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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.
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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.
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