Comparison with other wiring methods and benefits of conduit installation
– Electrical conduit provides protection to enclosed conductors from impact, moisture, and chemical vapors.
– Conduit allows for easy design and construction compared to multiple runs of cables.
– Wiring changes are simplified and safer with conduit, as existing conductors can be withdrawn and new ones installed.
– Conduit can be made waterproof or submersible.
– Metal conduit shields sensitive circuits from electromagnetic interference and prevents emission of such interference.
– Conduit protects against flammable gases and vapors, reducing fire and explosion hazards.
– Metal conduit can serve as a bonding conductor for grounding.
– Non-metallic conduits resist corrosion and are lightweight, reducing labor costs.
– Conduit allows for neat installations without excessive fittings, especially in irregular or curved building profiles.
– Conduit can be bent at the job site without kinking or denting, using special equipment.
Types of conduit
– Rigid metal conduit (RMC) is thick-walled and threaded, made of coated steel, stainless steel, or aluminum.
– Galvanized rigid conduit (GRC) is galvanized steel tubing used in commercial and industrial construction.
– Intermediate metal conduit (IMC) is heavier than EMT but lighter than RMC, and may be threaded.
– Electrical metallic tubing (EMT) is commonly used instead of GRC, as it is less costly and lighter.
– Aluminum conduit is rigid and corrosion-resistant, suitable for commercial and industrial applications.
– PVC conduit is lightweight, lower in cost, and resistant to moisture and corrosive substances.
– Reinforced thermosetting resin conduit (RTRC) or fiberglass conduit is light in weight.
– RTRC conduit can be used in a variety of indoor and outdoor applications.
– Fiberglass conduit is available in multiple wall thicknesses.
– Rigid nonmetallic conduit (RNC) is a non-metallic unthreaded smooth-walled tubing.
Flexible conduit
– Flexible conduits are used to connect to motors or other devices where isolation from vibration is useful.
– Flexible metallic conduit (FMC) is made by the helical coiling of a self-interlocked ribbed strip of aluminum or steel.
– FMC may be used as an equipment grounding conductor.
– Liquidtight flexible metal conduit (LFMC) is a metallic flexible conduit covered by a waterproof plastic coating.
– Flexible metallic tubing (FMT) is a raceway, but not a conduit, and is described in a separate NEC Article.
Underground conduit
– Conduit may be installed underground between buildings, structures, or devices.
– PVC, polyethylene, or polystyrene plastics are now used for underground conduit due to lower cost and better resistance to corrosion.
– Formerly, compressed asbestos fiber mixed with cement was used for some underground installations.
– Telephone and communications circuits were typically installed in fired-clay conduit.
– Duct banks allow replacement of damaged cables or addition of circuits without re-excavation of a trench.
Cost comparison, fittings, conduit bodies, surface mounted raceway, trunking, innerducts, and passive fire protection
– Cost relative to rigid galvanized steel (RGS) conduit varies depending on the size.
– Aluminum conduit has a lower labor cost and material cost compared to RGS conduit.
– PVC conduit has the lowest material cost among the listed types.
– EMT conduit has a lower labor cost compared to RGS conduit.
– RMC conduit has equal labor, weight, and material cost as RGS conduit.
– Box connectors join conduit to a junction box or other electrical box.
– Couplings connect two pieces of conduit together.
– Fittings for non-threaded conduits are secured with set screws or compression nuts.
– Grounding bushings are used to bond the metal conduit to a metal junction box.
– Gaskets are used with special fittings to keep water out of watertight conduit.
– Conduit bodies provide pulling access and allow more bends in a run of conduit.
– Conductors may not be spliced inside a conduit body unless it is specifically listed for such use.
– Conduit bodies are not required to be individually supported.
– Conduit bodies can be useful in practical applications.
– Conduit bodies are commonly referred to as a junction box.
– Surface mounted raceway provides an aesthetically acceptable passageway for wiring.
– Trunking includes rectangular wireways with removable lids.
– Innerducts are installed in existing underground conduit systems.
– Passive fire protection is relevant to firestopping and fireproofing. Source: https://en.wikipedia.org/wiki/Conduit_(electrical)
An electrical conduit is a tube used to protect and route electrical wiring in a building or structure. Electrical conduit may be made of metal, plastic, fiber, or fired clay. Most conduit is rigid, but flexible conduit is used for some purposes.
Conduit is generally installed by electricians at the site of installation of electrical equipment. Its use, form, and installation details are often specified by wiring regulations, such as the US National Electrical Code (NEC) and other building codes.
