"Wire conduit" refers to durable tubing or other types of enclosures used to protect and provide a path for individual electrical conductors. Conduit is often required where there are exposed wires or where wires may be damaged. Conduit can be made of metal or plastic and can be rigid or flexible. All conduits are fitted with compatible fittings (couplings, elbows, connectors) and electrical boxes, usually made of the same or similar materials. Wire conduit must be installed in accordance with the National Electrical Code (NEC) and all applicable local codes.
Rigid Metal Conduit RMC is heavy-duty galvanized steel tubing installed with threaded fittings. It is typically used outdoors to provide protection from damage and also to provide structural support for cables, panels and other equipment. rmc is available in 10 and 20 foot lengths and is threaded on both ends.
Intermediate Metal Conduit (IMC) is a thinner, lighter version of rigid metal conduit and is approved for all of the same applications as RMC. Because IMC is lighter and easier to use than RMC, it is more common in newer constructions.
Another example of rigid electrical conduit is EMT (electrical metallic tubing), which is most often made of galvanized steel, but can also be aluminum. The EMT is equipped with couplings and fittings, and is secured with set screws or compression type fasteners. The conduit itself is not threaded like RMC and IMC. common sizes of EMT include 1/2", 3/4" and 1". It is typically used for exposed indoor wiring in residential and light commercial construction. If it is installed outdoors in an exposed location, it must be assembled with special waterproof fittings.
Nonmetallic electrical conduit (ENT) is flexible, corrugated plastic pipe that is moisture resistant and flame retardant. It is easily bent and can be installed using spring locks or glued plastic fittings. Unlike EMT, non-metallic pipe cannot be installed in exposed locations and is therefore typically used inside walls. In addition to being installed in standard wood or metal framed walls, ENT can be installed within concrete block construction and can be covered with concrete. ENT is nicknamed "Smurf pipe" after the Smurf cartoon character due to the common branding of the conduit in blue.
Flexible Metal Conduit (FMC) is also referred to as "unexplored area" after its inventor's name. It has a spiral structure that makes it flexible, so it can snake through walls and other structures. Standard FMC is used in dry indoor locations and is typically used for short runs between wall boxes and motors or fixtures such as garbage disposals. Liquid-tight flexible metal conduit (LFMC) is a special type of flexible metal conduit that has a plastic coating and is used with sealing fittings to make it watertight. It is typically used with outdoor equipment, such as air conditioning units.
Rigid polyvinyl chloride (PVC) resembles plastic conduit and is fitted with plastic fittings that are glued in place. It can be bent after being heated in a portable heater box. Because the conduit and fittings are glued together, the conduit assembly can be impervious to water, making PVC suitable for a wide variety of applications where it is buried directly into the ground. Use in corrosive environments is also permitted.