7 Types of Electrical Conduit
Electrical conduit is durable tubing or other type of enclosure used to protect and provide a route for electrical wiring. Conduit is typically required where wiring would be exposed or where it might be subject to damage. A conduit can be made of metal or plastic and may be rigid or flexible. All conduit is installed with compatible fittings (couplings, elbows, connectors) and electrical boxes, usually made of the same or similar material. Conduit must be installed in accordance with the National Electrical Code (NEC) and all applicable local code rules.
Rigid Metal Conduit (RMC and IMC)
Rigid metal conduit, or RMC, is heavy-duty galvanized steel tubing that is installed with threaded fittings. It is typically used outdoors to provide protection from damage and can also provide structural support for electrical cables, panels, and other equipment. RMC is sold in 10- and 20-foot lengths and has threads on both ends.
Intermediate metal conduit, or IMC, is a thinner, lighter-weight version of rigid metal conduit and is approved for use in all of the same applications as RMC. Because IMC is lighter and easier to work with than RMC, it is used more commonly in new construction.
Electrical Metallic Tubing (EMT)
Another example of a rigid electrical conduit is EMT, which is most commonly made of galvanized steel but can be aluminum. EMT is also called "thin-wall" conduit because it is thin and lightweight, especially compared to RMC. EMT is rigid but can be bent with a simple tool called a conduit bender. EMT is installed with couplings and fittings that are secured with a setscrew or compression-type fastener. The tubing is not threaded like RMC is. Common sizes of EMT include 1/2-inch, 3/4-inch, and 1-inch.
It is commonly used for exposed indoor wiring runs in residential and light commercial construction. It must be used with special watertight fittings to be used outdoors in exposed locations.
Electrical Non-Metallic Tubing (ENT)
Electrical nonmetallic tubing (ENT) is flexible corrugated plastic tubing that is moisture-resistant and flame-retardant. It is easy to bend and installs with snap-lock or glued plastic fittings. Unlike EMT, non-metallic tubing cannot be exposed, so it is commonly used inside walls. In addition to standard wood- or metal-frame walls, It can be installed inside a concrete block and can be covered with concrete. Due to the blue color of one common brand of this conduit, ENT is nicknamed "smurf tube."
Flexible Metal Conduit (FMC and LFMC)
Flexible metal conduit (FMC) is also called "Greenfield," after the name of its inventor. It has a spiral construction that makes it flexible so it can snake through walls and other structures. Standard FMC is used in dry indoor locations, often for short runs between a wall box and a motor or fixed appliance, such as a garbage disposer.
Liguidtight flexible metal conduit (LFMC) is a special type of flexible metal conduit that has a plastic coating and is used with sealed fittings to make it watertight. It is commonly used with outdoor equipment, such as air conditioner units.
Rigid PVC Conduit
Rigid polyvinyl chloride (PVC) is similar to plastic plumbing pipe and installs with plastic fittings that are glued in place. It can be bent after being heated in a portable heater box. Because the conduit tubing and fittings are glued together, the conduit assemblies can be watertight, and PVC is suitable for direct burial in the ground in many applications. It is also allowed in corrosive environments.