross sectional formula. The NEC clearly States that, when checking pipe fill, a cable wire is to be considered "one conductor for calculating percentage conduit fill". That means you can use "53%" of the pipe. 1/2" schedule 40 at 53% is .1510. So why does every thread I read say its impermissible?
Click to expand...
I think that your problem is that you are using the area formula for an elliptical cross section. But for conduit fill calculations the code states:
"For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter."
That will almost certainly push your fill percentage over the limit.
 
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Btbamfan4

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Coss section area of a wire is A=pi(r^2). The diameter of the is .375. So the radius is .1875. A=pi(.1875^2) which equals .1104466167. That formula makes the cable into a single conductor. The pipe fill minimum requirement at 53%(single conductor) is .110446617÷.53=.2083. In the NEC schedule 40 1/2" pipe is .285
 
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Btbamfan4

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It was all I had on me and I was by myself. I pieced it together in the crawl space and didnt damage the wire. Last time I'll ever do this. I just wanted to make sure I dont have to go back out and repull it in thhn, because I will if I have to
 
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Btbamfan4

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GoldDigger said:
I think that your problem is that you are using the area formula for an elliptical cross section. But for conduit fill calculations the code states:
"For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter."
That will almost certainly push your fill percentage over the limit.
Click to expand...
Yeah I measured the diameter at.375. The Cross sectional area of a wire is A=pi(r^2). The diameter of the wire is .375. So the radius is .1875. A=pi(.1875^2) which equals .1104466167. That formula makes the cable into a single conductor. The pipe fill minimum requirement at 53%(single conductor) is .110446617÷.53=.2083. In the NEC schedule 40 1/2" pipe is .285. Please correct me if I'm wrong. That's why I'm on here lol, because I need to be reassured
 
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Btbamfan4

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I see what you're saying about the "circle diameter" as in not the radius, but what I took from it was, use the larger side of the wire as the diameter, not the smaller side.
 
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GoldDigger

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Btbamfan4 said:
I see what you're saying about the "circle diameter" as in not the radius, but what I took from it was, use the larger side of the wire as the diameter, not the smaller side.
Click to expand...
I was concerned that you said you used the formula for the actual area of an ellipse. That would have been wrong.

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Btbamfan4

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Srv52761 said:
South wire gives specs for 12/2 uf-b as 0.463 x 0.183.
At r=0.2315 the % fill comes out at ~59%.
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Thanks man! That's what I was looking for. I got the specs off another thread. So 3/4 minimum. Looks like I'm about to go push so thhn and redo everything smh lol
 
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suemarkp

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To me, .375 seemed pretty small for UF cable and I would have guessed 1/2" wide.. It has been a few years since I've bought it, and it seems all the cables are skinnier now, but .375 seems tight for NM let alone UF. Maybe you're not using Southwire, but whatever you have I'd measure it again...

If you use the conduit as a sleeve (at least one end open with a bushing), then I don't think the fill rules matter. I think the intent of this is a straight run, as you'll most likely never be able to pull NM or UF around multiple bends. Even one bend could be tough.
 
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