Metal Electrical Conduits
Rigid Metal Conduit (RMC):
RMC is composed of heavyweight galvanized steel and installed with threaded fittings. Known for being very strong, RMC is unfortunately one of the more expensive electrical conduits when it comes to both materials and labor. Aluminum is another material used for RMC, and may have additional coating applied to better resist corrosion.
Galvanized Rigid Steel (GRC):
Approved for indoor and outdoor applications, GRC is made from steel and is traditionally found in industrial and commercial applications, GRC has been a long-time industry standard and benefits from impressive impact resistance, as well as UV-stability and the ability to protect from EMI (electromagnetic interference). Unfortunately, its heavy weight and poor field handling make GRC particularly expensive to install and it can be highly susceptible to corrosion. GRC’s conductivity makes it susceptible to fault conditions in which the conduit and wire may weld together.
Intermediate Metal Conduit (IMC):
Approved for the same applications as RMC, IMC is a steel conduit that is slightly lighter than RMC and rated for outdoor use. It can be more cost-effective than RMC, available threaded or unthreaded, and may or may not be coated. Compared to GRC and RMC, IMC has much thinner walls that can handle more wire fill but is more susceptible to kink. IMC only goes up to 4 inches in trade sizes, so it is significantly smaller than other conduits.
Electrical Metallic Tubing (EMT):
Thin-walled and unthreaded, EMT is typically made of coated steel and used in place of GRC in commercial and industrial applications, though it is commonly found in residential applications as well. It can also be made of aluminum and is approved for use in concrete but is not permitted to be installed where subject to physical damage. EMT is not able to offer the same level of protection as GRC. It is easily bent but can not be field threaded because of its thinness. Common trade sizes run from .5 inch to 1.5 inches.