Copper THHN Electrical Wire

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WesBell THHN wire is Thermoplastic High Heat Nylon wire with bare copper strands. It's also used as machine tool wire and appliance wire as specific with the NEC. THHN wire (also rated as THWN-2) is rated for 600 volts and 90°C. It can be used in wet or dry locations per TEWN.

THHN Wire Construction

THHN wire is designed with bare copper strands in two possible options; solid and stranded. The solid version is manufactured as a single solid copper strand in order to form the wire and hold it in the same position. The stranded version is manufactured with 19 copper strands wound together, which has an equivalent diameter to the single solid strand (14 AWG, 12 AWG, etc.).

The insulation is thermoplastic with a nylon coating over it. The easiest way to describe the nylon coating is to envision the nylon piece at the end of a shoe lace. Together, the thermoplastic insulation and nylon coating resist water, moisture, heat, oil and gas.

THHN Wire Approvals

THHN wire sold by WesBell is approved as THHN, THWN-2, AWN, MTW, TEWN, UL83, UL1581, UL1063, VW-1, FT-1, RoHS and REACH. The first five acronyms are descriptions of the wire and its resistance to certain liquids. The three UL (Underwriter’s Laboratories) approvals are conducted at UL to assure end users that the wire is in fact 600 volts, 90°C, etc. There are two fire approvals (VW-1 and FT-1) that are tested to withstand flame and to make sure the insulation doesn’t support ongoing flames. Finally, RoHS and REACH restrict certain metals such as lead, and are approvals that make sure the metals (copper) used in electrical wire are safe.

THHN Wire Applications

Generally speaking, THHN wire can be used indoors, outdoors and in conduit or duct. Since THHN can resist most liquids and moisture it can be used in outdoor applications, but cannot be used directly underground. It’s known as Building Wire, which is used when building a home or structure that uses electricity. So when you’re connecting wire from the electrical box in a garage to outlets, switches and lights there’s no need to worry about moisture, water, oil or gas coming in contact with it.

THHN wire has a similar construction and set of approvals and attributes as TFFN wire, but it has gauge sizes that vary from 14 AWG to 1000 MCM. TFFN wire only comes in two gauge sizes: 18 and 16. When less current, or amps, are needed for fixtures TFFN wire can be used.

THHN Wire Manufacturers

Several manufacturers have designed their own version of THHN along with their own specifications and approvals. For example, some manufacturers are not approved with UL for UL83 and UL1581, which means UL has not tested that it’s approved for 600 volts and various other appliance wiring standards. Here is a blurb from UL’s website under UL83 approval, “This Standard specifies the requirements for 600 V, single-conductor, thermoplastic-insulated wires and cables, for use as follows: In the United States, in accordance with ANSI/NFPA 70, National Electrical Code (NEC).” Click the links to learn more about UL and how they are a third party that tests and approvals wire and cable products.

Common manufacturers are Southwire, Encore Wire, Cerro Wire, Republic Wire and Unified Wire and Cable. If you need a specific approval for an installation then I suggest you either request a PDF specification sheet from your distributor or you review the manufacturer’s website for the product specification in order to be sure it’s approved.

THHN Wire Colors

There are 10 standard colors available (Black, Brown, Blue, Gray, Green, Orange, Red, Violet, White and Green). As a distributor with equipment capabilities, WesBell can also add a spiral stripe to the wire in order to create more than 10 color options for a particular installation. WesBell can also cut, strip, crimp, terminate and spool special lengths as an ISO 9001 certified company.



  • Construction
  • Bare Copper
  • PVC Insulation
  • Nylon Coating
  • Approvals
  • THHN
  • THWN-2
  • MTW
  • AWN
  • TEWN
  • UL83
  • UL1581
  • UL1063
  • FT1
  • RoHS
  • REACH
  • Applications
  • Used indoors
  • Used outdoors
  • Used in Conduit
  • Heat resistant
  • Moisture resistant
  • Water resistant
  • Oil resistant
  • Gas resistant