Thhn Vs Romex

When it comes to wiring installations, THHN and Romex are two of the most commonly used electrical wires in the United States. Understanding the differences between THHN and Romex can help you make informed decisions about which wire to use for your specific needs.

THHN, which stands for thermoplastic high heat-resistant nylon, is a single conductor wire that is often used in wiring buildings and industrial settings. THHN wires are made from copper or aluminum and are coated with a thermoplastic insulation that provides a high level of heat resistance. THHN wires are sold in different sizes, referred to as gauge.

Romex, on the other hand, is a brand name for a type of electrical wire that is commonly used in residential wiring applications. It is also known as non-metallic sheathed cable or NM cable. Unlike THHN, Romex is made up of multiple wires bundled together in a jacket. The jacket is made of a PVC material that protects the wires from damage and moisture.

Now that we understand the basic differences between the two wires let’s dive into more specific details.

One of the most significant differences between THHN and Romex is cost. THHN is typically more costly than Romex, primarily because it is a single conductor wire that requires additional installation time and material than Romex. Additionally, THHN is often used in industrial settings, where the demand for high heat resistance requires more expensive materials.

THHN is typically used in high-heat applications or where wire strength and durability are important, such as industrial or commercial settings. The single conductor and insulation both provide a level of safety ideal for high-risk areas. In contrast, Romex wires are meant to be used mainly in residential settings for ordinary applications like powering lights, outlets, and small home appliances. The plastic jacket around the wires also offers extra protection in dry, indoor environments.

THHN is usually available in larger sizes or gauges than Romex. THHN wiring conducts electricity over a more extended distance since it is designed for larger electronic appliances. On the other hand, Romex usually measures 8-3 or smaller since it is designed to be used mostly in a single-family residence, but you may use larger sizes of Romex.

THHN wire is often used for wiring heavy-duty equipment as it supports a wider range of voltage variations. In contrast, Romex wires are tailored to the needs of a standard household where continuous voltage fluctuation is rare.

Ease of installation
While THHN and Romex may seem like similar wires, their installation is always different. THHN comes as a single wire, so its installation is more complicated than Romex since it comes bundled as multiple wires. THHN also requires additional materials like conduit and connectors, especially in harsh environments where wire damage may occur.

In contrast, the installation of Romex is much simpler than for THHN. The straight-forward applications of Romex wiring allow for it to be used in more casual settings around the home where limited expertise is required.


Choosing the right wire for your application is essential for safety, energy efficiency, and meeting regulatory requirements. THHN and Romex are both great options but serve different uses. While THHN wire brings versatility and durability to harsh environments, Romex is best suited for residential environments, providing an easy and cost-effective solution.

Overall, when determining which of these wires to use, it is important to evaluate the project requirements and application to make an informed decision that aligns with safety and economic objectives. Additionally, consult with a licensed electrician for optimal safety and compliance.