What kind of wire is used for undergrounding?

Getting Started

When it comes to underground installations, such as electrical wiring for outdoor lighting, irrigation systems or home power, choosing the right wire is critical. Underground wiring requires special cables that can withstand the harsh underground environment, including moisture, temperature fluctuations and physical stress.

In this article, we will explore the different types of wire used for underground applications and discuss their characteristics, advantages, and suitable applications. Understanding these options will help you make an informed decision when selecting the right wire for your underground project.

1. UF (Underground Feeder) Cable

The UF (Underground Feeder) cable is one of the most commonly used wires for underground installations. This cable is specifically designed for direct burial applications without the need for a conduit. UF cables consist of insulated copper conductors twisted together and covered with a moisture-resistant polyvinyl chloride (PVC) jacket.
One of the major advantages of UF cables is their ability to withstand moisture and damp environments. The PVC jacket provides excellent protection against water and moisture ingress, making them suitable for underground applications. UF cables are commonly used for outdoor lighting, landscaping and residential wiring.

2. THWN (Thermoplastic Heat and Water Resistant Nylon) cable

THWN (Thermoplastic Heat- and Water-Resistant Nylon) wire is another popular choice for underground wiring. It is a type of construction wire that consists of a single solid or stranded copper conductor insulated with a thermoplastic PVC compound, which is then covered with a nylon jacket.

THWN wire is known for its exceptional resistance to heat, moisture and chemicals. The PVC insulation provides protection against moisture, while the nylon jacket increases durability and abrasion resistance. THWN wire is suitable for both wet and dry locations, making it a versatile option for various underground applications, including residential and commercial installations.

3. Direct Buried Cable

Direct buried cables are specifically designed for underground installation without the need for conduit or additional protection. These cables have thick, durable insulation that provides excellent protection against moisture, temperature extremes and physical damage.

Direct burial cables are available in various configurations, such as copper or aluminum conductors with various insulation materials, including cross-linked polyethylene (XLPE) or high-density polyethylene (HDPE). These cables are commonly used for outdoor lighting, underground building power and irrigation systems.

4. Armored cables

Armored cables, also known as MC (Metal-Clad) cables, are a robust option for underground installations where additional protection is required. These cables consist of multiple insulated conductors wrapped in a flexible metal armor, typically aluminum or steel.

The metal armor provides excellent mechanical protection, making armored cables suitable for underground applications where the cable may be subject to physical stress or potential damage. Armored cables are commonly used in industrial settings, outdoor installations, and areas where rodents or other animals may pose a threat to the cable.

5. PVC pipe with THHN/THWN wire

For certain underground installations, the use of PVC conduit in combination with THHN/THWN (Thermoplastic High Heat and Water Resistant Nylon) wire is recommended. PVC conduit is a rigid polyvinyl chloride pipe that provides protection and a path for the wire.

THHN/THWN wire is commonly pulled through PVC tubing because of its excellent heat resistance, moisture resistance, and flexibility. This combination provides enhanced protection against moisture, physical damage, and corrosive environments. PVC conduit with THHN/THWN wire is widely used in commercial and industrial applications.

Conclusion

Choosing the right wire for underground installations is essential to ensure safety, longevity and reliable performance. The choice of wire, such as UF cable, THWN wire, direct buried cable, armored cable or PVC conduit with THHN/THWN wire, depends on the specific requirements of the project.

Factors such as moisture resistance, temperature tolerance, durability, and mechanical protection should be considered when making a decision. Consultation with a qualified electrician or professional is always recommended to ensure compliance with local electrical codes and regulations.

FAQs

What wire is used for underground?

The wire typically used for underground installations is called underground feeder (UF) cable. It is specifically designed to be buried directly in the ground and is commonly used for outdoor lighting, underground circuits, and other applications where electrical wiring needs to be installed underground.

What are the advantages of using underground feeder (UF) cable?

There are several advantages to using underground feeder (UF) cable for underground installations. UF cable is designed to be moisture-resistant and can withstand exposure to wet conditions, making it suitable for underground use where moisture is a concern. It also has a durable outer jacket that provides protection against physical damage, such as impact or abrasion. Additionally, UF cable is typically available in a range of sizes and configurations to accommodate different electrical loads and installation requirements.

Can any type of wire be used for underground installations?

No, not all types of wire are suitable for underground installations. It is important to use wire that is specifically designed and rated for underground use, such as underground feeder (UF) cable. Using the wrong type of wire can lead to safety hazards, electrical malfunctions, and code violations.

Are there any specific considerations when installing underground wiring?

Yes, there are several considerations to keep in mind when installing underground wiring. Here are a few important ones:

Always follow local building codes and regulations regarding underground wiring installations.

Before digging, make sure to locate and mark any existing underground utilities to avoid damaging them.

Use proper burial depth and methods as specified by local codes to ensure the safety and protection of the wiring.

Use appropriate conduit or protective tubing where required to provide additional protection to the underground wiring.

Consider using a professional electrician or contractor experienced in underground wiring installations for complex or large-scale projects.

Can underground feeder (UF) cable be used for above-ground installations?

No, underground feeder (UF) cable is specifically designed for underground use and is not suitable for above-ground installations. It lacks the necessary UV (ultraviolet) resistance that outdoor above-ground cables possess to withstand exposure to sunlight. If UF cable is used above ground, it can degrade quickly due to UV exposure, resulting in potential safety hazards and electrical failures.

What are some common applications of underground wiring?

Underground wiring finds various applications, including but not limited to:

Outdoor lighting systems: Underground wiring is commonly used to power landscape lighting, pathway lights, and other outdoor lighting fixtures.

Sprinkler systems: Irrigation systems often require underground wiring to power sprinkler valves, controllers, and sensors.

Electric fences: Underground wiring is used to supply power to electric fences, which are used for livestock containment or security purposes.

Outdoor outlets: Wiring is installed underground to provide power to outdoor outlets, allowing for the convenient use of electrical devices in outdoor spaces.

Submersible pumps: In applications such as well systems or fountains, underground wiring is used to connect and power submersible pumps.

Underground circuits: Wiring is installed underground to supply power to underground circuits, such as those used for powering sheds, detached garages, or other outbuildings.