CQD: 5/21/2015

NECA Online Help Desk
Please leave a message

Thursday, May 21, 2015

Question:

Re: CQD answer published Wednesday, May 13, 2015 - Grounded vs Equipment Grounding Conductors

Charlie, great forum as usual and we all benefit from questions and answers.

I would like to just point out something regarding the interconnection of various branch circuit grounded conductors.

When grounded conductors are interconnected, a potential for a shock hazard is created to maintenance personnel. When power is removed from one branch circuit for doing work on it, it's grounded conductor may still have current flowing in it from the other interconnected branch circuit. If that conductor's path is interrupted by doing maintenance, a difference of potential could be created, and this could pose a shock hazard. This shock hazard would be exacerbated for commercial or industrial lighting systems on 277V 3PY systems since higher voltage potentials could be experienced.

I highly recommend that different branch grounded conductors NOT be interconnected for just this reason unless all involved branch circuit OCP devices are tied together so one cannot be opened without removing power from the others.

Best regards, and thanks for the superlative forum.

Nick Abbatiello

Answer:

Hey Nick thanks for your comment and kind words. You have some good points about grounded conductors but the question was about equipment grounding conductors being interconnected by 250.148. We also need to be careful to not parallel grounded conductors smaller than 1/0 as stated in 310.10(H). Using the correct NEC terms helps us keep the rules clear but it is easy to misread them.

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 codequestion@necanet.org.

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.

National Electrical Installation Standards

Question:

Answer:

Follow Us on: