What's The Difference Between THHN, THWN, THWN-2, XHHW, and XHHW-2 Wires

General-purpose building wires are essential components in the construction industry, utilized for transmitting electrical power throughout various residential, commercial, and industrial structures. These versatile wires are designed to meet stringent safety and performance standards, ensuring the efficient distribution of electricity while minimizing potential hazards.

Among the most common types of building wires are THHN, THWN, THWN-2, XHHW, and XHHW-2, each offering unique features and benefits depending on the specific application and environment.

Published: May 9, 2023.

What letters T, HH, W, N, and X stand for?

In the context of the building wires discussed in this article, the letters T, HH, W, N, and X have specific meanings that describe the properties of each wire type:

• T: Thermoplastic – This refers to the insulation material used in the wires. Thermoplastic materials, such as PVC (polyvinyl chloride), soften when heated and harden when cooled and are commonly used in wire insulation.
• HH: High Heat-resistant – This indicates that the wire is designed to withstand higher temperatures, providing improved performance and durability in high-temperature environments.
• W: Water-resistant – This signifies that the wire has enhanced water resistance, making it suitable for use in wet locations or applications where exposure to moisture is a concern.
• N: Nylon-coated – This refers to the nylon outer jacket applied over the thermoplastic insulation, which serves as a moisture barrier and provides additional protection against abrasion.
• X: Cross-linked polyethylene – In the case of XHHW and XHHW-2 wires, the X represents the cross-linked polyethylene (XLPE) insulation. Cross-linked insulation offers improved heat resistance, mechanical strength, and chemical resistance compared to thermoplastic materials like PVC.

These letters are combined to describe the specific properties of each building wire type, such as:

• THHN: Thermoplastic High Heat-resistant Nylon-coated),
• THWN: Thermoplastic Heat and Water-resistant Nylon-coated, and
• XHHW: Cross-Linked High Heat-resistant Water-resistant.

THHN, THWN, THWN-2, XHHW, XHHW-2 Building Wires Comparison Table

The following comparison chart lists the most important features and specifications of the THHN, THWN, THWN-2, XHHW, and XHHW-2 wires:

Features and Specifications of THHN Wires

THHN (Thermoplastic High Heat-resistant Nylon-coated) wires are widely recognized for their durability and adaptability. These wires are designed with thermoplastic PVC insulation, providing excellent heat resistance and protection against abrasion.

Additionally, the nylon outer jacket serves as a moisture barrier, further enhancing the wire's resilience. THHN wires are suitable for use in dry locations with a maximum operating temperature of 90°C.

They are typically employed in conduit or cable trays for services, feeders, and branch circuits in residential, commercial, and industrial applications.

With a voltage rating of 600V, these wires provide efficient power transmission and are available in a variety of sizes, colors, and conductor materials, catering to diverse requirements.

Features and Specifications of THWN Wires

THWN (Thermoplastic Heat and Water-resistant Nylon-coated) wires share many similarities with THHN wires, such as the thermoplastic PVC insulation and nylon outer jacket.

However, THWN wires are specifically designed for enhanced water resistance, making them suitable for use in both dry and wet locations.

These wires can operate at a maximum temperature of 75°C in wet environments while retaining the 90°C rating in dry conditions. THWN wires are commonly used for underground service entrance conductors, branch circuits, and other installations exposed to moisture.

Like THHN wires, THWN wires are rated at 600V and come in various sizes, colors, and conductor materials.

Features and Specifications of THWN-2 Wires

THWN-2 wires offer the same benefits as THWN wires but with an added advantage: an increased maximum operating temperature of 90°C in wet locations.

This improvement makes THWN-2 wires a versatile choice for applications where higher temperature tolerances are required without compromising their water resistance.

They can be employed in conduit, cable trays, or underground installations, providing reliable power distribution in both dry and wet environments.

THWN-2 wires maintain the same 600V voltage rating as their THWN counterparts and are available in a wide range of sizes, colors, and conductor materials to suit various project needs.

Features and Specifications of XHHW Wires

XHHW (Cross-Linked High Heat-resistant Water-resistant) wires differ from THHN, THWN, and THWN-2 wires due to their unique insulation material.

These wires feature cross-linked polyethylene (XLPE) insulation, which offers superior heat resistance, improved mechanical strength, and enhanced chemical resistance compared to PVC insulation.

XHHW wires can operate at temperatures up to 90°C in dry and up to 75°C in wet locations, making them a preferred choice for many demanding applications.

These wires are also rated at 600V and are suitable for use in conduit or cable trays for services, feeders, and branch circuits in residential, commercial, and industrial settings.

Features and Specifications of XHHW-2 Wires

XHHW-2 wires build upon the impressive characteristics of XHHW wires by increasing the maximum operating temperature to 90°C in both dry and wet locations, ensuring consistent performance in diverse environments.

This enhancement allows for even greater versatility and adaptability, making XHHW-2 wires a popular choice for a wide array of applications.

Like their XHHW counterparts, these wires utilize cross-linked polyethylene (XLPE) insulation, offering exceptional heat resistance, mechanical strength, and chemical resistance.

XHHW-2 wires are rated at 600V and can be used in conduit, cable trays, or underground installations for services, feeders, and branch circuits in residential, commercial, and industrial projects.

They are available in various sizes, colors, and conductor materials to accommodate diverse specifications and requirements.

Few Final Words

The choice between THHN, THWN, THWN-2, XHHW, and XHHW-2 building wires largely depends on the specific demands and conditions of a given project.

Each wire type offers its own set of features and benefits, with variations in temperature ratings, moisture resistance, and insulation materials.

It is essential for engineers, architects, and contractors to carefully assess the requirements of each application to ensure the selection of the most suitable and efficient building wire.