PVC Conduit Thermal Expansion (NEC 352.44)
The longitudinal length change of a PVC raceway across its temperature swing (delta_L = coefficient x length x temperature change) against the NEC 352.44 quarter-inch expansion-fitting trigger, for outdoor or unconditioned runs. The AHJ and the conduit manufacturer govern.
Formula and source
delta_L = coefficient x (run_length_ft x 12) x temperature_change; an expansion fitting is required once delta_L reaches the 1/4-inch (0.25 in) trigger, sized for that travel. PVC coefficient 3.38e-5 in/in/deg-F.
NEC 2023 (NFPA 70). 352.44 (expansion fittings for rigid PVC conduit).
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