THHN and THWN are types of building wire with different characteristics, and the following shows thhn/thwn wire meaning and difference:
- THHN is short for Thermoplastic High Heat Resistant Nylon Coated. THHN wire is constructed from copper with thermoplastic insulation and a nylon covering for added physical protection. It performs well in hot weather and can endure temperatures of up to 90 °C in dry environments. However, it is restricted to 75 °C in humid conditions.
- THWN is an acronym for Thermoplastic High Water-resistant Nylon-coated. As an added benefit, the “W” in THWN is indicative of water proofing capability. THWN wire also has a flame resistant, extruded nylon or equivalent heat resistant thermoplastic coating. Thwn/thwn-2 can operate in wet and dry environments at temperatures up to 90°C, where the “-2” suffix indicates that the wet temperature rating is equal to the dry rating. Moreover, THWN cables have an enhanced structure similar to THW cables as well which are Thermoplastic high heat resistant and water resistant cables. The insulation material is a major distinguishing factor between the two; PVC is the insulating material of THW wires while a higher grade of XLPE is used for THWN wires.
So THWN and THWN cables still have a considerable difference in application. THWN cables are appropriate for use in indoor wiring of dry locations such as fixed installments, service entrances and branch circuits. On the other hand, due to the improved waterproofing features of THWN cables, they can be used not only in dry environments but are also recommended for use in areas with moisture particularly wiring in areas such as basements or outdoor applications. As such, the use of either THHN or THWN is therefore dependent on the humidity conditions of the intended area of installation and whether extra water resistance is required.
