Intermediate metal conduit, or IMC for short, is a rigid steel electrical conduit that is lighter in weight than another rigid conduit. It was designed specifically to protect insulated electrical conductors and cables. It does the work of a similar conduit, galvanized rigid conduit (GRC), but with much less weight and thickness size. By utilizing IMC in areas allowed, you can all but eliminate the need for a heavier wall conduit.
IMC has other advantages over GRC. It has a larger interior diameter than Galvanized Rigid Conduit and the smoother interior of the pipe allows for easier wire pulling through the conduit.
IMC was originally introduced by Allied Tube & Conduit Corporation. It is manufactured in accordance with Underwriters’ Laboratories safety standard 1242 and ANSI C80.6. Believe it or not, Allied claims that IMC is actually more rigid than GRC in applications such as service masts and other installations. It has been installed in industrial and commercial buildings. In fact, the National Electrical Code has a specific article about IMC, article 342.
IMC conduit is coated in a hot galvanized coating on the exterior and a special corrosive-resistant coating on the inside to extend the conduit’s lifespan for reliability. Common conduit sizes range from ½” to 4”.
Allied Tube & Conduit Corporation has done extensive studies on conduit strength and reliability of its product, IMC. On this product data sheet, they outline all of their testing and guidelines their product had to overcome to become a viable alternative of GRC. If you have any question of whether this conduit can stand up to GRC or exceed it, this article paints a pretty good picture of IMC’s strength and reliability.