The Inside Story of Steel Conduit and Tubing
Requirements for coatings on steel rigid metal conduit (RMC), intermediate metal conduit (IMC) and electrical metallic tubing (EMT) are included in the UL product standards as well as in the ANSI C80 standards for conduit and EMT. The National Electrical Code requires that these products be listed (see NEC sections 344.6, 342.6 and 358.6, respectively). STI Conduit Committee members list their products to the UL standards and manufacture them in accordance with the applicable ANSI C80 standards.
The UL and ANSI C80 standards require zinc or an alternate corrosion protection coating for the conduit / tubing exterior and a zinc or organic coating for the interior. All STI members supply steel RMC that is hot-dip galvanized, and so the interior of RMC is zinc-coated. For IMC and EMT, manufacturers typically use a low-friction interior coating that facilitates easy wire pulling, in addition to providing corrosion protection. For specific coating information by manufacturer, please contact our members.