Expansion Joint Calculator
Calculate PVC conduit thermal expansion and contraction with temperature changes to determine expansion fitting needs.
Results
Visualization
How It Works
PVC conduit expands and contracts significantly with temperature changes. Without expansion fittings, this thermal movement can crack fittings, pull apart glued joints, and damage conductors inside the raceway.
The Formula
Expansion (in) = Coefficient × Length (in) × ΔT
Coefficient for PVC = 3.38 × 10-5 in/in/°F
Coefficient for PVC = 3.38 × 10-5 in/in/°F
Variables
- Coefficient — Linear expansion rate of PVC: 3.38 x 10^-5 inches per inch per degree F
- Length — Total conduit run length converted to inches
- Delta T — Temperature change from installation temperature
Example
100 ft PVC conduit, installed at 70F, range 20F to 100F: Max expansion = 3.38e-5 x 1200 x 30 = 1.22 in. Max contraction = 3.38e-5 x 1200 x 50 = 2.03 in. Total movement = 3.25 in.
Tips
- Install expansion fittings every 25-30 feet in exposed PVC runs.
- Expansion joints must be installed with the piston centered at installation temperature.
- Metal conduit has much lower expansion (about 1/7th of PVC) and rarely needs joints.
- Exposed outdoor runs and rooftop installations experience the greatest temperature swings.
- Improper expansion compensation is the number one cause of PVC conduit failures.