Standards as High as Your Own
NECA Online Help Desk Please leave a message
Re: CQD answer published Thursday, August 22, 2019 - Demand Factor
Hello Mr. Trout, I read the questions and answers every day, and it is greatly informative. Regarding the question by Rick Gardner, "How can a main breaker of 1200 amps support feeders of 400 amps, 800 amps and 1000 amps (2200 total amps)?
I think there are many novice non-electricians, such as myself, who are interested in the theory of why this is allowed. I understand to an extent that the NEC has instituted certain calculations to determine proper sizing of breakers, and the proper sizing of wiring is straightforward enough that I understand that. What is confusing is that, contrary to the NEC, it is possible to run every light, the A/C, water heater, stove/oven, and operate three hair dryers simultaneously. I always thought the NEC erred on the side of ultimate safety, but in this case that doesn't seem to be true. I suppose should such an unusual overload occur, the main breaker would trip, but I thought that was also a situation to try to avoid, as breakers have such limited number of on/off tripping before they're suspect to failure.
Thank you for your help.
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 firstname.lastname@example.org.
CHARLIE TROUT: Charles M. Trout, better known as Charlie, was a nationally recognized NEC® expert and author. He served on several NEC technical committees and is past chairman of CMP-12. In 2006, Charlie was awarded NECA’s prestigious Coggeshall Award for outstanding contributions to the electrical contracting industry, codes and standards development and technical training. NECA continues to provide this public forum in memory and recognition of all his fine contributions that has made 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.
© 1999 – 2014 National Electrical Installation Standards. All rights reserved.
Brought to you by NECA. NECA is the voice of the electrical contracting industry NATIONAL ELECTRICAL INSTALLATION STANDARDS, NEIS and the NEIS logo are registered trademarks of the National Electrical Contractors Association.
Created by Matrix Group International, Inc.