Carlon Expansion Joints - Manual

All construction materials expand and contract
with fluctuations in temperature. These temperature
changes affect polyvinyl chloride (PVC) more than
traditional materials such as aluminum and steel.
For example, the coefficient of thermal expansion
for PVC (3.38 x 10
-5 in./in./°F) is almost three times
as high as for aluminum and six times as high as
for steel.
Thermal expansion and contraction have a
significant effect on long straight runs of conduit.
For this application, expansion fittings are used to
accommodate changes in length. This prevents
potentially harmful thermal stresses in the conduit
itself or in any supporting structures.
The National Electrical Code Requirements
Section 352.44 of the National Electric Code® requires that
expansion fittings be installed for rigid nonmetallic conduit to
compensate for thermal expansion and contraction where the
length change is anticipated to be 0.25 in. (6.36mm) or greater, in accordance with Table 352.44 of the NEC, in a straight run
between securely mounted items. Securely mounted items are
boxes, cabinets, elbows, or other conduit terminations.
When are expansion fittings used?
The importance of knowing when to use an expansion fitting is as
important as knowing how to use an expansion fitting. Expansion
fittings are used in aboveground installations where temperature
changes are anticipated to exceed 25°F (14°C). Expansion fittings are usually used where the straight run length is
greater than 25 feet and expected temperature change is greater
than 60°F. Rigid PVC conduit has a coefficient of expansion of
3.38 x 10
-5 in./in./°F. A 10 foot length will change in length about
3/8" with a change in temperature of 100°F. This equates to more
than 4 inches over a 100 foot run.
Barrel Piston Mid-Point Indicator
Male Terminal
Adapter End
Coupling End
Carlon ® Expansion Fittings for
PVC Rigid Nonmetallic Conduit
Gross Automation (877) 268-3700 · www.carlonsales.com · [email protected]