THHN stands for Thermoplastic High Heat-resistant Nylon-coated. It is one of the most common types of wire used in residential, commercial, and industrial electrical applications in the United States.
THHN wire features a thermoplastic insulation, is rated for high heat, and includes a nylon jacket for added protection. This versatile wire is frequently used for conduit and cable tray wiring in dry or damp locations.
THHN THWN THWN-2 Wire
THHN Wire: What Each Letter Means
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T – Thermoplastic: The insulation is made from a plastic polymer that melts at high temperatures, making it easy to manufacture and install.
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H – High Heat-Resistant: The wire can withstand temperatures up to 90°C (194°F) in dry environments.
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H – High Heat-Resistant (again): Reinforces its ability to handle high temperatures.
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N – Nylon Jacket: A tough outer coating that protects the wire from abrasion, chemicals, and moisture.
Key Features of THHN Wire
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Voltage Rating: 600 volts
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Temperature Rating: Up to 90°C in dry locations, 75°C in wet locations
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Jacket Material: Nylon for additional mechanical strength and chemical resistance
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Common Conductors: Copper or aluminum
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UL & NEC Compliance: Meets UL 83 and NEC Article 310 standards
Common Uses of THHN Wire
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Electrical wiring in conduit systems
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Wiring for commercial and industrial buildings
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Machine tool wiring
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Lighting and power distribution
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Control circuits
🔧 Note: THHN is only rated for dry and damp locations, not for direct burial unless it is dual-rated as THHN/THWN-2.
THHN vs THWN vs THWN-2: What’s the Difference?
| Type | Max Temp (Dry) | Max Temp (Wet) | Nylon Jacket | Wet Location Use |
|---|---|---|---|---|
| THHN | 90°C | 75°C | Yes | Limited |
| THWN | 75°C | 75°C | Yes | Yes |
| THWN-2 | 90°C | 90°C | Yes | Yes ✅ |
Many modern THHN wires are dual-rated as THHN/THWN-2, making them more versatile.
Need THHN Wire?
TOT Wire & Cable offers a wide range of THHN and THHN/THWN-2 copper wires from 14 AWG to 4/0 AWG, ideal for conduit systems and general-purpose wiring. Contact us for bulk pricing and specifications.
