THHN/THWN: The Basics

For electrical distributors, one of the most well-known types of cable is building wire. It is generally used to carry electrical current to all external uses of power in a building or a dwelling. This product is utilized in the construction of almost every industrial, residential and commercial building. The most popular type of building wire is THHN/THWN. It’s so versatile, it’s used for wiring machine tools, control circuits and certain appliances. 


THHN stands for Thermoplastic High Heat-Resistant Nylon and THWN stands for Thermoplastic Heat and Water-resistant Nylon. Thermoplastic is a type of PVC material that is thinner than other types, making it lightweight. The jacket on the outside of the wire is made of nylon, which allows for easy pulling. THHN can come in solid conductors (10-18 AWG) or stranded conductors (8 AWG-750 MCM), and it is manufactured with either copper or aluminum. A phrase that is used to describe THHN is “Spaghetti Wire” because of its stringy appearance. 

Ratings and Value Adds

THHN/THWN is approved for up to 600V and is dual rated. This means it can be used in dry locations not exceeding 90 degrees Celsius and 75 degrees Celsius in wet locations, as listed by the Underwriters Laboratory (UL). It is VW-1 rated, and AWG sizes 1/0 and larger are cable tray (CT) rated. Standard jacket colors come in black, blue, brown, green, gray, orange, pink, purple, red, tan, white and yellow, but other colors can be requested. Striping and twisting is offered for this product as well. Striping is especially helpful for technicians when applications have several wire runs. 

Versatile Applications

An advantage of THHN’s 600V rating is that it covers most household appliances. It’s the most common type of building wire used inside conduit or raceways. THHN is often used in unfinished areas, such as basements and garages, and for short exposed runs inside the home, like wiring connections for hot water heaters and garbage disposals. Stranded THHN has even been known to be used for wiring machine tools, but the only downfall of using it for this application is it’s lack of flexibility due to its nylon jacket.

Distributor Wire & Cable (DWC) is always stocking THHN/THWN at our cable distribution centers. Need it quick? We offer overnight shipping! Just let us know in a quote request or talk to an Account Manager today. 888.439.2947