National Electrical Installation Standards

Standards as High as Your Own

Tuesday, March 31, 2020


Good Morning Code questions, I have a working space question about a switchboard that is supplied by a 600/347-volt system. What is the minimum depth of working space required to a grounded surface installed directly in front of the equipment. I appreciate your views and response. Keep up the great work.


Mark Summers



Greetings Mark Summers, thanks for the comments and for the question. Although not a common voltage system in the U.S. there are systems like this in the field. The phase-to-ground voltage is 347 volts. Section 110.26(A) and Table 110.26(A) are applicable and condition 2 must be complied with, at minimum. The NEC requires 3 feet, 6 inches (42 inches) of working space depth in front of the equipment supplied with the voltage mentioned in the question. As a reminder, notes to tables in the NEC are mandatory requirements as compared to Informational Notes throughout the NEC, which are not. Condition 2 at the bottom of the table indicates that an installation with live parts on one side of the working space and grounded parts on the other side of the working space. Concrete, brick, or tile walls shall be considered as grounded.

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.