If the nylon on THHN is scuffed, is the insulation damaged?


In the process of pulling THHN conductors through raceway we encountered some scuffing and scraping of the outer nylon conductor covering at the final fitting. The engineer says we ruined the conductor and wants it replaced. Does damage to the nylon covering constitute damage to the conductor insulation?



A Type THHN wire is comprised of three basic parts, the conductor, PVC insulation, and a nylon jacket. Each part has a specific use. Damage to the nylon jacket only, does not constitute damage to the insulation. The nylon jacket does provide mechanical protection to the insulation during and after installation and also provides gasoline and oil resistance for the wire. The question concerning replacement of the damaged wire can only be answered by visually examining the wire to understand the extent of the damage; and if the PVC insulation is damaged, or if the conductor is exposed to gas and oil, then replacing the wire may be necessary.

UL certifies (Lists) THHN conductors under the product category Thermoplastic- Insulated Conductors (ZLGR), located on page 491 of the 2013 UL White Book and can also be found in UL’s Online Certification Directory at www.ul.com/database and enter ZLGR at the category code search field.

THHN conductors that are certified (Listed) under (ZLGR) are evaluated for compliance with the Standard for Safety for Thermoplastic-Insulated Wires and Cables, UL 83. UL 83 requires THHN conductors to be provided with a nylon jacket extruded tightly over the insulation with a minimum thickness of 4 mils for 14-10 AWG conductors and thicker for larger conductors.


Is there a PDF download available of the 2013 UL White Book?


Yes, the 2013 version has been improved and is more user friendly and intuitive providing linked navigation embedded into the document for ease of use and with an internet connection, direct access to Code-complaint UL Certified products. The Linked version of the 2013 UL White Book PDF is now posted at www.ul.com/whitebook just click on the banner on the right side of the page.

What does a “linked version” mean? The Table of Contents (TOC) and the Indexes of the UL Product Categories Correlated to the 2008 and 2011 NEC are all linked so that if you click on any TOC entry; or the page number or the category code in the NEC Indexes, it will link you to that page in the file/book. In addition, each of the product category titles in the book (that are not main product categories without any certifications) will link to all the UL Certifications for the product category in the UL Online Certification Directory at www.ul.com/database. This will provide you the proper categories for each code section and then the certifications for those categories, giving the user direct access to code-compliant products.

The links in the pdf will also work on iPads and iPhones by opening and using the file in Drop Box. If you save it directly to your Apple device outside of Drop Box, the links will not work and it will be a regular pdf file. The links in the pdf do not work on Android devices, even if opening in Drop Box. It will just be a regular pdf.

Drop Box is a free application that allows you to share files between all your devices and can be downloaded for free at www.dropbox.com.

About UL Solutions
UL Solutions helps create a better world by applying science to solve safety, security and sustainability challenges. We empower trust by enabling the safe adoption of innovative new products and technologies. Everyone at UL shares a passion to make the world a safer place. All of our work, from independent research and standards development, to testing and certification, to providing analytical and digital solutions, helps improve global well-being. Businesses, industries, governments, regulatory authorities and the public put their trust in us so they can make smarter decisions. To learn more, visit UL.com.