Electrical Conduits

TYPES OF ELECTRICAL CONDUITS

An electrical conduit system is a purpose-designed electrical piping system used for protection and routing of electrical wiring. Electrical conduit may be made of metal, plastic,

fibre, or fired clay. Flexible conduit is available for special purposes.

Types of conduit

Conduit systems are classified by the wall thickness of tubing, mechanical stiffness of the tubing, and material used to make the tubing. Tubing with thicker walls in the same

material offers better protection from impact, but increases the weight and cost of the conduit and also increases labor cost to install the system.

Rigid Metal Conduit (RMC)

Rigid Metal Conduit (RMC) is a thick threaded tubing, usually made of coated steel, though it may be aluminum.

Rigid Nonmetallic Conduit (RNC)

Rigid Nonmetallic Conduit (RNC) is a non-metallic unthreaded tubing.

Galvanised rigid conduit (GRC)

Galvanised rigid conduit (GRC) is galvanised steel tubing, with a tubing wall that is thick enough to allow it to be threaded. Its common applications are in commercial and industrial construction.

Electrical metallic tubing (EMT)

Electrical metallic tubing (EMT), sometimes called thin-wall, is commonly used instead of galvanised rigid conduit (GRC), as it is less costly and lighter than GRC.

EMT is not threaded. Lengths of conduit are connected to each other and to equipment with clamp-type fittings. Like GRC, EMT is more common in commercial and industrial buildings than in residential applications. EMT is generally made of coated steel, though it may be aluminum.

Electrical Nonmetallic Tubing (ENT)

Electrical Nonmetallic Tubing (ENT) is a thin-walled corrugated tubing that is moistureresistant and flame retardant. It is pliable such that it can be bent by hand and is often flexible although the fittings are not. It is not threaded due to its corrugated shape although the fittings might be.

Liquidtight Flexible Nonmetallic Conduit (LNFC)

Liquidtight Flexible Nonmetallic Conduit (LNFC) refers to several types of flameresistant non-metallic tubing. Interior surfaces may be smooth or corrugated. There may or

may not be integral reinforcement within the conduit wall. It is also known as FNMC.

Aluminium conduit

Aluminium conduit, similar to Galvanised Metal Conduit (GMC), is a rigid conduit, generally used in commercial and industrial applications, where a higher resistance to

corrosion is needed. Such locations would include food processing plants, where large amounts of water and cleaning chemicals would make galvanised conduit unsuitable.

Aluminium cannot be directly embedded in concrete, since the metal reacts with the alkalis in cement. The conduit may be coated to prevent corrosion by incidental contact with concrete.

The extra cost of aluminium is somewhat offset by the lower labour cost to install, since a ength of aluminium conduit will have about one-third the weight of an equally-sized rigid steel conduit.

Intermediate metal conduit (IMC)

Intermediate Metal Conduit (IMC) is a steel tubing heavier than EMT but lighter than RMC. It may be threaded.

PVC conduit

PVC conduit is the lightest in weight compared to other conduit materials, and usually lower in cost than other forms of conduit. In North American electrical practice, it is available in three different wall thicknesses, with the thin-wall variety only suitable for embedded use in concrete, and heavier grades suitable for direct burial and exposed work. The various fittings made for metal conduit are also made for PVC. The plastic material resists moisture and many corrosive substances, but since the tubing is non-conductive an extra bonding (grounding) conductor must be pulled into each conduit. PVC conduit may be heated and bent in the field.

Joints to fittings are made with slip-on solvent-welded connections,which set up rapidly after assembly and attain full strength in about one day. Since slip-fit sections do not need to be rotated during assembly, the special union fittings used with threaded conduit (Ericson) are not required. Since PVC conduit has a higher thermal coefficient of expansion than other types, it must be mounted so as to allow for expansion and contraction of each run.