PVC Raceway Expansion Fitting
PVC conduit thermal length change, whether an expansion fitting is required (>= 0.25 in).
Example
You enter
- Conduit run length (ft) 100
- Temperature range (°F) 100
- Alpha per f 0.0000338
- Fitting rated travel (in) 6
You get
- Length change 4.056
- Fittings needed 1
Checked against published worked examples from: NEC Article 352.44 / Table 352.44 (by name).
Details, formula, and sources
ScopePVC conduit thermal length change, whether an expansion fitting is required (>= 0.25 in), and the fitting count from the run length and temperature range (NEC 352.44).
Formula or tabledL = alpha * L * dT with alpha = 3.38e-5 in/in/F (NEC Table 352.44 PVC); an expansion fitting is required where dL >= 0.25 in in a straight run; fittings = ceil(dL / fitting_travel).
Source and editionPVC raceway thermal expansion and expansion-fitting sizing - the length change over the run from the temperature range, the 0.25 in straight-run threshold, and the fitting count - per NEC Article 352.44 and Table 352.44 (rigid PVC conduit), by name; first-principles linear expansion.
Free accessNEC is free to read at nfpa.org/freeaccess. The 3.38e-5 in/in/F PVC-conduit coefficient is the NEC Table 352.44 figure, distinct from PVC pipe.
What governsEstimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.
API field namesrun_length_ft, temp_range_f, alpha_per_f, fitting_travel_in, length_change_in, fittings_needed
- Conduit coefficient 3.38e-5 in/in/F for rigid PVC conduit per NEC Table 352.44; user-overridable for RTRC / other racewayNEC Table 352.44