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Expansion fittings

posted Mar 31, 2012 23:40:08 by DavidDashiells
Richard, I saw your presentation on expansion fittings and remembered that I had heard of a coefficient to use withh the PVC table for the expansion of steel conduit. This would have to be the type of conduit they had the problem with in Bakersfield, because the conduit served as a ground fault path (ie, it was conductive whereas PVC would not have been. I did a search and found this:
*A Fine Print Note in Section 300.7(B) of the NECĀ® refers the user to the Expansion Characteristics of PVC ,Table 352.44(A) for Rigid Nonmetallic Conduit
and suggests multiplying the lengths in that table by 0.20 in order to obtain a nominal number for steel conduit. Since the coefficient of steel conduit is
between 2-3 times less than that of PVC conduit you would need more expansion fittings for PVC conduit, for a given temperature and length than for
steel conduit. We have used the coefficient of expansion of steel, rather than the 0.20 multiplier, to calculate the exact length of change figures in Table 3.
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1 reply
SolPowerPeople said Apr 06, 2012 13:19:12
Hi David,

Thanks for the great information. I hadn't seen that fine print note on using .20 of the the PVC coefficient table. I'm a little surprised that the NEC wouldn't just post the coefficients for steel as listed in the .pdf you provided. I'll be sure to make this information available to people in future discussions on this issue.

Thanks again,

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