National Electrical Installation Standards

Standards as High as Your Own

Wednesday, August 21, 2019


I need to understand how the main breaker (in this case 1200A) can support by code feeders of 400A, 800A, & 1000A. The question my customer posed to me was how does the main of 800A support what appears to be a total of (400 + 800 + 1000A) 2200A. I understand the breakers are sized to protect the conductor size but I find limited information on how the 1200A main can support the 2200A feeder loads.  

Rick Gardner


Hey Rick thanks for your question. It doesn't but that doesn't mean that the installation is not acceptable. It seems you meant that the second time you mention "main" it should read 1200 instead of 800. Feeder conductors must be sized to carry the load as stated in 215.2(A)(1). Starting at the load end calculating the loads using Article 220 to ensure that the 400, 800, and 1000 ampere feeder conductors are properly sized using 215.2(A)(1). If the total of those loads is 1200 or less then they can be supplied by a 1200 ampere feeder. If it is more then the 1200 ampere size is not sufficient. Consider a typical 100 ampere panelboard in a dwelling unit. If you total all the overcurrent devices it will very likely exceed 100 amperes but they are not all loaded to their full ratings. Overcurrent protection is also necessary as stated in 240.4 but that is separate from the load calculations. If this is not what you are asking please rend in an additional question.

ABOUT CQD: NECA’s Code Question of the Day (CQD) is a leading National Electrical Code® forum for NECA and the industry. The CQD generates a lively dialogue and relative practical and Code-based responses to an ever-increasing and interactive audience.

IMPORTANT NOTICE: All answers are based on the latest edition of the National Electrical Code®, unless the question requests a response based on a specific edition. This correspondence is not a formal interpretation of the NEC®. Any responses expressed to the questions are opinions and do not necessarily represent the official position of NECA, NFPA, or any technical committee. In addition, this correspondence is neither intended, nor should it be relied upon, to provide professional consultation or services.

ABOUT CHARLIE: 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. Charlie was also a member of NECA’s Academy of Electrical Contracting. Charlie’s experienced team of industry experts keep the CQD dialogue and discussions active and informative in the spirit of the man himself, as he wanted.

NECA STANDARDS: NECA publishes the National Electrical Installation Standards™ (NEIS™), a series of ANSI-approved performance and quality standards for electrical construction. Visit for more information. NEISÔ can be purchased in three formats: as paper books, on CD, or as electronic downloads.

NECA SAFETY PRODUCTS: NECA publishes valuable electrical safety books and CDs for the industry. Visit to view or purchase NECA safety products.

 CONTACT US: To submit a Code question, subscribe, or unsubscribe from this list, please e-mail: