What is THHN Wire?

THHN (Thermoplastic High Heat-resistant Nylon-coated) wire is designed with a PVC (polyvinyl chloride) insulated nylon sheath. Most THHN building wire comes with the dual rating THHN/THWN, meaning it is usable in both wet and dry conditions, as well as both indoor and outdoor use. THHN carries a UL rating of 90 degrees Celsius in dry environments and 75 degrees Celsius in wet environments. The conductor can either be copper or aluminum and either stranded or solid. It is available in 12 colors and is generally used in electrical applications of 600V or less.

What Can THHN Wire Be Used For?

THHN is the number one commodity wire in the U.S. It is a general use wire for equipment and circuits. It is popular among electrical contractors as an inexpensive building wire that can be used in industrial environments. The NEC (National Electric Code) rating for THHN is NFPA 70- the benchmark for safe electrical design, installation, and inspection to protect people and property from electrical hazards. THHN can withstand grease, oil, and heat, and passes the FT1 flame test.

Because of its voltage capacity and insulation, THHN can be used for many indoor appliances such as garbage disposals or hot water heaters. When applied indoors, the wire is used in either a single- or multi-conductor form. Additionally, it can safely carry electrical currents between buildings and external power sources, signaling, control wiring, machine tools, and automated conveyor belt systems.

THHN wire can also be used as control wire for outdoor applications in addition to indoor. For underground outdoor applications, THHN must first be safely installed into a conduit (tubing that protects buried wire) before being run underground. The nylon jacket on the wire protects it from damage as it is pulled through the conduit.

Why Should Electrical Contractors Bundle THHN wire?

THHN is a popular choice for electrical contractors because of its ability to meet the requirements of electrical applications at a low price point. Its affordability often makes it a good alternative to wires such as XHHW-2. THHN’s relatively thin PVC insulation improves conductivity but reduces the flexibility of the wire. By using THHN in a cable bundle, it can minimize the disadvantage of inflexibility. 

To ensure safety between construction workers and running electrical equipment, THHN building wire can be bundled to fit the specifications of the worksite. Increasing accuracy and reducing the number of labor hours that would be needed if the wire was installed manually. One-pull can also bundle THHN wire together with protective UFB (Underground Feeder, Direct Burial) Jackets to save time in outdoor applications.  

THHN building wire is a useful product for electrical contractors in commercial applications. Its high heat and water resistance make it possible for use in both indoor and outdoor applications. The cost-effectiveness of THHN often makes it a better choice in comparison to other commercial use wires such as XHHW/XHHW-2 or THWN. Bundling THHN in a one-pull bundle cable can help to create flexibility and reduce the amount of labor hours needed for the project.

Interested in learning more about the different wire types available in one-pull bundles? Have a look at XHHW-2.