Intermediate Metal Conduit — IMC (ferrous metal). Developed in the '70s, IMC is a listed threaded steel raceway of circular cross section with a coupling that can be either a standard straight-tapped conduit coupling or the integral type . Just as with RMC, industry color-coded thread protectors protect the uncoupled ends of the conduit and keep them clean and sharp, and aid in trade size recognition. IMC is available in trade sizes ½ through 4. Thread protectors for trade sizes 1, 2, 3 and 4 are color-coded orange; trade sizes ½, 1½, 2½, and 3½ are yellow; and trade sizes ¾ and 1¼ are green. The standard finished length of IMC, with coupling, is 10 feet.
Steel Conduit Basics
Intermediate metal conduit (IMC) has a thinner wall than RMC and weighs about one-third less.
IMC has a thinner wall than RMC and weighs about one-third less than RMC. The outside has a zinc-based coating, and the inside has an approved organic corrosion-resistant coating. IMC is interchangeable with galvanized RMC. Both have threads with a 0.75-inch-per-foot taper, use the same couplings and fittings, have the same support requirements, and are permitted in the same locations.