PVC Expansion fittings

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superdave02

superdave02

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Does a 15', straight run of 3/4" PVC, between two securely mounted junction boxes, in NC, need an expansion fitting? Asking for a friend.
 
Well, (2017) 352.44 says that an expansion fitting is required if the expected thermal expansion exceeds 1/4", and that PVC has an expansion rate of 3.38 * 10-5 1/F. For a 15' straight run, 1/4" expansion is 1/4 / (12*15) = 1.38 * 10-3. So if the temperature range it will experience is larger than the ratio of those numbers, or 41 degrees F, an expansion fitting is required.

Cheers, Wayne
 
That's what I thought. I just needed someone smarter than I to confirm! A 10' stick of PVC would need an expansion fitting in NC! Crazy.
 
superdave02 said:
That's what I thought. I just needed someone smarter than I to confirm! A 10' stick of PVC would need an expansion fitting in NC! Crazy.
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My calculation in Florida is closer to needing on e at 12', and I m the only one I have seen actually do that here.
 
Strathead said:
My calculation in Florida is closer to needing on e at 12', and I m the only one I have seen actually do that here.
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1/4" / 3.38 * 10-5 1/F = 7.4 * 103 in-F, or 616 ft-F. So you take your high temp and your low temp in degrees F, take the difference and divide it into 616 to find the length in ft at which you need an expansion fitting for a straight run between two fixed points. E.g. high temp = 80F, low temp = 30F, and you get 12.3'.

Or you could can design your layout so that you don't have any straight runs between fixed points, that there's always an elbow or something in between. In which case I'm not sure what the design criterion is.

Cheers, Wayne
 
Don't forget to consider the temperature at installation time compared to the expected temperature extremes.
 
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