Question: What is the coefficient of expansion for steel conduit/EMT and why is this significant?

Answer: The coefficient of expansion for steel conduit/EMT is 6.5×10-6 in./in./°F. This is significant as it relates to whether or not expansion fittings would be required in a particular application. Expansion fittings are installed where significant temperature differentials are anticipated. These temperature shifts cause materials to expand and contract and could result in the conduit being pulled apart at the joint. Expansion fittings are not normally required with steel conduit/tubing because their coefficient of expansion is identical to or similar to that of other common building materials. However, where steel conduit is installed on bridges or rooftops or as an outdoor raceway span between buildings, expansion fittings may be required. In these types of installations, there is a probability that expansion and contraction would occur, resulting from the direct heat of the sun coupled with significant temperature drops at night. Expansion characteristics of steel conduit/tubing are shown in Table 3, at 5°F to 200°F in 5°F increments. The table also shows the length changes for steel conduit at each temperature differential. This will help determine the need for expansion fittings. For information about the use of expansion fittings please refer to Installation Guidelines for Expansion and Expansion/Deflection Fittings (NEMA FB 2.40) by NEMA.