National Electrical Installation Standards

Standards as High as Your Own

Tuesday, June 2, 2020



Is there a limit on how many extension rings are allowed on a four square junction box or any J-box for that matter?

Lucas Koomen



Hello Lucas,

Thanks for participating. The installation instructions for electrical equipment typically provide the requirements and any limitations on certified electrical equipment. Listed box extensions are covered in UL Product Category QCIT which indicates extension rings are suitable for extending properly secured flush- or surface-mounted boxes. One or more extensions may be used. An extension ring is intended to increase the box depth, volume, or both. See the following URL for more product certification information: 

The number of extensions that can be installed on a box is not provided and may be addressed by the manufacturer's installation instructions. There are also other NEC requirements for length of free conductor that must be provided, such as in Section 300.14, which is generally 6 inches of free conductor beyond the edge of the box opening. Section 314.22 provides additional information about installing box extensions securely and complying with equipment grounding requirements. Box extensions are often used for extending a flush-mounted box so a surface raceway adn be installed from it. Section 110.12 may also come into play regarding workmanship and the final approvals rest with the applicable authority having jurisdiction.

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.