Non-metal conduits are low cost and durable electrical pipes that protect the wiring in residential and commercial buildings. The conduits do not allow ingress of water nor suffer from corrosion compared to some types of the metallic conduits. For this reason, they can be perfectly used in wet and corrosive areas.
Although they do not provide a high degree of mechanical protection against heavy weights or impacts, the non-metal conduits are adequate for general applications. They are commonly used within the walls, above the ceilings, buried in the concrete during construction and even used for underground cabling in areas where there are no risk of excessive pressure.
Different types of non-metallic conduits based on construction material
The construction material varies from one conduit to another. Other characteristics that may differ include the wall thickness, diameter, temperature range, length, ease of installation, flexibility, and more.
Polyvinyl chloride (PVC) conduits
Unlike the metal conduits, it is very easy to bend the PVC according to the corners or over obstacles using either heat or a special bending tool. Since it requires fewer couplers and bends, the installation and fitting is easy, quick and less costly.
PVC conduit is the most common type for residential and commercial installations. It is usually available in three main wall thickness or gauges. The lightest wall is suitable for embedding in the walls or above the ceilings during construction or upgrades. Whereas applications such as underground cabling and others that require more strength may use the medium or heavy duty PVCs. The choice will depend on the amount of pressure on the conduits.
Fiberglass reinforced epoxy (FRE)
These are lightweight non-metal conduits that are less costly, easy to work with, and suitable for both indoor and outdoor applications. It is also referred to as reinforced thermosetting resin conduit (RTRC) or simply as fiberglass conduit. Just like the other conduits, it is available in different wall thicknesses to cater for a variety of environments and applications.
The fiberglass reinforced epoxy provides a superior protection almost comparable to steel. Generally, the fiber material is very strong mechanically, and some special types can withstand harsh conditions just like steel metal conduits. In addition, it has a long service life and not prone to stray eddy currents – properties that make it ideal for surface mounting in transit rail systems, stations, and tunnels.
Fiberglass is resistant to corrosive materials, chemicals, UV light, and impact. Further, it does not expand or sag due to high temperatures, neither does it brittle due to low temperatures.
The fiberglass non-metal conduits are, however, not easy to bend in the field. They requires cutting and use of appropriate fittings to change directions. In addition, it cannot be used to support the luminaires.
Electrical nonmetallic tubing (ENT)
This is a pliable, corrugated thin-walled conduit that is flame retardant and suitable for both dry and moist conditions. The conduit is often flexible, making it easy to bend by hand. This is usually buried within the walls, ceilings or floors. It is also installed on the exposed walls in locations where there is no risk of mechanical damage.
High-Density Polyethylene (HDPE) conduits
These are made of graded polyethylene raw materials such as PE 100, PE 60 or PE 63. The conduits are available in straight lengths of about 20 feet, or as 50 to 200 meters coils. Laying and fitting is much easier especially when using coils for outdoor applications. The HDPE conduits are suitable for several applications in dry, wet, corrosive, and moist environments
Flexible and rigid non-metal conduits
There are both rigid and flexible non-metal conduits. The choice depends on the application. Most often, the rigid types are installed in places where there are no movements such that once done, the wires will almost remain in the same place throughout their service life. On the other hand, the flexible conduits are for applications where there are movements and vibrations which can damage the stiff cables or adjoining walls.
Majority of the flexible conduits are not waterproofing hence not suitable for wet conditions. But there is a special type, the Liquid-Tight Flexible Nonmetallic Conduit (LFNC), that is designed for applications where there is moisture or water.
Main characteristic of non-metal conduits
Below are some of the advantages and disadvantages of the common types of non-mental conduits.
Benefits of non-metal conduits
- Easy to work with, cut, join, bend or pass around obstacles
- Less costly
- Not affected by water or chemicals
- Not corrosive
- Smooth internals that makes it easy to pull cables.
- Cannot withstand heavy weights and impacts
- Affected by high temperatures and may deform either from external or internally generated heat
- Poor heat dissipation properties
- My not be suitable for outdoor applications where it is exposed to the sun
- Does not provide a grounding for extra bonding such as the metallic types
- May burn with a flame hence accelerate fires
Non-metal conduits are popular due to their low weight, cost, and ease of installation. Compared to the metal conduits, some types such as PVC may not be as strong, and therefore not suitable for certain applications. However, fiberglass conduit has comparable strength with the metal types and is thus suitable for demanding indoor and outdoor applications.
Generally, the non-metal conduits have some superior properties such as high resistance to corrosion and ability to work in moist environments without degrading. But some such as the PVC have temperature limitations.All non-metallic conduits, including the fiberglass and HDPE, do not provide grounding, hence requires running the ground conductor throughout the entire conduit length.