THHN and THWN UL 83, 758, 1063, and 1581

THHN and THWN are commonly used thermoplastic, nylon-jacketed building wires for 600V applications, often combined as dual-rated THHN/THWN-2. THHN is designed for dry/damp locations up to 90°C, while THWN is engineered for wet/dry locations up to 75°C (or 90°C for THWN-2). They are ideal for conduit, feeders, and branch circuits.

THHN and THWN Key Differences and Features

Location Suitability: THHN is suitable only for dry locations, while THWN/THWN-2 is suitable for wet and damp locations, including outdoor conduit.

Temperature Ratings:

THHN: 90°C (194°F) in dry conditions.

THWN: 75°C (167°F) in wet/dry conditions (some versions are 90°C).

THWN-2: 90°C (194°F) in both wet and dry conditions.

THHN THWN Construction

Both feature a soft-annealed, stranded or solid copper/aluminum conductor, PVC insulation, and a nylon sheath for easy pulling.

Resistivity: Both are generally resistant to heat, moisture, oil, gasoline, and grease.

Common Use Cases

Used in commercial, industrial, and residential construction (e.g., inside conduit, machine tools, control circuits).

THHN AND THWN Building Wire

Insulation: PVC (Red, blue, black, brown, yellow, green, green/yellow or customized)

Jacket: Nylon

Maximum Operating Voltage: 600 volts

Maximum Conductor Temperature:

Dry locations (THHN): 90°C

Dry and wet locations (THWN): 75°C

In oil (Gasoline and Oil resistant II): 75°C

THHN THWN Features

1)Good resistance to moisture, heat, oil, gasoline, chemicals, and grease.

2)Suitable for installation where thermal overload exists.

3)Strict quality control during the manufacturing process.

4)Flame retardant, UL listed as VW-1.

5)Smooth nylon jacket aids in easier pulling.

6)Superior abrasion and mechanical properties.

The maximum voltage rating of the THHN cable is 600 volts. All THHN cables meet the UL 83 standard for safety thermoplastic-insulated wires and cables, as well as the UL 1063 standard for safety machine-tool wires and cables. You can request Canadian Standards Association (CSA) approval if desired, and certain THHN cables also meet the European Restriction of Hazardous Substances (RoHS) Directive for hazardous material compliance.

Key Features: THHN-THWN-2 Cables

Application: Screened and unscreened THHN/THWN-2 cables for the Oil, Gas and Petrochemical industry.

Suitability: Class 1 Division 2 Hazardous Areas. For installation in tray, wire ways, cable ducts, conduits and even as aerial cables when supported by messenger wires.

Standards & Voltage Rating: ICEA S-73-532, UL 1277, UL 83, ASTM B3/B8. 600V.

Construction: Stranded Copper conductor, Polyvinyl Chloride Flame-Retardant (PVC-FR) / Nylon insulation, and Special PVC outer sheath. Screened cable has Aluminium Foil screen with Tinned Copper drain wire.

Details: Offers protection from both aliphatic and aromatic hydrocarbons. Available in multicore configurations up to 50 cores and in sizes AWG10, AWG12 and AWG14.

The THHN/THWN-2 Cables are designed with the Oil, Gas and Petrochemical industry in mind. THHN/THWN-2 600V cables have an insulation layer of Nylon and Flame Retardant Polyvinyl Chloride. THHN referencing the Nylon coating and the THWN-2 referring to the 90oC PVC used. Both the screened and unscreened cables have a black PVC outer sheath. 

THHN/THWN-2 Cable Specification

The THHN/THWN-2 cable is classified as suitable for Class 1 Division 2 Hazardous Areas and offers protection from both aliphatic and aromatic hydrocarbons. Depending on the installation environment, there are screened and unscreened variants, the former being an aluminium tape with tinned copper drain wire.

Available in multicore configurations up to 50 cores and in sizes AWG10, AWG12 and AWG14, the THHN/THWN-2 cables are suitable for installation in tray, wire ways, cable ducts, conduits and even as aerial cables when supported by messenger wires. The cables are approved for direct burial where no risk of mechanical damage, and can be installed externally as the Special PVC sheathing offers UV resistance. They can be used in both wet and dry locations but are not suitable for immersion or submersion.

Support with specification and additional electrical characteristics are available on request. Please speak to one of our industry experts for more information.