National Electrical Installation Standards

Standards as High as Your Own

Thursday, March 16, 2023


Hello CQD. Thank you for providing this service and I look forward to reading it every morning. My question is, where is the line drawn from when you need to get a UL evaluation for field installation of devices in an enclosure, as compared to installing one or two listed UL devices in an enclosure? Do you need UL evaluation of even the smallest of devices installed? Not sure of the process how this is determined. Is it up the AHJ? Thank you and awaiting your response. Keith Bailey


Keith, great question. The AHJ is the ultimately the one that approves an installation. Section 110.2 requires an installation to be approved, and Section 110.3 offers guidance on considerations for evaluating and judging if equipment is suitable or safe. Listing is one element to consider when evaluating equipment. For example, Article 409 provides guidance on the field wiring of Industrial Control Panels, an AHJ may approve an installation because the field wired Industrial Control Panel complies with Article 409, whereas an AHJ would like to require a listing of a factory assembled Industrial Control Panel for approval.

Field Evaluations are a listing mechanism for when equipment has already been installed or is already on site. Often a Contractor or AHJ may have some concerns about a piece of equipment, or maybe the authenticity of the listing is in question. A National Recognized Testing Lab (NRTL) can be hired to come out and perform a field evaluation and if the evaluation deems the equipment meets the appropriate standards, the NRTL will apply their Field Evaluation marking label. That marking provides assurance to the AHJ that the equipment is acceptable for the intended use, ultimately aiding in the AHJ’s approval. One important note about Field Evaluations, they are a one-off, and only apply to the specific installation site and piece of equipment that was evaluated. Here is a complete up-to-date list of NRTLs in OSHA’s NRTL program.

ABOUT CQD: The Code Question of the Day (CQD) is NECA and ELECTRICAL CONTRACTOR Magazine’s flagship National Electrical Code (NEC®) public forum for the industry, sponsored by EATON. The daily distribution of Q&A generates a lively dialogue and shares relative Code-based practical responses.

SUBMIT YOUR CODE QUESTION: Click here to submit a question to for inclusion in an upcoming edition of the Code Question of the Day, or email

CHARLIE TROUT: Charles M. Trout, better known as Charlie, was a nationally known NEC® expert and author. He served on several NEC® technical committees and is past chairman of CMP-12. In 2006 Charlie was awarded the prestigious Coggeshall Award for outstanding contributions to the electrical contracting industry, codes and standards development, and technical training. Even though Charlie passed away in October of 2015, his work continues in spirit. NECA continues to maintain this question forum for its many subscribers in memory and recognition of all his significant contributions to making the NEC what it is today.

NECA STANDARDS: NECA publishes the National Electrical Installation Standards™ (NEIS™), a series of ANSI-approved performance and quality standards for electrical construction. NEIS can be purchased in the NECA Store in three formats: a printed or  PDF download of a standard or, as an  annual subscription service.

NECA SAFETY PRODUCTS & PUBLICATIONS: NECA produces electrical safety publications and products for the industry including jobsite safety guides, handbooks and resource kits. View a full listing of available resources and products »

IMPORTANT NOTICE: Unless the question requests a response based on a specific edition, all answers are based on the latest edition of NFPA 70® National Electrical Code®.

This correspondence is not a formal interpretation of the NEC® and any responses expressed to the questions are opinions and do not necessarily represent the official position of NECA, NFPA, the NEC Correlating Committee any Code-making panel or other electrical technical committee. In addition, this correspondence is neither intended, nor should it be relied upon, to provide professional consultation or services. 

UPDATE YOUR SUBSCRIPTION PREFERENCES: Subscribe or Unsubscribe from this list.