Apr. 10, 2026
THHN wire is a type of thermoplastic insulated electrical wire commonly used in residential, commercial, and industrial wiring systems. The name “THHN” stands for:
T – Thermoplastic insulation
H – Heat-resistant (up to 75°C)
HH – High heat-resistant (up to 90°C)
N – Nylon-coated
This construction makes THHN wire suitable for high-temperature environments and conduit-based electrical installations.

THHN wire is widely used due to its reliable performance and standardized specifications.
Typically rated for 600 volts
Up to 90°C in dry locations
Usually copper, available in solid or stranded forms
Thermoplastic insulation with a nylon outer jacket for added protection
THHN wire is available in various sizes depending on application needs:
14 AWG – Lighting and small circuits
12 AWG – General residential wiring
10 AWG – Appliances and higher loads
8 AWG and above – Industrial and heavy-duty applications
Choosing the correct gauge is essential for current capacity (ampacity) and safety.
THHN wire is primarily used in conduit systems and is suitable for:
Residential building wiring
Commercial electrical installations
Industrial electrical systems
Control panels and machinery
It is commonly installed in conduits or raceways, rather than exposed applications.
A common comparison is between THHN and THWN wire.
| Feature | THHN Wire | THWN Wire |
|---|---|---|
| Temperature Rating | 90°C (dry) | 75°C (wet) / 90°C (wet for THWN-2) |
| Water Resistance | Limited | Suitable for wet locations |
| Common Use | Indoor, dry conduit | Indoor & outdoor |