What Kind of Wire to Run in Conduit: A Comprehensive Guide

When running wire through a conduit, the best options are THHN (Thermoplastic High Heat-resistant Nylon-coated) or THWN (Thermoplastic Heat and Water-resistant Nylon-coated) wires. These types of wires are designed to withstand the rigors of being pulled through conduits and offer durability, flexibility, and safety. They are also approved for most residential, commercial, and industrial applications.

Conduits serve as a protective pathway for electrical wires, shielding them from environmental damage, abrasion, and potential interference. To ensure the safety and efficiency of your electrical system, selecting the right type of wire is essential. In this post, we will delve into the factors to consider when choosing wires for conduit, the characteristics of suitable wire types, and additional tips for installation.

Types of Wire Suitable for Conduit

  1. THHN/THWN Wires
    • THHN: Commonly used for dry indoor environments. Its nylon coating reduces friction, making it easier to pull through conduits.
    • THWN: Similar to THHN but includes water-resistance, making it suitable for damp or wet locations.
  2. XHHW Wires (Cross-linked Polyethylene High Heat-resistant Wire)
    • Designed for extreme conditions, XHHW wires are heat-resistant, moisture-resistant, and durable. Ideal for outdoor or underground conduit systems.
  3. UF-B (Underground Feeder) Cables
    • Suitable for running through conduit outdoors or underground. UF-B cables are rugged and resist water and corrosion.
  4. MTW (Machine Tool Wire)
    • Ideal for industrial applications, MTW wires offer flexibility and are resistant to oils, water, and abrasion.

Key Factors to Consider

  1. Environment
    Determine whether the conduit is installed indoors, outdoors, underground, or in a wet or dry environment. This will influence whether water-resistant or heat-resistant wires are necessary.
  2. Wire Gauge and Current Load
    Select the appropriate gauge (thickness) based on the circuit’s current load and voltage requirements. Overloading a wire can lead to overheating and safety hazards.
  3. Conduit Type and Size
    Ensure the wire fits comfortably within the conduit. Overcrowding wires in a conduit can lead to heat buildup and difficulty during installation.
  4. Local Electrical Codes
    Always refer to local codes and regulations to ensure compliance with safety standards.

Additional Tips for Running Wire in Conduit

  • Use Wire Lubricant: For easier installation, especially with long runs or bends in the conduit.
  • Avoid Sharp Bends: Minimize wire stress by keeping bends smooth and within the conduit’s bending radius.
  • Proper Labeling: Label wires at the ends to identify circuits and connections during installation and maintenance.
  • Grounding: Ensure that grounding wires are included for added safety.

Conclusion

When selecting wires for conduit, prioritize THHN, THWN, or XHHW wires for their durability, flexibility, and compliance with electrical standards. Assess the environment, current load, and conduit type to make the best choice. By adhering to local codes and following best practices, you can ensure a safe and reliable electrical system. If in doubt, consult a licensed electrician to guide you through the process.