The Advantages of XHHW-2 Wire Over THHN for Commercial Construction
Kris-Tech is joining us today with this definitive guide on THHN and XHHW-2 wires. Here, they’re laying out the differences between the two building wires for contractors everywhere.
While both THHN and XHHW-2 wires are designed for AC electrical distribution, these two building wires are suited for a wide range of applications. From branch circuits and conduit to cable trays for feeders, these highly versatile wires can also be used in automotive plants, wind energy distribution, forestry equipment, control circuits, and more.
If you’ve ever been stuck deciding between THHN and XHHW-2 wires for your type of application, you’ll want to check out this definitive guide.
THHN and XHHW-2 are two types of wire with a lot in common. Both are used for power distribution. Both are popular building wire choices for commercial and industrial construction and are available with either solid or stranded conductors. While THHN may be more widely used, XHHW-2 possesses physical and performance capabilities that make it the safer choice for many demanding applications. When choosing the best wire for your project, it’s critical to understand the differences between the two.
It’s All About the Jacket
While THHN and XHHW-2 look very similar, the difference lies in their jacket properties. THHN (Thermoplastic High Heat-Resistant Nylon-Coated) uses a thinner, less expensive PVC thermoplastic insulation found in many wiring products. XHHW-2 (Cross-Linked Polyethylene High Heat-Resistant) is made with a higher-quality, thermoset cross-linked polyethylene jacket.
The Advantages of XHHW-2
Contractors and engineers often choose XHHW-2 as a stronger, safer alternative to THHN. XHHW-2 provides many benefits:
Durability. XHHW-2 is more corrosion-resistant than THHN and performs better in chemically-interactive environments. It is also less prone to failure over time than THHN, reducing the need for replacement or emergency repairs. The nylon outer jacket of THHN, along with the PVC insulation, are specifically prone to degradation.
Flexibility. Even though it has a thicker jacket, XHHW-2 is more flexible than THHN wire. This is a significant advantage for jobs that require pulling wire through small areas or multiple tight turns. In many cases, this flexibility can translate into lower labor costs.
Higher voltage capacity. THHN wire is rated for a maximum of 600 volts. With XHHW-2, however, it’s common to have a rating of up to 1,000 volts. This higher rating is an important advantage in applications such as solar power, where circuits often exceed 600 volts.
Flame resistance. The cross-linked polyethylene (XLPE) insulation of XHHW-2 wire is more flame resistant than THHN’s PVC jacket. PVC also emits toxic fumes when burned, creating a potential safety risk.
Temperature and water resistance. XHHW-2 has a temperature rating of 90ºC for both dry and wet locations, while THHN is rated for 90ºC in dry locations only. The thin nylon jacket on THHN is hygroscopic (absorbs moisture); as a result, THHN should not be used in wet environments. THHN is now commonly found in a dual rated THWN-2 that adds a 90° dry/wet rating, however, XHHW CU still maintains a higher overload/emergency temperature rating, typically in excess of 135°.
Typical Applications for XHHW-2
XHHW-2 is most often used in industrial environments characterized by harsh conditions, such as:
Wastewater treatment facilities. Chemicals and other corrosive materials create challenging conditions for industrial wire. High temperatures and fire are also safety concerns. THHN is dangerous when it burns and offers very little protection in wet conditions. XHHW-2 is a better choice in this type of environment.
Department of Transport (DOT) projects. XHHW-2 is almost universally spec’ed for DOT work. In these applications, wire is often exposed to asphalt and other chemical elements — conditions that require an XLPE solution.
Hospitals and Medical Testing.XHHW-2 provides the higher temperature ratings and flame resistant properties needed to support specialized equipment like MRIs and X-ray machines. This is also available in 277 color code.
The Benefits of THHN
While not as robust as XHHW-2, THHN remains a popular choice for many commercial projects. Here are its key advantages:
Smaller Diameter.THHN uses less insulation, which means a thinner wire. This smaller size is an advantage when pulling multiple wires through a conduit or tight spaces.
Availability. THHN has been commonly used in construction for many years and is widely available in various sizes.
Price. Traditionally THHN has enjoyed a price advantage over XHHW-2; however, that cost delta continues to shrink. Large projects that don’t require the enhanced properties of XHHW-2 may find that THHN is a more budget-friendly option.
Common THHN Applications
THHN is the appropriate choice for many less-demanding scenarios, such as:
Residential construction. THHN is the most common wire used in homes and apartments. These facilities don’t present the same challenges found in heavy industrial environments.
Light commercial/public buildings. THHN meets or exceeds the technical and safety requirements for most public buildings and light commercial (retail) projects, and is often more cost-effective. As more schools and public buildings start to use low smoke and zero halogen products, THHN might be phased out in favor of XHHW.
Kris-Tech offers a full line of tray cables that utilize THHN and XHHW: VNTC tray cable (THHN inner, PVC outer jacket) and XPTC tray cable (XHHW insulation, PVC outer jacket). Tray cable is often considered ‘the workhorse cable’ for many industrial projects. Built for installation in cable trays or raceways, it can be used for power, lighting control, or signaling. Tray cable is tough and resistant to the elements and can be deployed in wet or dry locations and indoors or outdoors.
Safety is the Primary Consideration
Engineers and contractors always have to weigh performance versus budget when choosing the right wire for their projects. Safety, however, always takes precedence. THHN, a longtime staple in commercial construction, is an excellent choice for many residential and commercial applications, but for more hazardous or demanding environments, XHHW-2 is almost always a better fit.