What Type of Conduit to Use Underground?

Why choosing the correct electrical conduit is important

Electrical conduit provides valuable protection to electrical wiring and electrical cable from moisture, fire, corrosion, impact, electrocution and short-circuits. With many options available to project managers and engineers, it’s important to consider the location and environment specific to each project when selecting an electrical conduit to specify or source. Choosing the wrong conduit can result in risks to safety and significant financial implications.

Underground Conduit Options Available

Traditional Metal Conduits
Traditionally, heavy metal conduits made of steel or aluminum were commonly used for a majority of electrical conduit construction projects. In recent years the market has shifted away from traditional metal substrates as lighter, more cost-effective and durable conduits such as RTRC (fiberglass conduit) have become more widely used.

• Rigid Metal Conduit (RMC): RMC is composed of heavyweight galvanized steel, stainless steel, or aluminum, and installed with threaded fittings. RMC is very strong and unfortunately also very heavy, contributing to higher than average cost of both materials and labor.
• Electrical Metallic Tubing (EMT) Thin-walled and unthreaded, EMT is typically made of coated steel or aluminum and used in place of GRC in commercial, industrial, and residential applications. EMT is best for indoor applications and not typically recommended for outdoor or underground electrical applications because of its susceptibility to being damaged easily and need for special watertight fittings.

Fiberglass Conduit

In terms of raw material costs, fiberglass (RTRC) conduit is one of the more affordable electrical conduit options, and it is significantly lighter in weight than traditional conduit materials, resulting in more cost efficient labor installation rates. RTRC is an often preferred substrate for utilities, commercial and industrial applications requiring direct burial and encased burial below ground installations because it is resistant to temperature, moisture, and corrosion. Also to note, RTRC is non-toxic, making it an environmentally-friendly option, and chemically inert, which contributes to its longevity. Its light weight and unthreaded joints make it easy (and cost effective) to install, and its low coefficient of friction eliminates the risk of burn-through for long cable pulls.

PVC Conduit

Well known for being the lightest and cheapest electrical conduit, PVC electrical conduit is relatively durable and offers protection from moisture and corrosion. In recent years supply chain issues have increased the cost and lead-times for PVC, leading engineers and contractors to consider substituting more readily available American-made conduits. PVC is limited in its temperature range (+40℉ to +150℉), and emits toxic fumes when melted. If your outdoor installation may experience extreme heat or cold, PVC might not be suited for your project.

Which One Is Best for Your Below Ground Application?

Key factors to consider include:

• The protective qualities of the substrate
• Ease of installation (and the costs associated)
• Long term costs associated with durability and project lifespan
• Up-front materials and labor cost
• Availability and lead times

It’s important to consider a variety of attributes that will affect the lifespan of your installation, not limited to the conduit’s level of corrosion resistance, temperature range, and impact resistance.

To compare material and installation costs of fiberglass (RTRC), PVC, and a variety of traditional metal conduits including GRC, EMT, aluminum and stainless steel, visit the Champion Fiberglass Conduit Calculator.

For help selecting a conduit, reach out to an Electrical Sales Rep to learn more.