Quick (I hope) question: What do you guys use to calculate spans between expansion fittings?
NEC2008 300.7(B): Raceways shall be provided with expansion fittings where necessary to compensate for thermal expansion and contraction. FPN: Table 352.44 and Table 355.44 provide the expansion information for polyvinyl chloride (PVC) and for reinforced thermosetting resin conduit (RTRC), respectively. A nominal number for steel conduit can be determined by multiplying the expansion length in Table 352.44 by 0.20. The coefficient of expansion for steel electrical metallic tubing, intermediate metal conduit, and rigid conduit is 1.170 × 10−5 (0.0000117 mm per mm of conduit for each °C in temperature change) [0.650 × 10−5 (0.0000065 in. per inch of conduit for each °F in temperature change)]. 352.44: Expansion Fittings. Expansion fittings for PVC conduit shall be provided to compensate for thermal expansion and contraction where the length change, in accordance with Table 352.44, is expected to be 6 mm (1⁄4 in.) or greater in a straight run between securely mounted items such as boxes, cabinets, elbows, or other conduit terminations. By my calculations this leads to 3-4 expansion fittings per 100' of EMT for a temperature range of 100 degrees F, which seems like a lot. The rule of thumb I have heard is to use e-fittings for runs over 100' - why are these two so different? Is there really no variability with conduit diameter or thickness? Grassyass, Andrew Truitt Standard Solar Inc. -- "Don't get me wrong: I love nuclear energy! It's just that I prefer fusion to fission. And it just so happens that there's an enormous fusion reactor safely banked a few million miles from us. It delivers more than we could ever use in just about 8 minutes. And it's wireless!" ~William McDonough
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