What Type of Conduit to Use Underground

Conduits are primarily used for safety purposes - nullifying the threat of avoidable accidents such as short-circuits, fire and electrocution. Additionally, conduits group wires together, isolating them from other circuits, making maintenance far easier.

But which type of conduit is best for your project? It’s a question asked by many project managers, and with so many conduit types available, it can be difficult to know right from wrong.

For project managers overseeing an underground conduit project, it is especially important to make the right decision. Fortunately, there is an array of conduits available, ranging from traditional to the latest innovations.

Below Ground Conduit Systems

Traditional PVC and Metal Conduits

Conduits come in a wide range of builds and materials, each well-suited to a particular budget and project type. Below are several traditional options for underground conduits:

  • PVC Conduit: one of the cheapest and lightest conduit materials. It is mainly used for over-ground applications as it can withstand different weather conditions and resist moisture and corrosive substances. PVC conduits come with their very own set of elbows, connectors, couplings, and fittings.
  • Rigid Metal Conduit (RMC): a thick and heavy conduit typically made of coated steel, stainless steel, or aluminum. RMC is tremendously strong, which makes it a smart choice for extremely harsh areas. That being said, it’s weight makes installation difficult, and subsequently, more expensive than other options.
  • Electrical Metallic Tubing (EMT): a lightweight, bendable material that is typically used for conduits within walls. Its lightweight nature means it can be damaged easily and isn’t a preferred option for underground work given the harsh elements.
  • Flexible Metal Conduit (FMC): is manufactured using helical coiling with strips of interlocked aluminum or steel. The hollow tube can have wire pulled through it and can be bent into position. This conduit type is best used in narrow spaces with tight bends.

Disadvantages of Traditional Options

  • PVC can not handle temperatures below -5°C or above 60°C.
  • PVC emits toxic fumes when melted or subject to fire.
  • RMC connections are threaded, making wiring installation more difficult.
  • RMC and FMC have thick walls which make installation more labour-intensive and expensive.
  • EMT can only be used in projects where it will not encounter severe physical damage.
  • EMT is more difficult to cut and bend.
  • The fault-finding process is more arduous.

Below Ground Fiberglass Conduit

If the traditional options are not suitable for your project, fiberglass underground conduit is an innovative conduit often selected for its unique benefits.

Lighter than traditional metal conduits, fiberglass can be used in a variety of indoor and outdoor applications. Compared to PVC, steel and aluminum, fiberglass conduits offer a superior level of protection and cheaper installation. The material is an economical and long lasting alternative to the heavy, costly materials like PVC-coated steel and GRC.

The below ground fiberglass conduit system is the preferred choice around the world for power and telecommunications utilities, commercial, and industrial markets.

At FRE Composites, our Below Ground Fiberglass conduit is suitable for direct burial and encased burial, available in 3/4’’ through 8’’ diameters, and comes complete with fittings and adaptors.

Advantages of Fiberglass Conduit

  • Low coefficient of friction - allows cables to be pulled through without burn-through.
  • Corrosion and chemical resistant - Unsusceptible to degradation from UV, moisture, solvents and chemicals.
  • Year-round protection - Doesn’t crack at low temperatures in winter or expand during heat waves.
  • Superior impact and crush resistance - retains shape after compression or impact.
  • Non-conductive.
  • Lightweight - makes installation fast and easy.
  • Low installation rates.

Phenolic Conduit Systems

Using a phenolic resin-based matrix, phenolic conduit systems are a nonmetallic material that is corrosion-resistant, flame-resistant, low-smoke, non-toxic.

Because the conduit is nonmetallic, it will not rust or corrode. The conduit’s qualities make it particularly well-adept to high-temperature installations such as tunnels, subways, and similar underground confined areas.

Our BreathSaver® products are primarily used for above-ground installation where flame spread and smoke development are of common concern, but they are equally well-suited to below ground installations.

We are proud to be the only manufacturer offering this innovative UL 2196 Certified 2-Hour fire rated both vertically and horizontally conduit system (BreathSaver® XW - Following FHIT 25C).

If you have an outdoor conduit project and you are unsure which material is best, get in touch with FRE Composites. Our experts will consider water exposures, compression, temperature, and location to make an informed decision to your needs.